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8024 | |transformer| | <p>In multiple winding transformer, each winding(including a centre tapping if any and multiple tappings) are denoted by a seperate cable color.that is, the winding with a center has a different color,and the one with no tapping has a different color.in addition,they have different cable size </p>
| <p>Let's say I have a transformer with 3 coils. When primary coil is connected to 230V, two secondaries output 12V. Wires are color coded, but I don't know what colors stand for and there is no information about that on manufacturer's website.</p>
<p>Is there any relatively easy way to determine which wire is primary, which is secondary and which is start to the secondary and which is end of the secondary coil?</p>
| How to determine which wire is which on a transformer? | 2010-12-17T19:46:38.340 |
8027 | |motor-controller| | <p>Here is an introduction to electronic speed control systems: <a href="http://www.stefanv.com/electronics/escprimer.html" rel="nofollow">http://www.stefanv.com/electronics/escprimer.html</a></p>
<p>Actual design depends on the type of motor you want to drive. A 300A high-torque gear motor is much different from those tiny featherweight propeller motors. At the heavy-duty end of the scale (300A) is something like this: <a href="http://www.robotpower.com/products/osmc_info.html" rel="nofollow">Open Source Motor Control</a>. All designs are online and there are a few articles explaining what the heck is going on. At the other end of the scale are small prop motors, like those in the <a href="http://www.mikrokopter.com/ucwiki/en/BrushlessCtrl" rel="nofollow">MikroKopter</a>.</p>
| <p>I have a project that uses an ESC to run a brushless motor (Hobbyist RC plane sized, 24 gram, 1300-1500 KV).</p>
<p>I would like to experiment with eliminating the ESC and driving the motor with my own circuitry and control software. Are there any good tutorials or other starting points?</p>
<p>(I realize it's more practical to just keep using my $8 ESC, but I'm interested in this as a learning exercise.)</p>
| Implementing my own ESC (electronic speed controller)? | 2010-12-17T23:04:55.533 |
8036 | |video| | <p>In my breif examination, it appears that there are two basic approaches. The first is to use an analog mux such as the one you have identified, and then buffer the resulting signal with a high input impedance amplifier. <a href="http://www.maxim-ic.com/app-notes/index.mvp/id/3823" rel="nofollow noreferrer">Maxim</a> has a pretty good write-up on how to do this using a separate mux and amplifier. They use the switch on-resistance as part of the 75 ohm matching network. </p>
<pre><code>(95 ohms in parallel with (300 ohms + mux resistance))
</code></pre>
<p><img src="https://i.stack.imgur.com/PCHQD.gif" alt="Maxim example video switching circuit"></p>
<p>I found a single chip <a href="http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=NJM2244M%23-ND" rel="nofollow noreferrer">(NJM2244)</a> that combines the analog switches with a matched 75 ohm driver. This would allow you to have only one very small chip with very simple controls.</p>
<p><img src="https://i.stack.imgur.com/gYqxB.png" alt="NJM2244 Block Diagram"></p>
<p>Another <a href="http://www.engadget.com/2007/03/13/how-to-make-a-solid-state-a-v-switcher/" rel="nofollow noreferrer">method</a> uses much lower resistance switches. This particular writeup uses <a href="http://www.mouser.com/ProductDetail/NXP-Semiconductors/CBT3244AD118/?qs=sGAEpiMZZMutXGli8Ay4kDE4J8KCiPsF9uIMu%2F9QFBU%3D" rel="nofollow noreferrer">switches</a> intended for high-speed logic, and they have an on-resistance of about 5-8 ohms. That small of a resistance could probably be tolerated fairly easily.</p>
<p><img src="https://i.stack.imgur.com/aJb39.jpg" alt="Bus wiring diagram"><img src="https://i.stack.imgur.com/WtfNP.jpg" alt="Bus switching chip CBT3244A"></p>
<p>Each bus switch chip has two banks of SP4T switches, so you could switch stereo audio in addition to the video signal. If you're switching only two sources, this could be a single-chip solution as well.</p>
<p>Regarding the bandwidth of composite video, the highest figure I've seen is 6.5MHz, which isn't really that high frequency. You won't have difficulty finding amplifiers for these frequencies, and the wiring shouldn't be very sensitive (aside from adjacent noise sources).</p>
| <p>I'm looking for a device to switch video signals; a video switch. I want to use a dual/triple switch for two purposes, first to switch between two video signals, and secondly to switch the signal between open and +3.3V (which drives the pixel on the frame high.) (The third channel may be used to switch between on and off for the pixel.) It's for an on screen display application.</p>
<p>However, most chips I've seen have an on resistance of nearly 60-80 ohms. This is way too much surely for video which is terminated with 75 ohms? If I'm switching with 75 ohms in series with the required 75 ohm termination, I've effectively created a voltage divider and halved the video signal. It might work, but the video would probably lose considerable quality; at worst, I'd probably lose sync.</p>
