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Sense vibrations in audible range I am interested in making a small circuit that could sense the vibrational frequency of the object that it is attached to. The resonant frequencies would be in the audible range (likely 5kHz to 10kHz) Imagine a small circuit attached to a tuning fork, I would like to 'ping' the tuning fork and have the circuit be able to output what frequency at which it is resonating. I have read that Piezo devices would be capable of this but I haven't been able to find anything suitable. Does anyone have any suggestions of what I could use? <Q> You could use a piezoelectric tuner for an acoustic guitar. <S> These clip onto the guitar, amplify the vibrations and measure the frequency. <S> eg. <S> http://guitar.lovetoknow.com/Classical_Guitar_Tuners <A> I would use a piezoelectric disk and attach it to your object, connect a small amplifier circuit , and use the output to go to a speaker or a an ADC pin of a uC of your choice. <A> If you attach something to the tuning fork the added mass of the device will affect the frequency, so you might be better off using a microphone and MCU to measure the sound frequency directly. <S> You could simply use a PC and sound card with a microphone and sound analysis software, if you don't want to build anything. <A> The thing you are looking for is called a Contact Microphone. <S> There are lots of good DIY links on google . <S> Alternatively, you should just be able to use any common audio microphone, since the vibrations are in the audible range. <S> All microphones pick up vibrations in the microphone body, in addition to vibrations in the air. <S> Therefore, just touching a microphone to the tuning fork should pick up a pretty strong signal. <S> Basically, Since the microphone diaphragm has mass, moving the body will cause it to move around the diaphragm, producing a signal. <S> It's worth noting that most microphones will be much more sensitive to motion in one axis than the others. <S> Basically, since the diaphragm is sprung so it's only free to move along one axis, movement in the other axises will not have much effect. <A> In their Analog Dialogue vol.43 no.1 Analog Devices published an article titled "Sonic Nirvana - Using MEMS Accelerometers as Acoustic Pickups in Musical Instruments" Further reading: <S> The full Volume 43 Number 1 issue of Analog Dialogue <S> The Analog Dialogue <S> archives : lots of interesting articles!
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If you want to reduce ambient pickup, you could use something like a little electret capsule , plug the opening, and mechanically coupling the microphone body to your tuning fork (or what ever you want to sense vibrations in).
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How can a car battery be charged by dynamo (or is it an alternator?) at the same time it is being used by the car components? note and question * Is it an alternator or dynamo? I am not an electrical engineer and neither have any core knowledge but, this is a simple procedure of car battery charging using a dynamo, which is present in all cars and bicycles. But what i don't understand is how can a battery be utilised and charged at the same time? * That is, head lights drawing current.* But dynamo is giving current.* Everything done by using same battery terminals.* So BHOOM must be a explosion!! <Q> In short, it can't. <S> It is the charger/dynamo/alternator that is powering the components whilst charging. <S> In the case of a dynamo or alternator, if the output drops below the open-circuit terminal voltage of the battery, the battery takes over powering the components and is therefore no longer charging. <A> The battery is only being used when the alternator is not running. <S> While the alternator is running (delivering power), the battery is essentially just another load like lights, radio, etc. <S> For most of the time, the alternator is just maintaining the battery charge and thus supply little actual current into the battery. <A> The same way a laptop battery can be used and be charging. <S> And if you have more current from your dynamo than is needed to power the lights, etc. <S> those can be powered while charging the battery.
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If the battery is being charged then current is flowing into it, so it can't be powering anything.
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Wireless Module with over 1.5Km range? I'm working with Micro Controller Mega-32 (SMD). I'm looking for a Wireless module to transfer and receive the data that I created with the micro. Could you please guide me ? <Q> You could get to that range in the 900Mhz band with reasonable power. <S> LS Research makes a couple 900Mhz modules <S> that could do it with the right antenna (directional and high gain). <S> Just note that usable range can vary a lot based on environment (through a city? <S> through woods? <S> etc). <A> Bit rates go from hundreds of baud to over 1.5 megabaud. <S> Interface to your micro can be serial, USB or ethernet. <S> we use them on our Robots <S> and they a have a 90-100km range. <S> In a built up area that drops to only 30-40Km or so. <S> If you need to you can run a radio realy an get 2-300 km range. <S> (Very handy for us as our biggest robot has a 300km range.) <S> All quite legal in any country, just say where you are and they'll send you the right radios. <A> I've heard good things about the DNT900 from RFM. <S> The guys over at DIY Drones say they can get it up to 40 miles at only $69US. <A> we have had lots of success with the this. <S> http://www.digi.com/products/wireless-wired-embedded-solutions/zigbee-rf-modules/point-multipoint-rfmodules/xtend-module.jsp#overview <S> we use it in our UAVs as a the telemetry modem. <S> It is logic level UART and very easy to interface. <S> We have seen performance with low gain antennas at up to 5 miles. <S> Tested buadrate 9600. <A> I think you are out of the range of a "wireless module". <S> I think you are getting into the realm of Long Distance WiFi . <S> The problem is that you need to go 1.5km. <S> The solution would be good antennas on either end to transmit and receive the signals and a wireless radio to encode/decode the signals to bit/bytes. <S> The actual micro you use should not matter. <A> An XBee pro (if they're still making them) might be able to achieve 1.5km with line-of-sight on the highest power rating. <S> I think I saw them rated for 1km <S> , so 1.5km might be a stretch, but it could be worth testing depending on how often you need to transmit. <A> There are several Chinese vendors that take ISM-band chips and add a power amplifier (and sometimes LNA) to boost the range. <S> http://www.satistronics.com/nrf24l01-with-pa-and-lna-1000m-long-distance-24g-wireless-module-with-antenna_p2862.html <S> This is all of dubious legality in the US, of course. <S> I haven't ordered any of these modules to see if they get seized by customs. <S> An advantage to this approach is that you can prototype with the low power device, and "upgrade" as needed.
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A Candian Company called Microhard systems makes the ISM 900Mhz band radio you need.
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Don't understand how these resistors operate in this circuit When reading a manual on using a PICAXE and an I2C device I saw this diagram. I can't work how this would behave as wouldn't it make the connection on the lines constantly high due to the connection to the power rail, so never goes low. I understand that they are open-drain lines and they are needed inorder to make the lines go high but how can it make them go low with that connection to the positive rail? <Q> I2C is a communication bus that allows multiple devices to talk on it. <S> Since there is only a clock and data line there is no way to ensure that two devices won't start talking at the same time, or a device mis-identifies a message as being for it and responds out of turn. <S> If two devices try to control the data line and one wants it '1' and <S> the other '0 <S> ' you end up with a condition called contention. <S> Internally a normal digital output is built up out of two transistors: one connects the signal line to +V and the other to ground. <S> The device turns on one transistor or the other to set the output signal to the appropriate level. <S> When two devices are trying to make the same signal two different voltages you end up with <S> +V connected to ground through two transistors. <S> This is known as contention and is something you want to avoid because it causes high currents and can damage one or both of the output drivers. <S> In order to get around this problem, the I2C specification requires the use of "open collector" or "open drain" (same thing) drivers. <S> This means that the devices on the bus can ONLY connect the signal to ground. <S> The only way for a device to output a '1' is to not drive the line to zero. <S> Something has to bring the line to a logic '1' and that something is the pull-up resistor. <S> What happens now if two devices try to drive the data line is that one is not doing anything (it wants the line to be '1') and <S> the other device has its output transistor turned on, connecting the signal to ground. <S> The resulting signal is a '0' -- there is no contention because the only thing holding trying to make the line a '1' is a resistor which by design limits the amount of current it allows through. <S> Pull-up resistors are usually selected to offer a bit of resistance to a changing signal but not too much. <S> For I2C the value for a pull up is usually 4700-10000 ohms. <S> Check out <S> http://en.wikipedia.org/wiki/Open_collector and http://en.wikipedia.org/wiki/I%C2%B2C for more information. <A> Those are pull-up resistors. <S> When devices aren't communicating the resistors pull both lines to high. <S> A device is able to pull the lines low. <S> It has to supply current that gets dissipated by the pull up resistors. <S> You can think of this like a basic V=IR problem to determine how much current is required. <S> The reasoning for this setup is the situation where you want to have multiple devices communicating on a single line. <S> If you had a device pulling the line high instead of the pull up resistors, when a different device tries to communicate it will be forced to overcome the other device in order to pull the line low. <S> In this situation you still have a V=IR problem, except this time your R is very very small which makes I very very large. <A> They are required by the I2C specification. <S> They can be driven low by making the output pin low.
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The resistors you see are called "pull up" resistors; they literally "pull up" the signal to the positive voltage rail.
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How to buy difficult-to-find electronic parts? A RF receiver project I'm working on calls for a very specific SAW bandpass filter. I've checked all the usual sources here in the US (Jameco, Mouser, Digikey, Newark, etc) without success. What I'm finding is that the part I'm looking for is highly specialized and thus difficult to find anyone that sells them in low, hobbyist quantities. What are some approaches for buying difficult-to-find parts in low quantities? <Q> However don't be surprised if you have to buy a whole reel/tube/tray and wait a few weeks, but you might be lucky and find someone with stock. <S> You may be able to get small qtys as samples from the manufacturer or distributors. <S> However there are many parts that you just can't buy in small quantities. <A> Suppliers may be prepared to provide the name of customers who have purchased the part in quantity. <S> Sometimes they may be willing to pass on your name to a buyer if the identity is confidential. <S> I've only done this very occasionally and long long ago <S> but it can be successful. <A> First, find the original manufacturer of this part. <S> After that, you can go to the relevant supplier website to find out if there is inventory. <S> If the supplier does not have this part, you can seek local traders, or electronic parts. <S> Inventory recycling company，maybe，you will find this parts
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Go to the manufacturer's website, find their list of franchised distributors and talk to them.
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What is 'best' temperature sensor for an array of sensors I'm looking to make an array of sensors to record the temperatures in a house at various points eg. Above flat metal roof, inside flat roof cavity (above 1st floor), ceiling of room (1st floor), floor of room (1st floor), floor cavity (first floor), ground floor room ceiling, sub-floor/basement space. I guess I need accuracy tolerance of about ± 1ºC. More important is that once initially calibrated, the sensor do not drift relative to temperature or the data comparison will be bunk. I hope to run the sensors for weeks in winter, summer, spring, autumn to get a full profile of the thermal performance. So which sensors are good for me. Few seem to be good for ± 1ºC and I need a way to deal with the wiring of them too. So I2C or another digital bus might be good, anything that stops the length of the wire introducing errors into the values. Digital also means I can run a cat5 daisy chain of sensors rather than a separate lead to each sensor which seems reasonable. <Q> For such a sensor network I would absolutely consider using Dallas 1-wire components for great flexibility and reasonable price. <S> It is well supported in Linux via owfs . <S> At www.hobby-boards.com there is a small T3-R1-A ready made board which you just connect with cat5/RJ45 priced at 18USD. <S> According to the documentation it uses the DS18S20 sensor like already mentioned by BG100. <A> I've had very good results from the DS18S20 . <S> I found it to be very accurate. <S> You can easily get a resolution of 0.5 degrees (Celsius), or if your prepared to do a bit more work you can get 0.1. <S> You can also string together lots of them on a single data wire, and get readings from each of them by addressing them by their in-built serial code. <A> They're IIC, and support up to 8 devices on a single bus. <S> Their absolute precision is only +- 2°C, but they're repeatable, and have 0.0625° relative resolution. <S> Also, you can calibrate out (most) of the +- 2° offset, if you put the effort in. <S> I can also confirm that ~20' strings with sensors spaced evenly along it work without trouble. <S> TI Also make some higher precision, but more expensive IIC sensors, such as the TMP275 . <S> I have a project which scans 14 strings of 8 sensors, and dumps the code out over a serial port a ~2 hz. <S> It's built around a Propeller Microcontroller , and I could post the code and PCB layouts, if you would like.
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I've used TI TMP100 sensors with success.
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Do I have a ground loop or another problem? Okay, I know this is an electronics Q&A site, and this question is mildly computer related. But I've got this problem with my VGA monitor, a graphics card and a computer. The problem is the video output is blurred in one direction quite badly. This looks very similar to a low pass filter - i.e. parasitic capacitance. The confusing part is - this only occurs with one card, an Nvidia 9800 GT. I have a somewhat broken ATI card (GPU started melting and now all 3D games have misplaced polygons), and this doesn't occur. So I'm thinking something else is up with either the card or some configuration involving it. I've also noticed that there is an odd ripple to the black in the image. Could it be a ground loop? I'm using a cheap DVI to VGA adapter which could also be suspect. I've attached an image of the problem. <Q> This is usually caused by a long VGA cable. <S> If you are only seeing it on 1 video card then I would suspect the video card is very poorly designed. <S> To add a technical note, the ghosting is usually caused from a mismatched line causing reflections and ringing which shows up as what you are seeing. <A> As you have tried the monitor on two different cards, one it works with, the other smears the signal - <S> this would indicate that the Monitor is OK and the video card is faulty. <S> And as the caps were quite old - the printing looked grey/brown instead of silver/white <S> - an indication of age or overheating - When Caps get old - they loose capacitance and the ESR (Effective series resistance) increases. <A> Wohhh, now now, wait a bit right there. <S> The 9800 GT is a card made by Nvidia, who made the 8800 GTX ultra, the current 4XX cards, and other INCREDIBLY complicated and high end graphic cards. <S> They most certainly did not "very poorly" design this card, besides, it is based on the 8800gt, which is pretty much the same card, and the 8800gt's were very popular and did not have much problems like this. <S> I suggest you first try to re install the newest drivers for your graphic card, which can be found on here. <S> http://www.nvidia.com/Download/index.aspx?lang=en-us <S> Then, contact the location you bought it from, such as best buy or where ever you bought the card, and tell them you problem and for them to give you a new 9800 GT. <S> If the stores says no for what ever reason, you can do a RMA with the brad that the graphic card is made from, such as EVGA, BFG, PNY or XFX. <S> If it is neither of those, you contact Nvidia and also ask for a RMA. <S> Most of the time this is a painless process, and you pay only for shipping the card to the company. <S> Here is a perfect site for computer hardware, it is called Newegg, and it provides you with computer parts for the cheapest you can find (most of the time), and it also has excellent customer support. <S> If you need further help, just ask on a forum such as this http://www.overclock.net/graphics-cards-general/ <S> The people there are very helpful, and can practically hold your hand through the process. <S> Best of luck! <S> though I think this question should be closed, because it seeems similar to other questions that are closed usually.
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I have seen this smearing effect on a very old video card, and it was caused by either a faulty DAC (Digital to Analogue Converter) or the smoothing caps around the DAC ( This looks exactly like VGA ghosting.
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Streaming a section of video to an external display I want to be able to connect an external display to my Windows PC (in addition to the existing one), and stream a selected portion of the screen to this display. For example, if I have a small terminal window open on my main monitor, then this smaller display will show only that terminal window, not the rest of my desktop. I guess it's like Picture In Picture (PIP) on a TV, but for a PC instead. Can anyone recommend the easiest way to achieve this? I don't mind getting into the video programming side of it (maybe using DirectShow?), but if there is a hardware solution, eg on a DSP board,then that would be great. <Q> This is probably off-topic, because the easiest way to achieve this is to use the tools already provided by your graphics card. <S> Mirror your display, adjust the resolution of your screen to that of the window, and pan the screen until the desired area is displayed. <S> If you want to be able to select an arbitrary window to be mirrored, you need to add this functionality to your window manager, which is impossible on Windows (but should be doable for most Linux window managers). <S> If you want to do this with an app you're developing (or an open-source terminal), just use a second display. <A> would a usb display work? <S> http://www.mimomonitors.com/products/mimo-720-s <S> it may be easier then trying to stream part of the window and sending it to a display. <S> the other option i can see working is if you have a second vga or DVI port and adding a cheap LCD monitor to clone or extend your desktop not trying to be discouraging but what you want to do would require you to create a PC program to send that part of the screen ( not sure how in SW) and a communication line like a serial port or usb to control your display. <S> Edit: after rethinking the whole issue, I would still use a prebuilt solution, but if you want something from scratch, you could get an ARM processor(cortex <S> -Mx) add a LCD screen (your choice on resolution) and build an API so you can send straight data to draw the screen through the com port(rs232 serial) or use Ethernet connection. <A> Your graphics card driver can put windowed video played in a video player to some external monitor or TV in full screen.
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If we are not talking about video, but just a window of some software application running on your pc, then you can use UltraVNC and share just that single window for displaying on remote pc.
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Timing differences with a 27 MHz data clock I'm considering using a chip which outputs 8-bit data on a 27 MHz clock. The data will go from the chip to a FPGA, a distance of a few cm max. Do I need to be concerned about timing differences between traces on a PCB, and if so, how can I mitigate these? I've often seen motherboards with traces in small coil shapes, presumably to act as little delay lines. <Q> Leon is right, it probably doesn't matter for 27MHz signals on traces that are only a few cm long. <S> However, you can mitigate skew by making the trace lengths equal. <S> If you've got the time to ask a question about it, and you have the board space, why wouldn't you want to do this? <S> There's very little reason to build skew into your circuit. <S> Make little 45 o <S> wiggles in the traces to make the distances the same and avoid building in reflections. <S> This makes equalizing the trace length easy if your PCB program doesn't do it for you. <S> Or, you can use rounded traces, but keeping the trace lengths equal gets more difficult. <S> Here's a PCB which uses LVDS. <S> There's an NI board connected to this one through a 2m, 100-pin ribbon cable, and the other side of the LVDS transcievers connects to a parallel bus, so there are many sources of skew. <S> Why not eliminate the PCB as a source of skew? <S> Note: On this PCB, the paired traces are supposed to be coupled together. <S> In a non-differential bus, running pairs like this will give you really bad cross-talk. <A> Try doing some calculations involving the speed of light, allowing for the velocity factor. <A> In addition to the good answers by others, there's still things you can do if you've got functional failures due to trace mismatch on your board (though at 27 MHz, there's not much to worry about). <S> Most modern FPGAs from Xilinx (and maybe Altera, not sure) have reconfigurable delay element inside of the I/ <S> O pin <S> so you could adjust with very fine resolution when the signal is captured. <S> Look for the 'IDELAY' and 'ODELAY' primitives.
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At 27 MHz any differences in track length over a few cm will have a negligible effect.
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Extra negative battery cable when charging outside car? If you go to: http://www.battery-chargers.com/charging_instructions.htm ...Under "Operating Instructions" part "B: Charging battery outside of vehicle", it says you have to attach an extra jumper cable to the negative battery post, that is then clamped to the charger's actual negative cable. See below: Both my charger's instructions and these look identical on this point (Indeed, they might be the same instruction sheet). Why is this extra cable needed? (Not like I don't have one, just rather curious...) Thanks! <Q> So that you can connect/disconnect while not standing over the battery. <S> The batteries contain sulfuric acid which is not a very pleasant substance to splash. <S> Even the fumes are dangerous. <S> While connecting inside a vehicle, connect the positive first and the negative on the vehicle body while not facing the battery. <S> Similarly while disconnecting, disconnect the negative first and then the positive cable. <S> The reason is that the vehicle body is connected to the negative terminal. <S> If the positive cable slips and touches any other vehicle body part, it will cause a short. <A> Lead acid batteries, like those used in vehicles, create hydrogen gas from the sulphuric acid. <S> If the gas concentration is high enough and you get a spark, it explodes, the acid goes everywhere including in your eyes. <S> You almost always get a spark when completing the circuit, sometime even if the charger if off. <S> By making the last connection away from the battery this lessens the chance of an explosion. <S> If the battery is still in the vehicle, attach the positive to the battery terminal then attach the negative to a ground point away from the battery. <S> Many people use a point on the engine block. <A> Just a guess, but perhaps it forms a makeshift switch? <S> Disconnect to stop charging.
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The negative can be connected to any exposed metal part on the vehicle (and at a distance from the battery). With the battery removed, you don't have a ground point to connect to, so make the last connection away from the battery by using an extra ground cable.
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What is the most common way ethernet ports experience harware failure? Modern electronics are incredibly reliable, however, I have had about 5 ethernet routers experience hardware failure on one or more ports on my home network. Is this unusual, and if it is, what precautions can I take to avoid it. If it is "common", is there a component in the system that is prone to failure? <Q> Consumer gear isn't usually tested nearly as rigorously as "business" or industrial equipment when it comes to dealing with environmental variations. <S> They can be hard to find, you usually need to check them carefully like with a magnifying glass or similar equipment. <A> I agree with Brian on this one. <S> I have just recently had to modify a design to replace a particularly static sensitive Ethernet PHY IC from Davicom. <S> This part failed constantly and the only thing we could pin it down to was static. <S> The new design moved to a National Semi part which incorporated static protection in the IC plus we added an ethernet specific tranzorb style device right at the jack input. <S> This drove the cost up by more than $15USD <S> so it's easy to believe that inexpensive routers / switches deliberately leave these components out. <A> Static electricity is a killer of ethernet ports too. <S> I've not yet managed to ever kill a port, but have replaced NICs and routers for other people that grab the cable by the very end, get a "poke" from it, and then it doesn't work... <S> If the cable is plugged in on either end, make sure you always hold it on the cable behind the connector. <S> Don't grab the connector itself, the conducting surfaces aren't very deep, doesn't take much static to jump the gap.
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In my experience for something like that its generally solder joints coming loose/cracking, often times in consumer gear its a result of thermal stress.
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How to convert PDF to Gerber for PCB layout? I've got a PDF file with a PCB layout I'de like to produce - however, I need the file in Gerber format first. Is there an easy way to convert between the two? I've found this: https://swannman.wordpress.com/projects/pdf2gerb/ - does anyone have some experience with it? Does it work well? Are there better alternatives? <Q> It seemed to work OK on the PDF provided in the example - the Gerbers looked OK when I imported them into GC-Prevue. <S> However, when I created a PDF file from a PCB designed in the Pulsonix software I use, and converted it with pdf2gerb.pl, the resultant Gerber file wouldn't import into GC-Prevue. <S> There are some PCB manufacturers which can work from artwork supplied as Postscript files. <A> The best way is to ask the company that did the layout for Gerbers or CAD originals. <S> Most companies that sell evaluation boards for their chips (e.g. TI, Altera) will do this. <A> It's not directly possible, as a set of gerber files (including the drill file, which I count as a "gerber" even though it isn't really) contain more information than the average PDF, for example drill sizes and parameters of vias. <A> Its doable but is error-prone. <S> 1) convert PDF to SVG. <S> For this I would recommend Inkscape as it can import PDF files and then save as SVG 2) import SVG. <S> KiCAD can import SVG as a graphic and then assign to a layer.
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You could convert the PDF file to Postscript by printing it to a file, using a Postscript driver.
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Detecting the type of surface/medium a robot is on top of I am looking for a way to detect what sort of terrain a bot is travelling on. To keep it simple lets start with grass vs sand vs tarmac. It is to be used with arduino, and for a hobby project so cant cost an arm and a leg. I figured it could be done with a camera but hoping to find a better way. maybe with sonar or something. tx Edit:Im taking this info to do some more research on the problem. Will be back with some more info and hopefully and answer. i think bouncing light/sound off the ground and somehow measuring the amount reflected/absorbed, maybe with the color filters to aid the readings as the start. 1) I think this is a start. http://embedded-lab.com/blog/?p=1671 sending out light and reading how much has been returned. that would just be picking up the highs and lows. <Q> Those three different types of ground (grass, sand and tarmac) will be predominantly three different colours - green, yellow and black. <S> Simple light sensors and appropriate colour filters might work. <S> I just remembered an aid for the blind that was developed many years ago, based on sonar. <S> The person swept the sound source backwards and forwards in front of him or her, and was able to detect obstacles from the returned signal. <S> It was possible for different textures to be detected, such as grass and leaves. <S> I looked up sonar and texture on Google and found this . <S> It looks as though the technique is suitable for detecting terrain. <S> Both techniques could be used, with some form of sensor fusion, to maximise the probability of a correct identification. <A> Have you thought about an accelerometer? <S> Could measure the frequency of bumps. <S> You might also be best served by a combination of several different methods... <A> Based off of how much light is reflected you can get a good idea of the type of surface that you are on. <A> I wonder if you could do it by sound? <S> A rolling vehicle would make different sounds going over those different terrains, and if the motor is quiet enough... <A> Let the robot measure the torque/force at one or more joints of each leg. <S> Or perhaps you can get an adequate approximation by using "sensorless" measurements of the back-EMF of that leg's motor, or the amount of power going into that leg's motor. <S> Say the robot is using some gait that is efficient for tarmac: the robot puts the foot down in front until it touches the tarmac, then it stays at that vertical position and pushes the foot straight straight back, then lifts the leg up a little and pulls it forward, then puts the foot back down and repeats. <S> If you really are moving over tarmac, you expect the robot to measure a high torque/force when it is pushing the leg back, and close to zero when it is pulling the leg through the air forwards. <S> If the torque in one leg feels low when the robot pushes it back, then perhaps that leg (not necessarily any other leg) is slipping across the surface of some sand. <S> So the robot should push that leg down a little deeper into the sand, and perhaps move the leg back a little faster, until that leg gives the robot the forward thrust you want. <S> If the torque in one leg feels high when the robot pulls it forward, perhaps it is rubbing against grass. <S> Or perhaps the other legs have dug in deeply into sand, and that leg is brushing the top layer of sand. <S> So the robot should lift that leg up a little higher to avoid that <S> obstacle.(And perhaps lift all the legs up a little higher on the return stroke for the next few steps, so other legs can avoid that obstacle or similar nearby obstacles). <S> I'm assuming your goal is to get the robot to adaptively change its gait, because different gaits are more efficient on different substrates. <S> If your real goal is to get the robot to stay on a tarmac track, rather than wandering off over grass and sand, you'll need some other approach.
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You might want to look into reflecting a light off of the surface you are driving on. Perhaps measure torque directly using a discrete strain gage or other force/torque sensor.
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How do constant current power supplies work? How do constant current power supplies work? For example I have a power supply that is constant voltage that can supply up to 5A and I have a 12V motor that takes ~500mA so I crank up the supply to 12v and my motor pulls ~500mA from the supply. But how does this work for a constant current power supply? Would it determine its own voltage output depending on the resistance of the load(ohms law)? <Q> The short answer is yes. <S> So a 100 ohm load will have twice the voltage across it as a 50 ohm load. <S> Of course, the CC supply will not be able to increase output voltage forever, just as a CV supply cannot increase output current above a certain limit. <S> A CV supply will supply more power as the load resistance gets smaller, but a CC supply will supply more power as the load resistance gets larger. <A> The simplest constant current supply is a large value resistor in series with a much smaller load resistance. <S> Suppose we have a 12V supply to a 1k resistor in series with a 10R resistor: <S> the current flowing through the load will be 12/1010 amps or 11.88 mA. <S> If the load is 20R, the current will be 11.76 mA. <S> It's almost the same although the load resistance has been doubled. <S> The voltage across the load has been doubled, in the second case, keeping the current at about the same value. <A> A simple model of a real current source is an ideal source I_S in parallel with an internal resistance R_S. The current and voltage at the load R_L is as follows: I_L = R_S/(R_S + R_L) <S> * <S> I_SandV_L = R_L*I_L <S> = <S> R_S*R_L/(R_S + R_L) <S> * I_S = <S> (R_S // <S> R_L) <S> * I_S <S> As long as the load resistance R_L is much smaller than the internal resistance R_S, the load receives most of I_S. <S> In this case the equivalent resistance of R_S in parallel with R_L is approximately R_L, and the source voltage is approximately I_S*R_L . <S> In the extremely non-ideal case, the load resistance R_L is much larger than the source resistance R_S, and the load <S> current I_L is then approximately zero. <S> Also, the equivalent resistance in this case is approximately R_S, so the source voltage reaches its maximum of I_S*R_S . <S> To make a current source as ideal as possible, it needs a large internal resistance to be able to source a high voltage. <A> Typically it would measure the current using a resistor and regulate the voltage so that the current is the desired value (i.e. doesn't exceed it).
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The CC supply will output as much voltage as necessary to generate the current.
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what is an average CPH speed for hand SMD assembly? What would be the average speed (an experienced) person would assemble surface mount components on to a PCB? Assuming they have desk that is correctly set up (pick and place station) and the PCB has solder paste already applied. Reason for the question: Pick and place machines talk about components per hour (CPM) speed, interested to know how to compare this against a person. Looking into doing small runs (100 units) of a product, need to determine if I hire staff or purchase a small scale pick and place machine instead. I know Sparkfun say they do this sort of work by hand, but I have a part count of 90! <Q> Small runs like that are best sub-contracted. <S> ASK Technology <S> is a company I use. <A> Here are the largest factors for me when I am soldering: <S> The pitch of the components. <S> I have this cover both IC pitch and 2 pin size. <S> The smaller they are the slower the human has to go to get it set properly. <S> Through Hole components or SMD or both? <S> Through hole components will actually take a lot more time to solder in my experience. <S> How closely spaced the components are. <S> Humans will always make mistakes and the closer the parts are together the harder it will be to fix them. <S> Also the closer they are together the more likely a slip of the hand will cause another component to get hit and have to be fixed. <S> How organized the parts and documents of assembly are. <S> This one is pretty clear, if it is hard to figure what to put where it is going to take longer. <S> The board can then be baking while more boards are assembled. <S> Where you have to be careful in time estimating is the time it will take to check for shorts and fix them. <S> There will be errors, maybe just a couple out of the whole batch, but there will need to be more testing time when soldered by hand. <A> I've had a little job at an internship of soldering 250 small boards. <S> It consisted of about 3 resistors, 1 SOT23, 1 chip and 1 capacitor (all SMD). <S> It took a total of about 3 work days (x7 hours) to assemble them. <S> Doing it by a company was expensive (very small run - only 1500 components) and we were interns, <S> so you know how things work out. <S> That was about 12 boards per hour, but I am not an incredible good/fast solderer either. <S> So expect 45 - 1 minute per component. <S> Note that the chip was only a 6 pin device. <S> Unless you have a board that consists of 25x resistors of the same value right next to each other, it sounds that 9000 components is going to take you at least 10 workdays. <S> I can hardly imagine that sparkfun does their work by hand. <S> It only is worth it in China when loans are a few dollars per hour. <S> If you need to pay someone in a company environment and costs $10 - $15 per hour (which is cheap I suppose), that's still 15 - 20cts per component added. <A> Agree with Leon, for this number of units. <S> Depending on the product and margins, it can still be economical to contract out at 1000+.The big contract manufacture companies (who generally also manufacture PCB's) can source your components at cheaper prices than you. <S> We've even had them suggest changes that can cut costs from a product. <S> You agree prices at various price breaks and then place orders when you want. <S> If you want, they'll even conduct the required tests, box-up and ship products straight to customers. <S> This all obviously has associated costs, but when you factor in the time for procurement, managing the manufacturing, testing and logistics and delivery, you'll struggle to come close to their prices. <S> That is what these companies specialise in after all!
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When soldering is done by hand there are lots of aspects that factor into how fast it can be done. In general though, I would say it takes me about 45 seconds per part to place the parts on the board.
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Powering Thin Client PC from car's battery I have a thin client PC manufactured by HP (t5720). The following specs are written on the power supply: Input: 100-240V AC 50-60Hz 2.4A(2,4A) Output: 12V DC 4.16A(4,16A) Max Output: 50W I would like to use the thin client in my car, but don't have any power supply for it. Now my thoughts and questions: Do I even need some special transformation device as the supply's output is around 12V? The car has between 10.5 and 13 V, depending on whether it's running or not. How tolerant is a device such a thin client? Could this actually damage the car? If I actually need some transformation, what would it be? There are websites selling such transforming supplies. But some of them cost a lot of money and before buying something I would like to know whether I even need it. And I wouldn't want to just try it out and plug the thing in before I know what could get damaged. I have some very basic knowledge about electronics but I can't estimate it. <Q> It is very unlikely to damage the car, especially if it is properly fused (I'd fuse both leads), and should work OK as the nominal input is 12V. <S> The units you mention would incorporate such protection, and it might be easier to simply buy one of them. <A> You're probably better off getting an inexpensive automotive inverter to bring the automotive DC up to 120VAC, then using an appropriately-rated AC/DC power supply to generate the 12V you need. <S> Automotive DC can be very dirty due to the mechanical nature of how it is generated and the non-ideal load characteristics of the rest of the car. <S> Boosting to 120VAC first should help avoid any brown-out issues, plus the inverter will have appropriate protections (fusing/TVS). <S> It should not be hard to find a 12V/5A power supply for the thin client. <A> Linear Technology has various parts and app notes that will help. <S> But I agree with @Leon Heller that the environment is hostile. <S> I think he is understating it; you may see spikes up to 80 V.
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However, the car is a somewhat hostile environment for electronic equipment, because of the likelihood of high-voltage spikes on the 12V supply. I would use a suitable filter on the supply input to the unit, combined with transient voltage protection, in addition to the fuses.
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Is there a text or markup standard for describing a Bill of Materials? I'm an electronics newbie, and recently purchased empty PCBs for GoodFET and Ubertooth. While trying to put together an order for all the parts in the bill of materials, I realized I'd very much like to have a computer parseable format I could dump into a parts search engine like octopart. I started hacking up a simple website to do this using the octopart API but I can't find any sort of xml standard for a BoM. Has anyone heard of such a thing? I'd be particularly interested in some sort of standard format that's available from gEDA, EagleCAD, etc <Q> What I've run across most often is .CSV files with user-customizable headings. <S> I don't know of any more specific standard for BOMs. <A> I don't think there is a standard, but that doesn't mean that you can't make one. <S> I've written my own part searcher for EAGLE and Kicad which loads a bom from EAGLE or the parts list from kicad, produces search URLs for my preferred supplier and accepts SKUs in return. <S> What I'd do is to specify an xml format to hold the BOM and write a bunch of converters that can produce that format. <S> My eagle and kicad scripts are here: https://github.com/dren-dk/HAL900/tree/master/door-ctrl/kicad2elfa <A> Arena Solutions actually offers a free tool to assist with what you're trying to do called PartsList. <S> (There is a $9 price tag listed on the website, but I think it's currently free to try as it was recently developed.) <S> PartsList will let you create a PDX version of your BOM (which it sounds like you are trying to do.) <S> You can upload your CSV list of parts into the PartsList, click "autofill" to grab the rest of the documentation from Octopart, and then share the list with whoever. <S> You share by exporting as a CSV or PDX file. <S> (PDX = Product data eXchange (PDX) and is an XML-based standard that is commonly used for file sharing in manufacturing.) <S> When you share files as a PDX, you're sharing a searchable, in-context form of the BOM. <S> Arena also offers a free, cloud PDX Viewer, so you can look at the PDX file you created. <S> Here are some links to these tools, hopefully this helps you - - PDXViewer - http://www.arenasolutions.com/pdxviewer/?ifid=pdxblog1 PartsList - http://www.arenasolutions.com/partslist/ <A> Arena now has a BOM manager that integrates with the Octopart API, this is really the sort of thing I wanted. <A> Eventually the data is tabular with three fields/columns: designator (a list of identifiers to refer to parts in your design) value (an identifier of the part) description (textual) <S> The bill of material is presented this way with links to http://octopart.com . <S> Unfortunately there seems to be no unique standard of part-identifiers, isn't it? <A> Digi-Key also has a BOM manager that allows you to upload a BOM as a either a text file, CSV file, or spreadsheet (XLS), which includes a column with a Digi-Key part numbers and another with quantities, and it will automatically create an order from that BOM. <S> The BOM can contain other columns of your choice (you specify the mapping when you upload the file), so you can use the same file to capture whatever information you need for your project. <A> Here is a good online example of Bill of Materials . <S> You can export the BOM to excel and save to local as a BOM template.
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The Open source hardware platform Solderpad uses a JSON based format, see this example .
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Two diodes in parallel for over-voltage protection I've got a power supply circuit that needs the input to be protected against some pretty big voltage spikes. To do this, I need a really beefy clamping diode (D1) that will handle the voltage and current associated with those spikes. I also have a second diode in parallel with less current/voltage handling capability, but with a higher breakdown voltage (D2). My thought was that the secondary diode might react faster, but the primary diode would do the real voltage clamping. The circuit below is a simplified version (not including additional bias components). My hope is that the two diodes will provide the response as shown below. Is this a bad idea? Any cautions or warnings for this type of implementation? <Q> The 2nd is useless. <S> You might put 2 in series, but this has its own problems (they don't split the applied V equally). <S> Best to get a single component rated for what you want to do. <A> Two 5KP22CA (5 kW, 22 V TVS) in parallel can clamp an SAE J1455 load dump (unloaded 100 V peak, 0.4 Ω impedance, <S> 0.4 s fall-time <S> if I recall correctly) to <30 V. <S> So long as your duty cycle is fairly low or the diodes thermally coupled, you can parallel TVS fairly well. <S> They are far from perfect Zeners as their standoff/breakdown/max voltage range is quite broad so one robbing all the surge from the other is unlikely. <A> You may want to research Gas Discharge Tube Arrestors. <S> These usually have higher current ratings than the equivalent TVS diodes. <S> I would replace the higher breakdown voltage diode with a GDT. <S> The TVS diode would start conducting for the small spikes and the GDT would suppress the large spikes. <A> Depending on the details of your circuit you may be able to use one of these http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1142,C1029,P38400
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It won't work -- if you put 2 diodes in parallel, I can't easily say how they will share current in the forward (conducting) direction, but in blocking, the LOWEST breakdown one will breakdown.
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LDO with low-voltage cutoff? I'm building a circuit powered by a small Li-Ion battery. The battery will be connected to a 3.3V LDO, which then powers the entire circuit. Li-Ion batteries are damaged if they are allowed to drain below about 3V. There are chips to do this LVC cutoff. But I figure the LDO will already have the pass transistor and voltage reference, so it seems wasteful to add another part. This seems to be the kind of thing that could be easily integrated. Does anyone make an LDO with low-voltage cutoff? Parametric searches and Google seem to be failing me. <Q> I have never seen ready-made ICs with such a feature. <S> pass transistor, a reference <S> (LT1431, LM4121-ADJ, LM4051-ADJ or <S> even TL431 come to mind), some discrete components and some sort of 2nd comparator for the under-voltage lock out. <S> Take care about the regulator's stability (ESR of output capacitor must neither be too small nor too large, cf. " <S> Tunnel of Death"). <S> These links are helpful: <S> Short and good Application Note by NSC <S> A paper that offers some really good theroetical background An entire thesis by the same author as the paper, also a good read Building your own LDO has the disadvantage that you don't get features like thermal shutdown or short-circuit protection without additional effort, but it offers a great deal of flexibility (and it's fun). <A> One option is the LT1120 , which has a comparator, reference and shutdown pin in one package. <S> It's a simple enough matter of tying them together. <S> You can also get LDOs with a UVLO pin. <S> The UVLO pin has a reference comparator. <S> It could be something like UVLO falling below 1.25V or so triggers the shutdown of the regulator. <S> Tie a voltage divider to the UVLO pin to tweak the shutdown point. <S> Here's one example ; it's for USB, but I'd expect you'll be able to find more suitable chips. <A> This looks like an old question but there is a new (modern) answer: <S> Microchip has introduced their MCP1791 regulator: 70 mA, 30 Vdc max input, surge input <S> 48 Vdc (they don't say for how long). <S> This is not a true LDO in that the minimum input voltage is 6.0 Vdc for a 5 Vdc output <S> but it has several features that are useful: <S> 1) the output voltage turns OFF when the input voltage drops below about 4 Vdc. <S> 2) <S> The PG output goes LO (sinking) when the output voltage drops below about 90% of rated output. <S> Combine those two features and you have a voltage regulator that turns OFF cleanly when the input voltage is too low. <S> This part is rapidly becoming my "go-to" regulator for certain designs.
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There are, however, ICs that have a shutdown (or enable) input that might be used for such a feature when you add an external comparator and/or reference. You might also want to consider building your own LDO, using a PMOS (or pnp)
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My boss has asked me make a device which is capable of scanning rooms for bugs! Well this as I searched on the net is advertising, making money and fools out of those who want to make/buy such a bug scanner. I am not an electronics engineer but am being forced to. I do have access to all the hardware I may need. There are lots of shops claiming that they have devices which can scan a area to see if there are bugs or spy listener devices installed, but how do I know if these work? Personally I think this type of device only exists in James Bond movies :)) My boss's reason He seems to hear some sound in the conference room, and his room where he has to stay for another month. He claims the sound is something like "tii-eee, tii, teee ti ti" and so on. lol Deliver Okay, so now I have to reply to him with a gadget to scan his rooms for potential wireless transmitter bugs. <Q> Consider a new job. <S> :) <S> Apart from that, you could try and rent a spectrum analyzer from an equipment rental service, build a simple loop antenna (cut the end off a coax cable, loop some wire from the center conductor to the ground braid) and 'sniff' around the room to see if there's any spurious RF transmissions coincident with the "tii-ee, tii, teee ti ti <S> " noises. <A> You can detect some "bugs" which use radio waves to transmit sound (e.g. speech) to a remote listener or recorder. <S> It seems unlikely that a properly functioning bug of this sort would emit a noise your boss can hear. <S> Check for faulty "wall-wart" power supplies and other electrical devices. <S> You might have one of <S> these :-) <S> I'd suggest to him that if he considers it important enough he allocate you a budget for hiring a security consultant. <S> I'd also get him to purchase some bugs that could be used to test the effectiveness of the bug-detector. <S> If he insists you build a detector yourself, I'd first look for self-construction kits and equipment you can get him to pay for. <S> Maybe he'll pay for training? <S> You can find circuit examples from Google, for example the Talking Electronics' kit or an old Popular Electronics' article <S> - I've no idea if these are any good but looking at a selection of these might give you an idea where to start. <S> If you are very unhappy with this, you will have considered looking for employment elsewhere. <S> In the short term I'd try to look at it as an opportunity to gain experience and/or to demonstrate competence that could later be used (e.g. in an annual-review) to influence promotion or advancement. <A> Get a quote for renting a proper spectrum analyzer for a month. <S> It probably won't accomplish anything since there's likely nothing there to find, but they are quite fun to play with. <S> And useful to know about - you might really need one at some point in the future, and knowing your way around test equipment is always good, so make lemons out of lemonade and further your professional experience. <S> Given the cost of such equipment, rental is extremely common amongst even primary users. <S> There are of course cheap, limited devices out there, but it's good to know about the traditional instrument. <A> Maybe you should build a dummy device, that actually detects a mobile signal, such as this project . <S> You can then show it to your boss, and test it with a mobile phone to prove it works, and tell him it will also work with eavesdropping bugs... <S> Who knows, it might actually work! <A> Think geek wi-spy spectrum analyzer ? <S> Will only do around 2.4GHz (the $300 version says it covers 2.400 - 2.4835 GHz ), but it will find obvious things (cell phones/wifi devices). <S> Since he's probably delusional (or legitimately paranoid due to breaking the law), its worth the $90 shot. <S> Or buy a proper spectrum analyzer for a couple thousand dollars.
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In your shoes I'd get the boss to sign a purchase requisition for a commercial bug detector. There are devices that cotain radio receivers which can detect a nearby radio transmitter - if the bug uses a radio-frequency in the range detectable by the detector.
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What is needed to control 200 LED's from an Arduino I am new to Arduino and want to use two 74HC595 shift registers to control 200 leds. What will I need to consider / get to make this possible? These are your average starter LED's. Thank you! <Q> With Charlieplexing, you can directly drive n*(n-1) LEDs from n pins. <S> This means 210 LEDs from 15 pins. <S> This can be done with a regular Arduino Uno if you use some of the analog pins as output. <S> If you need different colors with different resistors, you have to do some smart segmenting. <S> You also have to think about the time multiplex, high pulse current. <S> This is probably easier if you know you will only have a few leds on at each time. <S> See application here: http://www.evilmadscientist.com/article.php/bulbdial3 <A> But if you would build 8 parallel shiftout streams, you can do that 8 times faster :-) <S> Also, make sure to provide sufficient power to all these 595's, total power consumption might get quite significant. <A> Your circuit would then connect a few LEDs to ground, and power whichever ones among them it needs. <S> A few milliseconds later, you connect a different set of LEDs to ground, and repeat, very quickly. <S> Among the Arduino pages there is one that discusses this . <S> It doesn't include 595's, as they will slow it down a bit, but it's simple enough to combine the ideas. <A> It depends a bit on your application. <S> Do you want individual control of each led? <S> What is your refresh rate. <S> How bright do you need the led's..... <S> Can you give some more info?
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The only way to control 64 (8 2 ) LEDs from your 2 8-bit registers would be to set up a matrix of LEDs (the matrix is simply how the circuit is electrically, you could place them wherever (in a line, circle...), though you will have a great deal of wiring. The only thing to consider is time to shift out your data.
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If mobile phones have to go through such extensive FCC/CE/EMI testing, why do they interfere with my radio? It seems that to sell a GSM mobile phone, companies like Apple, Motorola, Sony Ericsson and many others invest a considerable amount of money in EMI testing them. Yet they still interfere with my stereo, radio, computer speakers, and other devices. Why? <Q> I tend to blame the other devices for not shielding well enough. <S> Any wireless device is going to have harmonics, its just a way of life <S> and it just so happens that one of the harmonics with many GSM devices is in an audible range. <A> Take a close look at a typical FCC declaration of conformity: <S> "This device complies with Part 15 of the FCC Rules. <S> Operation is subject to the following two conditions: (1) <S> This device may not cause harmful interference, and (2) <S> This device must accept any interference received, including interference that may cause undesired operation." <S> The key word is harmful . <S> Distortion or buzzing on speakers is not considered harmful. <S> Annoying, yes, but not harmful. <A> Consumer goods like radios, stereos, etc. are built down to a price and typically have very poor immunity to out of band signals from devices like mobile phones. <S> You could modify your equipment with filters, better quality mixers, and so on, but it will be expensive and a lot of work. <S> Military equipment has to operate in close proximity to high-power signals, and a lot of attention is paid to screening and filtering, as well as circuit design, to avoid such problems, which is one reason why it is so expensive. <A> At least in Europe, although the EMC directive does not have a frequency limit, and the specifications often start by saying they cover d.c. to 400 GHz, in practice limits were only given up to 1 GHz. <S> I believe this was because it was deemed unlikely that any device would efficiently emit much unintentionally beyond this frequency, but that was all written before 2.4 GHz became so widely used (Wifi, Bluetooth, Zigbee etc). <S> Therefore the audio kit wasn't tested for immunity beyond 1 GHz. <S> In any case, it is usual to accept temporary deviations in analogue equipment, or any equipment, which self corrects with no intervention from the user. <S> Otherwise you have the problem, in analogue equipment of deciding what level of noise is acceptable during an interference event. <A> It's worthwhile to note that a lot of audio equipment assumes that signals going into it will consist of audio frequencies, and thus that they do not have to worry about higher-frequency signals. <S> Unfortunately, if the signals going into an amplifier cause distortion at any stage of the process, such distortion can generate unwanted frequencies from any combination of the input frequencies that happen to be present. <S> Something like a crystal radio set can exploit this phenomenon; a 900Khz AM carrier modulated at e.g. 1000Hz will have frequency components at 900.5Khz, 900Khz, and 899.5Khz. <S> Putting the signal through a diode will distort it in such a way as to generate 0Hz (DC), 500Hz, and 1KHz components (though hopefully the two sources of 500Hz components will cancel). <S> The 1Khz component may then be used to drive an earpiece. <S> Unfortunately, it's easy for an amplifier input and output stages to exhibit such distortion effects in response to high-frequency signals. <S> It is curious that such signals can become clearly audible even when they're just crudely coupled to relatively low-impedance audio cables, but it's worth noting that it's possible for the distance between a cell phone and an audio system to be a tiny fraction of its distance to the tower; consequently, a nearby audio device may pick up a signal that's a million times as strong as the one picked up by the tower. <A> The other answers here are mainly on track, but one aspect they haven't mentioned is proximity . <S> When I hear interference from a GSM device, it's usually when someone is standing within 2-3 feet of a land-line telephone or telephone-related device (my home answering machine and the conference phones at my office are the main victims I've noticed). <S> However, the radiated emission limits (both FCC and CE) are based on limiting the emissions from the radiator at a distance of 10 m or more. <S> This means the regulations are not designed so much to ensure that two devices sitting right next to each other won't interfere, but to sure that your phone doesn't interfere with a device in the next room, or in your neighbor's house. <S> In part, the specification at 10 m distance is simply meant to ensure a uniform test condition, because it gives a reasonable distance for "near-field" radiation effects to have fallen off and ensure the measured radiation pattern will be consistent with the interference effects at any distance in the far field. <S> But also, the regulations were developed in consultation with electronics manufacturers and they would have considered that trying to reduce radiation to a level where they won't interfere with each other at 0-1 m distance would increase costs (as alluded to in Leon's answer) to a point that would make many consumer electronic products unsaleable. <A> Short answer: because your radio didn't go through all that testing.
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The interference caused by GSM phones is an intentional radiator that is within the required limits of regulations.
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How to connect decoupling capacitor when VCC/GND pins aren't close I'm making a board which will host an ATmega 162 microcontroller in PDIP package. Unfortunately, VCC and GND pins are diagonally arranged. From what I've read, the capacitors should be as close to the pins as possible for maximum effect. Right now, I can see 3 ways to connect the capacitors. Run wires to the capacitors so that they are at equal distance from both pins, place capacitors near ground and run wire to VCC or place capacitors near VCC and run wire to ground. There's always the "none of the above" option too. How do I make right decision in this case? Or is is irrelevant? <Q> For these types of packages you should use at least two equal bypass capacitors, one at each side of the IC (one near ground and one near VCC). <S> The parallel inductance of two traces to two different caps lowers the total trace inductance and the current flowing from each bypass cap in opposite directions helps cancel out EMI. <S> See Henry Ott's book "Electromagnetic Compatibility Engineering" for more details here. <S> Apparently this technique reduces noise by a significant amount and will also help functionally. <S> This technique taken to the extreme would involve using a power and ground plane and surrounding the entire chip with bypass capacitors, or if you have the money to spare, using buried capacitance planes, but simply using two caps at either side of the package makes a large and measurable difference (as opposed to just at the VCC side) <S> (I'm too lazy to look it up <S> but I think we're talking 10dB+ improvement). <S> EDIT: <S> Added my cheesy drawing. <S> The arrows are supposed to show the canceling current loops (one clockwise the other counterclockwise), but note the capacitors should be placed closer to the chip then I drew. <A> <A> The decoupling capacitor goes as close to the power pin as possible, as the power line has a higher impedance than the ground reference. <S> There should be a large ground plane, ready to provide a very low impedance path. <S> A power plane is sometimes employed in multilayer (4+) designs for, among other things, a low impedance source. <S> You talk about wires, which leads me to believe you are using a breadboard. <S> In this case, decoupling capacitors are just as important, but parasitic inductance and capacitance and ohmic contacts will mask their effects. <S> Use the power rails for power and ground, and tie them together in multiple locations -- no ground loops! <S> I wouldn't bother with anything other than a large electrolytic (10uF) in a breadboard unless it doesn't work, as it is only for prototyping simple circuits. <S> (Does this work?) <S> Troubleshooting decoupling requires the real layout (if the final product is in a breadboard, then go for it). <A> The ground plane has a low inductance which reduces the effect compared to wiring a single trace to Vss. <S> The goal of the decoupling cap is to provide a local current source for the chip, so this works well. <S> If it's a breadboard, I usually just solder some wires to a 100n cap and wire it over the chip. <S> Messy, but it works. <A> However, the position of the capacitor along this wire should not matter.
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For a PCB design, I almost always use a ground plane and for chips with opposite power pins I place a cap next to the power pin and ground the other end. Overall distance matters, as inductance increases as you increase the wire distance.
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Are discrete MOSFETs ESD sensitive? CMOS inputs on microcontrollers and other ICs can be damaged by ESD discharges. Can the gate of a big discrete MOSFET (2N7000, IRF9530, etc.) be damaged by ESD discharges? <Q> Yes. <S> I've used MOSFETs which had a conductive rubber band around the pins to protect the gate(s) by shorting the pins, to be removed after soldering. <S> (TO-39, IIRC) <A> MOSFETs in circuits very frequently have explicit protection (Zeners on gates or clamping diodes in drivers) and other incidental ESD protections like pulldowns or possibly increased capacitance. <S> More to the point of "are big (and/or) discrete MOSFETs less sensitive", they are for two reasons: <S> The gate oxide is likely to be thicker and take more voltage to breakdown (though the input lines on an IC are probably overengineered in this manner as well), and The gate capacitance will be vastly larger, so it will take much more charge to build up a lethal voltage. <S> In a circuit, the more common failure modes (in my experience) are inductive spikes on the source pin blowing the gate, or those on the drain which can cause a fatal avalanche breakdown. <S> I don't think I've ever positively identified a dV/dt failure, which is where the voltage rise on the MOSFET is so fast, the parasitic capacitances between drain-gate-source are able to turn on the MOSFET causing bad things to happen. <S> Nevertheless, if you ground your source well and blast the gate right at the package with an ESD gun on 11, you might be able to kill it. <S> Users shouldn't be able to stick their grubby little hands on your gate lines because they could have just shuffled their wool socks along the polyester carpet, but if they can for some reason (???), a Zener should protect nearly everything. <A> YES absolutely. <S> I made the mistake of putting 2N7000 in my designs before and worked on them in environments that were not well ESD protected. <S> I have destroyed literally dozens of 2N7000's doing this. <S> The key issue for me is "how much" protection is necessary in designs. <S> Especially for production when adding protection costs money. <A> There is a second source of 2n7000 whith " KL " at the end of the reference made from VISHAY and is totally protected.
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Any MOSFET outside of a circuit will be extremely ESD sensitive as one spike on the gate that raises its voltage above the maximum and it will be dead.
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Heating an object with a circuit I would like to make a circuit that can heat up an object to a very high temperature, similar to an electric griddle or coffee cup warmer. What kind of heating elements do they typically use and where can I buy them? They should be pretty easy to power with 120VAC right? I just need to be able to switch it on and off from an MCU. Target temperature is ~200°C <Q> <A> A metal-clad wirewound resistor makes a pretty good ready-made heating element <A> Fortunately, cartridge heaters are very cheap. <S> McMaster Carr Cartridge Heaters Google Shopping <A> I would recommend looking at silicone heater pads, which take 120VAC. <S> McMaster is one place that has them. <S> http://www.mcmaster.com/#silicone-heaters/=aypumy . <S> You can pair them with a thermocouple and inexpensive PID controller to regulate the temperature. <A> Any electronic item can dissipate heat. <S> The temperature achieved depends on the thermal resistance to ambient. <S> Usually the temperature will rise linearly at a certain number of degrees per watt. <S> This is determined almost entirely by the load, and not by the element you are using to heat the load. <S> For further reading look at heatsinking app notes. <S> Notice that heat rise is above ambient. <S> If you care about the exact temperature you should plan to have some kind of feedback system to measure the temperature and turn the heating element on / off. <S> 200C is hot! <S> Most electrical components will be damaged by such heat. <S> Look for cartridge heaters as mentioned in other answers. <S> You can buy replacement electric range heating elements in an appliance store. <S> A complete electric heating plate is about $20 at discount stores. <S> These wirewound resistors are spec'ed up to 250C: http://www.mouser.com/catalog/specsheets/rhnh.pdf <A> I've seen a heater design that used fat-ish PCB traces as a resistive heating element. <A> Peltier Junction is a thermoelectric device, which is a kind of an electronic heat pump. <S> When you input DC, peltier element transfers heat from one side to another one. <S> Turn the DC around, and hot/cool change sides. <S> Also it is a good idea to monitor the device and regulate current accordingly. <S> One cool fact, if you heat it up on one side and keep the other cool, it will generate a current.. <S> http://en.wikipedia.org/wiki/Thermoelectric_effect <S> http://customthermoelectric.com/tecs_imax.html?gclid=CIK45N6F_KYCFYbb4Aodw3MjFg <A> Have a chat with these people (disclaimer: I have never used them) http://www.omega.com/ <S> This enclosure heater claims to have a surface temp of 170C. Not sure if you can get higher temp ones or whether it will heat the load you want: http://www.omega.com/pptst/RC016_Series.html <S> Resistance wire details: <S> http://www.omega.com/Temperature/pdf/NI60.pdf <A> I would like to make a circuit that can heat up an object to a very high temperature, similar to an electric griddle or coffee cup warmer. <S> If this is a hobby project or other one-off, why don't you repurpose an electric griddle or coffee cup warmer or iron <S> or...?
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You want a cartridge heater. Resistance wire is what you want. This is used in (at least older) space headers. But make sure you have a fail-safe. Just don't change polarity when it is very hot, this will stress the device and blow it up. Your local thrift store has a ready-made supply of these.
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Very low frequency (<1Hz) high pass filter design I want to design a very low frequency (<1Hz) high pass filter. I was thinking of using a 2 pole sallen-key opamp design with a pair of r's and c's. Is there anything special I need to consider when choosing component values/types. It looks as though the caps will need to be in the 100's of µF range. Thanks <Q> It depends on how accurately you are expecting to control your cutoff frequency. <S> A few point come to mind ... <S> Tolerance <S> High value electrolytic capacitors have wide tolerances, indeed cheap ones can be as wide as +100%/-50%. <S> You won't get much better than ±10% and stability could still be an issue. <S> Solid electrolyte (aluminium/tantalum) have better stability but will be much more expensive. <S> Leakage <S> Polarization Make sure that your circuit biasing keeps capacitors correcty polarized. <S> Charge/ <S> Discharge <S> High value capacitors will have to charge & discharge somehow if there is a non-zero dc bias (ie single rail). <S> This will cause turn-on 'thumps' as the circuit settles-down which may take a many (tens of) seconds. <S> At turn-off, the capacitors may discharge into the op-amp causing damage although given that your resistor values will also be large, this is less likely to be a problem. <S> The lowest frequency filter I have ever built was a 5Hz ±20% two-stage S&K (4 pole) maximally flat design which worked perfectly well. <S> You might also want to look at a Gyrator circuit to simulate a high value inductor. <A> I would vote for 10-100uF ceramic capacitor with large resistor + temperature controlled chamber OR ceramic cap + programmable resistor to compensate for temperature changes. <S> This should be more stable over time, but less stable over temperature. <S> Also, ceramic caps should have way less leakage. <A> It's very difficult (or even impossible) to do such filter with a simple 2-pole analog filter, depending on your requirements (fp, fs, As).Download and install <S> FilterPro (from Texas Instruments) and test some configurations. <S> That's a very good and simple program. <S> You enter the requirements of your filter, click on a button and then you get the circuit and the values for resistors and capacitors automatically. <S> Probably, with a digital filter you can achieve much better results. <S> Take a look at IIR filters. <S> What's the application of your high pass filter? <S> Maybe DC removal? <S> If so, google for IIR+DC removal, you'll get plenty of results.
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Electrolytic capacitors will have a finite leakage current which will produce dc offsets given that your resistor values will also be high.
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How to build cheap radio propagation beacon? I want to build a Radio Propagation Beacon but I would like to find an integrated circuit that does most or all of the work of the transmitter. Transmit to 28Mhz (Ham 10-meter band) Allow me to feed it Morse code audio and for it to transmit that. As cheap and simple as possible, such as a single-chip solution. I'll write some code on an Arduino to produce the Morse code. It doesn't have to be high power, 200mw range is perfectly fine. I do have an radio amateur license. <Q> Honestly, there isn't a lot of work to sending Morse Code. <S> The closest I can find to a "single chip" solution is one of these oscillators . <S> Add in some low-pass filtering and you're there... <S> The way I'd expect to make a circuit is to use a discrete crystal oscillator (like something you'd find in the ARRL handbook) and add another transistor to be able to switch the oscillator on and off. <S> A simple Morse Code radio is a good place to start. <S> A straight key can be replaced with a transistor, and that transistor can be driven by your Arduino. <A> Don't know if this helps but here, have a look at this: http://www.sparkfun.com/categories/16 and this more specifically: http://www.sparkfun.com/products/9411 <S> (This unit is legal without a licence in some countries !!! <A> I found a ten meter beacon kit which got a writeup in CQ Magazine (PDF) a while back. <S> It's 30 bucks, and looks like a quality product. <S> Should be a fun build!
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All you need is a frequency-stable oscillator that you can turn on and off.
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I want to be able to measure weight (typical range of human weight), what sensor can I use? I've seen this force plate from Vernier and it requires another USB interface device. They have an SDK that will they allow us to communicate with the force plate. Is there something that I can create on my own that also measures weight?I think that I've seen a strain gauge thread on this forum. There's this load sensor from Sparkfun (mentioned in thread) but it maxes out at 125lbs. I essentially want to create a plate for someone to step onto and be able to measure their weight. <Q> Like this? <S> http://www.walmart.com/catalog/product.do?product_id=5740778 <S> Or even its measurement electronics. <S> If you are making a computer interface to a scale, try to stick to the SMA Serial Communication standard: <S> http://www.scalemanufacturers.org/smastandards.htm <S> Then your scale will be instantly compatible with all software. <A> You can use a Nintendo Wii Balance Board. <S> It can be used to calculate weight, as this is what the Wii Fit games do. <S> You can connect to the balance board using Bluetooth HID. <S> http://wiibrew.org/wiki/Wii_Balance_Board <A> You could use levers to reduce the load on the sensor. <S> Take apart a typical mechanical/analog bathroom scale and you'll see that your entire weight is being carried by a small spring, with the help of some levers. <S> I have a picture at home that I can upload if you need more explanation. <S> I'd design a platform that gives you some horizontal stability before looking for a sensor, because the platform may have some mechanical multiplier in it. <S> If this is a one-off project, I'd re-use an existing mechanical scale and replace the spring with a different sensor, or a digital one and piggyback on the sensor or LCD readout. <A> Based on the discussion on Sparkfun (as found by following the link you provided) I understand that the general idea is to use more than one of these sensors to support your measuring platform, so that they share the load. <S> For example, you could put one of these sensors at each of the four corners of a plate and you would be able to measure up to 200 kg/500 lbs. <A> There is some discussion on this topic at this question: How to wire up a 3-wire load cell/strain guage and an amplifier? <S> In my answer <S> I discuss a project I built using a gutted bathroom scale and a Stellaris LM3S6965 evaluation kit to give the scale a web server that could be used to monitor the weight remotely. <S> From your description I could conclude that you should just buy a bathroom scale and weigh people and write the results down on a piece of paper <S> but I assume you have something in mind that requires customize hardware and software <S> or you wouldn't be asking. <A> There isn't a sparsity of sensors you could use; clearly mass-balance scales fill out a myriad of well documented critical design, leaving the choice of sensor up to your ingenuity and your subjects' (should they decide to form a human pyramid or play Twister as they shuffle over your foyer.) <S> If you pick a fiber laser spectrometer to sense weight though, the data should be worth the trouble...is it worth knowing who came in wearing Farragamo v. Jimmy Choos?