<p>As an additional question, related to this one, would there be any bandwidth issues with video switches? I'm using composite (CVBS) NTSC or PAL colour video.</p>
| How much resistance is too much resistance for a video switch? | 2010-12-18T00:37:36.063 |
8041 | |fpga|xilinx| | <p>On my system they are here:</p>
<p>C:\Xilinx\12.3\ISE_DS\ISE\ISEexamples</p>
<p>The ones you mentioned can be downloaded as zip files from that web page. You want the ISE In-Depth Tutorial and the associated zip files. They are included amongst those that should already be on your system in the ISEExamples directory.</p>
<p>I don't think that the hardware for that example is still available. If you get a Digilent Spartan 3 kit a similar alarm clock example can be downloaded from the Digilent web site.</p>
<p>The best place to get questions about Xilinx software answered are the <a href="http://forums.xilinx.com/" rel="nofollow">Xilinx forums</a>.</p>
| <p>I've been trying to learn to use the ISE WebPack and the link they give in their documentation( <a href="http://bit.ly/fsy8iD" rel="nofollow">http://bit.ly/fsy8iD</a> page 11) points to <a href="http://www.xilinx.com/support/documentation/dt_ise12-3_tutorials.htm" rel="nofollow">http://www.xilinx.com/support/documentation/dt_ise12-3_tutorials.htm</a></p>
<p>On that page I do not see any zip files or any tutorial files at all except for PDF files. Where do you get these files? </p>
| Where are the tutorial files for ISE WebPack? | 2010-12-18T01:46:12.167 |
8050 | |motor| | <p>I believe that the ice maker in a refrigerator uses an auger-type delivery system. You could make something like that with copper tubing or something else that's malleable enough to bend into that shape. I'd use a stepper motor as suggested above and have a photosensor determine when a single ice cube has dropped and then open a door (if it absolutely has to be one-at-time).</p>
| <p>For a University project I have to build a small box containing ice cubes. The box is a shoe box, isolated with newspaper and aluminium foil, cooled by thermal packs. In this box I want to store ice cubes for about one to three hours.</p>
<p>Now comes the tricky part: The ice cubes should drop out of the box, one after another, about every minute.</p>
<p>I was thinking of a motor with an oval disk which opens a flap gate. The second idea was a small conveyor band which transports the cubes out. Are there better solutions than that? What minimum motor power do I need for this? How do I control the motor?</p>
<p>It's a low-budget project, so the cheapest solution is the best.</p>
| How to release ice cubes out of a box? | 2010-12-18T10:30:54.777 |
8059 | |pll|synthesizer| | <p>Another Excellent PLL reference is this one</p>
<p><a href="http://www.national.com/analog/timing/pll_designbook" rel="nofollow">http://www.national.com/analog/timing/pll_designbook</a></p>
| <p>Frequency synthesizers, like <a href="http://www.analog.com/static/imported-files/data_sheets/ADF4110_4111_4112_4113.pdf">Analog's ADF411x</a> often have prescalers in their PLL which divide by 16/17, 32/33 or 64/65? What's the 2^N+1 value used for?</p>
| Why do frequency synthesizers often use N/N+1 prescalers? | 2010-12-18T15:00:11.370 |
8068 | |prototyping|adapter| | <p>Some other sites that might carry something suitable - I've not ordered from any of them so I can't endorse them personally, but I thought the links might be helpful.</p>
<ul>
<li><a href="http://www.proto-advantage.com" rel="nofollow">proto-advantage.com</a></li>
<li><a href="http://www.winslowadaptics.com" rel="nofollow">winslowadaptics.com</a></li>
<li><a href="http://www.schmartboard.com" rel="nofollow">schmartboard.com</a></li>
<li><a href="http://www.beldynsys.com" rel="nofollow">beldynsys.com</a></li>
</ul>
| <p>I need a prototyping adapter for a ssop 24-pin package. Google turns up plenty of dip adapters for 5-7mm chips, but the chip I have is 3.9mm across the body and 6mm to the tips of the pins.</p>
<p>Anyone know of source of a suitable adapter? Doesn't necessarily have to be a dip, just something solderable by humans.</p>
| Source for a ssop to dip adapter? | 2010-12-18T21:05:41.000 |
8078 | |avr|atmega|rs485| | <p>I'm currently working on a maglock door security system, and am using these same chips to transmit data from the RFID reader to an Arduino about 200ft away. I as well have had all kinds of problems with these annoying, but awesome :), chips. I'm not sure I'm operating at 100% fool-proof yet, but here's a few things I've found out:</p>
<p>• There's a tradeoff between transfer rate and susceptibility to EMI. The MAX485 has a high transfer rate, but is very influenced by EMI. Try the MAX483. Same chip with slower transfer rate, but very little EMI.</p>
<p>• In some cases, such as with a long cable distance, I've found it to work better without any terminating resistor...don't ask me why. :)</p>
<p>• Make sure both DE and RE pins are connected to either ground or +5V. They aren't required to be connected depending on whether you're in transmit or receive mode, but I could swear I've had better results when neither of them are left floating.</p>
| <p>I want two atmega32s to communicate over a range of 1000ft, so I decided to use a serial wire for it. I know rs232 is not a good way to communicate over this large range, so I decided to use RS485 which is a balanced pair. For this I want to use MAX485 chips like these.</p>
<p><img src="https://i.stack.imgur.com/NeQ4e.jpg" alt="MAX485 Chip diagram"></p>
<p>Now I wrote all the code to use it and got it working for short wire communication with a battery powering my ATmegas (and the MAX485 chips) (I cannot produce the code here as it is for a company where I am just an intern, but as it works in short wire the code is not the problem). What the program basically does is, one atmega sends "Paresh" on serial, the other atmega receives it, does a strcmp if it is indeed recieved as "Paresh" it sends out "Mathur". If the first atmega receives "Mathur" it again sends paresh and the cycle continues.</p>
<p>All this works just fine for serial mode, short wire and on a 6V battery. But as soon as I switch to a CAT-5 cable I get packet loss. I printed what ever one receives on an LCD and after a few cycles (and sometimes even for the first transfer) there is strange strings received. The problems are:</p>
<ol>
<li>It works for short wire but not a 30ft CAT-5 cable</li>
<li>It works for 6V battery but not for 12 volt battery or a 12V adapter.</li>
<li>It works for normal serial wire upto 10ft but not more than that.</li>
</ol>
<p>The things I have tried are:</p>
<ol>
<li>Added capacitors to fade out any ripples in the supply. (470uf caps).</li>
<li>Increased delays between switching from transmit to receive modes ( _delay_ms(3); ).</li>
<li>added caps to the supply to the modules.</li>
<li>Adding 120ohm terminal resistance to both modules.</li>
</ol>
<p>What should I do? Please do no suggest any alternatives to the the thing, it would hurt the hacker in me. Why cannot I use an RS485 communication for exactly the purpose it was designed .i.e long distance communication over serial.</p>
<p><strong>Update 1:</strong> I used 120ohm terminal resistance.
<strong>Update 2:</strong> I am on a 9600 baudrate.</p>
| MAX485 half duplex Atmega communication problem | 2010-12-19T17:26:21.527 |
8080 | |bluetooth|accelerometer|rtc| | <p>It sounds like your measurements are already on an even interval controlled by your device, so you could simply add a serial number to each measurement or block of measurements to ensure that you don't lose one. This could be as simple as a single byte, which would have lower overhead than a full time stamp.</p>
<p>While a dedicated RTC could provide very accurate time stamps, it would not necessarily make the timing of your measurements any more accurate unless you drive those samples off an interrupt from the RTC. What matters from a filtering standpoint is how low the jitter is on the sampling of the signal, not on receiving the data. </p>
| <p>I am working on a project where I want to get very accurate data from an accelerometer. I plan on sending my data over bluetooth to be interpreted by a computer.</p>
<p>I am assuming that bluetooth will have some unknown delays that come from things such as how Windows handles the data.</p>
<p>So, since the accelerometer data is time depended, would I be benefited by using a clock that can easily create time in some even divisor of seconds? Or possibly add a RTC? I would then be able to "time-stamp" my data before sending it over bluetooth.</p>
<p>Is this worth it or am I just over thinking how accurate I can actually get my data to be? </p>
<p><strong>Clarification:</strong></p>
<p>I will be pulling in data based off of a timer interrupt. I am wondering if my timer needs to be something like 0.5ms. I would go ahead and "time-stamp" the messages I am sending so I know if I loose a message for some reason.</p>
<p>Also, I am using a digital accelerometer, so I am not doing an ADC, instead I am getting the measurements over I2C.</p>
| Do I need an accurate clock for an accelerometer? | 2010-12-19T18:18:23.170 |
8091 | |pcb| | <p>Ultimately, the grid your design actually uses is built into the Gerber file you export from your PCB tool. The files that I generate from Eagle are in inches, with either 3 or 4 digits to the right of the decimal place. That puts me on a 1 mil grid. </p>
<p>When you're using parts with different units (Metric vs. Inches), you're bound to have some grid mis-alignment, but it will be very small. If your design uses the minimum spacing rules, it's possible some spacing violations may come up.</p>
<p>In short, the only grid that really matters is the one you export your design to. Any other grid is for convenience.</p>