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Since you don't really describe your project goals I don't know if that will be useful or not, but hacking a bathroom scale is certainly an option and it will likely be a lot cheaper and easier than building something with pieces you buy from the various hobby vendors, especially since their stuff always seems to have a very limited range while a bathroom scale is already designed to weigh people. You could buy one and interface to its strain gage.
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How do I convert 12Vdc solar to AC? We are using 12V DC solar power at home, and I want to use it for home appliances. Can you suggest what should I have to use for this? At present we are using 4 (12V) lights and one DC fan. Now we want to use this source for AC fans also. <Q> Normally the way to convert 12v DC to 120v AC is to use a inverter like this one , designed for automobiles. <S> I don't know if your solar device would have enough power to run this or not. <A> You will need to use an Inverter to run AC devices off of your solar panels. <S> However as tcrosley stated you did not supply us with sufficient information on your setup as to the amount of current your panels output. <S> If your panels output 12 Volts at 10 Amps and you used a theoretically perfect inverter (no losses) you will only be able to drive a load at 120 Volts 1 Amp. <S> However there will be conversion losses. <S> Be careful using inductive loads with cheap equipment as you have a possibility of frying your inverter. <S> Hope this helps! <A> For solar applications you've got to design or buy special solar inverters which can track the Maximum Power Point of the Panel (Vmp and Imp). <S> A normal inverter would not do much justice to solar powered applications as the voltage of solar panel varies all round the day.
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There are several kinds of inverters and if you have large panels that you plan to run constantly such as off-grid you will want a pure sine wave inverter.
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Is it possible to repair a PCB which has suffered a DRC failure? Okay, so I was a bit of an idiot while designing my PCB. The specifications of my PCB fab were 6/6 mil trace/space, and the boards did not meet this. So, below is the design for the PCB: The trace going to C16 (a ground) is way too close to the pad which is connected through a trace to an inductor (it's a switch mode buck converter.) This basically connects the +3.3V line next to the filter capacitor to GND, shorting it. I verified this with the continuity test on my multimeter. My PCB: I have already bought 10 PCBs, so I'd like to know if it's possible to hack these and repair them. I'm okay with having to provide them with an external 3.3V source; in future, I'd like to get the converter working, but it's the rest of the circuit which is important. Obviously I won't make this mistake in the next version... I might actually run the DRC. This is only for development. <Q> If this is the case, find anything that you can place to add an insulator. <S> The hard part is going to be finding something that wont melt while soldering. <S> Maybe someone else has a suggestion with this, I would try electrical tape and hot air gun soldering. <A> If I were you, I would try to burn the small copper bridge with a current surge. <S> Using some cheap probes or solid wire, touch between the two points you don't want connected with a power source current limited to about 5A. <S> If it doesn't work, increase current limit -- I wouldn't go past 50A, though. <S> Note that the points you touch will oxidize immediately, and possibly also release magical smoke, so it'd be best if they were the edges of relatively large pads. <S> Of course, everything between the two wires will be destroyed by 5A-50A, so don't miss any current paths... <S> Now, I don't mind blowing stuff up -- <S> kinda' enjoy it, really -- but this method carries quite a bit of product risk. <S> Don't get too mad at me when you burn your fingers, break your PSU, and melt some FR-4 on your desk. <S> (You can get a little bit mad, though -- I understand.) <A> It's always a good idea to have a rotary tool with a fine tip handy when dealing with PCB rework. <S> I prefer a rotary tool to a utility knife, but have been known to resort to a blade at points (no pun intended). <S> It's quite acceptable to do PCB rework like this on small quantities, even in professional environments. <S> Make your cuts however you can, use your meter to make sure the circuit is OK, then fix the artwork. <A> I'd get out my magnifying glass and scalpel, it doesn't have to be pretty <S> so it's worth a try, just make light repeated scrateches next to the track, in a couple of minutes the grooves will ge deep enough to sever any contact. <S> I've had mixed success with this method.
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When ever I have PCB errors that cause something to be shorted to something else, I pull out my handy dandy razor blade and go at it. In your situation it looks like you might also have an issue with solder causing a short.
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When a battery is your power source, what is ground? For the sake of not incorrectly connecting my power supply and damaging my board I'm going to ask a relatively dumb question. Is ground on my board the negative terminal on my battery? Explicitly should I connect the ground to the negative terminal of the battery? <Q> Yes - just remember that your ground in that case will only be relative to the battery. <S> If you go to connect this to another device (serial interface, etc) you need to link the ground lines so they're a common ground. <S> So long as it is isolated, you're fine. <A> The ground pin on the microcontroller is two things: (1) a voltage reference, and (2) a current return. <S> Voltage Reference: <S> Voltages don't really exist at single points, voltages are differences between points. <S> This means that to speak sensibly about some single point in a circuit being at a given voltage, it has to be relative to some other point in the circuit. <S> With a microcontroller, the ground pin is the reference against which the inputs are 'measured' to determine whether they are high or low. <S> Current Return: <S> All the current that flows into a micro-controller has to flow back out again somewhere. <S> You're certainly aware that current flows into the +5V pin. <S> Note that some current will flow out various pins as signal outputs, but then some outputs will actually admit current into the chip. <S> Input pins can also source or sink current. <S> Regardless, whatever current is left over is expected to flow out the ground pin of the micro-controller. <S> In essence, the supply current is returned to the supply through the ground connection. <S> So when your power supply is a battery, it makes perfect sense to connect the (-) side of the battery to your system's ground pin. <S> Notice that this isn't just a voltage reference though <S> ; it is also the supply return. <S> In practical terms, what this means that the wire you use to connect (-) to the board's ground should be at the same size as the wire you use to connect (+) to the board's power input. <A> The potential is relative. <S> Ground is an arbitrary designation. <S> — <S> Fake Name <S> This is something I worked out recently, only then realising why the hydraulic analogy was causing me cognitive dissonance. <S> If a "voltage supply" was a waterfall, the image of a 12m top-to-bottom waterfall stuck in the middle of the sky, somewhere above my 5m waterfall which started 5m above the "ground" just didn't make any sense. <S> And then I tied the negative pin on my Arduino (powered by a 12V wall wart) to the drain on the transistors I was using to switch current to my LED strips and the circuit worked.
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The common convention is to pick one node in the circuit and call it 'ground', and then all voltages are specified relative to that.
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Vias on QFN centre pad in Eagle PCB I'm using some QFN devices in a PCB I'm designing using the Eagle PCB software. The QFN packages have a centre pad that is grounded and intended to help with thermal dissipation. When creating the package, if I have the centre pad as an actual pad then I get DRC errors when I come to place vias on the pad to connect it through to the ground plane on the opposite side of the board. Another possibility would be to leave the centre pad off the package and draw it in on the board, but this is a pretty unsatisfactory solution. What's the best way of dealing with this problem? <Q> Ok, I've found a solution to this problem. <S> The answer is to place the centre pad in the package with "stop" and "cream" turned off, then manually draw in rectangles for the "stop" and "cream" layers over the pad as they would've appeared anyway. <S> The physical end result is the same, but placing vias on the pad doesn't produce DRC errors. <A> When you create the package/schematic for the part assign the center pad to an extra pin on the schematic symbol and tie it to the proper signal (usually GND or occasionally VCC). <S> If you don't want to confuse the schematic, in most design tools you can hide a pin and internally connect it to another pin. <S> So you'd just hide the pin for the center pad and tell it that its grouped with a GND pin or whatever signal it should be coupled to. <S> Doing that should allow you to pass DRC checks. <S> Some design tools would treat multiple VIAs as a signal loop and remove them, you may have to set flag for the particular signal to avoid that check. <S> I've had to do this with Altium in the past <S> but i don't think Eagle does automatic loop removal <S> so you can probably skip this. <S> If the center pad is for thermal management, you need to make sure your using enough vias to conduct the heat. <S> In that situation i usually include the required number/size of vias in the actual package design and only nudge them around in the final PCB layout if I really need to. <S> I don't recall off the top of my head if eagle allows exploding package footprints for editing on the PCB or not. <A> Just put the vias in the pad and live with the DRC errors. <S> Perhaps you can do the same with Eagle. <S> I can also create pads of any shape with one or more vias in them.
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With the Pulsonix software I use I can put vias in pads without DRC errors provided they are assigned to the same net.
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I've done breadboards and programming, where is a good place to move on? I have a decent (equivalent of introductory college level) with circuit design, all on breadboards, as well as programming on a variety of microprocessors and a couple FPGAs. I'm just wondering where would be a good place to go on from here in more advanced and higher level circuit designs, but I'm not sure if I'm at the point where I should make the jump to PCB layouts, or is there an intermediate step that's recommended? I was highly considering making something like Arduino on pcb. I've also never actually used a soldering gun, and that's something I know I should learn, but I'm not sure really what kind of devices are good to learn that on, and circuits to do stuff like that. <Q> That will also get you soldering components. <S> Don't get a soldering gun, BTW, get a temperature-controlled soldering station with suitable tips. <A> A great way to learn how to solder is to buy a few electronic project kits ( <S> Quasar Electronics is a great site), and solder these together. <S> You can also find some good soldering tutorials on the internet. <S> A good intermediate step up from breadboards to PCBs is to use stripboard <S> which is a board pre-drilled with a grid of holes and strips of copper you can solder to. <A> Another way to learn how to solder it to disassemble old electronic devices. <S> You could try to desolder everything on an old radio or DVD player or something similar. <S> This way, you'll be able to see for yourself how different devices behave when being soldered and what kinds of damage they can take. <S> Also, you may be able to get some broken devices for free, if you're lucky. <S> Plus, you'll get a supply of various components which may or may not be useful. <A> Before you begin designing PCB's, you may want to familiarize yourself with a circuit simulation program such as PSPICE. <S> I would recommend getting PSPICE version 8 (student edition), which you can easily find for free. <S> It's older, but it has an easier-to-learn interface and does everything. <S> From there, you can design a circuit, and then run simulations on it to ensure proper functionality. <S> There are tons of PSPICE tutorials out there <S> and it is commonly used in college electronics courses. <S> Once you've designed a circuit in PSPICE, it can be exported to a PCB layout program.
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Try transferring the circuits you have been working on to stripboard.
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Need help with LiPO batteries I am planning on a 1 cubic inch robot as my next project in robotics and the biggest challenge I am facing is on the battery. Lithium polymer seems to be the best option in terms of weight and the required current output and rechargeable! The requirement in circuit is around 400mA with 3.5V, After searching a lot in Internet I could best get to this battery which fits my dimension and voltage requirements. But its still low on current so I plan on using them in parallel. I read that Li-ion and Lipo batteries are very sensitive and might damage the battery or cause fire if used incorrectly So I need some help on this! Can I use them in parallel ? Is that the right and safe thing to do ? If I use them in parallel then can I charge them to in parallel ? or do I need some special balancer circuit ? Can somebody help me with a decent charger circuit for this cell ? Anybody knows a better battery than this one that I can use in my application? Any other points/suggestions that will help me on this project that I missed out ? <Q> We have used LiPo in parallel successfully. <S> Parallel cells must have the same batch #. <S> When charging, use a voltage regulated source set to (slightly less than) the 4.2 volt cell charging voltage. <S> Look at a DC-DC converter with a current limit at 1C (240mA) <S> So you need a modular DC-DC converter for rated at 400mA, at <S> 4.2V.The upright-PCB ones are available from RS etc... <A> you can use it in parallel, and this does make things more complex. <S> And depending on how long your robot is supposed to run for will decide if its right or wrong for your application you can charge them in parallel but you will need a 2 cell charging circuit <S> I wish i could help you with this circuit but, but thats over my head here <S> is one from spark fun 1000mAh - <S> link <S> this one has the protection included, other places to look would be place that sell micro heli replacement parts <A> 1) You can use them in parallel without a balancing circuit if this is a one-unit school or hobby project. <S> The worst case scenario is that your robot prototype will burn up or blow up in the lab. <S> 2) You can charge them in parallel without a balancer, but you might want to cut the charging rate down to less than 1C of the whole pack so that an unbalanced cell is only getting 1C for that cell as a worst case. <S> So if you used 2 x 240mA-hr cells, you'd want to charge the battery at 240mA for a 2-hour charge. <S> For 4 cells, the same 240mA gives C/4 for roughly a 4-hour charge. <S> Extra: you need to make sure the battery is disconnected as a power input to the robot when it gets discharged to the minimum voltage, 2.75V for the example listed. <S> If your robot keeps trying to run until the battery is over-discharged, the battery could be permanently damaged and might have to be replaced. <S> Don't treat it like a capacitor that can be run down to zero volts. <A> I would suggest not using the two cells in parrallel. <S> Instead: Use the two cells in series, Use a simple buck converter to step the voltage down, Protect the cells from over-disharge (low voltage), Use a two cell charge IC for charge control (loads of these available from microchip, TI, Linear Technologies, Intersil, maxim and so on) <S> Not worry about charge balancing (not essential for a two cell pack - still useful) <S> Some part numbers of two cell charger IC's to consider:ISL6251, bq24170, <S> LTC1731, MAX1873, MCP73861. <S> Also the microchip website has a great application note for simple DC/DC (buck) converters using a small PIC - AN216 Going parallel will lead to potential issues in the life of the battery pack - series <S> will be much better <A> A buck conveter and multicell battery charger is way to complicated for a school project. <S> I work developing hardware <S> and im <S> telling you, that would take you a long time. <S> If you dont need more than 4 v use as many cells as you want in parallel. <S> Parallel batteries are inherently ballanced. <S> Use a simple dc power supply @4.1v to charge them. <S> Make sure not to discharge them lower than 3.5 so their life time is not affected. <S> Dont charge them higher than 4.1v, and dont leave them charging once they reached 4.1vIf <S> you're designing a robot ease your time in mechanical and software improvements. <S> Good luck
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If you were building this for mass deployment you might get a custom battery made, as big as you have space for and the right shape, that would have a higher capacity without having to use multiple cells in parallel.
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Earning a living in analog IC design w/o an EE degree I've asked other questions about having a career in electronics without an EE degree. I'm wondering specifically about being an analog IC designer. What would it take to land a position doing that before having that degree? What would convince an employer to hire me despite lacking that piece of paper? What kind of employer would I best off sending my resume and other info to? <Q> I can't imagine how you'd work your way up in less time, or that many companies would give you the opportunity. <S> Most analog IC designers have advanced degrees, and so there is a high barrier of entry. <S> A BS in EE actually provides very little in the way of analog IC design, and unlike things like programming, you can't really build an impressive resume hacking away in you're mom's basement. <S> The amount of money you have to drop for getting your own designs fabricated would be better spent on a degree. <S> Analog IC design is something where the "piece of paper" really comes in handy. <S> If you can't devote all your time to schooling, try getting a job at a tech company and go to school part time. <S> They may help pay for some of your education. <A> I have an MSEE and spent around 15 years doing analog IC design for several companies including large multinationals and a few startups (especially around 1999-2000). <S> I don't do that kind of work anymore because it has largely been outsourced to cheap but highly qualified labor in India (mostly) and China (more recently). <S> A few years ago, my department head finally told me he had more Phds than products he needed to be designed and since I didn't have a Phd, he could no longer let me do analog design anymore <S> (Phds like to do this kind of work because they can publish papers and eventually most hope to move on to teaching. <S> But don't worry, there are plenty more coming in the pipe all the time to take their place). <S> This even though I had a proven track record of high quality design work and many products in production. <S> Not sure why you would want to go down that path at all and certainly can't imagine anyone hiring someone for that kind of work with no degree. <S> The field is very mature, highly theoretical ( <S> which is why the emphasis on an advanced degree - you're not going to learn that on the job), heavily outsourced and with few entry level openings. <S> The large US multinational <S> I last worked for hires mostly at their Asia design centers. <S> Any US based hiring (which has been almost nil for the past 3 years and included huge layoffs of top experienced people in 2009) is highly targeted to specific tasks with solid qualification requirements. <S> I think you might want to look at a different line of work. <S> Maybe one hope is if you happen to speak Mandarin and are willing to work in sales and are familiar with Asia, that could be a possible back door way in. <S> Not kidding. <S> Good luck. <A> Is it possible? <S> Absolutely! <S> Are you going to get a job doing full-blown IC design straight off the bat? <S> No. <S> The best (and really only reliable) way to get a job doing high-level engineering without a related degree is to work your way up the chain. <S> Basically, get a job doing scut-work at a IC design company. <S> Ask lots of intelligent questions, do lots of reading, and try to make intelligent suggestions. <S> Assuming the company you work for is at all open to new talent, eventually you should be able to start working on more advanced topics. <S> Take your time, work your way up, and learn as much as you can as you go. <S> Now, the viability of this sort of approach is highly dependent on how rigid the corporate structure at the place you work is. <S> Personally speaking, it's how I got my current jobs (Consulting/Board layout/CAD). <A> Experience and track record, especially for analog. <S> You'd probably need to start at the bottom & work your way up. <S> Pubished hobby projects in the area will also be useful to show enthusiasm. <A> Not designing ICs. <S> The costs are high and the risks of bad ICs are high. <S> You would be better off with analog board design. <S> @bt2 is right. <A> The only thing I can think of outside of what is mentioned above would be to dive into a program like Electric , teach yourself how to use it (hopefully with guidance from an experienced engineer), make some kind of awesome and before unseen circuit, and finally get it in the hands of someone who matters and has the ability to hire you. <S> Jeri Ellsworth took a similar path with digital (granted, which has lower entry costs and less need to be near the process node and device physics) but did not have any education. <S> She stated in a recent interview that it was all because of mentors. <S> So in the event you think it's something you'd really want to do, that'd be a first step. <S> Even with a MS, a good mentor will get you farther than anything else IMHO.
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The fastest route would be to get an EE degree, then a Masters specializing in analog IC design. A rigidly structured organization is less willing to consider people without degrees, but a lot of it just depends on the people you are working with.
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How to secure components to a wire-wrap board I used to use a breadboard, and it would hold the components put into it. A wire wrap board is different. The components are don't seem to be secured to the board. How are they supposed to be secured to the board? <Q> I'm not sure if this is what you're asking, but you are supposed to use sockets specific to wire-wrapping. <S> The pins in these sockets are square and have very sharp edges. <S> The mere act of wrapping the wire will hold the socket in place. <S> Then you press your components into the socket. <A> You can also buy dedicated pins that allow you to solder on one side (usually bifurcated) and wire wrap on the other. <S> The pins have a shoulder that you can jam into the PCB through hole to secure it. <S> Basically, if you want to attach a component to a wire wrap board that component has to be connected to a wire wrap pin. <S> Whether that's a dedicated terminal, a single piece of a strip socket, a repurposed DIP socket, or a component carrier plugged into a DIP socket - that's your choice. <S> As an aside, unless you're dealing with exotic components or have a stash of wire wrap stuff, wire wrap components seem pretty expensive. <S> Digikey wants $3 to $7 for a 16 pin DIP socket. <S> You might be better served by doing point-to-point wiring on a Veroboard. <S> Edit to add: OK, given the specific example of a voltage regulator, how would you add that? <S> Let's assume this is a TO-220 or similar package. <S> There are three leads that need to be connected, so you need to connect them to three wire wrap pins. <S> Exactly how you do this depends on what kind of wire wrap pins you have: <S> Terminal pins (bifurcated or not) <S> : I'd solder the pins to the component, then plug the whole thing into the perfboard, then wire-wrap to the pins. <S> DIP socket: plug the three leads into 3 adjacent socket pins (bending if necessary), then wire-wrap to those pins. <S> SIP or discrete sockets: same as DIP sockets. <S> If this were a TO-92 with an off-pitch triangular lead layout, you might have to "normalize" the leads to fit the 100 mil pitch of the perfboard. <S> Just use good pliers to make it fit (or cheat and get the 3 leads started into 3 holes, and use the perfboard to leadform it - this is what I'd do). <S> Other tips: <S> Don't forget that you can cut skeletonized wire wrap sockets apart to make discrete socket pins/SIP socket strips. <A> I used to solder them to carriers plugged into wire-wrap sockets.
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You might have to glue the wire wrap sockets in place, especially when using single-pin connections.
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multi turn potentiometers to measure degrees I want to display degrees in a seven segment display when rotate multi turn potentiometers.After rotating one round it should be reset to 0 degree.I can use A to D converter ICs.But how I give voltage signal to it when potentiometer rotates after one round. <Q> First of all, it's kinda bad idea <S> - potentiometers have noise while in movement, and this will distract your readings. <S> For multiturn potentiometers you just have to calibrate them: <S> rotate by 90' write down ADC reading, then again and again until you reach the limit. <S> Then you do interpolation to get reading between your calibration marks. <S> In order to reset to 0 - you just add %360 in your code (so that calculated value would 'wrap' after 360'). <A> You haven't told us what type of potentiometer you're using or what you are using to drive the display, so I'll assume that you're using a linear potentiometer and a microcontroller to drive the display. <S> I that is so <S> , you could measure the voltage difference for one turn of the potentiometer and use the microcontroller to remove full turns. <S> For linear potentiometer, it's going to be easy. <S> Just measure how big voltage difference is for one turn and then do a module of that. <S> In C that would be something live Voltage= Input_Voltage % Turn_Voltage; and the just feed the Voltage into the routine which calculates number of degrees. <S> Some logarithmic potentiometers have actually two (or more) different linear elements inside, so you'll need to get a graph of voltage and number of turns. <S> If you aren't using a microcontroller, you can do this using discrete components too, but it's going to be more complicated. <S> Also, I haven't done something like that for quite a while, so I can't give you any advice there. <A> It would be helpful to know more about the background of your project. <S> However, this implies that you expect the potentiometer to rotate more than one full rotation. <S> But how many full rotations do you expect from the user? <S> 5? <S> 10? <S> infinite? <S> The issue is that you'd basically need a 1:1 ratio from input rotations (from the knob) to output rotations (connected to the pot) on a multi-turn pot, but this is going to limit your angle resolution. <S> If you want 5 turns, then you need to buy a 5 turn pot, and the entire resistance over the 5 turns "shares" the ADC range. <S> In other words, for every N turns, you reduce your angle resolution by 1/N. <S> It would be disappointing to fiddle with a knob and only see something like 15 degree increments. <S> Of course this is also a function of your ADC resolution. <S> If you need high resolution and you have a low resolution ADC, then you'd probably want to "gear down" the knob. <S> In other words, one rotation of the knob = <S> N rotations of the pot. <S> This way, the one rotation of the knob gets the full ADC range. <S> But then you wouldn't get multiple turns of the knob. <S> If you need infinite rotations, then you need to put in a rotary incremental encoder. <S> Something like that from an old mouse could work, and then you'd similarly gear the system down. <S> Then implement a really simple lookup table in the microcontroller to keep track of where you are. <S> Of course, this means you'll also need to use an input to set 0 degrees.
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If the potentiometer is logarithmic, you'll have to record its voltage over whole range of motion and then make a function which will be used by the microcontroller to see where the dial is. Proper solution is to use encoder - they already have digital output and way way more reliable. The fact that you want the display to reset to 0 after a full rotation is not an issue, and implementation is easy.
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Is the Microblaze soft cpu better than the Cortex M3 soft cpu Is the Microblaze soft cpu better than the Cortex M3 soft cpu in terms of functionality? Given all the buzz about the ARM based processors, I was wondering if to implement an ARM processor on my FPGA or if I should stick to the Microblaze that comes with it. Is there any major difference in terms of performance or functionality that I should consider? <Q> The two major points are: <S> The Microblaze is a well supported soft core. <S> Many other IP designs are made to interface with it. <S> ARM is popular, but you'll have less support available, especially from Xilinx, who designed the Microblaze. <S> Using an ARM core will let you use compilers (and code) designed for the ARM architecture, which is desirable because (according to my totally unbased guess) <S> more code is written for ARM than for Microblaze. <S> I'm not familiar enough with either processor to make further comparisons without a list of priorities. <S> What do you value in this processor? <A> A 'standard' CPU core will use a lot more resources in an FPGA than one specifically targetted at a particular FPGA. <A> It also has additional features such as hardware floating-point operations. <A> regarding functionality MB vs ARM Cortex-M3, basically the Cortex-M3 contains a ARMv7-M CPU and that means it's based on ARMv6-M. Check out some screenshots showing off mainstream features. <S> MB will definitely be better integrated on Xilinx FPGA fabric and its 'in the field' since many years. <S> For more info on MB, search UG081 - MicroBlaze Processor Reference Guide. <S> Kind regards
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The Microblaze processor has the advantage that it was designed for use on Xilinx FPGAs and will therefore offer more performance than the ARM.
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how to drive a 1.35V led with a 1.4V AA battery I would like to mount a TSAL6400 led on a single AA size battery box, with a simple ON/OFF switch. My problem is that the LED needs exactly 1.35V to function at its rated brightness. At this voltage it uses 100 mA current. I would like to use Sanyo Eneloop batteries. I've measured them and they have 1.405V one day after charging. I think they will drop to about 1.395V @ 100mA. I've followed the LED tutorials, which all say I have to wire a resistor in serial with the LED. My problem is that if I calculate, that resistor needs to have (1.4-1.35)/0.1 = 0.5 Ohm resistance. My question is that what would you recommend me to do this project? I would like to make the box as little as possible, I'm planning on mounting everything directly on a single AA box. Shell I use two 1 Ohm resistors in parallel, to get a 0.5 Ohm resistor? Can I possibily use some micro turn potentiometers for my problem? It would be the best solution, as then I could just use different batteries, as all I would need to do is to set it after changing batteries. I am mostly interested in this solution. Can someone explain to me what is the best way to get 1.35V from 1.4V-1.6V sources using a simple potentiometer? Maybe it's an overkill, and I really don't know how to use them, but can I use a voltage regulator for this purpose? I mean is there a voltage regulator which is small and can provide as little as 0.4V drop? UPDATE:I've made some measurements on my LED: 1.184 V - 12 mA 1.315 V - 75 mA 1.345 V - 93 mA 1.357 V - 100 mA 1.380 V - 110 mA The last one is when I connected it directly to a Eneloop AA battery. By definition it's overdriving, but I don't know how dangerous it is for the LED. <Q> Use a switching boost converter to, say, 3V. The output will be regulated, so you will be able to get a stable 100 mA through the LED with a suitable resistor, and the battery will last much longer than if you connected it directly to the LED and resistor. <A> Such a circuit will allowyou to pull useful current out of a single AA, AAA, etc battery even when the voltageis far below the LED's threshold voltage. <S> Not sure this will generate a full 100mAthough-- this will depend on the inductor and resistor values. <S> Schematic: <S> http://www.prc68.com/I/JouleThief.shtml <S> References: <S> http://www.emanator.demon.co.uk/bigclive/joule.htm <S> http://www.instructables.com/id/Make-a-Joule-Thief/ <A> By coincidence I was looking for a bycycle dynamo operated LED lamp. <S> White LEDs require about 3.6V, but because the supply varies from the speed you cycle (6V max, AC) I had to put a bunch of electronics in there for it anyway. <S> Furthermore I wished high effiency, I don't want to be cycling for a resistor converting my power into heat.. <S> So I started looking. <S> Also note that if you get a 1.4V battery, if you drain it, the voltage will slowly drop to about 1V. <S> At 0.8V it's completely dead. <S> You may want to consider to have a working product at 1.2V or 1.1V for example, also if you want to support rechargeable batteries. <S> For that you really need a DC/DC converter to boost a voltage up. <S> The LT1932 is probably even more suitable for your purpose. <S> It converts a low voltage to a constant current (which you need for a LED). <S> It's a bit expensive (because 1) it's linear technologies, 2) <S> you're trying to do something low-voltage), but it is able to drive a single LED from 1V. <S> It also has a SHDN pin <S> so you can control it <S> : It can drive several white LEDs (they require over 3V drop each) from 2V input. <S> This figure shows 4 white LEDs, so that's why it needs 2.7V minimal. <S> I don't know how it will behave if you put only 1 LED in there, but I think it will work just fine. <S> All you need for this driver is shown there. <S> Rset sets the current through the LEDs(in the datasheet is probably a table). <S> It drives the LEDs in this example with 15mA. <S> And as said, LEDs are controlled by current not by voltage. <S> The resistor you normally use only sets a 'fixed' current (for a certain voltage you apply on the system). <S> This regulator is set to a certain current with the resistor Rset, and then you're done. <S> If you put another LED in series, it will adjust the voltage so the current stays the same. <S> Ofcourse, this has limits, but you won't reach that I suppose. <S> There are more of these IC's and are quite handy. <S> You probably find more examples that are cheaper, but might not be able to work from 1V. <A> LEDs need current, not voltage. <S> When an LED is conducting it imposes a certain voltage at its terminals but <S> the current that flows through is conditioned by a "conditioning circuit" (which can be a simple resistor in series). <S> You are right, you need 0.5Ohm resistance (which, just like you said, you can get with two 1Ohm resistors in parallel) but once is a very small value it probably will work well without it. <S> If you want to turn led ON/OFF maybe the use of a transistor should be a better option. <S> The transistor works as a LED drive. <A> As Leon Heller says, you will need to boost the voltage to something higher. <S> From the data sheet, it could be as high as 1.6V and as low as ... <S> who knows, the data sheet doesn't say. <S> If we suppose that the distribution is symmetrical, it could be as low as 1.1V, in which case the current you will get with a 1.4V battery and a 0.5Ω resistor could be anything between zero and 600mA. <S> If you are only building one of these, you might well get a fairly 'average' LED and get a reasonable brightness - but you can't guarantee it. <A> You don't always have to have a resistor. <S> They are there to limit the amount of current going through the LED. <S> LEDs have a maximum current rating, and can also handle a higher current if you PWM them for short periods of time. <S> Anyhow, if your battery has a limited output current, you don't even need the resistor. <S> For example, with LED throwies, you typically use a coin cell. <S> I can't remember the exact amount, but I think they max out at 20mA, which is well within the rating of most LEDs. <A> The 1.35V indicates to me that it is an infrared or IR LED. <S> In its simplest form this is a chip with a few components such as an inductor, resistors and capacitors. <S> One maker of these is Maxim.
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Instead of a voltage regulated circuit and a resistor, you should use a current regulated circuit. The simplest circuit you want is commonly called a "Joule thief", which consistsof a resitor, NPN transitor, and a hand-wound inductor. The 1.35V forward voltage you mention is not an accurate reflection of the voltage you will get with 100mA forward current, but a statistical average.
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Crude/inexpensive AC to DC transformer I am working on a circuit that is completly powered by 5VDC from a USB port. The circuit uses SSR's to turn on and off 120VAC from a standard wall plug; the 120VAC powers a high-power heater of sorts. Now it appears as though I am also going to need to add a PC fan into the mix. Most of the PC fans that I have seen run off 12 VDC. So what would be the cheapest and easiest way to get 12VDC to my fan. I am thinking that it doesn't have to be well regulated and smooth becuase the ONLY thing it will be used for is powering this fan. I will likely use another lower power SSR to turn the 12VDC on and off from my MCU. Extra points for a space saving solution as well! <Q> Looks like MPJA.com has 12V, 300mA power supplies for $1.25 and if you buy 50 they're $0.99. <S> That is hard to beat! <S> But they aren't the smallest solution. <S> http://www.mpja.com/prodinfo.asp?number=18295+PD <A> Has the transformer, rectifier, filter and regulator built in. <S> can get fans cheap also. <S> Check these links, $8.50 for all. <S> http://www.allelectronics.com/index.php?page=search&search_query=dctx-1227&x=39&y=7 http://www.allelectronics.com/index.php?page=search&search_query=CF-387&x=29&y=12 <A> Why would you not just use a 5 volt fan? <S> http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=259-1345-ND <A> Ok here's my best guess. <S> I can get a transform at Radioshack for $4.49 that will drop the 120VAC down to 12.6VAC. <S> (Suprising I couldn't find a transformer of this type cheaper on digikey or mouser)Transformer: <S> http://www.radioshack.com/product/index.jsp?productId=2102494#inTheBox <S> Then I could use four 1N4007 diodes to make a full wave rectifier. <S> Cost of diodes is about a dollar total. <S> Finally stick a large capacitor at the output to smooth out the signal. <S> This puts the total cost around $7. <S> I know the output won't be prefect and it will be a little higher than 12VDC <S> but I think it should be fine for a PC fan... <A> I'd think outside the box on this one: <S> Go get a 12VDC wall wart from Goodwill and switch with a relay on the DC side (or a solid-state solution to taste). <S> For your $2 you may even be able to find one with an on/off switch.
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You could just get a 12VDC wall supply.
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Weird Toyota Prius and USB behavior My brother in law bought a Prius recently. He's experiencing something strange with his iPod.If he has his iPod plugged in via the USB cable to the Prius, everytime he starts up his car, it resets his iPod. If he unplugs his iPod first, starts the car and then plug in the iPod, the iPod is fine. What can be the problem? Is there some sort of surge in the Prius circuitry that resets the iPod? Is there an electronic hack for the USB cable to fix this? <Q> I would say it is very very dangerous for iPod. <S> Eventually it might die instead of reset. <S> This must be the transient spike going through USB. <S> So, I would take a look at it at oscilloscope. <S> And before that I would switch to separate 12v->USB adaptor, not the bundled one. <A> How about decoupling capacitors for the iPod? <S> You could have one male and one female USB port on the device and put the capacitors between the GND and +5 V pins. <S> The data pins should be directly connected between two plugs, because iPods may need some circuitry there and since the charger does work, it would be best to use its circuitry for that. <S> Here 's USB pinout. <S> From what I've read, if we have 3 V of ripple when the car is starting, 2200µF electrolytic capacitor would probably be enough for full USB 2.0 load, but I'm not too sure. <S> For voltage rating, I'd take at least 25 V, but more is better in that area. <S> You could also look for low ESR capacitors. <S> They should work a bit better. <S> Some people say that it's a good idea to put in parallel capacitors of several different values, because they all block noise at different frequencies. <S> Another option worth considering is to get Toyota's iPod connector, but it's going to be more expensive and defeat the purpose if having a hack. <A> I wouldn't be so sure that it is a voltage spike issue. <S> In a Prius you don't have an engine starting when you first turn on the car <S> so there isn't as high as noise as most standard engine cars. <S> I am going to guess it is 1 of 2 things: <S> I believe the Prius is one of the cars that will actually communicate with the iPod and pull off data over USB. <S> If this is the case I could see the negotiation with the iPod getting interrupted on start up causing the iPod to think something funny was going on and resetting itself. <S> There is a large amount of electronics getting turned on at the same time that are all pulling from a battery. <S> This situation could cause a dip in power that could cause the iPod to go in a brownout state that it is smart enough to recover from. <S> If either of my guesses are true, then most of what has been mentioned before wont work. <S> Ex: voltage regulator - the car runs at higher then 5v <S> so they already have to have a voltage regulator of some sort. <S> I don't think regulating again will help at all Switching to your own 12v to 5v regulator - <S> If you do this then you will loose the ability to pull data over USB. <S> Decoupling Caps - <S> This might help, the tricky part is figuring out where to put them. <S> If it is a negotiation issue the cap will need to be placed on what ever component handles this negotiation. <S> Probably will be hard to find and will most likely void a warranty. <A> When the car is started there is either a voltage spike or drop, as for a fix, Create your on DC-DC converter, 12v(car battery) to 5v(usb). <S> you could easily use a simple 7805 regulator and a few caps to even out the signal, and prevent those spikes/drops. <A> Not sure about the Prius, but normal automotive power surges are a very nasty environment for electronics. <S> You can have low dips and high voltage surges. <S> Special care is required with caps as discussed above as well as diode protection at the input. <S> The car lighter converter is probably a little light for the job. <S> [update] An related article from a vendor http://www.maxim-ic.com/app-notes/index.mvp/id/760 .
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Capacitors basically resist voltage change, so you could design a device which will go in between the iPod and USB cable and have some decoupling capacitors which should be strong enough to power the iPod while the car is starting.
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Determining the ramp-up speed for a stepper motor with its drive system How can the required ramp-up speed for a stepper motor which is attached to its drive system be determined? Given that a stepper motor requires ramping-up to full velocity, and that ramp speed must be slow enough so that the motor doesn't simply vibrate in place, is there a known method for determining the ramp-up speed? <Q> There is, of course, some amount of lag time between when power is applied and when the shaft actually starts turning. <S> Perhaps you can get some idea of where your motor is by temporarily attaching a potentiometer to the system. <S> Note, depending on the package, you may have to break off the little tab to enable it to rotate completely. <S> There will be a "blank" spot in its rotation but it will still give you at least some idea of where you are at. <S> Apply a voltage across the pot and watch it on a scope relative to the stepper control signals. <S> If you are ramp is too slow you can see when the stepper starts turning backwards for a bit until it settles in its next step position. <S> Adjust you ramp speed to make the next step so that the motor does not move backwards at all. <S> Also note that attaching a pot to your system changes the system by adding at least a tiny amount mechanical load to the stepper motor. <S> Hopefully this will not be too great <S> and you can still get fairly close to optimum timing on the ramp up and ramp down. <A> In my experience, stepper motors either run fine, or vibrate. <S> The disconnect between working and too rapid acceleration is VERY obvious. <S> Assuming you have the whole thing set up, and you can freely run the axes back and forth, determining acceleration rates is therefore easy. <S> Basically, set the system up to cycle one of the axes back and forth, and then gradually increase the acceleration rate until it stops moving. <S> Then back it off about 10-20% Repeat for other axes. <S> Note: The system has to be loaded while testing. <A> If you visit the web sites of companies that manufacturer quality stepper motors, you'll likely find documentation giving the theoretical way to calculate this. <S> You'll need to know a lot about the mechanical load, and be prepared to do a fair amount of math. <S> But if you are designing a printer to sell at a loss and make it up on ink... it's worth optimizing these things so you can use the cheapest motor that can meet your ramp speed requirements. <S> But in the more likely case, if you are building a one-off robot or hobby CNC machine or whatever, chances are you are going to buy the biggest motors you can get a good deal on (or you've already extracted them from that ancient printer), and then crank up the ramp-rate until you find it unreliable, then back off whatever safety factor you desire. <S> A well engineered and adjusted high voltage chopping drive amplifier will be necessary to get the maximum performance out of the motor without damaging its magnets.
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To have the stepper motor ramp up as quickly as possible, but no too quickly so that it stalls requires knowing when the motor shaft has actually turned to the next step.
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Do I have to use a MAX232 chip? I am trying to interface my ATmega chips to the computer using a serial interface. I have read that this can be done directly by connecting the appropriate pin between the chips and the serial pin. But it is advised that I use a MAX232 chip. What is the purpose of this chip and do I really need to use it? I ask this because in a project I am making, there is a big size constraint and the chip might take up valuable space. <Q> If you need to connect the AVR to the computer using the serial port and a "standard" DB9-DB9 serial cable, yes, you need to use an RS232 transceiver in circuit. <S> The AVR's UART outputs 0-5V signaling. <S> The RS232 spec is +/-15V signaling, and I believe it's also "inverted" with compared to UART signaling. <S> These chips (plus some external capacitors) handle the voltage level conversions (via charge pumping) in either direction as well as the signal inversion, and act as "line drivers" driving longer lengths of wire allowed by the RS232 standard. <S> Alternatively, you can use a cable that includes such a transceiver circuit embedded in the DB9 shell if you are space constrained on your board. <S> Yet another alternative involving a cable is to use a cable that includes an FTDI FT232 chip in it, which has the advantage of making it look like a COM port over USB to the computer, but you're looking at upwards of $15 for that cable. <A> The RS232 specification requires a signal voltage of between -3 and -30V for a logical '1', and a signal voltage of between +3V and +30V for a logical 0, input impedance is around 3k and output impedance should be around 300 ohms. <S> If you're going to implement a fully complient interface then <S> Alternatively you could utilise one of the handshaking lines from the DTE (PC or similar) to supply the negative voltage and use a simple transistor level changer to handle the signal inversion (from the MCU) and level shifting. <S> This does however require that the DTE is configured such that it's handshaking lines are in a suitable state. <S> Another option is to take advantage of the fact that most equipment these days implements RS232 using something like a MAX232 device. <S> While these are fully complient with the specification they also extend things so that the input levels are basically +2.8 to +30 for a logical '0', +1.4 to -30V for a logical zero (from memory) <S> - in other words the receivers actually include TTL signal levels. <S> So you can just invert the signal on the UART pins and pass it out directly to the DTE device. <S> This technique is used on quite a few devices including many handheld GPSes. <S> I'm not saying you be 100% compatible <S> but you'll find this works more often than not. <S> You still need to invert the UART signals ( <S> unless you're bit-banging the pins yourself), two inverters should be smaller than the MAX232 plus associated circuitry, but probably not by much. <A> As vicatcu said, you do need something to translate the signal levels from the mcu to something the PC's serial port expects. <S> You don't have to use a MAX232 or similar -- <S> Sparkfun has something that would work.
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You don't have to use specifically the MAX232, but you do have to use a RS232 transceiver. yes, you will need something like the MAX232 - or an alternative, like the MAX3221 which does come in a quite small TSSOP package.
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How to use AD 676 Analogue to Digital IC I want to measure degrees using linear potentiometer, so I thought to use the AD 676 analogue to digital converter (ADC) IC. Is this a good ADC for monitoring a potentiometer? If so, how can I use it? A schematic of an example implementation would be helpful. <Q> Why did you choose the AD676 in particular? <S> It's a 16-bit ADC, which is much more than you need. <S> A potmeter rotates over about 270°, so an 8-bit ADC would give you a resolution of about 1°. <S> Nowadays it's often easier to find a 10-bit ADC, and they don't cost much more. <S> Normally you should also look at the ADC's speed, but for reading a potmeter 10 samples per second should do and any SAR (Successive Approximation) <S> ADC will do here (most will easily be a thousand times faster). <S> How do you want to interface it to your microcontroller? <S> I2C, SPI? <S> A standard serial protocol makes it ridiculously easy to interface your ADC with your microcontroller. <S> As an example the following "schematic" from the Microchip MCP3021 datasheet : The MCP3021 is a 10-bit ADC which interfaces through I2C. <S> It comes in a 5 pin SOT23 package: 2 x power (Vdd, Gnd) 2 <S> x I2C (SDA, SCL) 1 <S> x Analog input <S> That's all you need. <A> This data sheet contains one example circuit. <S> You will need to specify a bit more on your requirements to get a better answer. <S> I think that particular chip is a bit overkill if you just want a simple measurement of a potentiometer. <S> I would go for a chip with 1) <S> a breakout board and 2) sample code <S> if this is your first chip you're talking to. <S> It's just easier to get started and will save your potential problems the your first time around. <A> If you'd use the full scale of your ADC (so if it can read 0 - 5V, you would use min 0V and max 5V), you have over 65000 positions.. and a lot of noise to deal with. <S> A 10 bit ADC has about 1024 positions. <S> If you want to encode 360 degrees , you could get up to 0.36 degrees resolution. <S> However, potentiometers don't turn full 360 degrees or circles, so you will likely be limited to about 270 degrees. <S> Stevenvh showed a simple example of how to connect the ADC. <S> Connect the SDA and SCL signals on your microcontroller on the appriotate pins. <S> Look up the datasheet for your devices to see what pin that is, that's different for every chip. <S> The analog input would just be the middle tapoff from the potentionmeter, and just apply +5V and 0 to it <S> (if your potentiometer can read up to +5V)
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A AD676 ADC is way too extreme for your purpose of reading an analog potentiometer signal.
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Is it possible to generate basic dual rail power from two bridge rectifiers? As in the question title. Is it possible to generate basic dual rail power from two bridge rectifiers? I tried wiring one forwards and one backwards in a simulator, but I found that it did not work. Does anyone know if it's possible? Instincts say no, because it would require doubling the supply voltage, and that's tricky with just diodes. <Q> If the bridge rectifier follows a transformer, and the transformer has a center tap, then the center tap is at the middle (ground) potential. <S> This is the standard linear power supply fpr hifi amplifiers or to make +/-15V for op-amps. <A> There's no such thing as a "backwards" bridge rectifier, it's just a regular rectifier with the schematic laid out in the mirror. <S> Therefore, you would get exactly the same voltage levels from both rectifiers. <S> Another option is to use two half-wave rectifiers instead of bridge rectifiers, with large caps to smooth out the blank sections. <S> This would likely yield less voltage overall, but should be workable. <S> Yet another option is to use a voltage doubling rectifier and tap a virtual ground off the middle of the doubling ladder. <A> Yes it is: ( source ) <S> I didn't know about this before, but you can make a split rail PSU this way - from a single bridge rectifier. <S> Tap off the center as ground and you've got a positive and negative rail from the caps.
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What you obviously could do is use a single rectifier, and then split the voltage to make a virtual ground.
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SSL from a Microcontroller I am wanting make an embedded device that can communicate with a web-server in a secure fashion. My preference would be for it to use standard SSL so the web-server views my device similar to a web browser. Are there any prebuit libraries forthe embedded side to do this? What about an IC that can handle thehandshaking and decryption for me? If not how would I go about doingthis myself? <Q> Consider these embedded SSL libraries: http://www.yassl.com/yaSSL/Products-cyassl.html <S> http://polarssl.org/ <S> http://www.matrixssl.org/ <S> And maybe http://gitorious.org/tropicssl/ Tropicssl and polarssl originated from http://www.ohloh.net/p/xyssl <S> Tropicssl and xyssl are BSD licensed, whereas as all the others are GPL with an option for a proprietary license for $. <A> I suggest the Microchip TCP stack . <S> Microchip offers a free licensed TCP/IP stack optimized for the PIC18, PIC24, dsPIC <S> and PIC32. <S> But it's not free. <S> See below: To comply with US Export Control restrictions, the encryption portion of the SSL module must be purchased separately from Microchip. <S> The library of Data Encryption Routines (SW300052) is available for a nominal fee from http://www.microchipdirect.com/productsearch.aspx?Keywords=SW300052 . <S> For better results, you can use ENCx24J600 <S> that has built-in AES encrypt/decrypt engine and other securities engines. <A> If the system can be complicated enough to run an operating system, there are plenty of tools and libraries that can do the job. <S> On an embedded Linux system, you can use wget with SSL. <S> If you only have access to C, you could write something using the OpenSSL library . <S> If there's no OS, I think you're in for a lot of work. <S> At minimum, you need a TCP/IP stack. <S> I'd build a prototype with an mbed-- <S> there's a forum post <S> that suggests they might have an SSL library by now. <A> This seems to support AES SSL as well: http://www.lantronix.com/device-networking/embedded-device-servers/xport.html
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On any system with higher level languages like Python or Ruby, the networking library ( Python SSL ) will support SSL. Microchip’s TCP/IP stack includes the Secure Sockets Layer (SSL) feature.
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Can I use 10\$\mu\$F caps in a MAX232? this is just a quick and dirty question. I don't understand the purpose of the 1 \$\mu\$F caps in the MAX232 circuit. What do they do, exactly? Can they be skipped? Can they be swapped with 10 \$\mu\$F caps? <Q> They're definitely required! <S> For their function look at the block diagram <S> You'll see that they're connected to the voltage doubler and voltage inverter. <S> These create +10V from the 5V power supply and -10V resp. <S> This is done by charge pumps . <S> An oscillator will control the switches so that either S1 and S3 are closed or S2 and S4. <S> When S1 and S3 are closed C1 is connected to ground and V+ and charged to V+. <S> When S2 and S4 are closed the top of C2, which is V+ higher than the bottom is connected to ground, so that the bottom now is V+ below ground. <S> Via <S> the switches the charge flows to C2, which will then have a negative voltage. <S> So that's for the inverter. <S> The same principle is used to double the incoming voltage. <S> C1 and C2 are the external 1\$\mu\$F capacitors. <S> If they're omitted there won't be any +10V or -10V <S> and no signal at the drivers' outputs. <S> The switches might have some resistance and the capacitor may not get fully charged in the time one pair of switches is closed. <S> edit <S> In a comment to another answer which said 10\$\mu\$F will probably be OK <S> someone said: It should always be OK to use larger sized caps but they are required. <S> ~7 volts for RS-232 (I measured mine). <S> He didn't say, but it looks like he used 10\$\mu\$F. <S> If you use the recommended value of 1\$\mu\$F you should get \$\pm\$10V. <S> The 7V seems to confirm my doubts about the charging of the larger capacitors. <A> The purpose of the 4 capacitors is to generate the +/-12 <S> volts needed for RS232 communications. <S> The MAXIM and TI MAX232 datasheets recommend 1uF capacitors. <A> The MAX202 is a better choice, it can use 100n ceramic capacitors. <A> They are used for the converter inside to make a negative voltage for the RS232 lines (which is +/-). <S> Honestly, I don't see why you would prefer a bigger cap, as they normally become more expensive and larger.. <A> From the data sheet for the ESD protected version under Applications Information (page 13): <S> The MAX202E, MAX206–MAX208E, MAX211E, and MAX213E require 0.1µF capacitors, and the MAX232E and MAX241E require 1µF capacitors, although in all cases capacitors up to 10µF can be used without harm. <S> and Use larger capacitors (up to 10µF) to reduce the output impedance at V+ and V-. <S> This can be useful when "stealing" power from V+ or from V-. <S> The data sheet for the non-ESD-protected version doesn't include this information. <S> From reading the data sheets, I find the following differences between the MAX202E and MAX232E: MAX202E MAX232EIcc <S> mA <S> 8 - 15 5 - 10Iclk kHz <S> 230 <S> 140Caps <S> µF <S> 0.1 <S> 1 <S> Otherwise, they seem to be the same.
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In its datasheet Maxim recommends 1\$\mu\$F for the MAX232, 100nF for the MAX232A. I wouldn't recommend using 10\$\mu\$F instead of the 1\$\mu\$F. The caps are part of charge pumps that produce and store +/-
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How to remove glued capacitor from the board? How to remove that capacitor from the board? capacitor http://vi-server.org/vi/_/cap1.jpg In the question about damaged power supply I was told to use "a sharp utility knife", but it don't cut that thing (is it epoxy?). Also tried old not-so-sharp scalpel (it can punch that things if pressed hard, but not cut). knife http://vi-server.org/vi/_/cap2.jpg What other methods of removing it can you propose? Update : Mission accomplished: removed capacitor http://vi-server.org/vi/_/cap3.jpg <Q> The cap is made of aluminum, wrapped in a plastic jacket. <S> The jacket is glued down. <S> Can you slit the plastic and remove the capacitor, leaving the jacket where it is? <S> Otherwise, try a bit of acetone on the glue and see if it softens any. <S> (Acetone + perfume = <S> nail polish remover.) <S> If that doesn't work, try a bigger hammer! <S> Last resort: <A> Do you need to keep the cap intact? <S> If not, I would cut the leads, desolder them, and get pliers and gently roll the cap side to side to remove it. <S> I haven't encountered anything yet that has been epoxy-like, so it might come off pretty easily. <A> I'd try to figure out what the substance is - is it softish? <S> That would be either hot-melt or silicone. <S> If it's one of those you can either just cut the leads and pull the thing off (neither one will damage the board in the process), or if it's hot-melt you can heat it up a bit <S> and the thing will come right off. <S> Given that you can't cut it easily, I'm guessing it's hard as a rock. <S> That means either epoxy, or superglue, and of the two I'd guess epoxy. <S> the only chemical that would work is pretty carcinogenic and thus not readily available). <S> At that point I'd cut the leads and break the cap off - either chiseling it off, or using a thin bladed saw to cut the epoxy above the board (breaking the cap into pieces if need be). <A> If it is epoxy, heat might work. <S> Try going outside (or at least open the window wide), and use an old soldering iron. <S> Remember that you don't want to save the cap, but you want to keep the board in good shape. <S> Cutting the leads before attacking the glue will be a good idea. <A> I had same issue. <S> I was trying to replace a bad cap and noticed they're all glued down to the circuit board with epoxy. <S> Carefully cut the joint where the epoxy touches the bad piece with a dremel and try "rocking" the bad piece side to side with some pliers.
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If it were superglue, you could get some remover (yea, they make a chemical that will soften superglue!), but if it's epoxy you've no such luck ( If it's a hard brittle substance, try using a hammer and punch to dislodge the capacitor. Of course, you have to use your judgement, so if it doesn't seem to want to release, don't force it. Then, once you've got the cap off, use silicone or hot melt to attach the new one.
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Questions about wires in a DB9 cable I stripped a DB9 extension cable which I will use to connect to a DB9 connector on one end and an RJ45 on another. I need to make connections to pin 2, 3, and 5 on the DB9 side. When I stripped the DB9 wire, I was surprised to find 5 wires, since there are 9 pins in a DB9 connector. Why are there 9 pins but only 5 wires? One of the wires is unshielded. Why is that? The other wires are red, brown, orange, and black. Which pins do these go to? <Q> It's very rare for all nine pins to be connected, here are the details. <S> I only use three for anything I design - Ground, TxD and RxD. <S> The other two will depend on the hardware and software. <A> There is no standard for the colours used to connect to a DB9 for serial data. <S> The only way to find out what colour goes to which pin is to use a multimeter on continuity or a low ohms range. <A> I believe you are asking which specific wire goes to which specific pin, based on the wire color. <S> If that is correct, I'll try to give you some guidance, but I must also warn you that although there is an accepted standard for wire colors on DB9 and RJ45 connectors, it is also common to find them with non-standard wire colors. <S> DB9_ Wire _RJ45 1 <S> N/C_ Green _5 2_ Black _3 3 <S> _ Yellow _6 <S> 4_ Brown _7 5 <S> _ Red _4 <S> 6 <S> _ Orange <S> _2 7 <S> _ White _8 8_ Blue _1 <S> If this is not what you are looking for, please clarify and I'll try to help you. <A> The cable in between could be any type of cable and have any number of wires. <S> There may or may not be a standard involved with your cable. <S> You also don't need all of the 9 pins in order to have a functioning serial cable. <S> Most have VCC, TX, RX, and sometimes CTS and RTS. <S> That might explain the 5 wire you have. <S> Use a continuity checker to verify which wire goes to which pin. <A> I just had the same thing. <S> There is this cable which I've been using for about half a year now. <S> I was convinced that it only had 3 wires. <S> However, when I opened it today, I discovered it has 5 wires as well. <S> They are connected as follows: Male side: <S> pin 1 <S> = brown + also connected to pin 8 pin 2 = <S> red pin 3 = <S> orange <S> pin 4 = <S> yellow + also connected to pin 6 <S> pin 5 = <S> black Female side: <S> pin 1 <S> = connected to pin 8 <S> pin 2 = <S> orange <S> pin 3 = <S> red pin 4 <S> = yellow + also connected to pin 6 pin 5 = <S> black <S> I opened the cable because it was broken. <S> And I noticed that the brown wire was disconnected on the female side. <S> I assume that it needs to be connected to wire 1 though. <S> Well, the basic 3 wires are there and in right position: <S> pin 5 to pin 5. <S> pin 2 and pin 3 are crossed. <S> I had expected a simple loopback with pins 1,4,6 and pins 7,8 connected.
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What it appears to be is some kind of cable that someone connected a DB9 connector to one end and a RJ45 connector to the other. The other pins are for controlling the flow of data via hardware. You can get away with using just TX, RX and ground sometimes. So think of this as more of a rule of thumb, rather than a certainty.
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What is the best low-power color indicator? The project I am working on requires a color indicator which shows the current state (either red, green, or yellow). Ideally the indicator would have a large surface area so you can quickly glance at the device and determine the state. 2" x 2" would be nice. The device is battery powered and would ideally be able to operate for months at a time without recharging. What would be the best solution to use for this kind of application? <Q> How often does the indicator need to change? <S> If it's only occasionally, then you could place color swatches on a rotor or scroll mechanism and move it mechanically to different positions. <S> The power consumption while not changing would be zero, but it'd be considerable while changing. <S> You can often buy them in craft stores for about $5 US. <A> Most often found in arrays, flip-disk (or flip-dot) indicators only use power while changing. <S> Finding single dot units may be difficult, though if you're just making a 1-off prototype, you may be able to fabricate your own. <S> Alternatively, you could use an LCD with a colored reflector you could have either black or the color showing (you may be able to have additional colors besides black). <S> If you want more than two states, you could flash the LCD. <A> If you want red, green, yellow, and black, you could perhaps get a set of automotive door-lock actuators, and mount them at right angles to each other. <S> (both filters uncovering the square would yield yellow; red and green both covering would yield black; one or the other alone would yield that color). <S> Automotive door-lock actuators are designed to operate off twelve volts, but they would probably work acceptably at lower voltages; they would simply take longer to switch colors.
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One option for the motor/mechanism would be to hack an inexpensive clock movement to be controlled by your project rather than the quartz oscillator it comes with, and stick a disc with your color swatches on in place of the second hand. Have a yellow square that's always visible, and have the actuators slide red and green filters to either cover or uncover the square
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Different ways to digitally control an adjustable SMPS I want to make a battery powered, adjustable SMPS for use in situations when I cannot have an outlet near me, so I would like some more information or suggestions about this topic. The SMPS chip I am basing this off is a LM2733 . The power source would be a LiPo, voltage output 3V to 25V, and at most 500mA. There are a few ways I think I can control a SMPS chip digitally: one is a digital pot controlled with a MCU via SPI or I2C. A 1024 step pot would give me 20mV stepping, which is more than enough. What I saw in datasheets is that the pots are only able to go up to 5V for the digital resistor. Would that be a limiting factor in such a design? This way seems the simplest and least demanding way from what I see. Another way would be using a DAC, but I am not sure if it would need to go faster than the switching speed of the SMPS, because in data sheets I always see the voltage dividers before the output capacitor. Problem is that I do not know what the feedback pin wants to see. Does it want the entire ramp up and down from the inductor and compare it to the reference voltage, or does it just find the average voltage of each cycle? I know it is similar to {this question} , but I'm looking for some more information or discussion. <Q> The feedback pin is expecting a DC error voltage, with some usual stuff (ripple, noise, etc.) <S> riding on it. <S> The analog voltage loop is bandwidth-limited so that only useful information is used to determine the duty cycle of the converter. <S> The easiest way is to use a DAC output and a series resistor to either sink or source amount of current out of / into the FB node. <S> The size of the injection resistor will determine the adjustment range. <S> The FB reference voltage is 1.23V, so as long as the DAC can go above and below that reference, you can control the voltage both up and down. <S> This is the digital equivalent of having the bottom resistor adjustable. <A> What about adding several bottom resistors to the feedback divider and switching one of them (or several at once) to ground with an NPN array to switch the output voltage? <S> EDIT: You should be able to do this with only normal GPIO pins since they really should not see more than 1.23V (the feedback voltage) so they can work as open collector/drain switches. <A> Having read the datasheet I'm going to venture a guess. <S> The chip expects 1.23V at the FB pin when the output is at the desired level. <S> Usually this is set by a resistive divider, but I don't think it will be too much of a problem to generate it with a D/A. <S> However, the 13.3K resistor seems to be important, so I'd leave that there but remove the other resistor that connects to the output voltage and basically replace it with your microcontroller/DAC combo. <S> I think that all you should have to do is ensure that the output of the DAC is 1.23V when the output voltage is where you want it. <S> To keep things realistic <S> You'll probably want to make the output of the DAC mimic a resistive divider - just divide the output voltage of the SMPS by a magic number that gives you 1.23V at the FB pin when you have the desired output voltage. <S> You are however right to question how fast you have to update the DAC. <S> While the switching frequency of the SMPS is either 600KHz or 1.6MHz <S> this is NOT the bandwidth of the control loop in the chip. <S> I don't see much in the datasheet about what it is, but it does mention using CF to put a zero in the root-locus at 8KHz. <S> So by wild-guess I'd say try to change your DAC at 10KHz - every 100us if possible. <A> I'm not sure how committed you are to the LM2733. <S> For example, LT3495 . <S> This will let you adjust the voltage without worrying about what you're doing to the stability of the regulator.
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You may want to look for a chip that provides output voltage control separate from the main feedback path.
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Harvest power from an electric fence Many farms use electric fences to discourage animals breaking through to neighbouring paddocks. These electric fences have regular (say once per second) high-voltage spikes of between around 100 V and 120 kV. Would it be possible to "harvest" this as a power supply for remotely-deployed electronics? e.g. a coil wrapped round the electric fence wire, with a high resistance to ground, trickle-charging a battery. Ideas welcome. <Q> Those fence chargers usually generate a high voltage spike on the wire fence, relative to ground. <S> The wire fence is on insulators to make sure that almost no current flows, unless something touches it. <S> I've heard that wet grass leaning on them can draw enough current to effectively neutralize such a fence. <S> So here's the take-away: there isn't so much a current through the wire as there is a voltage on <S> the wire (capacitive charging currents neglected). <S> Caveat <S> if you try this with a flyback liberated from an old CRT: they often embed a diode in series with the HV winding in those units, and they're usually potted, too. <A> Possibly. <S> I live on a small horse farm and recently made a fence tester using a resistor and a small neon bulb. <S> Even with 10k resistor, I get a really bright flash from the bulb: clearly visible in broad daylight. <S> The thing I'd want to be careful with is how you get power off the line: intuition says wrap a few turns of insulate wire around it, but that will make a step up transformer and give even more voltage. <S> If I get a chance tonight I'll try to see if I can power an LED with a single turn around the fence's hot wire. <A> I'd try connecting a small transformer (one designed for a flyback power-supply) with a high step-down ratio between the energized cable and ground, you could then rectify the output and do whatever with it. <S> The HV coil impedance should be high enough to avoid a tremendous draw on the cattle killer, but I don't know much about them. <S> It may take a long while to charge a battery, but possible. <S> If you just want to power a sensor, I'd use a capacitor. <A> We did this about 22 years ago ,when solar cells were much more expensive and less efficient .The unit was birdsnested and bench tested using a middle of the road fence energiser. <S> It did trickle charge a 12V SLA battery. <S> The reasoning was that 10J was typical for an electric fence and they beat at roughly 1 pulse per second .This <S> implies that you could harvest say up to 1 watt without dropping the fence peak volts too much .I <S> used a transformer out of a dead electric fence backwards. <S> There were some power electronic components between the transformer low voltage winding and the battery but nothing expensive exotic or tricky .The bench tests implied good grounding which is not unreasonable because many electric fences have the bottom wire grounded anyway. <S> This never went into production because there was not sufficient demand at the time.
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So if you connected one end of the high-voltage side of a flyback transformer to the fence, and the other end of same winding to ground, you ought to be able to pick off slugs of current on the low-voltage side of the transformer, at a reduced voltage.
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Regulator solution for 5 volts at +2ish amps I have been looking at a lot of different regulators. Generally speaking switching regulators will give me a wide range of input voltages at the out put amps I am looking for with added efficiency. However, the simplicity of a linear regulator is really appealing for the project that I'm looking at. The problem that leaves me with is that most linear regulators will do between 0.5 and 1.5 amps. Is there a way to hook up two regulators so that they provide my 5 volts with their combined amp output like with batteries? <Q> You can use an external pass transistor with a fixed 7805 regulator, see for example page 14 of National Semiconductor's datasheet . <S> It's also possible to use the LM317 to build tracking regulators that can be connected together so that they share the power. <S> But the reason the integrated packages don't go much above 1A is the dissipation due to the product of the difference between input and output voltages times the current. <S> Switching regulators are much better for higher currents than linears because of this thermal problem. <A> Ti's UC385-ADJ may do the trick. <S> You didn't specify the input voltage. <S> You don't wish to parallel regulators; it isn't that simple. <S> You might consider Point of Load (PoL) switching regulators. <S> They are just about as simple since they have the parts on-board. <A> If you want to stay with linear there's the LM323 . <S> I can deliver up to 3A, and can dissipate up to 30W, thanks to a TO-3 package. <A> Depending on the input voltage, a linear regulator is more complex in my opinion due to the cooling. <S> Sometimes it's hard to fit a giant heatsink in your project than it is to add a simple switching supply. <S> However, they are rated at 1.5A max, but that's with a very low input-output difference. <S> If that becomes above 15V, it's degrading quickly (to about 0.4A at 40V difference). <S> Maybe you should look at a LM2596 . <S> You only need a 5pin regulator, an inductor and a diode. <S> If you keep in mind to place the diode and inductor close to the regulator, it's relatively easy. <S> And ofcourse some input/output caps, but you would use them on a LM317 too if you want to drive 2A. Watch out that the On/off pin on the device can't handle <S> >25V inputs, whilst the regulating part can go up to 45V. <A> They should be capable of providing 2A if the difference between input and output voltage is lower than 20 V, if I remember correctly. <S> Control circuit is also relatively easy to build. <S> You will need a big heatsink if you want to run it at full power <A> This might do the trick: http://www.fairchildsemi.com/ds/LM/LM7812.pdf <S> See fig.14. <S> It uses a simple resistor and a PNP transistor to increase the output current capability of a standard regulator. <S> Even the required formulas are included. <S> regards
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You could try paralleling LM317's to the desired current. You could take a look at L200 regulators.
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Is there a development system for the MSP430F series microcontrollers? I'm hoping for an IDE of some kind, but I'll take any compiler or assembler! Can't seem to find anything by googling. <Q> I use MSPgcc for msp430 series, IAR is another CSS <S> The later have restrictions. <S> What chip are you trying to program or code for? <S> Edit- <A> Of course there is. <S> I use emacs + mspgcc4 <S> + make + <S> mspdebug + gdb + ddd . <S> There is an IAR compiler for download from TI. <S> The free one is code-size-limited. <S> It comes with some kind of IDE as well. <S> But MSP programs are pretty small by definition, and a simple makefile is all you need to compile and program code. <A> at sourceforge you can find both mspgcc (mspgcc.sf.net) and mspgcc4 (mspgcc4.sf.net). <S> I had trouble recently building mspgcc on a modern Linux (finally did succeed), but mspgcc4 builds just fine no problem. <S> If all you need is an assembler and linker for now, it is somewhat trivial to cross compile gnu binutils. <S> ./configure <S> --target <S> = <S> msp430 <S> --prefix=/opt <S> /msp430 or something like that. <S> Also, out of the box, llvm includes the various targets, <S> unlike gcc you do not pick one target when compiling the compiler. <S> The downside is that llvm's msp430 support is considered experimental (as in we probably wont bother with the bug reports). <S> And you will still need binutils to assemble and/or link. <A> I use Rowley CrossWorks . <S> It's very good, with excellent support. <A> just recently there was a new release of mspgcc, dubbed temporarily "uniarch", here are som installation instructions for ubuntu <S> https://github.com/sergiocampama/Launchpad/blob/master/README.md <S> i think that all the recent devices are supported in that version... <S> my setup is a vmware machine running ubuntu server 11.04, with netatalk and ssh... <S> so with my mac, i connect with terminal over ssh, and mount the ubuntu drive over afp with netatalk... <S> so I use xcode as the development ide, and run the commands on terminal.. <S> it's SO comfortable... <S> i also have a rakefile that does all the handywork (which can be found in the above repo), and <S> thus I only 'rake mcu= <S> msp430g2211 build install' and it compiles, links and installs on the launchpad...
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Uniarch mspgcc has been released, It supports newer msp430 chips and is now the preferred compiler over mspgcc4Build directions for uniarch mspgcc
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Why are there 3 pins on some batteries? Lots of new batteries (for mobile devices, MP3 players, etc) have connectors with 3 pins.I would like to know what is the purpose of this and how should I use these three pins? They are usually marked as (+) plus, (-) minus, and T. <Q> The third pin is usually for an internal temperature sensor, to ensure safety during charging. <S> Cheap knock-off batteries sometimes have a dummy sensor that returns a "temp OK" value regardless of actual temperature. <S> Some higher-end batteries have internal intelligence for charge control and status monitoring, in which case the third pin is for communications. <A> That third contact is connected to an internal thermistor, enabling the charger to measure the battery temperature. <A> In mobile phones, some Li+ battery packs have 3 terminals. <S> Two possibilities: positive, negative, thermistor (as was already mentioned in previous answers) positive, negative, 1-wire bus. <S> The latter is a digital communication bus that’s connected to a gas gauge IC inside the pack. <S> If you want to explore what’s inside single-cell Li+ battery packs <S> , look-up bq27000 gas gauge <S> IC and associated application notes. <S> Could be a good starting point. <S> Some packs have 4 terminals: positive, negative, SDA, SCL. <S> The latter 2 lines are I2C or SMBus. <S> Look up the bq27200 gas gauge IC <S> (shares datasheet with bq27000). <S> EDIT: <S> This was written as an answer to a duplicate question , which got merged with this one. <A> For Nokia batteries, one of the pins may be a BSI (Battery Size Indicator) pin, which contains a fixed resistor to ground, enabling the handset to identify which battery is connected. <S> Examples of BSI resistor values include: - BMC-2 <S> 3k3 <S> NiMH <S> 640mAh - BMC-3 5k6 <S> NiMH <S> 900mAh - BLD-3 22k <S> Li-Ion 780mAh - BL-4B <S> 68k <S> Li-Ion 700mAh - BL-5B <S> 75k <S> Li-Ion 820mAh - BL-4U 82k <S> Li-Ion 1000mAh - BL-5C 82k <S> Li-Ion 1050mAh - BL-4J <S> 100k <S> Li-Ion <S> 1200mAh - BL-5J <S> 110k Li-Ion 1450mAh <S> See also: BSI - cpkb.org <A> The third pin is usually found on Li-Poly, or Lithium Polymer batteries and is required in order to charge the battery safely.
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Because these batteries are usually multi-cell, the third pin is used for balancing the charge between each of the cells.
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Is there another Arduino ethernet module besides the "Arduino Ethernet Shield"? On the official Arduino website only the Arduino Ethernet Shield is referenced for Ethernet programming. Are there any other modules for Ethernet on the Arduino? <Q> You can also get a nice PoE adapter from them. <S> Their shield is also based on the Wiznet 5100 chip, and has incorporated the following design features to hopefully help with any issues with the Arduino Ethernet Shield (taken from their website) <S> SPI Fixes <S> Combining Ethernet with other SPI devices can be really tricky because the Wiznet chip doesn't relinquish the bus properly when it's deselected. <S> To fix that problem we slaved the Wiznet's SEN (SPI Enable) line to the CS (Chip Select) line, which means <S> that whenever your sketch deselects the Ethernet connection in order to talk to another SPI device it will work exactly the way it should. <S> No more messing around with cutting tracks and other nasty hacks you may have seen mentioned on the forums. <S> Reset Fixes <S> We've also slaved the Ethernet Shield's reset line to the Arduino reset line, so if your Arduino is reset the Ethernet Shield will automatically reset as well. <S> The Wiznet reset line is also held active for long enough to make it restart reliably each time the Arduino itself restarts. <S> Power Filtering Fixes <S> Ethernet connections are very susceptible to electrical noise, so the Wiznet chip has multiple ground <S> pins on two separate buses and they need to be individually decoupled and the buses linked by an inductor. <S> We took care of that by implementing proper decoupling on the power and ground rails, ensuring you get maximum reliability even in electrically noisy environments. <A> The official is implemented with a Wiznet 5100 chip. <S> There is another ethernet shield from NueEletronics implemented with the ENC28J60. <A> I can think of two options off the top of my head: <S> An Xport <S> A custom solution with an ethernet PHY, a magjack, a SPI connection and a bunch of custom software.
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There is also one from Freetronics , which works with Arduino and I have also tested it with Netduino.
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How do I attenuate 30kHz noise? I'm trying to design an LC low pass filter to attenuate 30-35kHz noise on a 3.3V power rail. It's preferable to attenuate higher frequencies as well. So I designed an LC filter with L=10u, C=1u (which is wrong, but this is just an example) - and I found it boosted frequencies near the cut-off point. Is there any way to avoid this? The boost of 22dB corresponded to an increase in 12.5x the voltage. The rail will be powering a microcontroller, which draws 100mA, so this increase in voltage would likely damage it. <Q> Put linear regulator before uC - they will react fast enough to cut low-freq noise. <S> Especially good if you have some margin between power supply voltage & uC voltage. <S> Just add large(some 10-1000 <S> uF) caps before uC: <S> some electrolytic and some 1uF and 0.01uF ceramic ones all in parallel to prevent resonance. <S> Ceramic ones should be as close as possible to power pins of uC. <S> If it were more powerful uC, I would consider adding ferrite bead, but it might be not needed in this case. <A> In simple terms, add a resistor in series with the inductor. <S> But then you could rather use a RC filter because you're decreasing the quality of your inductor. <S> Why do you prefer and LC filter? <S> The filters are harder because at a certain frequency, you will get a resonance point. <S> The voltage you put on the filter will be 'amplified'. <S> The amplitude of how much it will shoot up , is called the Q factor. <S> To dampen the Q , you add a series resistance to the coil to dampen it out. <S> A lot of math stored on: http://en.wikipedia.org/wiki/RLC_circuit <S> But because you're only operating at 30kHz, I think a RC filter might do the job better/easier. <S> Edit:Sorry your post was confusing because first you were talking about a 3.3V >signal< and then about a power line. <S> Alternatively you can better add a filter which <S> it's cutoffpoint is way less than your noise. <S> I.e. if you have 30kHz noise, add a filter with a cutoff point at 3kHz or something. <S> You won't get the increase in amplitude at the noisy frequency and a pretty good attenuation. <S> However, as mentioned, patching the source is always better. <A> If you are using LC filter for any voltage (power supply). <S> Don't select the cutoff frequency of filter has same as frequency you want to attenuate. <S> Generally , you should select 10 times less than the frequency you want to reject. <S> Make sure that Inductor SRF is away from the frequency. <S> Inductor current rating should be 2 times of the max current comsumption of load and voltage rating for capacitor should be greater than 3 times of the selected voltage.
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The answer still stays similar, add a small resistor, but it will reduce the steepness of the filter.
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Keep the voltage under 5V I have a battery pack consisting of 4x1.2V AA Sanyo NiMH Rechargeable batteries used to charge a Beagleboard device. I want their discharge output to not exceed 5V. But when they're fully charged, the voltage output is over 5V (it triggers the overvoltage detector of the Beagleboard). What is a simple (and relatively small) intermediate component I can place between the battery pack and the Beagleboard to limit the voltage to under 5V? <Q> Unfortunately, you've spec'ed batteries which are awfully close to the operating voltage of your system. <S> If you can use 5 batteries instead of 4 (giving you 6.something to 5V, instead of 5.something to 4V) , a low-dropout linear regulator will be a simple, easy solution. <S> The standard 7805 has too high a dropout for this purpose, but there are other pin compatible regulators; you'll want a TO-220 to dissipate the power that the Beagleboard can draw at full charge. <S> If you must use 4 batteries, you need to dissipate the excess voltage as heat through a MOSFET when the voltage is greater than 5V, and turn the MOSFET on if the voltage is less than 5V. <S> You are running slightly out of spec when you're below 5V, though I'm not sure what the absolute minimum voltage is for the board. <S> If you want the best solution possible, a buck-boost regulator would get you optimum efficiency for voltages slightly above and slightly below 5V. <S> You could even run it off a single battery, or from voltages much higher than 5V. <S> However, this is an expensive and complicated solution. <S> I'd recommend just using 5 batteries and an LDO. <A> You need a "voltage regulator". <S> The standard answer to " <S> I just want 5 volts with no hassles" is to use a 7805 voltage regulator chip, but they "eat" 2 volts, so you need at least 7v of batteries. <S> The datasheet will contain an example circuit. <S> Just go to a junk store and buy a car cellphone charger for an obsolete phone. <S> These are dirt cheap and typically contain an efficient 5v "switch mode" regulatorcapable of delivering up to 1 amp. <S> (Motorola 34063 is the usual regulator deviceinside these). <A> You use a voltage regulator to keep a power supply voltage at a fixed level. <S> Linear regulators require an input voltage higher than the output voltage, often a few volts, less with LDOs (Low DropOut). <S> So that's no good. <S> Then there are switching regulators. <S> They are a bit more complex, but more efficient. <S> They exist as "buck" (input voltage higher than output voltage) or "boost" ( <S> input voltage lower than output voltage). <S> But there's also a "buck/boost" which can handle both situations. <S> Since your input voltage is near the output voltage, with fresh batteries higher than 5V, with partly drained batteries lower than 5V, the buck/boost regulator is the way to go. <A> Maybe a 5V Zener diode + resistor will be good enough? <A> Could you permanently place a 5.6V 3W zener (maybe make one from a TL431 and a power transistor) over the battery pack, so it woill be charged only up to that level? <S> But note that I am not sure how your charger will respond to this, and you will need a charger for the battery pack, not for the individual cells.
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You have two good options: Use a "low dropout" 5v regulator (eg LM117). You need a voltage regulator. The Linear LTC3785 requires quite a few external components, but gives you an efficiency to 95%.
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Best way to cut mounting squares out of plastic project boxes? My electronic kit-building to date has included pre-drilled kit boxes for mounting. My latest purchase, however, has a plastic project box, and no pre-made cutouts. I need a rectangular hole for a small LCD screen - and I don't want to mess it up! How best to cut the hole? Tools to use? <Q> Mark out the rectangle you want to cut out. <S> Using a very sharp knife, score the edges of the rectangle against the side of a metal ruler. <S> Cut deeper and deeper grooves with the knife, until you can eventually push out the rectangle. <S> File any rough edges, and remove the tape. <A> Drill a 6mm hole and use a step drill to open it out to at least 10mm. <S> A step drill is the best way to make large holes in thin materials, it doesn't grab as much as a large twist drill will. <S> Then use a ' hand nibbler ' to open it out to rectangular. <S> You can drill more large holes with the step drill to reduce the amount of nibbling required. <S> I made the cutouts for this project with a nibbler: <A> The question is old, but I also had a lot of trouble to get this right, so it's worth answering. <S> Draw the rectangle with a pencil or a thin felt tip pen. <S> You can clean it later. <S> I sometimes draw the whole panel in milimeter graph paper and tape it on the plastic box, so things are perfectly aligned and distributed. <S> Make sure you got the measurements right. <S> With a 1mm or smaller drill bit (you probably have one for drilling PCBs), make a hole on each corner of the rectangle. <S> Using a ruler and the holes as a guide, draw an X across the rectangle, and make a 1mm hole on the center, where the lines intersect. <S> Using the jigsaw, carefully cut along the X lines, until you reach the 1mm holes on the corners. <S> This will leave 4 triangles. <S> With a very sharp knife (I use a box cutter) and a ruler, carefully make an incision along the edges of the rectangle, using the holes on the corners as a guide. <S> You might want to always cut from the corner to the center, half at a time, to avoid damaging the opposite corner. <S> Make the cut deeper and deeper, while pushing the triangle, until you can break it off. <S> If you can, do it on both sides, it gives a cleaner cut. <S> Finish with the knife and sandpaper. <S> It gives perfect cuts every time. <A> Use a square drill bit !
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With a larger drill bit, and using the 1mm hole as a guide, make the central hole big enough to fit a jigsaw blade. If the plastic isn't too thick, then you could try this: Cover the surface of the plastic with masking tape, so you don't scratch it.
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Is UL approval required on all items sold in the USA I have a spray tan machine which I wish to sell in the USA. I have had the machine tested by a CE test house. Do I have to have a UL approval as well? <Q> This does not apply to your personal use items, but does apply to any fixed appliances or electrical equipment that is installed within your home or commercial facility. <S> If your local jurisdiction has adopted the national electrical code then this requirement applies. <S> Maybe... <S> Assuming this is a mains powered device? <S> There is US Federal law and there are also local laws. <S> If you only sell a few you may get away with not getting a Nationally Recognized Testing Laboratories (NRTL) approval (there are many NRTLs, UL is just the most well known). <S> However, besides pingswept's point, local electrical inspectors may prevent business owners from using your equipment based on local regulations unless they see an NRTL mark (even though the Federal gov may not require it). <S> Check with the test house that did your CE approval <S> , if they are big enough they may also grant NRTL marks (we use TUV Rheinland). <S> Note that not using UL or CSA may cause problems in some jurisdictions that are old fashioned. <S> We have <S> a $4.5M medical device and the City of Baltimore wanted UL, CSA or MET Labs <S> so we gave MET Labs the TUV test reports and a check for a few thousand dollars <S> and they gave us an approval. <S> UL is a pain to work with, I would go with CSA before UL (even though CSA is Canadian they can grant US NRTL marks in general). <S> Also note that as part of getting an NRTL mark, you will be signing up for periodic (typically four times a year) factory inspections where the NRTL will make sure you are still building your product in the approved way. <S> Of course you pay for that privilege. <S> http://www.greenexpo365.com/portals/asf0001/resources/intertek/The_Q&A_Guide_for_NA_Product_Certification%28US%29.pdf <S> I think the bottom line for mains powered equipment is, if you want the US to be a significant market, you want an NRTL approval. <S> While getting the NRTL approval, throw in the Canadian approval, there are only small differences in the requirements and you open up both markets. <S> Eric <A> No, UL approval is not legally required. <S> It's only common because many large companies will not buy equipment that has not passed UL's safety tests. <A> The rub comes when one wants to buy product liability insurance and finds that it's unavailable without certification by, say, UL, the reason being that the insurance underwriters are simply unwilling to take the risk of being sued because someone's house burned down because of a rogue widget. <S> Without some agency like UL and their imprimatur attesting to the safety of the widget, getting goods to market, unless you want to sell them out of the trunk of your car, is going to be difficult, at best. <S> To add insult to injury, if you manage to get a widget into someone's home and the house burns down, for any reason, the homeowner's lawyers are going to have a field day with you <S> and you're likely to have to spend more time in court than you want to, and <S> even more time on the street, since they'll strip every speck of meat from your bones, just to prove they can. <A> You cannot be sure about selling in the US without an NRTL mark (it doesn't have to be UL per se, but has to be a recognized mark). <S> You can be sure that if the product has a recognized mark, you can sell it. <S> The CE mark has no weight in North America. <A> To add to what others have said, anyone who does buy and install a system that is not certified will probably not be able to get insurance coverage. <S> UL was created for insurance purposes. <A> Insurance companies can not deny coverage based on certification. <S> It's strange as UL or any other certification house will stand by your side if for example a toaster catches fire <S> but you have no recourse against them as they are not liable for the products tested. <S> Hhhhmmmm so why do manufacturers pay for this? <S> And the costs are passed to the consumer. <S> Another way of an private company using scare tactics to make money.
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The National Electrical Code requires that all items installed in a building be tested by an NRTL , generally that means UL listed. As far as I know, there is no legislation mandating certification by UL or any other agency, public or private, prior to sale of consumer electrical goods in the US.
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Differential to single-ended conversion - transformer or instrumentation amp? I need to convert the output of differential output DAC to single ended. It's a 2 Vpp signal with a 1 V common-mode output. The output is 100 ohms. Should I use a transformer or a instrumentation amp. to do this conversion? The output could be up to 10 MHz (it's a communication signal) and the power is < -10 dBm. Update 1 Since the signal is a RF communications signal, there is no DC component. Update 2 Avoiding a +/- power supply would be nice, so in that case, a transformer would be better, correct? <Q> I think Analog Devices has some slick isolators based on transformers packaged into normal IC packages. <S> INAs could work, but you might want to bias your signal up a bit to get it off the ground power rail (assuming you don't just reference it and use a dual supply), for better performance. <S> That might not be true so much anymore, but it sure used to be. <A> As a crazy solution you may move ground&supplies of your DAC 1v higher. <S> In this case you will get your shifted signal without any distorsions. <S> Level-converting of digital signals is much easier, does not intoduce analog error, and sometimes is not needed. <A> Instrumentation amp. <S> The transformer won't work if the signal is static.
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I think, depending on the specifics of the datasheets, that the transformer will give you a better BW, and galvanic isolation, if you like that.
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Negative voltage on AA battery Last night I pulled the battery holder out of a toy RC car to test the voltage with my meter. The pack has 4 AA batteries. The combined voltage at the terminals of the pack was well under 1 volt, and then I tested each battery individually. These are ordinary AA alkalines (not rechargables). They were in good condition, with no leakage. The first two batteries showed about 1.2V; the third had a small negative voltage, about -0.2, which I thought was pretty interesting, and the last showed about -1.2v. I have never come across a negative voltage on a battery. Now before you ask, yes, I double-checked, and then triple-checked, that my leads were plugged in correctly. And I was not holding the batteries upside down. I had all four right in front of me, all pointing the same way. Two showed a positive voltage, one slightly negative, and one -1.2v. I did this repeatedly, So my question is, what the heck? How does a battery get a negative voltage on it? The pack had been in the RC car for a couple of weeks, with the car switched on. I think, but cannot prove now, that they were all inserted the right way in the holder. But even if one or two were in backward, how could this happen? Now the batteries are Canadian, and my meter was made in the USA, but I don't think that explains it. [That's just a joke.] <Q> Batteries when are fully discharged they can reverse their polarity. <S> Other times the cell is ruined and needs to be replaced. <S> I used to see this on the large batteries used on aircraft. <A> It happens if one cell is somehow "weaker" and gets charged by the other cells. <S> http://en.wikipedia.org/wiki/Rechargeable_battery#Reverse_charging <A> Alkaline and other batteries can switch polarity in a series configuration. <S> The battery doesnt actually have a negative charge, the positive terminal became the negative end and will meter -V when tested normally. <S> A common occurrence, although rare that someone volt checks 'dead' batteries. <S> HOW IT HAPPENS: a single cell depletes before the other batteries drop below half power and is deep cycled to 0.00v. <S> This zero voltage state makes the + & - field unstable. <S> Most batteries,on their own, will rebound to a low voltage when drained too far. <S> But at that critical moment the positive tip is against a negative end of a charged battery and the electromagnetic field re-stabalizes backwards and starts taking positive charge from the negative terminal.
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Sometimes you can carefully discharge this reverse voltage on a single cell and the battery will then successfully charge back up.
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Do any devices support handshaking on SPI-ish bus without extra wires The 4-wire SPI bus has a considerable speed advantage over I²C, but unfortunately so far as I know has no standard way to perform handshaking without using extra wires beyond the four (and four wires is already annoying enough as it is). For a recent project where the slave was a CPLD, I implemented a nice approach to provide handshaking in one direction (slave can make master wait) and also incidentally eliminate the need for the /FS line. The signals are Clock, MOSI (master-out/slave-in) and MISO (master-in slave-out). Clock idles low; both MISO and MOSI output on the rising edge of Clock and are sampled on the falling edge. Two or more consecutive rising edges on MOSI wire while Clock is low will reset communication. When Clock is low and MOSI is high, MISO will indicate whether the slave is ready. When clock and MOSI are both low, MISO will indicate whether the slave wants attention. While this approach works very nicely when communicating between my CPLD and my controller, it would be nice if the same approach could be used when communicating between two standard microcontrollers. The biggest features that would be necessary to make this work nicely would be: the ability of the slave controllerto reset itself upon receiving somenumber (probably 2 or 3) of risingedges on MOSI while clock is idle; the ability of the slave to controlthe clock-idle state of MISO, andpreferably load separate values foruse when MOSI is high or when it islow; preferably, the ability for themaster to control the state of MOSIthat will be output when the clockis idle between bytes (in myprotocol, the commands which needhandshaking have the LSB set, butthat's a bit of a nuisance); for buffered SPI ports, the abilityfor the master to wait on theslave's data line. Do any common controllers or slave devices offer such features, or work in such a way? <Q> The closest thing I know for what you're asking is UART/ <S> National Semiconductor's LMX9838 <S> (it's a Bluetooth module) uses that communication protocol as a slave device. <S> And you can implement it with 2 extra GPIOs in any microcontroller. <S> Ultimately you can implement any type of handshaking with any pair of Master-Slave devices, as long as you have control over a couple of extra GPIOs in both (i.e.: Using uC, FPGA, CPLD...). <A> "An introduction to asynchronous circuit design" by Davis and Nowick(in particular, Figure 1 and Figure 2 and the nearby text)describes two handshaking protocols as "pervasive". <S> The 4-cycle protocol, aka RZ (return to zero), 4-phase protocol, and level-signaling. <S> And the similar but more complicated to implement 2-cycle protocol, aka transition, 2-phase, or NRZ (non-return to zero) signaling -- which is very similar to the "data strobe encoding" used by SpaceWire and FireWire. <S> Either one sounds like it has most of the features you requested <S> --it's SPI-like in that there are exactly 4 signals <S> , all 4 signals are one-way (no passive pull-ups), the master can pause the slave indefinitely until it is ready for the next bit from the slave, etc. <S> It also has a feature supercat requested that SPI doesn't have: the slave can pause the master indefinitely until it is ready for the next bit from the master. <S> I don't know of any chips that have the 4-cycle protocol built in, but it looks like it would be easy to bit-bang on a microcontroller or a CPLD.In fact <S> , it looks like it would be easier to bit-bang than SPI, since (like SPI) the master has no timing requirements, and (unlike SPI) <S> the slave has no timing requirement either. <S> Is it possible to use the 4-phase protocol for synchronous bit transfers, and somehow build a higher-level protocol on top of that to get the other things supercat wants -- byte alignment, start-of-command frame alignment, attention/busy/idle states, etc? <A> If you're looking for something compatible with off-the-shelf SPI systems, and yet somehow uses fewer wires, you might like the Roman Black Shift1 system for 1-wire shift registers .
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RS-232 with RTS/CTS handshaking (4 wires total).
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Understanding when to use basic Components So I understand AVR assembly for the most part, and generally understand the overview of microcontrollers. but when it comes to specific components (besides the obvious stuff like resistors/batterys) I dont understand what they do....and more specifically WHEN to use them? Stuff like Capacitors,Regulators,Inductors,Crystals,Etc Where can I find a generally overview of When and what these components do? to further my knowledge. I can of course wikipedia the definitions....but I more want to know when I should use these specific things because I figure it's probably a good idea to know more than "what" they are and also What to use... <Q> I recommend the Art of Electronics by Horowitz and Hill. <A> The site All About Circuits has free textbooks about these. <A> After some searching, I found this site which seems to have a nice level of explanation: <S> http://www.piclist.com/images/www/hobby_elec/e_parts.htm <S> I personally dont know of a nice, comprehensive book to teach the whole topic, <S> but then it is a huge field and hard to condense. <S> But there is Elektors 300 circuit series, which may or may not be still available. <S> Each book contains about 300 circuits to try out. <S> I learned a lot from these books once I had the basics down. <S> University of Madras has a lenghty set of lectures on Youtube for that topic. <S> Have a look at http://www.youtube.com/watch?v=w8Dq8blTmSA <S> Stuff like http://www.makershed.com/productdetails.asp?productcode=mkgk19 <S> or so. <S> The bachelor student I am currently responsible for, I introduced to electronics with an arduino experimentation kit. <S> I know I can only teach him very basic stuff, <S> but then he is studying computer sciences, and doesnt need (or have time for) <S> a full blown study in applied electronics. <A> this may help some: http://www.opencircuits.com/Components and http://www.opencircuits.com/Basic_Circuits_and_Circuit_Building_Blocks
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There's also a slew of experimental kits out there to teach you.
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MCU: saving data directy on flash. What's the advantage? I know on some MCUs its possible to save data directly on program memory (flash memory). AVRGCC compiler uses "PROGMEM" keyworkd, MPLAB C18 uses a similar one with the same effect.However, what's the advantage of having data on program memory? Maybe because those MCUs have a Harvard arquitecture and so read data from program memory is faster than read it from data memory? Is it "really so much faster" that it's worth to use it? Thanks! <Q> These microcontrollers have very limited RAM. <S> So if you want a look-up table, it makes sense to store the large, constant data in program flash instead of the precious RAM. <A> You have two options for constant data on these flash microcontrollers. <S> Load from flash when needed (PROGMEM) <S> Load from flash into ram on program startup (not PROGMEM). <S> The C compiler does this for you automatically if you forget to use PROGMEM because data is normally read/write in C. <S> It is much slower to load data from the program memory compared to loading from ram, but when you only have 128 bytes of ram, and the data has to be stored in the flash anyway, <S> it pays off. <S> AVRs also tend to have, say, 128 bytes of EEPROM, and whatever flash memory you didn't need for your program. <S> The microcontroller can then program its own flash memory to save measurements and settings. <S> The flash memory is more plentiful than the EEPROM but, unlike EEPROM which usually appears to be rewritable 1 byte at a time, the Flash must be erased and rewritten in blocks. <A> This is only good for data that is updated infrequently (such as configuration data or user preferences), since there is a limit to the number of times you can rewrite the flash (typically a minimum of 10,000 erase/write cycles). <S> The advantage to saving data in this way is that it won't be lost when the MCU loses power. <S> Without some sort of non-volatile storage, you would need to have a battery-backed up RAM to save data during power shutdown. <S> The second reason for allowing a program to write to the flash, is that it allows programs to be updated remotely in the field. <S> To do this, you need a portion of the program to be resident all of the time (the part that will write the new code to the updateable portion of the flash memory), and a means to download the updated code (e.g. Bluetooth, cellular, etc.). <S> You want to make sure the always-resident portion of the code is as bug-free as possible, since it is harder to update that.
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If an MCU doesn't have a separate EEPROM area to save data in, then yes, you can save persistent data to an area of the flash memory not used by program code.
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Wiring a DC socket - why three pins? I have this DC socket: Which I intend to wire up to a circuit to provide power. I have a DC power supply which has a positive tip polarity. I'm good to go and wire up the socket but I am a little stuck as there are 3 pins on my socket. From the look of the socket it's fairly obvious which pin is for the center pin (which I will wire pos) so I assume the other two are for the outside (which I will wire neg). Is this assumption correct? And if so why two pins instead of one? <Q> This might be something similar to the female single channel audio connector where two of the 3 pins will be shorted when unplugged and when its plugged one of those 2 ping will be floating which usually goes to a battery and the remaining 2 pins will be connected to your plug. <S> This diagram might help you understand better. <S> Here pin 3 will got to the battery, pin 2 & 1 to the circuit. <S> When you plug in the socket pin 1 & 2 would provide the power to the circuit and battery will be disconnected. <S> when unplugged the battery would be connected back to the circuit. <S> Though there are other configuration also in which it can be used but this is a simple example which might help you understand the way these socket works. <A> The other possibility is that a 3 pin design is simply to provide a more robust and secure mechanical mounting. <S> Connectors are subjected to mechanical stress when connected and disconnected, so a better connector will have "over-sized" pins that provide a good mechanical connection to the circuit board (or enclosure), beyond the physical connection necessary for the power supply's voltage and current flow. <S> While I believe the normally-closed switch (to outer-connector ground ) is the most common make of these DC power connectors (aka barrel or coaxial connectors), personally speaking, I have always just ignored the switch and soldered both switch pins to ground in my own projects. <S> I believe the switching is for the outer connector of the barrel portion of the jack (rather than the center pin), this can be used to drain larger capacitors such as large electrolytic capacitors being used to filter the DC supply from an unregulated power supply, so that after the circuit is disconnected, to reduce the shock (or jolt) <S> risk if you open up the case, the capacitors drain to ground via a bleeder resistor. <S> In digital circuits, an active low SHUTDOWN <S> * <S> signal can be used to force a microcontroller off to prevent unstable operation after the power has been disconnected, even if there is a brief residual power such as from large-ish filter capacitors or inductors in a switching mode power supply. <S> Similar connector with better view of the 3 pins in a different layout (and closed frame which fully encases the power jack, something I prefer). <S> ( larger image ) <S> More information is available from Ada Fruit Industries' PartFinder . <S> Note: <A> It's difficult to tell from this image, and the Maplins website is very poor when it comes to datasheets and specs, so my answer is just a guess... <S> The two outside pins may act as a switch so that you can build a circuit that is powered by a battery until an external power supply is connected. <S> You can test this with a continuity meter, when unplugged these pins should be open circuit, but when something is plugged into it, these pins should be connected together.
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Usage of these DC power connectors (or other appropriate types in special uses) is encouraged because the design helps prevent the power supply jack being accidentally shorted out, which could permanently damn many of the cheaper wall-wart style power supplies.
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How to set a digital out to 24V Vcc I want a curcuit with 3.3V and 24V supply. The micro will use the 3.3V supply, which needs to be able to set multiple industrial 24V digital outputs. My plan was a simple op amp, but as far as I know no op amp will actually achieve an output of 100% of Vcc, no matter the gain. Is there a cheap and simple way to do this? Relays seems expensive and big. <Q> Use a NPN/NFET transistor as an open collector/open drain output. <S> Use a resistor pull-up if your load doesn't have one. <S> Alternatively, opto-isolators will give you the same functionality with the freedom to separate your power and ground domains. <S> I would not recommend using an op-amp. <S> Now, to clear up some misconceptions: <S> CMOS <S> op-amps will get you pretty close to the power supply rails. <S> For example, the OPA211 from TI will get you within 0.2V of your power supply rails when sinking or sourcing load of 1-3mA, which isn't too bad. <S> Unless your load is insanely picky about logic levels, (which makes no sense at all on industrial equipment), you don't actually need exactly 24V and 0V. Most equipment I've seen can tolerate +/- <S> 10%, and logic levels are fairly forgiving. <S> Check your load's datasheet, and you will find input logic high and logic low thresholds. <S> Sparkfun has an excellent writeup on logic levels . <A> Just to piggy-back on Leon's answer... <S> Use the 3.3V signal to turn on and off a transistor. <S> The bottom of the transistor is tied to GND. <S> The top has a pull-up resistor to +24V and a tap go to the output. <S> When the signal is off, the transistor is off, and the output is pull-up to +24V. <S> When the signal is on, the transistor turns on, and the output is shorted to GND. <A> In environments like this you usually want to make sure you have some protection against back flow. <S> One of the easiest ways to deal with this is with an opto-coupler or Opto-isolator. <S> You can then use this in your circuit to turn on or off your 24V output. <S> The big advantage here is that if you have a back flow of current on the 24V side, there is no way for the lower voltage LED side to be affected. <A> Use suitable BJTs or MOSFETs. <S> Types will depend on the current to be controlled.
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You can buy ICs that are an all in 1 package, but from a functional level it is an LED (something like IR LED) that is turned on by your microcontroller, it then shines on a receiver that acts like a switch based off of the LED shining on it or not.
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Need ideas for 5->3.3 voltage conversion for micro SD cards I'm thinking about connecting a micro SD card to my ATmega162 perfboard, but for that I need 3.3 V source which can provide up to 100 mA. Most obvious option would be to run the whole board at 3.3 V because all components seem to be working at 3.3 V, but I'd like to keep the 5 V input voltage. Next option and the most obvious one would be to use voltage divider. The downsides of that would be need for high precision resistors, bad stability, space taken and power consumption. Another option would be to use a 3.3 V regulator. After checking which regulators I can easily obtain, choice comes down to LF33CV or LP2950CZ-3.0. The LF33CV fits from the electrical side with its dropout voltage of 0.45 V and very low power consumption. It can also provide up to 500 mA, which should be enough for most micro SD cards. I'd need two capacitors, one 0.1 µF on input and one 10 µF at output. On the other hand, the regulator is TO-220 and I'd like to save as much space as possible on the board. The LP2950CZ-3.0 is under just acceptable category from the electrical point of view. It has dropout voltage of 0.38 V and is guaranteed to provide up to 100 mA, which is exactly the amount I expect to need. On the other hand it's much smaller and comes in TO-92 package. It also only needs one 3.3 µF capacitor at its output in order to work properly. <Q> Why use 5V if you don't need to? <S> 100 mA * (5-3.3) is 170 mW. <S> No big deal for TO-92. <S> A cheapskate hobbyist approach is three silicon diodes in series. <S> This will get you in the neighborhood of 3V. <S> Might need to add a load resistor to set the max voltage with no card. <S> Have you thought about how you will level-shift the signal lines? <S> SPI lines are all unidirectional, which should simplify things. <S> 3.3V is a logic "high" for a 5V input. <S> A two-resistor divider would work ok. <S> Use a 1.5k and 3.0 k resistor to get pretty close to 1000 ohms output impedance. <S> You'll need this on clock, MOSI, chip select at least. <S> Related: <S> How do I get an Arduino (5 V) and MPR121 (3.3 V) to talk? <A> Go with all 3v3 if you can. <S> If not, interfacing between 5v and 3v3 can be done with 74LCX series glue chips. <S> You can get 3.3v buffer chips with 5v tolerant input such as the 74LCX244 (the X in the code <S> means 5v tolerant). <S> (you'll need a 3v3 regulator to power the chip, a teeny <S> TO92 5v->3v3 one is fine, and about 20c). <S> In the other direction (3v3 to 5v) you can just use pullup resistors to go from 3v output to 5v input. <A> A voltage divider is NOT a solution in this application. <S> Also, think about the resistor sizes you would need to make a divider without significant droop when 100ma is drawn from it. <S> Now, a series resistor will work in cases where the drawn current is extremely fixed, but think about what would happen if you were to change the current load - the voltage would increase when the current decreases, and vice-versa. <S> You really HAVE to use a voltage regulator here.
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Really, a voltage divider is not a solution anywhere you have any variance in the current drawn, or really in any power section of anything. You can hook these straight to 5v outputs and they give 3v3 outputs. The outputs should be level-shifted somehow.
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Best Electronics and Robotics Resources for a Novice I know guys hanging around here are quite experienced in electronics and robotics. But I am rather new to this area. I have only A/L physics knowledge in electronics. But I am working as a software engineer. Can anybody tell me the best resources that I can follow to become throughly acquainted with the subject. Thanks in advance. <Q> I have the same background as you, and one of the first things I bought was an EasyPIC5 pic microcontroller development board. <S> It allows you to play around with pics without having to know too much about the electronics side. <S> When you want to build a circuit using your newly programmed pic, you can start by prototyping it on a breadboard... and then move on to soldering it on to stripboard. <S> You can get lots of circuit schematic ideas by searching on Google images. <A> http://hackaday.com/ <S> - this will give you the idea of what can possibly be done in limited resources. <S> Then get an Arduino and start playing http://arduino.cc/en/Tutorial/HomePage . <S> Meanwhile find out local/internet shops where you will be able to buy parts without waiting too long. <A> My professor last year had us buy a 3pi Robot . <S> I thought it was a pretty cool beginners robot. <S> There is a lot of documentation and even a user forum on Pololu's website. <S> If you get an expansion board, you will have more space to add sensors or more sophisticated circuitry. <A> <A> Trossen Robotics has some excellent forums for getting your questions answered. <S> Both BotJunkie and Robots <S> -Dreams are two good blogs for keeping up with robotics news. <S> There are several very good robotics communities which you should check out, <S> Letsmakerobots and DIY Drones are two of the best. <S> I've also created a site ( RobotBox ) where robot builders post their projects. <S> You might get some inspiration there. <S> For purchasing parts, I recommend Trossen Robotics , Pololu , Solarbotics , or Lynxmotion . <S> Those folks have been around for a long time. <S> There are tons of smaller specialty outfits, but you can explore those as you gain knowledge.
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Another great place for a beginner is Letsmakerobots.com , the site is geared more toward the hobbyist/hacker crowd.
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What's the difference between an inverter with a bubble at the input and one with a bubble at the output? See this datasheet , page 2: the internal logic diagram for the MM74HC138. The diagram shows logic inverters with bubbles at the input or at the output. Is there an actual difference between them? <Q> Bubbles signify whether a signal is active low or active high. <S> On the digram, signals A, B, C, and G1 are active high. <S> Note that the truth table uses Ls and Hs instead of 0s and 1s. <S> For active-low circuits, a low voltage is logical 1. <S> The operation of a gate depends on how you interpret the signal levels. <S> For example, an AND gate with all active-high signals can be redrawn as an OR gate with all active-low signals, and vice versa. <S> In mixed logic design, bubbles always pair up. <S> You draw out the basic equation with AND and OR gates, and insert a vertical line with a bubble everywhere <S> there's a signal complement. <S> Then replace all the logic gates with the type you're actually using (e.g. NAND and the equivalent active-low input OR). <S> Finally, insert inverters anywhere that the bubbles don't pair up. <S> This makes it effortless to read the equation right off the schematic. <S> For examples of bubble pairing with mixed logic and a mix of active-low and active-high signals, see the following archived page from a Georgia Tech class: Mixed Logic Analysis and Synthesis Examples . <S> Either an input or an output bubble is used on each inverter in order to clearly show the bubble pairs. <S> The bubbles with slashes are just for reading the equation from the schematic. <S> They can be removed (as in example 4), and then anywhere there's a bubble mismatch is a logical inversion. <S> An inverter is a level inverting buffer. <S> It's not always a logic inverter. <S> In example 2 from the above link, when Y, B, and D are implemented as active-high signals, the circuit requires inverters even though the logic function doesn't call for the complement. <S> This is because NAND is equivalent to OR with active-low inputs, so the active-high inputs need to first be inverted. <S> In the schematic linked to in the question, note that the inputs and outputs of active-low signals in the schematic on page 2 have matching bubbles in the connection diagram on page 1. <S> I would have repeated those bubbles on the page 2 schematic for completeness. <A> NO.... <S> Both are same. <A> If someone's stumbled upon this question looking for a slightly different usage the circles as in this picture: <S> You might want to check this answer: https://electronics.stackexchange.com/a/452460
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The buffer with a bubble at the output or bubble at the input is always an inverter
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Modifying AA powered toy engine to be remotely turned on/off I want to make a remote for Thomas Battery Powered Engine that will allow it to be turned on and off, but I don't even know where to start. I assume I'll need a receiver that can toggle power on and off to the motor in the engine and an external transmitter. Can I use the AA battery in the engine to power the receiver? My hope was to be able to control multiple units via bluetooth from a smartphone. What should I read/ask/buy to get started? I'm not even sure this is on topic for this site. <Q> I can't help much on the remote part. <S> You'll most likely want to use radio, but I can't provide anything more specific than that. <S> I also can't give good advice right now, but that's because of the low amount of information in the question. <S> So first step would be to carefully disassemble the engine and post some photos of the circuits. <S> You'll most likely find one or even two motors inside (they do mention 4x4 drive) and see how they are controlled. <S> Next step would be to decide what you are going to do. <S> The description is a bit vague but I think that they mention multiple buttons on the unit. <S> You'll have to decide if you want to completely switch to remote control, just have remote on-off control and local controls or have full remote and local control. <S> It could be easier to just switch completely to remote control, but again that depends on internal wiring and available volume. <S> I'd have to think a bit for full remote and local control. <S> As for the switch itself, to me a MOSFET in TO-92 package looks like a good idea. <S> If you can afford it, get one of the more expensive ones. <S> They'll most likely be around 1€, but will have much lower internal resistance than cheaper ones which means that they'll consume less power for themselves. <S> Also for the radio power supply could be a problem. <S> Common voltage levels for hobby electronics are 3.3 V and 5 V. <S> On the other hand, AA battery provides between 1.6 V and 0.8 V, so you may have to make or get prefabricated converter. <S> Of course, this will negatively affect power consumption. <A> You might want something like this DC Toggle switch , but to be sure, we'd need more information on how this train works <A> Are you ok with the remote working in Line of sight ? <S> If yes you can use IR to control it. <S> I think there will not be any circuit that drives motor in them and will be rigged directly to the battery. <S> In case it produces some kinda music <S> then there might be a circuit for it in parallel. <S> But you can get this working pretty easily even if it does have a circuit but for any result you will have to open it and see inside :D <S> With a small circuit you should be able toggle the power to the motor. <S> I would first connect my motors directly to the battery and see how much current it draws and then decide on using either some motor controller or MOSFET for this JOB and the use a simple IR receiver and few electronics component to rig up a small circuit. <S> This should be fairly easy. <S> For having circuit level help you need to post the details as of how much motor it uses (my guess is 1) and how many batteries it is powered with.
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Basically, if you want remote on/off control, you could accomplish that in two ways: place the extra switch at engine's main power connector or place extra switch on engine's motor power connector.
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Why do PBX systems use -48 V? It seems common that PBX and other telephone hardware use a positive-ground power supply, where the "hot" line is at -48v. What's the reason for that? <Q> I remember this coming up many years ago in the alt.telecom newsgroup <S> and I managed to find it for you <S> (aren't I kind?) <S> : <S> Why most telecommunication equipment use <S> -48V supply voltage <S> In summary (from the thread): <S> "From a book I've been reading lately <S> (Instruction in Army telegraphy and telephony, vol 1, 1917), the reason is for fault tracing. <S> An earth fault will tend to decrease in resistance, i.e. tend towards a dead earth, if the earth is positive with respect to the conductor, thus enabling it to be located." <S> "48V (or in the UK, 50V) seems to be arbitrary, many of the earlier CB systems of the Post Office used 22 volts or 40 volts. <S> The automatic systems in some early exchanges of the Siemens 17 type used 60 volts IIRC. <S> 48 to 50V may have been a happy medium (remembering that years ago, telecommunication companies were VERY conservative, and standardized across their entire network), allowing the use of long thin lines, but not risking electrocution of linemen or overheating on short circuits." <S> "A negative voltage is really a positive earth potential. <S> If your positive conductor i(+) is earth, you can't short it to earth. <S> It can be shorted to the exchange earth connection if it comes into contact with a suitable conductor in the cable, <S> but as this 'earth' is the negative battery terminal (technically) <S> you don't get the massive current flow to earth for a conductor to earth. <S> The only way you can get massive current flow is if you short the pair together or put the positive earth to a foreign wire connected to the negative battery terminal." <S> "corrosion reduction—the leakage to earth that would occur if insulation were damaged opposes the corrosion." <S> "Why negative? <S> AFAIK to reduce electrolytic corrosion of buried cables, which were lead-sheathed." <A> Electrically it makes no difference if the ground is positive or negative the components will be connected accordingly. <S> However in the early discovery days when electric trams and telephone cables were laid. <S> They were first connected as negative ground and it was found over a short time that corrosion and eating away at cables was a serious problem. <S> Especially for the delicate telephone cables which where insulated by paper wrapped around each wire. <S> In the UK, tests were done over period of time using both systems and significant improvement was found with the positive ground system. <S> Due to the long life that was expected from these cables it was obvious that positive ground at the telephone exchange had to be the new standard. <S> It still is today, world wide all telcos still use the minus 48 volts to the subscribers house and positive ground at the exchange battery. <S> Now as for car electrical systems, I can only assume that the lack of longevity of the car made positive ground an inconvenience and in the mid fifties after the war world trade and standardisation was required hence the 12volt negative ground system. <A> As an ex-Bell employee, this was my first question as my tendency (from school) was negative ground. <S> The post referencing the trams nailed it. <S> It was found positive voltage cable corroded much faster as also mentioned in a post above - it's basically electrolysis. <S> -48 volts was used to minimize resistance loss on cables from the central office to the customer and PBX / station equipment on the customer site used -24 V. <S> I've been out a while - I'm not sure if subscriber equipment still uses -24V anymore. <A> Now there are tons of chips and brick for -48 V to 12 V/5 V, etc. <S> conversion. <S> And for UL and other safety limits it is easier to get approved if it is less than ~60 V. <A> Telephone lines originally were all LONG HAUL from the SLIC generating the V-borsht (battery, overvoltage, ringing, supervision, coding, hybrid and test access). <S> And with line drop over long hauls the end phone line will experience much less. <S> Normal phone lines being -48V <S> On Hook at the Telco's SLIC(FXS). <S> Where at the FXO (or phone) <S> that same voltage may drop to as low as 20V. Where on OFF hook will pull the line to approximately 7-9V. <S> Also note that using a simple doubler the On Hook is about 90V, which can produce enough current to move the physical clapper of the Ringing Bell. <S> Now a days. <S> FXS to FXO are all mostly short in that they are kilometers. <S> And the REN (Ringer Equivalency Number) load is so low, the FXO/phone devices sees nearly 100% of the voltages. <S> So it is best not to lick Tip/Ring while the phone rings. <A> In addition to the reasons given above, I also think the reason for using 48V in particular is that batteries come in 12V or multiples thereof (24V). <S> It is easy connect four 12V or two 24V in series to obtain 48V.
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Also they use 48 V (regardless of polarity) because that is lower current so easier to distributed.
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How do I improve efficiency of a boost converter? I have built a 3V to 5V boost converter with discrete components. L = 220uH Vf(Diode) = 0.25V ZVN4210A MOSFET C = 470uF f = 47KHz My load is a microcontroller board (M16C QSK62P Plus) that takes upto 90mA of current. I am using the PWM signal from the same microcontroller for the switching pulse for the converter.I tested my circuit for a constant load of R = 100Ohm I measured average current flowing through the inductor and output voltage. From that I calculated powers Pin and Pout. I am getting the efficiency of approx. 75%. I know that boost converters can be more efficient (90%). So, I need some suggestion about modifications in my circuit to improve the efficiency. <Q> Your inductor probably have high serial resistence. <S> You might want to take lower value with thicker wire. <S> Use ulta-low ESR caps, tantalum ones. <S> Add some 0.1 + 22-66uF of ceramic cap in parralel. <S> If frequency is high enough just leave ceramic. <S> Implement synchronious rectification to get rid of that 0.25 vDrop <S> (and I am not sure it's really 0.25, should be higher) <S> Use proper MOSFET. <S> Why take 100V part? <S> 1.5Ohm <S> Rds? <S> This is not suitable for efficient DCDC. <S> You want some 12-24V logic-level MOSFET with some 0.1 - 0.01 Rds. <A> As noted - MOSFET is not very suitable. <S> As well as poor Rdson it has marginal gate turnon voltage (Vgth or Vgsth) for use at 3V. <S> It will work (and it does) but could be better. <S> With your oscilloscope observe the voltage when turned on. <S> If you can measure it its too large :-). <S> You have not said what inductor you are using. <S> Please advise. <S> Inductor value is possibly a bit high. <S> Ignore <S> probably: At, say, 3V available and assuming a current ramp to double <S> I avg <S> it will take 220 uH/3V <S> x 0.1A x 2 =~~~ <S> 14 uS to reach required current. <S> with continuous mode operation 220 uH is OK. <S> Diode drop is suspiciously low. <S> What diode are you using? <S> At 0.25V, as you state, the diode loss at 5V is > 0.25V/5V = <S> 5%.Done less than properly add MOSFET 5%, Inductor 5%, other 5% = 80% overall. <S> Sound familiar :-) <S> Ensuring FET and inductor are OK <S> will help.90% is hard without synchronous rectification,which has its own issues. <S> Well over 80% should be possible. <A> Or you could buy a properly implemented ready-made boost converter with > 90% efficiency for under $5.If <S> you make many of these, vendors like Recom or Murata may actually have pre-built modules. <S> If you only need one or a few, Pololu has a nice 5V 200 <S> mA boost converter with 90% efficiency for $4.95.Link, while it lasts: http://www.pololu.com/catalog/product/798 <A> Here is a trick I learned some time ago. <S> The best way to improve efficiency is to have the field of the inductor collapse as quickly as possible. <S> Adding the PNP/Signal Diode combination will improve efficiency a lot.
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As noted also, the inductor should have a small enough resistance to drop minimal voltage with FET on and it must have a core designed not to saturate at your operating current. Increase frequency if needed (but not too high, switching losses increases).
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How much overclocking is "okay"? So I'm using a PIC32, it's rated for 80 MHz operation. But my crystal might be inaccurate, so it could oscillate at 80.01 MHz. I can presume this is okay, but what if I were to use a 7.3728 MHz crystal and an 11x PLL, would running it at ~81 MHz be okay? I suppose what I'm asking is how far is too far? And why do manufacturers not include a bit of overun (for example rating it at 81 MHz?) <Q> Manufacturers specify a maximum clock speed for a reason, as it guarantees correct operation under all conditions specified in the data sheet. <S> You will have to test the system and see if it is sufficiently reliable for your requirements, under all circumstances. <S> I can't see 81 MHz causing a problem, but it can't be guaranteed. <A> more seriously something like bumping an 80MHz clock to 81MHz is not a big deal (puts on chip designer hat) when we tape out a chip we don't have complete control over what happens at the fab - they might put a little too much dopant (or to little) in one step, or under etch a step so that wires are slightly wider (with higher capacitance) <S> - instead we design for the 'worst case corners of the process' and try and make internal timing there - that way any functional chip coming out the other end should work and meet the spec - from you point of view it means that most of what you get from us is somewhere in the middle of the yield curve and happy to run over spec .... <S> but some percentage will be just at spec and will fail if you overclock (and some percentage will go much faster still). <S> We don't normally test chips for speed (maybe sometimes a test patch on a dies to test the process) <S> - it's way too expensive - <S> we plan on them all working. <S> Some expensive chips (high end processors for example) will get tested and binned because it makes sense for both practical (yield) and marketing reasons to do so <A> In fact, most of these low-speed chips can work on 1.5x frequency in normal conditions, the only problems are at extreme temperatures (like -55 or 125) + flash/EEPROM writing. <S> So if you you are building device which will be operated at 15-40C range, you may test that it works at 120Mhz and leave at 100 permanently. :-) <S> Manufacturers underspec devices to increase yeld rates & reduce reclaims. <A> If you're working with a single device you can just try and see what frequency still works. <S> 81 MHz will still work, no doubt about it. <S> It's a bit different if you're working with production quantities. <S> You can't make a production run and hope everything will be all right. <S> In the early 90's I worked for Philips Audio and we had a design which used a Motorola 56002 DSP running at 27 MHz. <S> This was an audio application, and the 4th harmonic of 27 MHz is 108 MHz, just at the edge of the FM band. <S> Because we feared interference we wanted to run the DSP at 27.1 MHz. <S> Would this work? <S> Yes. <S> For sure? <S> No. <S> Motorola guaranteed it for 27 MHz, no more. <S> We requested and got a custom version of the specification which stated 27.1 MHz as the maximum frequency. <S> Did we get different, selected devices, or was there a die redesign? <S> Of course not, but in unlikely the event that a DSP would not work Motorola would be liable. <A> Back in the 1970's, it was pretty common to run 6502 microprocessors at above the rated speed, even though the data sheet gave a minimum cycle time of 1000ns for the 1MHz part. <S> The popular Atari 2600 Video Computer System ran its processor at 1.1932MHz; the Apple II, Commodore VIC-20, and Commodore 64, all ran at 1.0227MHz. <S> Since there were no speed grades between 1MHz and 2MHz, I would expect all of those machines were overclocked (by almost 20% in the case of the Atari 2600 Video Computer System).
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Well the right answer is "you can overclock until it stops working" .... Operating a device outside its specification might be OK in a hobbyist application, where an occasional failure can be tolerated, but isn't a good idea if reliability is important.
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When should you use a fuse? When is it actually practical to use a fuse?Like lets say your building a robot using an Arduino.....what area would you want to protect the most with a fuse? I mean do they even make fuses that small (5v's and such) and how do you go about "connecting" them to wires, since the smaller ones seem to be a solid cylinder <Q> This is defenetly possible with non-protected LiIon batteries for example. <S> For low-voltage applications there are self-healing fuses (often found on motherboards, especially for USB protection). <S> For non-autonomous robot I would just have 1 fuse on battery, so that it would not burn. <S> For autonomous one you might need one per each power consumer + sensors to react on shorted engines e.t.c. <A> The use of fuses often springs from an FMEA (Failure Mode and Effect Analysis). <S> You evaluate what the consequences of certain failures are, and how you can avoid them from turning into disasters. <S> A failing component may cause a short-circuit, which in turn may lead to overheating, and eventually a fire. <S> A simple solution is to protect the device as a whole by placing a fuse even before the mains transformer, so that this is protected as well. <S> When I worked at Philips Audio we often would use PCB solderable fuses (a smaller version of these ). <S> They look a bit like small cylindrical capacitors. <S> They have the advantage that electronics hobbyists won't go about replacing them; you have to recognize them as being fuses to begin with. <S> Why don't you want the fuse replaced? <S> Most of the time there's a good reason why a fuse blows: some defective component. <S> If you just replace the fuse and power the device again you may destroy more components, making the problem even worse and make a repair more costly. <S> While there are low-voltage fuses (like the PTH ones we used at Philips) <S> you don't really need them. <S> The voltage rating of a fuse refers to the separation when they're gone. <S> You can perfectly use any 20x5mm glass fuse for lower voltage applications. <A> I would connect the fuses inline, if you can't make your own board with through-hole fuse holders. <S> Something like this: http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_109330_-1
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You need a fuse if you want to limit possible damage if something got shorted.
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Powering an old alarm clock LCD (need to invert DC to 3 V AC) I'm tinkering with a cheap old alarm clock LCD screen. I think the LCD is multiplexed (there is only one row of connectors along the top of the screen, etched (or something) into the glass, and there doesn't appear to be any common ground or anything from the circuit board the LCD rests against). The clock itself is powered by a single AAA battery. There is no driver circuit board or anything directly attached to the LCD (as many hobbyist purpose-built ones seem to have), so I need to provide the current directly to the LCD. It appears that the screen itself receives about 3 V AC to activate a given region, as measured by a multimeter from the alarm clock circuit board. So my question: how can I create this AC current from a DC source of around 1.5 V DC? Would it be possible to also do this from 5 V DC (provided by my Arduino)? I would like to avoid (if at all possible) up-converting to 110 V AC first (it seems to be a common recommendation from google searches). I have many basic components (resistors, caps, transistors, pots, diodes, etc) laying around in my 'nerd boxes' which I would prefer to use over specialized components, such as purpose-made inverters or the such, to do this. As may be evident, I am somewhat new to electronics tinkering and as such may be way off with my expectations. I will respond to comments/answers, and can post pictures once I get home if it would help. I appreciate any help I can get on this :) <Q> You identified the LCD as being multiplexed—which it very likely is—so the AC you're seeing is probably just some segment being sequenced. <S> It is better described as a multiplexed signal with such a frequency and some voltage (amplitude, not AC voltage as measured by a meter). <S> Atmel's app note AVR340: <S> Direct Driving of LCD Using GeneralPurpose IO may be of use to you. <S> This portion describes the "AC" that you're seeing and shows why. <S> To energize a segment, the waveform to that segment must be 180 degrees out of phase with its COM waveform. <S> The voltage difference between the segment and COM signals will therefore be typically 5 Volts AC, which causes the segment to become visible after 300-400 msec of refresh cycles. <S> To de-energize (turn off) a segment, the COM and segment waveforms should be in phase with each other while that segment’s COM is active, that is, not at 2.5 volts. <S> So, a LCD with all segments OFF will have the segment inputs IN PHASE with each COM input. <S> (COM3 was omitted from Figure 2-2, since only 4 channels were available.) <A> Incidentally, it's possible to drive a 3-way multiplexed LCD entirely with logic-level signals. <S> To drive the display, run the common wires through all eight combinations of high and low, and drive each segment wire such that at least two of the three segments it controls will be "correct" (a segment will be "clear" if the state of the segment wire matches the state of its common wire, and "dark" if it differs). <S> It turns out that no matter what pattern of light and dark segments one wishes to display, every segment that's supposed to be "dark" will be energized 3/4 of the time, and every segment that's supposed to be "light" will be energized 1/4 of the time. <S> This is a technique I invented myself in the 1990's, and have used in a couple of product designs. <S> The contrast ratio is the same as what one would get using 1/2-bias (as shown above), but not as good as what would be obtained using 1/3 bias. <S> In my implementation, I had to clock data through shift registers every frame, which used some current; if the circuitry were built into an ASIC <S> I'm not sure how the efficiency would compare with that of a conventional multi-voltage technique. <S> Note, that Motorola claims a patent on a technique somewhat like this, but they use a six-phase waveform rather than an eight-phase waveform, and they only achieve a 2:1 drive ratio rather than 3:1. <S> Their patent would cover the use of a four-phase waveform to drive a 2-way multiplex LCD, but explicitly specifies the use of 2n phases rather than 2^n. <A> Does your LCD look something like what's in this datasheet ? <S> You may find that using a micro (to generate PWM) is more practical than inverting DC to AC. <S> I doubt that the LCD will draw much current.
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A microcontroller toggling pins in succession will indeed produce AC, however calling "x V AC" that is an extreme red herring.
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Is my inductor really 22µH? I have a package of 10 inductors, all of which are supposed to be 22µH, but they all have "220" printed on the case. It does not seem right when I compare to an otherwise identical (same type) inductor with an inductance of 3.3µH, which has "3R3" printed on it. Is it just odd ordering or am I missing something? Inductor is an SDR0604 type. <Q> There are two ways of marking parts... <S> A Three digit code for values from 10 and up X Y ZX - First digitY - Second digitZ - Power of ten220 would be 22 = 22 <S> x 10^0 <S> (1)221 would be 220 = 22 <S> x 10 <S> ^1 <S> (10)222 would be 2,200 = 22 <S> x 10 <S> ^ <S> 2 <S> (100)223 would be 22,000 = 22 <S> x 10^3 (1000) <S> The Minimum for this coding would be 100 = 10 <S> x 10 <S> ^ <S> 0and <S> the Maximum would be999 = <S> 99,000,000,000 = 99 <S> x 10 <S> ^9 <S> (1,000,000,000) <S> For values under 10 <S> you use a character to replace the decimal point <S> e.g. 3R3 = <S> 3.3R33 = 0.33 <S> R is used for Ohms. <S> For resistors the value is usually in OhmsFor Capacitors the value is usually in pico farads <S> e.g. a Capacitor marked <S> 103 would be 103 pF = <S> 10 <S> x 10^3 (1000) <S> pF = <S> 10nF = <S> 0.01uF <S> For Inductors the value is usually in micro henryse.g. <S> a Inductor marked 220 woulf be 22uH = 22 <S> x 10^0 <S> (1) <S> uH <S> The part marked 3R3 is a 3.3 ohm resistor as R is used on resistors. <A> That should be read as 22 × 10 0 µH and 3.3 µH respectively. <S> The R is a decimal, the last digit otherwise is an exponent. <A> 220 means that the value is 22 times 10^0, or 22uH. <S> It's a similar notation to that used for small value capacitors. <A> Panasonic SM inductors use R in the part marking (for example, 2R6 corresponds to the 2.6 microhenry part on the specified datasheet).
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If they were really 220uH they would have the value 221.
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What is "forward" and "reverse" voltage when working with diodes? What is the difference between "forward" and "reverse" voltages when working with diodes and LEDs? I realize this question is answered elsewhere on the interwebs such as wikipedia, but I am looking for a short summary that is less of a technical discussion and more a useful tip to someone using diodes in a hobby circuit. <Q> The forward voltage is the voltage drop across the diode if the voltage at the anode is more positive than the voltage at the cathode (if you connect + to the anode). <S> You will be using this value to calculate the power dissipation of the diode and the voltage after the diode. <S> This is usually much higher than the forward voltage. <S> As with forward voltage, a current will flow if the connected voltage exceeds this value. <S> This is called a "breakdown". <S> Common diodes are usually destroyed but with Z and Zener diodes this effect is used deliberately. <A> Forward-bias is when the anode (the pointy part of the symbol) is positive and the cathode (the bar) is negative. <S> Reverse-bias is when the anode is negative and the cathode is positive. <S> A lot of current flows when the diode is forward-biased, provided that the voltage is higher than 0.6V <S> or so for a silicon diode or 0.3V or so for a germanium device. <S> A very small amount of current flows if a diode is reverse-biased. <S> If you have a DVM and some diodes, you can check it for yourself. <S> Diode cathode leads are usually identified with a band, so if you switch the DVM to a low resistance setting, and connect the leads across the diode in both directions, you should see a low resistance in one direction and a high resistance in the other direction, provided that the DVM is supplying a high enough voltage. <S> Some DVMs have a special diode test setting that is easier to use. <S> LEDs usually have a flat against the cathode lead. <A> Typically the forward voltage is the voltage at which current starts to flow in the normal conducting direction (as mentioned above it's somewhere in the range 0.3-0.6v) <S> Reverse voltage is sort of the same thing - it's the voltage where current starts to flow when the diode is in the normally non-conducting region - this is also the point where the diode is likely to turn into a charred mess as all the internal semiconductor stuff turns to mush (choose a value somewhat larger than the largest PEAK [not RMS] <S> AC voltage the diode will see) <A> Excavating in 3 <S> ... 2... 1... <S> Just so that the information is condensed here <S> and I like to know where to find my offspring <S> , I'd add typical forward voltages for common LED as a quick reference for everyone. <S> (And also because I like to dig an old thread on the 18th December.) <S> As per Wikipedia : <S> Typically, the forward voltage of an LED is about 1.8–3.3 volts; it varies by the color of the LED. <S> A red LED typically drops 1.8 volts, but voltage drop normally rises as the light frequency increases, so a blue LED may drop around 3.3 volts. <S> LED forward voltage quick reference <S> IR LED drops about 1.5V <S> Red : ~2V Amber : <S> ~2V Yellow : ~2V <S> Green : <S> ~2.5V <S> Blue : <S> ~3.5V <S> White : <S> ~3.5V <S> Laser <S> diodes: <S> ~1.5V <S> but may vary a lot with wavelength (like 375nm to 3300nm ) <A> Although you mention "voltage," I believe you mean bias. <S> If this is correct, then "forward bias" is the application of a voltage in such a way that the diode "shows" a low resistance . <S> "Reverse bias" causes the diode to show a high resistance . <A> Forward voltage is the one that makes the diode to conduct while the reverse voltage is the one that makes a diode very bad conductor or almost an open circuit unless diode "breaks down".
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The reverse voltage is the voltage drop across the diode if the voltage at the cathode is more positive than the voltage at the anode (if you connect + to the cathode).
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How can you tell how many layers a PCB has? This is a question purely out of curiosity. I have several various PCBs, and I'm curious as to how many layers they use, which helps me decide how many layers to use in my project (for example a cheap competing product using 4 layers suggests to me it is possible to do my product with a 4 layer design). From looking at the vias (and where they connect to), I can usually determine if they have 2 layers or more, and I can tell apart single layer boards too because they don't have a top or a bottom side, however, I've never been able to actually count the number of layers a more complex board like a motherboard or graphics card uses. Any clues? <Q> As far as non-destructive methods, you may be able to shine a bright light into the edge and through a corner see the copper planes. <S> Signal traces may be hiding though, and this only works if the copper comes fairly close to the edge, which it may not. <S> Using a bright light, it's easy to see if a board has inner layers even if it doesn't have blind vias. <S> If it's blocked in some places, that's probably copper. <S> Even without that, most multi-layer boards I've dealt with using the standard green LPI have a darker appearance than their 2-layer counterparts. <S> If the board designer had space to kill or the manufacturing engineer wanted for some reason (not sure why), I've also seen boards with a "stair-step"; each layer labeled with a copper number and cutouts in the other layer to be able to see it. <S> This might be unique to my old company though, as our layout tech did all sorts of strange things. <A> Cut the board in half and inspect the copper. <A> I don't know about other PCB's but all of our boards have little numbers on the corner designating what layer it is, so the top has a 1 and the back has an 8 or something, you can see the hints of other numbers too. <A>
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Find some place on the board where there aren't traces/planes on the visible, outer layers and see if you can see light through it. Normally all PCB's have a little number in the corner designating what layer it is, L1 in the picture below for the top side of the PCB and L6 for the bottom layer,so this PCB has 6 layers.
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How do step-up transformers work? I’m trying to figure out how a step-up transformer works. A step-down transformer is simple and logical enough; you start out with a higher voltage and end with less, the remainder being wasted as heat. But with a step-up transformer, you end up with more voltage than you start with. I tried looking it up, but all I can find (whether online or even in some electronics texts) is general information on how transformers work (induction, Faraday’s law, construction, etc.) and explanations of the difference between step-ups and step-downs in terms of the number of turns, but not specifically how step-ups result in more voltage. Where does that extra voltage come from? Not magic… <Q> I think what you're missing is the current... <S> Step down transformers change a high voltage/low current, to low voltage/high current. <S> So, in an ideal 100% efficient transformer, the power doesn't change and no heat will be generated by the transformer <S> , i.e. the power in = the power out, because Power = Volts x Amps. <A> Think of a transformer as being a like gearbox (or pulley system, or lever, or other such machine). <S> A 10:1 gearbox can turn a 60rpm rotation into 600rpm, but if the output requires a certain amount of torque to rotate, the input will require at least ten times that much (slightly more, in practice, because of friction in the gearbox itself). <A> Think about it this way: magnetic field have no idea how many loops you have on the second half of transformer. <S> So, each loop on second side works like a small 'bettery' connected in series, the more loops - the more batteries - the more voltage. <S> But as there is the same amount of magnetic field is divided on all loops, achivable current is less. <S> Same works another way: Less loops - less voltage, but more current as more magnetic field is left for 1 loop. <S> In ideal situation no heat is generated. <S> Heat is generated the way you say only in linear regulators. <A> "you start out with a higher voltage and end with less, the remainder being wasted as heat" <S> That's absolutely false. <S> In an ideal transformer no heat would be generated, no matter how much the voltage difference is. <S> A transformer transforms the input voltage (actually input power) into a variable magnetic field. <S> That magnetic field generates a voltage in the secondary winding, and the voltage ratio between primary and secondary is equal to the ratio of the number of turns. <S> So you can get a higher output voltage by giving the secondary winding <S> more turns that the primary's.
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Step up transformers change a low voltage/high current, to high voltage/low current.
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Which servo motors for a precise but not powerful robotic arm? I've just got into electronics with an Arduino explorer kit from Oomlout and I have learned a lot about electronics so far, but now I want to start my first proper project. A robotic arm. It should be precise but barely needs to lift any weight at all (a laser pen). I would like it to be 30cm or so long, it would have one servo at the bottom for rotating the whole arm left and right, another up and down, then two more to lift the other segments up and down. Does anyone have any recommendations on servo's I should use? They don't need to be fast or powerful, just precise. And, of course, being cheap will be a bonus. <Q> You might start with motors made by the Swiss manufacturer Maxon . <S> They're used in high-end robotic arms. <S> They're expensive when bought new, but you might be able to get them cheaper off Ebay if you just need a few. <S> You should also think about how you will measure position and connect the motor to the arm. <S> A lot of your position error will be in the backlash in the mechanism you build, error in the position encoder, and flex in the arm itself. <S> You might also google "harmonic drive" or "anti-backlash gears." <A> I wouldn't necessarily start with motors right off the bat. <S> You have to look at your entire system. <S> How are you going to mount the motors, and where? <S> If you put a motor at every joint, you have to remember that you're increasing the payload requirements for each motor in the chain. <S> Think about whether or not your first project really needs to be so precise. <S> And how do you define precise? <S> Within 2mm? <S> 0.5mm? <S> 10 microns? <S> For gripping, maybe you can get away with a simple RC servo. <S> Now you've just reduced the payload for the other motors. <S> Antibacklash is very important, and you could use anti-backlash gears and nuts, or you could go a little simpler and cheaper with belts and one or more idler pulleys. <S> The potential advantage here is that you can move a motor off of a joint and have it somewhere else where the weight of the motor doesn't adversely affect the system. <S> I'd like to hear what others think about this, but ultimately your servo's precision is going to boil down to your encoder and the gearing in your system, and the quality of your servo controller. <S> So perhaps the motor doesn't need to be a Maxon or a MicroMo, but something less expensive that still lets you connect a high-resolution encoder. <A> I like the idea of building first with cheap imprecise servos ( at less than 10 bucks each ) <S> I think you will learn enough to justify the expense. <S> Putting the mass at the end of a 30 cm lever will greatly increase the load on the servo. <S> Consider using different servos in different places. <S> Using the smallest one at each place ( joint? ) <S> that will do the job, that will lessen the load on the servo that has to move it.
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While I am not a fan of stepper motors, you could even go with steppers and encoders, which would simplify the system further.
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Tips for keeping lots of cables tidy I'm working on a project with a lot of external peripherals, so this means lots of wires. Any recommendations on how to keep them tidy while working on it? I don't want to use cable ties just yet, as I need to keep moving them so would have to keep cutting the cable ties. <Q> I like to use Velcro Cable ties . <S> Basically used the same way as ones you would have to cut, but instead you just have to pull them apart. <S> Depending on what you are doing a Wire Duct might benefit you more. <S> They tend to get more messy on the inside, but can produce neater results on the outside. <A> "flexible plastic conduit" "corrugated flex tubing" "split loom" <S> I'm having trouble finding a good search term for it, but I've used flexible plastic/PVC wire conduit to bundle wires together in text fixtures outside of enclosures. <S> The stuff is commonly used in wire harnesses, especially in automotive. <S> It's essentially a thin, corrugated plastic hose with a slit running through it <S> so you can shove in or pull out cables and wires, available in a wide range of sizes, from about 1/4" (almost pointless; fits about (3) <S> 16-AWG wires) up to 2". <A> Not sure where you can get it, but I've encountered this stuff that looks like spirally-cut polyethylene tubing. <S> The stuff I've seen comes on a big reel, and you cut off as much or as little as you need. <S> So you lop off a few inches of it, and then wind it around the wires <S> /cables you want to bundle. <S> It's very quick to put to use, it's quick to take off, it's re-usable, and it's neat, too. <A> <A> Insulation tape... <S> cheap, firm hold, easy to remove. <A> I don't know what this is called, but I think this would help.
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Using twist ties to shorthen cables is a very simple first step, gets rid of long lengths of cable waiting to get tangled.
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How can I control many LEDs with just a few pins on my micro? I am using an Atmel ATtiny13 which has a 6-pin I/O. I'd like to control about 15 LEDs but am unsure how to connect everything. Without multiplexing of any sort, it seems I'd only be able to control 6 LEDs at a time. Am I limited to only 6 LEDs because of the size of the microcontroller? <Q> The simplest is standard row/column display multiplexing. <S> With this technique, you can drive \$( n / 2 ) <S> ^2\$ LEDs with \$n\$ IO pins. <S> Mathematically, the duty cycle is: $$\frac{1}{minimum(\text{unique row patterns, unique column <S> patterns})}$$ <S> This means that this technique has a duty cycle of 100% when all LEDs are lit (or all rows or all columns are identical) and a duty cycle of \$1 / n\$ when a diagonal line needs to be lit (or all the rows are different). <S> You're only guaranteed 100% duty cycle when lighting every LED or one LED (or zero LEDs, but that doesn't really count for much). <S> Slightly more complex is Charlieplexing . <S> With this technique, you can drive \$n^2 - n\$ LEDs with \$n\$ IO pins. <S> Only \$n - 1\$ LEDs can be lit simultaneously with this technique. <S> Mathematically, the duty cycle is: $$\frac{1}{\text{minimum simultaneous sets}}$$ where a simultaneous set is a unique group of LEDs which has a common anode or common cathode. <S> (This hasn't been proven, it's just what I arrived at after pondering the problem for a minute. <S> If duty cycle is important to you, you'll want to look into this further.) <S> This is a much more complex calculation both intellectually and computationally than the equivalent calculation for standard multiplexing. <S> Effectively, you get a duty cycle of \$1 / n\$ when all LEDs are lit but some (only some) patterns of n-1 or fewer LEDs can have a duty cycle of 100%. <S> You're only guaranteed 100% duty cycle when lighting 1 LED. <S> The last method I'll mention is to use a shift register or IO expander. <S> With two pins (Either the raw data/clock interface, I2C, or unidirectional SPI), you can control an arbitrarily large number of LEDs. <S> The duty cycle for any pattern is 100%, but the update rate is inversely proportional to the number of LEDs. <S> This is the most costly method. <S> For 15 LEDs, it will probably be cheaper to just upgrade to a micro with that many IO pins. <A> Using Charlieplexing <S> you can directly drive \$n \times (n-1)\$ LEDs from \$n\$ pins. <S> Exemple: <S> Six LED's on 3 Pins: PINS <S> LEDS0 1 2 <S> 1 <S> 2 3 4 5 60 0 0 0 0 0 0 0 00 1 <S> Z 1 0 0 0 0 01 0 <S> Z 0 1 0 0 0 0Z 0 1 0 0 1 0 0 0Z 1 0 0 0 0 1 0 00 <S> Z 1 0 0 0 0 <S> 1 01 Z 0 0 0 0 0 0 10 0 1 0 0 1 0 1 00 1 0 1 0 0 1 0 00 1 1 1 0 0 0 1 01 0 0 0 1 0 0 0 11 0 1 0 1 1 0 0 01 1 0 0 0 0 1 0 11 1 1 0 0 0 0 0 0 <A> Without multiplexing (direct drive) you are limited to 6 LEDs. <S> With charlieplexing you can drive n*(n-1) LEDs from n pins. <S> With I/O expanders or shift registers you can drive a virtually unlimited number of LEDs. <S> Example: MCP23008 <S> 8-bit <S> I2C <S> I/ <S> O Expander <A> As @mjh2007 suggested with an I2C expander. <S> But there are ones specifically for driving LEDs which will avoid the need for external current-limiting resistors. <A> Here's an example of charlieplexing that I have built. <S> It's a lighthouse beam simulator and uses a series of 12 LEDs charlieplexed to 4 GPIOs to sweep a beam of light around a disc. <S> There's a video of it here . <S> The project is PIC based, I use a PIC12f683 which is also an 8pin <S> uP <S> and could be considered comparable to the 8pin AVRs. <S> The LED's intensity is driven by an interupt that provides a 32 step PWM at around 60Hz. <S> Only two LEDs are allowed to be lit at any one time giving a 50% duty for each LED as that was all I needed. <S> It also gives a good trade off of PWM refresh rate against resolution. <S> I work out the required PORT and TRIS (pic specific registers) first on paper then store the results in a static array. <S> To light LED <S> x the PIC just has to lookup the value at the array's index[x] and write them directly to the PORT (with a bit of masking to preserve the state of the other pins not used in the charliplex) <S> My project only has 12 LED <S> not 15 or the maximum 20 the 5 GPIO will allow as I wanted to keep one GPIO spare for future development. <S> Anyway... <S> I just thought it might be helpfull to have a working example similar to your request. <S> Full source code and schematics are available on my blog. <A> Another option would be to use the Neopixel LEDs. <S> They have a built-in control IC and you only need one pin to control as many LEDs as you like. <S> Of course you will need an adequate separate LED power source then.
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There are several methods which can be used to drive large numbers of LEDs from a few IO pins. The coding for using charlieplexing as actually pretty simple if you stick to the "classic" method of only lighting a single LED at any one point in time at a very fast refresh rate.
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What's the difference between a potentiometer and a rheostat? I've seen that a number of schematics will connect the center (common) pin of a potentiometer to one or the other leg, and it then functions more like a rheostat. Is that how a rheostat is wired internally? What's the difference between a potentiometer and a rheostat? Finally, why connect the common to a leg at all on a potentiometer, instead of just ignoring the unused leg? <Q> The correct term for the common terminal of a potentiometer is the slider. <S> Only the slider and one other terminal are used. <S> A potentiometer uses all three terminals, enabling a variable voltage or signal to be tapped off from the slider. <S> Potentiometers and rheostats are made the same way, but rheostats are usually much "beefier", as they are generally used in high-power situations. <S> The slider is often connected to one or other terminal for safety reasons, in case it loses contact with the track. <A> One difference not yet mentioned between devices intended for rheostats versus those intended for use as pots: if a device will be used as a rheostat, it is important that the wiper resistance be fairly small, and even more important that it be 'well-behaved'. <S> If the device will be used as a pot, and the amount of current flowing through the wiper will be minimal, wiper resistance is relatively unimportant. <S> A 100-ohm rheostat with a wiper resistance of 10 ohms in some spots and 1,000 ohms in other spots would be totally useless. <S> A 100-ohm pot with such behavior could be just fine, however, if it was being used to drive a high-impedance input. <S> Note that such a pot would be roughly equivalent to a 1,000-ohm pot in parallel that had a 110-ohm fixed resistor tied between the ends. <A> A Rheostat is used to vary the amount of current in the circuit but a potentiometer used to vary the voltage between the second terminal and one of the outside terminal <A> It appears the Wikipedia article about potentiometers quite clearly and concisely points out the difference: A potentiometer /pɵˌtɛnʃiˈɒmɨtər/, informally a pot , is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. <S> [1] If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat . <S> It also has a dedicated section for the (historical) meaning of "Rheostat", and <S> how rheostats were/are built, but admits that the word "rheostat" is becoming obsolete in favor of the more general "potentiometer", which, as already highlighted in the introduction paragraph, is just a rheostat if you ignore one of its terminals. <S> The term "rheostat" is becoming obsolete, [9] with the general term "potentiometer" replacing it. <S> For low-power applications (less than about 1 watt) a three-terminal potentiometer is often used, with one terminal unconnected or connected to the wiper. <A> Another difference not mentioned here is accuracy. <S> If you use a potentiometer you are using it as a ratio between two values. <S> Like a voltage divider. <S> Its absolute value tolerance may not be very good, but if you only care about the ratio set by the wiper, the pot is much more consistent over many devices and temperature. <S> But if a rheostat configuration is used, say in series to vary the current through a load, its absolute value is used. <S> Not as consistent. <S> This applies to digital pots as well. <S> See any datasheet to see error curves between the two. <S> For example this is the more accurate way to use a pot for variable opamp gain. <S> Below is not the way to get the best accuracy from a variable gain amp. <S> It's using the absolute value of the pot not the ratio set by the wiper.
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A rheostat is simply a variable resistance used to control power to a load and you are correct about the wiring.
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How do I eliminate PWM noise when driving a fan? I'm driving a 12V 0.11A brushless DC fan with PWM using an MSP430Gxxxx --> TC427CPA FET driver --> BS170 N-FET. The fan is on the low side of the FET. Even with a duty cycle of 90% and a frequency of 10kHz, there's audible buzzing coming from the fan. Lower duty cycle = more noise. I tried to eliminate the noise by adding a 4.7uF cap in parallel with the fan, and it's a little less noisy, but still very audible. How do I make the noise go away? <Q> Driving a fan by switching the supply is firstly risky. <S> BLDC fans have electronics in them and your switching these on and off at high speed. <S> Not how they were designed. <S> You risk killing the electronics like this over time. <S> Adding the cap helps because you are removing nasty power spikes into the fan. <S> This way you PWM the FET that is feeding energy into the inductor (energy store) and place a fly back diode to circulate the power when the FET is off. <S> This will keep a steady flow of power in the fan, minimal noise and not risk killing the fan long term. <A> The easy way is to drive it either at an ultrasonic frequency (>20 kHz) or at a lower frequency (<100-200 Hz). <S> As for <S> why you see that a lower duty cycle yields more noise, you're essentially increasing the content of the 10 kHz frequency you're sending to the motor until you hit 50%, then it will drop again. <A> In fact I am working on exactly same problem at the moment. <S> 1) Freq <S> > 25Khz <S> - first of all 2 <S> ) BIG cap at the output, 1-4.7uF ceramic + <S> some 100-1000uF electrolytic would do the trick. <S> 3) Add some inductance before the cap + diode in reverse to cut negative spikes.
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Adding the inductor is a good idea and if you look at what people are suggesting you will see that the best way to speed control a BLDC fan is with a constant current buck regulator. That low end there isn't really infrasonic, but a "hum" is usually far less objectionable, if it can be heard at all over the noise of the fan itself.
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Will current flow through my digital multimeter while it is powered off? I've just got a cheapo < $20 digital multimeter here and was curious if anyone could tell me whether current might still flow through it after i turn the dial so that the power is off. Some background: I have a wireless bluetooth mouse that always gave me problems charging because the contacts don't seem to line up properly. The mouse itself doesn't seem to give any indication whether it is charging or not but I am able to watch current start to flow on my multimeter when I move the mouse into just the right position within the cradle to make a proper connection. Now that it is seated correctly I'd like to just leave it charge for a while without disturbing it by disconnecting the leads and reconnecting the +5V wire. I'll probably figure something out for this specific problem (just disconnect the leads from DMM and jumper them together for now) but I'm still kind of curious as to the original question of whether or not current flow is completely shut off when the DMM power is off. It might vary by model but maybe somebody out there with 2 multimeters could test this for me? <Q> In short, yes. <S> The way a digital multimeter measures current (not a loop current meter) is that it measures the voltage drop across a small precision resistor. <S> For reliability, simplicity, and repeatability, no switches or contacts are placed in series with this shunt resistor. <S> Basically, the switches will control the electronics hooked up to the shunt resistor, but they won't disconnect it. <S> You can perform an experiment with your meter as some degree of proof that this is true. <S> If you configure your meter to read resistance, put the positive probe into the positive current probe socket. <S> You should measure a very small resistance. <S> This shows that the meter doesn't disconnect the shunt resistor while in a separate mode. <S> It would be a small leap of logic to say that if it didn't switch off the shunt resistor then, it probably couldn't when the meter is off. <S> Alternatively, you could measure the current using a second meter. <A> Just hook up a light bulb or LED through the current connections on the meter and observe that it remains lit when the meter is powered off. <S> Or pop the case open and observe the wiring of the current connections. <S> Current is inferred by measuring the voltage drop across big hefty resistor (but with quite low resistance). <S> You should see a big thick wire (a low-value resistor called a "shunt") joining the common and current sockets. <A> There are multimeters with separate inputs for voltage and for current measurement <S> and there are multimeters that have a single input for both. <S> With those that have a single input, current will flow through the meter only if it's in current range. <S> With those that have separate inputs, current will always flow when the red lead is plugged into the current measurement plug. <S> However, there will flow a very small leakage current even in voltage mode, but that is usually negligible.
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Some meters will have a fast-acting fuse to protect the shunt resistor.
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What logic family is best for general-purpose hobbyist stuff? I need to buy a few logic ICs. Which family should I get? HC? HCT? Which kind is best to have lying around in a parts box, for maximum compatibility with unpredictable future projects? Wide supply range, no extreme frequency requirements, etc. Schmitt inputs? Open outputs? <Q> HC is the most useful. <S> It has a very wide supply voltage range, is easy to interface to most MCUs, has good noise immunity, has plenty of speed, and is widely available. <S> HC is also available as single gates in tiny packages. <S> Forget TTL and LS TTL, no one uses them for new designs these days. <S> It's also worth learning to use CPLDs, Using them often makes a lot more sense than designing with individual logic chips. <A> If you're working with designs that require very high speed or extremely low power, you're not really in the realm of general purpose anymore. <S> It is pretty common to run into mixed power supply situations, though, like needing to go from 5V to 3V or vice versa. <S> HC has CMOS inputs and input protection diodes, so it's not a very useful family for logic level translation. <S> You can make 5 to 3 work with input resistors to limit the diode current, but it's not ideal. <S> For 3 to 5, you might just be out of luck. <S> For 5V to 3V <S> (5V inputs driving a chip powered by 3V), AHC and LVC have 5V tolerant inputs and work well. <S> For that, families like HCT and AHCT are useful. <S> Unfortunately, there's no general family that can be powered from any voltage and accept inputs of any voltage, although there are plenty of specialized level-shifting buffers (some bi-directional) that have separate power supply pins for just this purpose. <A> HCT is nice. <S> All the advantages @Leon Heller mentioned, but also TTL compatible inputs. <S> If you need speed, consider ACT. <S> Ti's Logic Guide has lots of details. <A> You’ll actually want AHC(T) instead of HC(T). <S> HC(T) is okay, but there is little reason not to choose AHC(T). <S> Other families I will reject include AC and its low-voltage equivalent, LVC. <S> These families have sub-nanosecond rise times, too fast for a breadboard. <S> I also recommend avoiding the bipolar TTL families, including 7400 TTL, STTL, LSTTL, AS, ALS, F, etc. <S> Bipolar logic has become basically outmoded. <S> And it goes without saying to avoid using any ECL 10k or 100k parts, but those are probably outside of the awareness of most beginner electrical engineers. <S> 20 years ago, TI had the following marketing points for their then-new AHC logic family: <S> “Graduate to new performance levels with AHC... <S> • <S> 3-times <S> faster than HCMOS• Half the static power consumption of HCMOS• Same low noise as HCMOS... <S> for the same market price as HCMOS.” <S> TI’s claims about AHC are correct. <S> The most important thing to hobbyists is edge rates. <S> They want to be able to use ICs without much or any regard for transmission line effects. <S> Because of their nasty parasitic elements, breadboards demand transition speeds of a few nanoseconds at least. <S> AHC has the same rise and fall times as HC, so the usability on a breadboard is similar. <S> AHC devices share the wide operating range of HCMOS, but are also 5V-tolerant when run from a lower supply voltage. <S> This is a really useful feature which I have always felt was missing from HCMOS. <S> AHC’s <S> output drive current is slightly greater than HC, but <S> still just 8 mA max at 5V. <S> This contributes to the slow edges and good signal integrity on a breadboard we expect from AHC and HC. <S> See TI’s <S> full AHC(T) designer’s guide for more details: http://www.ti.com/lit/ug/scla013d/scla013d.pdf <S> Now, I’ll give some further clarification on the “T” variants: HCT, AHCT, ACT, etc. <S> The “T” stands for TTL-compatible inputs. <S> If the chip is to receive signals from a bipolar TTL device, incl. <S> 7400, 74S, <S> 74LS, 74ALS, 74F, then you must either choose a “T” device, such as HCT, or use a 5V-tolerant non-“T” device run at 3.3V or so, and design your system to accommodate the 3.3V output levels.
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With its wide operating voltage and general availability, I'd agree that HC is the most useful family to keep around. For 3V to 5V, you need a family with TTL-compatible inputs, so that the lower 3V signals will satisfy the high input voltage requirement of the 5V powered chips.
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Why the use of resistors when pulling something up or down? When pulling something up or down why is a resistor used and it not just connected straight to the +V or 0V rail? <Q> It limits current to protect the switch (transistor, etc.) and allows signal sources with limited driving capability to change that node's voltage. <S> Rails generally have high drive capability, or low resistance. <S> Think voltage divider, including source impedance of signal and rail, then let the rail impedance be 0-ohms <S> for simplicity. <S> Other factors, other than operating current and voltage drops, to determine the pull resistance is charge time and substrate leakage. <S> A 2M-ohm pull-down resistor on a top layer exposed to humidity and salts won't do anything due to sub-1M-ohm electrical resistance of grime layer. <A> Another point not mentioned is that if it's necessary to alter the board, it's possible to pull off the resistor and replace it with a wire connecting one of the resistor pads to something else. <S> By comparison, trying to rework a surface-mount pin which connects to a power ground plane using a via which is under the chip can be difficult or impossible (at least difficult enough that scrapping the board would be cheaper). <A> Depending on the situation, you'd either cause problems for your power supply, or the input source, or both. <S> With the resistor, the input can be controlled by the input source without inordinate currents. <S> The situation for output pull-ups is similar, except that the 'input source' is the device's output transistor. <A> Another reason is that it makes it very easy to alter the input - just connect it to the positive supply if it is pulled down, for instance, rather than rewiring the connection. <S> A couple of pins for a jumper are all that is required. <S> A typical example is pin P0.14 on an NXP ARM chip, which determines whether it boots from a serial input or from internal flash memory. <A> If you only want to supply a defined logical level to a definitely unused input, a direct connection to ground or vcc would be ok in my opinion. <S> BUT: if you do that, it is impossible to drive the input from other sources. <S> (see posts above)
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You can also think of it this way - without a pull-up (or pull-down) resistor in place on an input, the source of the input would have to directly oppose your device's power supply to change the voltage at that input.
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Do surface mount components tend to use less power than through hole components? Or is the packaging just different? <Q> If it is the same base part number, same power, different packaging. <S> Heck, its frequently the same die. <A> No. <S> But through hole components can often handle more power than surface-mount components. <S> Because they are larger, they have lower junction-to-ambient thermal resistance. <A> What they said. <S> Plus: "Power used' is very largely a matter of the circuit parameters rather than the components themselves. <S> Something like a resistor will use exactly the same power for a given task regardless of it's packaging as the designer has complete control over power dissipation. <S> Differences that do occur are liable to be due to secondary effects. <S> For example: 1) More modern ICs for switch mode power supplies, operating at higher frequencies with potentially improved efficiency may be available only in SM packages, so their "lower power' may not be available in an older package. <S> This is thus a factor of availability rather than inherent difference due to package. <S> 2) <S> A MOSFET may operate more efficiently at lower junction temperature due to eg increasing Rdson with temperature. <S> Identical die with different packaging will then produce different results based on thermal resistance from Junction to air. <S> This is made up of Rth_junction_case + Rth_case_sink + Rth_sink_air. <S> At high power levels a larger through hole case may have a higher Rth_junction_case, but have better access to gross ambient heat sinking. <S> At power levels below 1 Watt the ease of access to PCB thermal sinking for SM part may encourage a lower temperature design so higher efficiency <S> so lower power overall. <S> As others have noted, 3rd order effects such as lead lengths, perhaps reduced capacitance and similar will have some effect, but usually minimal <S> Summary: <S> Overall neither SM or through hole have an explicit power difference <S> BUT factors specific to each implementation may make a difference either way on a case by case basis. <A> For example high-efficiency DC-DC converters often operate in the MHz range, which isn't practical in TH due to lead inductance.
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Generally no difference between the same part in different packages, the more important difference is that 'better' parts tend to only be available in SMD as that is where the market for efficient parts has gone. Depending on implementation and power level (not to mention phase of the moon) the result may go either way.
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Does Vs+ and Vs- need to be connected on a TRS232E? I have a TRS232 RS-232 Driver(max232 equivalent). On the data sheet , it shows a capacitor on Vs+ and Vs- (1uF)and they just have arrows saying they go somewhere. Can I omit these connections and capacitors and if I do what are the side effects or issues that may arise from this omission? <Q> This transceiver conveniently includes a charge pump to create the proper voltages for RS232 signaling. <S> All four capacitors listed (as well as the standard decoupling cap) must be connected for the device to operate. <S> Your positive logic level referrence will oscillate at about 400kH between drawing power from 5V through a diode, and getting a boost to about 10V, depleting the charge in C1 or C2 (I don't know which). <S> The inverting supply will be even worse - I'd guess it will jump between 0V minus a diode drop and -5V until the capacitor is depleted, but I'm not really sure without knowing the topology of the charge pump they're using. <S> When your logic level reference is jumping around like this, the chip will not be able to determine what is a high voltage and what is a low voltage, and it certainly won't be able to transmit anything. <S> Worst case is that a signal on the RX pin will try to power the chip through the ESD protection diodes because the charge pump isn't working, and fuse the diodes into a conducting state, destroying the transceiver. <S> The datasheet says that 0.1uF capacitors may be used, but lists 1uF capacitors as the recommended value. <S> If you must attempt to transmit or receive immediately on applying power to the chip, you'll want to go with the 0.1uF caps, but if you can wait for a millisecond before doing this, 1uF caps will give you a more stable voltage. <S> Larger values than that won't help much. <S> The 'arrows saying they go somewhere' are just voltage markers. <S> You don't need to connect these to anything. <S> If you wanted to test the operation of the charge pump, you would probe these points. <S> You might also be able to sneak off with a little bit of current from these pins if you had to for some other purpose, like powering devices like opamps that require differential supplies, though you'd need to do some extensive testing to be sure that you didn't draw too much current. <S> A buffer powered from 5V would be a good thing to have. <A> Definitely required. <S> Your drivers won't output anything without them. <S> In this answer <S> I explain how the charge pumps work using these capacitors and also why it's not a good idea to use 10\$\mu\$F instead of 1\$\mu\$F. <A> Those capacitors are essential. <S> If they are omitted the charge pumps won't work properly. <S> The +8.5V and -8.5V outputs can be useful for powering devices that need two supplies, such as op amps. <S> I've used them for that purpose, enabling the whole system to be powered from 5V. <S> You also need the decoupling capacitor on the Vcc pin.
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If you omit these capacitors, the charge pump won't work.
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Software to manage packaging all files related to a product (for hand off to customer) I want to provide my client with a Product Lifecycle Management (PLM) and Product Data Management (PDM) style package of all the documentation related to the project (in house user manual for their technical writers to use as reference, board bring documentation, Test campaign docs, etc...), Hardware files (release verision of schematics, gerbers, etc..), datasheets and parts list (BOM), and finally release binaries. Is there any good software geared towards small design studios (I have a 4 person group...with often only 2 people on a project). So far I have only found enterprise level PLM/PDM software that goes way over board for what I need. And yes, I know, I could just make a folder with all that stuff and just zip it. But there are lots of reasons why that is not the greatest solution. :P <Q> It sounds like you're more interested in the release packaging than PLM. <S> Just putting all the files together isn't a bad solution. <S> It works for a lot of projects! <S> With a few caveats and policies, it can be a fine solution. <S> I'd recommend that it start with a version control system, not a plain folder on disk. <S> It should also have a well-defined, well-planned structure. <S> This can be changed, but I'd recommend starting every project with the same basic structure. <S> For four people, doing what sounds like standard embedded system design, I don't think this will get out of hand. <S> There are other things that you'll want to control besides the release, however, and a bug tracking/feature request tool will be required somewhere in the system. <S> There are plenty of those available. <S> I've used Redmine . <S> I work at a company with 5000 employees, and while we use the PLM/PDM bundled with various tools as much as we have to, our day-to-day development and product management is done through a combination of a few Subversion repositories and Redmine. <A> Use a check-list. <S> List all the files or documents that your client will need. <S> At the end of the project, go through the check-list and mark off each item as you move it to the final folder that will be zipped up for the client. <A> http://www.arenasolutions.com/ <S> Not quite what I want, (too BOM oriented and too enterprise) but getting closer. <A> Have you looked into PDX? <S> It's an XML-based file standard. <S> If you have access to a PDM or PLM system, and are putting your files together, I would recommend exporting the build package (including BOM data, AML, AVL, change data) as a PDX and then sending your recipient the PDX package via email along with a link to a PDX Viewer. <S> Here's a link to info <S> re: PDXViewer - http://blog.arenasolutions.com/arena-pdx-viewer/ <S> And here's a link to the PDX Viewer itself - http://www.arenasolutions.com/pdxviewer/
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Arena offers a great (free) PDXViewer that makes it easy to view PDX files exported from any PLM, PDM or other business system.
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Arduino powered by 24 volt battery My question is probably pretty easy to answer for you smart people. But basically I'm building a Segway clone using an Arduino, two Jaguar speed controllers, and two 24 volt batteries (wired in parallel). I want to power my Arduino from the 24 volt batteries and am just wondering if I need any additional circuits to step down the voltage/current, stabilize/condition the power, or anything else that may need to be done before the Arduino can use the power. I'm fairly new to basic electronic circuits and am more of a programmer. Can someone help me with my question? Thanks! <Q> You are going to want to use a linear regulator . <S> This will be very inefficient with respect to power efficiency, but your arduino should not use much power and this should make the power point moot. <S> Here is an example search for the part you would need on mouser. <S> If you are going to pull very much current you are going to need a heatsink, this would probably amount to anything greater than 100mA in your case(just <S> a ballpark <S> so you have a way to estimate your threshhold). <S> It will require a couple of capacitors, but any good datasheet will tell you exactly what components you need. <A> The older NG used a 7805 regulator which is good for up to 40v (but may overheat if drawing a lot of current from a 24v source, since linear regulators are not very efficient). <S> If you have a newer model Arduino with the 20v limit, definitely use an external regulator. <S> A convenient way to get an efficient 24v->5v regulator is to buy a phone charger intended for trucks (which have 24v batteries not 12v as in most cars). <S> You can get these on ebay and elsewhere for about $7. <A> There are switching regulators that are drop-in replacements for 78xx regulators. <S> Digi-Key has a whole category for them. <S> For getting 5V, you might want to try something such as this .
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The hardware documentation for the arduino uno says it can take up to 20v input, so powering it directly off 24v is likely to damage it.
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Can I wire a dimmer switch into a soldering iron? So I have a really cheap soldering iron and a dimmer switch meant to be wall-mounted. The soldering iron has a standard, ungrounded cord. The dimmer switch has four wires: a green (for ground), a black and a red, and another red that's "only for use in 3-way switches". How can I wire this into the soldering iron to allow for variable soldering iron intensities? I tried cutting the soldering iron cord, binding neutral back to neutral and binding the positive to the dimmer's red, through the dimmer, and back through the dimemr's black to the other side of the positive. This did not work. I also tried it with the red to red, and the black to the other red, and neither worked. Is it possible to insert a wall-mounted dimmer into a standard appliance cord such as a soldering iron? <Q> It sounds like you are connecting power and the iron to the runners travelers, instead of through the output pole terminal. <S> ___[traveler]____hot _____./ <S> \. <S> ____ switched wire ___[traveler] <S> ____ | | O [light socket (on)] | neutral ___[traveler]____hot _____. <S> \. <S> ____ switched wire \___[traveler] <S> ____ | | O [light socket (off)] | neutral <S> Make sure you don't have your's set up like this: ___ pwrwirecap _____./ <S> ___ iron Also make sure you have clicked over the dimmer to the correct traveler or wire <S> the two travelers together (the switch will always be on then). <S> of the <S> There are some electronic dimmers that detect the other switch's position and go to full brightness, which would probably not work correctly if only partly wired. <S> You could look at a simpler dimmer switch or cord like this http://goo.gl/Mnwbe , <S> though as other's mentioned in the comments, it's probably only $20-30 more to get a new variable wattage iron. <S> Whatever you do, please be careful. <A> Yes, you can. <S> I did it with a iron solder sucker. <S> The temperature will continue to rise to some maximum. <S> That value will be a lower temperature than with a higher voltage. <S> So yes it does work, only not like a temperature controlled iron. <A> Ofcourse you can. <S> Dimmering the solder iron won't alloy you to set temperature directly, but with some little practice you'll be able to obtain great results with a cheap iron. <S> Pofessional soldering sets allow you to set temperature in degrees but who says which temperature to use ? <S> The same practice that will tell you how to adjust not degrees but dimmer scale. <S> Another thing the professional set can do is to control temperature by a sensor and feedback loop. <S> This is a nice feature that a dimmered iron won't have but again, with some practice you'll be able to overtake this. <S> Note the dimmer's point where your iron still can melt the soldering alloy. <S> Keep the soldering iron on this position or a little lower when idle, or to solder smallest pieces, increase it according your experience as you need more power to solder bigger pieces. <S> If the alloy can't stay on your iron's top, you're using too much power.
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It does reduce the voltage to the iron, however that alone does not control the temperature. The problem is likely the 3-wayness of your dimmer switch. I mounted the dimmer in a project box, and added an outlet receptacle in the rear to accommodate the iron.
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Is there a crimp tool, or something, for when you're soldering leads to leads Are there any tools or parts that help when soldering a free-floating component to another one, for example a resistor to an LED? Something that will make some kind of mechanical connection instead of just relying on the solder. I imagine someone has to make some kind of little sleeve or collar that you slide both leads into and then crush, but I've never come across anything. <Q> There are butt splice crimps such as this Molex one which go down to 22 AWG.Or this Amp one . <S> But the best way is a solder sleeve like this which is heatshrunk onto the pair of wires. <S> The solder melts at the same time as the sleeving shrinks. <A> At www.modk.it they do this with ordinary 1/16" or 3/32" aluminium tube from hobby stores, which is crimped with crimping pliers. <S> There was a writeup in the latest issue of Make magazine: http://makezine.com/25/modkit/ or http://www.make-digital.com/make/vol25?pg=56#pg56 (not sure if you need to be a subscriber to see that last link). <S> Here's modkit's doco: http://www.modk.it/hardware/knobcard <S> http://www.youtube.com/watch?v=haN3LBplVu4 <S> Having said that, I always just solder the two leads with about 4mm <S> overlap <S> ---------- <S> ----------- <S> And then cover with a 10mm length of heat-shrink tubing. <S> LEDs with integral resistorsoldered onto one like like this have withstood all the abuse I've given them. <A> I always just bend each lead into a hook shape, hook the leads together, and then close the hooks into loops. <S> It makes a pretty good physical connection. <A> You might be able to do a "Western Union" ( http://www.tpub.com/neets/book4/32NE0334.GIF ) <S> splice <S> if the wires are flexible enough, I have done them with LEDs to resistors before (I've also made a mess of it before), although I always soldered them as well. <S> You could combine a union splice with the aluminum tubing idea <S> unixbigot mentioned.
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I recommend clamping the base of the lead with some pliers before twisting the end lest you break it off the component. There are butt crimps, but I've never seen one small enough that I would want to use it directly with component leads.
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Reading and understanding electrical specs on laptop AC adapters My Dell laptop comes with an AC adapter with the following specs: 65 WInput AC: 100 - 240 V, ~1.5 A, 50 - 60 HzOutput DC: 19.5 V, 3.34 A My HP laptop: 65 WInput AC: 100 - 240 V, ~1.7 A, 50 - 60 HzOutput DC: 18.5 V, 3.5 A I have 3 questions: On the Input AC, why 1.5 A vs 1.7 A? I just have one type of power outlet for everything, such as lamp, TV, refrigerator, etc. So this number is not too significant? The output DC voltage and current are different. Would it be safe for me to interchange the adapters, i.e. use the HP laptop with the Dell AC adapter and vice versa. Which way would be safe and which is not? If there's another adapter with the same output DC but higher wattage, would I be able to use it as well? <Q> First, the over arching thing is that if the voltages match and the charger can supply more current the the original you were given, you are fine. <S> If it supplies less, it may still be enough, especially if the battery is already charged. <S> Your wall socket will general be able to deliver in excess of 15A(depends on your country). <S> The input current they expect is based on how much power their circuit actually uses. <S> Actually, their voltage is different, which is normally a larger issue for the adapters but the reason that interchanging is somewhat safe is for a hidden reason. <S> Let me note first, plugging in a mismatched adapter can damage your device, and easily, if it is not able to handle the voltage you are going to supply. <S> Most adapters user a communication protocol to verify the adapter was purchased from the original equipment manufacturer(OEM). <S> If they do not detect this they often limit their power draw to "protect" the charger. <S> This gives the advantage of protecting the charger if it is underrated. <S> Yes, you should be able to if the computer believes it is acceptable to use(no comm protocol to recognize a mismatched adapter). <S> This voltage output is what primarily determines function. <S> In electronics voltage controlled circuits are much easier to generate and use. <S> This gets a bit too detailed, but I hope this information helps. <A> The AC current rating on the power supply label indicates the maximum steady-state current draw at the lowest specified line and the maximum specified load. <S> If both power supplies are delivering 65W on the nose, the one drawing 1.5A may be marginally more efficient than the one drawing 1.7A. <S> It's usually not a good idea to use an adapter set to a higher voltage on a piece of equipment expecting a lower voltage. <S> The device being powered could end up dissipating higher than expected power, causing possible thermal issues and/or shortened life. <S> Having more power available to crank into an abnormal condition can lead to bad things like fire. <S> If we're talking a few extra watts, that's one thing. <S> A few hundred more, well, that could be dangerous... <A> 2) I wouldn't do that. <S> Laptops repairs are quite expensive. <S> Aftermarket chargers, not so much. ;] In any case you could try using the one with lower output voltage with a computer expecting a higher one. <S> But it may not work properly (like powering but not charging and such). <S> 3) <S> Yes.
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Using an adapter with the same voltage and higher current will be OK as long as the device being powered doesn't have a fault.
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LM394 is obsolete. What is the new standard log amp circuit? The traditional logarithmic amplifier circuit is described in National Appnote 311 : This circuit uses the difference of two transistor currents to generate the log of the input over a pretty wide range. The well-matched transistor pair Q1a and Q1b are halves of the LM394 "supermatch" transistor pair. But National discontinued this part last year with no clear replacement. I can use LM3406 array, but the specs are far worse. There are plenty of arrays of '2222 or '3904 available, but there is no mention of matching in the datasheet. The transistors might be on separate dies for all I know. TI still sells some Burr Brown log amps but they are expensive. LOG101 is $18.37 in onesies. Analog makes the AD606 for $43.88 each or the AD830x parts for $12 - $20. How can I (cheaply) make a logarithm? <Q> The Analog Devices <S> SSM2212 is a cheaper ($2.50 in quantity) alternative to the MAT12, with similar headline specs. <S> Cheaper matched NPN pairs <S> include the DMMT3904W and DMMT5551 from Diodes Inc., the PMP4501, PMP4201 and BCM847 from NXP, and the NST45011M/ <S> NST65011 <S> M from ON Semi, which are roughly an order of magnitude cheaper than the SSM2212 but have a maximum offset voltage an order of magnitude worse (1-2mV). <A> How about the LS312 from Linear Systems? <S> Some people in other forums claim it's better than the 5% worst-case matching described on the datasheet. <A> I remember some years ago using the Analog Devices MAT02 for this purpose. <S> It seems that this is not recommended for new designs but the replacement is the MAT12 . <A> A year ago, I tried to build Thomas Henry's X-4046 VCO where the LM394 is used. <S> 10-15$ for for this rare beast <S> is too high and there are a lot of fakes on Ebay <S> and I decided to substitute. <S> I don't know what a miracle happened but I have found the 100% substitution of it, produced by reincarnated plant in Riga owned by Russians. <S> The chip has almost the same name: AS394. <S> The specs are identical to the original. <S> Same cases: dip8 and CAN. <S> You can find them here <S> But the plant does not sell them directly. <S> You have to find the dealer in Moscow (can find an email or phone in case someone need it). <S> The price for 1 unit is around 2-3$ (depend on quantity). <A> I had this idea for a quick and dirty log amp. <S> If you modulated the reference voltage by 3dB, the output would probably average to about the right value. <S> That would more-or-less be an interpolation between 3dB values. <S> Two LM3915s can be stacked to get 60 dB range. <S> This is probably not the way to go unless there is a need for an LED bargraph in the circuit already. <A> However, I'm not sure how suitable it is for your application. <S> Screenshot: <A> TI manufactures the LM194/394 now. <S> You can also go to THAT corporation and use their PNP/NPN oairs and quads. <S> THAT 300 series: 36 V, 30 mA, hfe 75-100, Ft 320 MHz <A> Maxim-IC has a couple of log amps , and so does TI , but Analog Devices makes I think the biggest selection . <S> Intersil makes a number of transistor arrays <S> some are certainly single die and well matched. <A> TI has a bunch of chips that implement log amps. <S> There's LOG101, LOG102, LOG112 and others. <S> I don't know what the definitive chip is <S> but there are many chips that implement the whole circuit. <S> They're wildly expensive for some reason <S> but you can find LOG102 on Fleabay for $5. <A> Devices equivalent to the LM394 are now being made by another company: http://www.alfarzpp.lv/eng/sc/AS394CH.php
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This circuit looks to be a log amplifier using two op-amps, two transistors, a few passives and a current source. As Roman mentions in another answer, at the time of writing (2020), Alfa RPAR make the AS394 ( http://www.alfarzpp.lv/eng/sc/AS394CH.php ), an LM394 substitute stocked by a number of specialist electronic music distributors.
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12V DC UPS for Network Equipment My requirement is to keep running supply of low power devices like DSL modems, etc.Most of these devices input 12V/9V DC so i don't see the value in using ordinary UPS which converts DC to AC then back to DC, lots of conversion lots of power loss lots of money involved.I want a DC UPS output which can be directly input into these devices. I am not pro, so I need a circuit diagram for a DC UPS, that: Takes 12V input. Gives 12V output to devices. If input current is available it will also charge the battery. If input current is not available, will provide current from battery to attached devices. <Q> First of all you need to realize that a 12V SLA battery is not, ever 12V, if it's charging then it sits around <S> 14.3V <S> (but that's dependent on chemistry and temperature) <S> when it's discharging then it can be as low as 10V. <S> The most robust solution is to make sure that all the equipment can tolerate 10-15 V, because that will allow you to get rid of any output regulator which will waste some energy while on battery. <S> Almost all electronics that says 12V will easily tolerate 10-15V, much of it will be happy with 8-24V as well, the main exception are computers that feed the 12V input directly to harddisks, those devices really like <S> a regulated 12V. A good charger will be needed that regulates the float voltage according to temperature and also limits the charging current. <S> One solution would be: <S> A Buck DC/DC converter handling charging, but a simple LM317 could also be used. <S> A Buck DC/DC converter handling the on-line output regulation. <S> A switch (2 FETs) which switches over to battery if the output of the online-converter drops out of regulation. <S> Buck converters tend to be simpler and more efficient than buck/boost converters, so that's a good reason to prefer those in a design, but if you really want a regulated 12V output <S> then there is no way to avoid a buck/boost converter and the plan becomes: A beefy AC/DC off-the-shelf mains supply, a 19V power brick for a laptop would do nicely. <S> A Buck DC/DC converter handling charging, but a simple LM317 could also be used, especially if the battery is stored at a fixed temperature, (look up "SLA charger lm317). <S> A switch (an opamp controllring two 2 FETs) which switches the input of the output regulator from the primary input DC over to battery if it drops below the battery voltage or simply two diodes. <S> A Buck/boost DC/DC converter handling the output regulation. <S> A good buck/boost converter topology is SEPIC, because you only need one FET and a single coil, so it's cheaper than two converters back-to-back: http://dren.dk/carpower.html <S> the linked design will output the same voltage no matter what the input voltage is (8-24 V) ... or, if you are lucky, you can just buy one: http://www.mini-box.com/micro-UPS-load-sharing <A> My suggestion would be to use an above-voltage battery - like a 24V, 36V or 48V battery. <S> The voltage can be stepped up to charge it, and stepped down to run devices. <S> I'd highly recommend a switching boost regulator for the charging (use a dedicated charging IC) and a buck converter for the discharging. <S> Make sure any converter is rated to handle the maximum voltage of the battery - for example a 48V battery may reach 58V when fully charged! <S> Also, be careful of voltages over about 60V (dc; 30V for ac) - they are generally considered hazardous as they can cause electric shock and require proper wiring standards. <A> As a starting point I would research voltage regulators and search for a battery that meets your needs. <S> There are different types that could be used such as linear(cheap but inefficient) and switching(little more pricey but efficient). <S> Making sure that the battery will only output current when there is no input voltage is pretty simple. <S> As long as the input voltage is greater than that of the battery, the battery will act as a power sink, and the input will charge the battery. <S> Otherwise the battery will act as a power source. <S> It might also be useful for you to know that a 12 volt car or deep cycle battery is typically around 12.5 volts when it is fully charged. <S> That means that you could set your input voltage at around 12.5 volts to charge the battery and set the voltage regulator output at 12 volts.. <S> Hope this helps. <A> My approach would select a 24 volt battery or two car batteries or similar in series. <S> Then regulate that 24 volts to produce your 12 volt output . <S> Then buy or build a AC charger for the battery(ies). <S> http://www.batterystuff.com/battery-chargers/12-volt/marine-chargers/GEN2.html
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A beefy AC/DC off-the-shelf mains supply, a 19V power brick for a laptop could do.
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Switching Voltage Regulator with WiFi Ethernet Controller Bad? I a working on a circuit that has components that need 3.3V and 5V. My power input is 12VDC and can not be changed. The 3.3V components use about 510mA of current and the 5V components use about 155mA. My first attempt at a circuit used two linear voltage regulators in SOT-223 packages. The 5V reg use 12V as it's input voltage and the 3.3V reg used 5V as it's input. Of course the 5V regulator get's extremly hot and then shuts off (luckily it has thermal protection!) I have read some other posts on this forum about how to dissipate the heat with the PCB traces and also to do it using the case (which is a possibility in my case), however it would be much preferable for this design for the enclosure to not get warm. People using it may complain. So I am considering using a switching-mode voltage regulator like this AD1509 . My concern is with the noise. My board has a WiFi module on it and I am wondering if the performance will be affected by the switching noise. The AD1509 switches at 150kHz and I think WiFi is in the 2.5GHz range so I should be okay right? Also, do you think the switching voltage regulator will also get hot or if I just a big copper pad under it will it be okay? <Q> A switching power supply will be noisier than a linear regulator, no question. <S> The only way to know if it will disturb the wifi is to power it up and see what happens. <S> These parts with an integrated MOSFET do need PCB cooling - usually a multilayer PCB with relatively large 'islands' of copper interconnected with vias. <S> Again, you'll have to do some math to figure out a loss estimate, and gauge the copper size accordingly. <S> The datasheet says that the 5V part at 2A load and 12V in operates at around 83% efficiency. <S> So, for 10W out you're losing just over 2W in the device (and the external diode that completes the buck converter). <S> This will scale down somewhat with your reduced loading (conduction losses will drop, switching losses probably won't). <A> Don't use traces; use a heat sink instead. <S> They are cheap and easy to use. <S> Don't use the switching regulator directly, use it for 12 to ~6 V then regulate down. <S> That saves power and still gets a clean final output. <A> If you follow the IC manufacturers tips about component selection and layout you should not have any problems with the WiFi chipset running from a switched power supply. <S> You may consider going for a switcher at 3.3V while using a linear regulator for 5V.
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Any switching regulator will dissipate power as a function of conduction losses and switching losses.
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Problem loading sketch to arduino MiniQ This is the first time I have used this product (an Arduino-compatible robot) and I'm having some trouble. I've done this on 2 different boards now. I select the serial port, load up the blink sketch.... First time - it loads beautifully and I get the Blink sketch I loaded. I then change the values for a longer blink....load it and get the error avrdude: stk500_recv(): programmer is not responding I get a pause as though its about to start loading the code....but then the error. Any suggestions? <Q> That error usually means that AVRdude missed the window to send something before the bootloader dropped through to the already loaded sketch. <S> Some arduino bootloaders have a different wait-for-program delay (or none at all)depending on the reset source (poweron, reset pin, or watchdog). <S> Do you have a schematic (didn't find one on DFR site)? <S> Are you applying reset thesame way each time, or differently the first time (power on vs reset-from-serial-DTR maybe?) <A> Try to reset it while holding the button for some time, ive expereienced the same problem. <S> Eventhough that not be the original source of the problem. <S> but i think it has something to do with how long the mcu takes to initialize before it will accept the flashing process. <S> Does this only come as soon as you try to change something ? <S> Your reset button may also be damaged. <S> Is your LED Pin13 on ? <S> Can you see action on the TX and RX line ? <A> The answer(workaround): <S> Moving from an Ubuntu platform to Windows7 fix those problems for me. <S> The context: I normally work on Ubuntu (currently 11.04) and using the Arduino 0022 software and Arduino UNO board. <S> I have 5 Atmega328p chips. <S> Out of the 5, 3 are not Working under Ubuntu (error 'not in sync' or 'not responding') <S> , 1 I have to trick into working under Ubuntu by setting the download speed to 19200 and then back to 57600 <S> and, finally, 1 that works just fine all the time!!!?? <S> ?!!! <S> For some reason they all work perfectly under Windows7 with the Arduino 0022 software. <S> I'll post here if I ever fix my problem on Ubuntu.
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What i found out helps me best when i get errors like those, is that resetting with a long button hold works for me.
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Why we need to complete circuit Why can't we light an LED with a single positive wire on the anode, leaving the cathode unconnected? Let's suppose I connect a wire with a positive voltage to the anode of the LED. Now, I think, current will flow past the light emitting diode. This should, by my understanding, make it glow, even though the cathode isn't connected to anything. However, experimental evidence and common knowledge show that this isn't the case. Is it possible in any situation(IDEAL) that we calculate current and voltage value so that this circuit will work, and automatically flow to ground after passing through the circuit? If so, do we need a connection to ground in the real world? Please point out my mistake if you notice a simple error I've made, and let me know what is right. <Q> The idea of a closed circuit works for low frequencies - where the corresponding wavelength is much larger than the components and wires. <S> Kirchoff's laws hold. <S> Things get tricky when the frequency is higher. <S> A sudden change in voltage propagates at the speed of light (or some good fraction of it in cables, transmission lines) and there is more current at one point than at another. <S> But it would be extremely brief. <S> So what if you send a series of pulses? <S> A good rule of thumb to remember is at light speed, one nanosecond is about one foot (30+ cm). <S> LEDs and the pulse-pushing circuitry I imagine would be a few inches (or cm) and so things happen on a scale of maybe tenths of nanoseconds. <S> You'd have to work with frequencies at several GHz. <S> Another problem - every positive pulse you put on the anode lead will go through the LED and add positive charge to the non-connected cathode lead. <S> Each positive pulse will add more. <S> That charge has nowhere to escape to - just a tiny bit can flow back as leakage current, no diode being perfect. <S> From a physics point of view, so <S> what? <S> Just let the whole contraption develop a positive charge. <S> Figure a few milliamps lasting for say 50 ns, <S> times 5 billion times per second (just making up numbers), you quickly get to coulombs of charge, and many volts in just seconds. <S> At a practical level, it's not very practical at all. <S> I wonder if it would work better to have two LEDs wired anti-parallel, and feed GHz pulses to one end of the pair and leave the other end disconnected? <S> (I leave that thought for others to discuss.) <A> In order for current to flow between two points (in general) <S> the fundamental requirement is that ther must be some potential (voltage) difference between those points. <S> Current is physically the effect of electrons moving through your circuit (as prescribed by electromotive forces given rise to by the aforementioned existent potential difference). <S> If those electrons have no place to go (i.e. back to ground), and current were somehow flowing into a floating node like the LED situation you described, then you would get a build-up of electrical charge on the on the floating node that would violate energy conservation principles. <S> Edit <S> In response to the comment, think of it like this. <S> Current will only flow from a higher potential to a lower potential (again electromotive force governs this). <S> If a current were able to flow into a floating node, charge would build up there, and the result of this would be that the potential (voltage) at that node would increase. <S> Eventually it would increase to a point where there was no potential difference between that node and the source node, and current would no longer flow. <A> Yes, you could do that. <S> If you use a high-voltage generator to suck charge out of one metal sphere and deposit it onto another, you would then have a potential without a complete circuit, and you could connect the two spheres together to get a current. <S> This would only last for a short time, however, because the charge imbalance would decrease as you discharge them. <S> If the spheres are oppositely charged at first, they will become neutral after the current flows. <S> if one sphere was neutral and the other charged, then the equilibrium they reach will be half as much charge on each, instead of becoming neutral. <S> But what if you want charge to flow continuously from one sphere to the other? <S> Then you need a conveyor of some type to force the charge back to the other side. <S> In this case, you've completed the circuit with a voltage or current source. <A> There would be some capacitance between the unconnected terminals of the LED and battery, so a little current would have to flow before the unconnected terminals before their potentials was equal to those of the connected terminals. <S> In practice, however, that level of capacitance would likely be so small as to be impossible to measure much less use. <S> Note that while a one farad capacitor can accept a whole coulomb of electrons (one amp for one second) before building up a volt of potential difference, that doesn't mean a coulomb of electrons flowing in with none flowing out. <S> In order for one side of a capacitor to accept a negative charge, the other side must have a balancing positive charge. <S> Essentially what happens is that as electrons flow into the negative side, their nearby presence makes electrons want to leave the positive side. <S> Likewise as capacitors leave the positive side, their relative absence makes electrons want to enter the negative side. <S> It's possible for substantial AC electric currents to flow without a complete circuit, if there's enough capacitance. <S> Two leads some distance apart, however, aren't going to have enough electrostatic effect to yield any useful capacitance, though.
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In theory, you could put a sharp-edged voltage pulse on one lead of an LED, have nothing connected to the other, and for a tiny instant in time, as the pulse passes through the LED, have enough current for it to glow.
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