| <p>As in the title. I've just noticed in one of my PCB designs the components are not aligned to a grid and neither are the traces. It passes DRC, but I'm wondering if it will cause further problems. I'll be using standard PCB houses like PCBcart, SeeedStudio etc.</p>
| Is it important to keep components and traces on a PCB aligned to a grid? | 2010-12-20T02:09:46.903 |
8093 | |control-system| | <p>I've also had this problem...even though I've done controls work for a living. My part of the controls work has been dealing with what the system identification guys give me, so I never developed that skill as well as I wanted. After a while, I've picked up a couple of additional books and relearned how to do it in some cases. </p>
<p>The method that I use is by constructing lagrangian equations that describe the system. The lagrangian describes the kinetic and potential energy in a system. I've found that <a href="http://rads.stackoverflow.com/amzn/click/0486442780" rel="noreferrer">Control system design: An Introduction to state-space methods</a> (cheap) actually has a decent reference for performing system identification. I recommend going through all of the examples and problems in chapter 2. </p>
<p>Additionally, the thermal problem you describe can be handled by converting the components of the model to electrical equivalents. This can be found in the book or by doing a bit of googling.</p>
| <p>After taking classes in control theory as an undergraduate, I ended up not using them at all after I graduated. I've started to fix that by starting a hobby project in controls. My textbooks are pretty good references for the theory, but my biggest problem is that I have not found a good reference on determining system parameters in models. For example, say I have a temperature sensor located some distance away from a heating element, and on top of that it has some non-trivial amount of thermal mass. How should I model this non-ideality? And even after I've modeled the error function for the element, how do I determine the actual numerical coefficients from bench experiments?</p>
<p>Does anyone here have any good textbooks or references to recommend? </p>
| System Modeling for Control Systems | 2010-12-20T03:12:51.780 |
8094 | |mechanical-assembly| | <p>If you bent the leads after the package was soldered in, the solder joints may have cracked. It is worth touching them up. Ensure you don't dry them out by using flux and a reasonable temperature.</p>
<p>The regulator itself will be fine. Leads are meant to be bent.</p>
| <p>I was installing a heatsink which didn't quite fit and after installing it, I noticed that I've twisted the L200CV about 5° when looking from above the chip. What kind of damage, if any, can I expect? </p>
| I twisted a L200CV in Pentawatt package; what kind of damage can I expect? | 2010-12-20T11:48:58.010 |
8097 | |arduino|audio|filter|basic| | <p>If you expect to recover a 200 Hz waveform (down in the bass), you need to sample MINIMALLY at 400 Hz for the ideal case, but 450 Hz would be better. If your filter isn't good ( and it probably won't be), you will have aliasing which will screw up your detection algorithms.</p>
<p>You NEED your sample frequency to be at least double the cutoff frequency of your filter to avoid aliasing. The cruddier the filter, the faster beyond that mathematical ideal you'll need to sample. With an IDEAL brick wall 500Hz filter, you need to sample at 1ms intervals.</p>
| <p>I want my Arduino project to listen to the ambient music and sync its light show output to the beat.</p>
<p>It seems that <a href="http://www.gamedev.net/reference/programming/features/beatdetection/" rel="nofollow">doing BPM detection properly</a> is fiendishly difficult in software, but if your music is sufficiently <a href="http://en.wikipedia.org/wiki/Techno" rel="nofollow">doofy</a> in nature and you use a little bit of hardware you can cheat and get away with it.</p>
<p>So my plan is to hook a <a href="http://www.sparkfun.com/products/9964" rel="nofollow">mic/opamp breakout board</a> to a simple <a href="http://www.electronics-tutorials.ws/filter/filter_2.html" rel="nofollow">1st order passive low-pass filter</a> and sample the input on an interrupt every 5ms or so. <a href="http://audacity.sourceforge.net/" rel="nofollow">Audacity</a> tells me a bass beat is around 15ms long, so every 5ms should be plenty to make sure I don't, er, "miss a beat".</p>
<p>If my low-pass'd sample is over a volume threshold, I'll record the time since the last beat, do some kind of weighted average calculation over the past few samples and that will allow me to predict how many ms until the next beat (some other software trickery might be necessary to account for bass drops and <a href="http://www.youtube.com/watch?v=5SaFTm2bcac" rel="nofollow">breakbeats</a>.)</p>
<p>Firstly, do I have roughly the right idea?</p>
<p>Secondly, can anyone tell me what order-of-magnitude values I'll need for the resistor and capacitor? I figure I want my cutoff frequency to be something like 500-1000Hz. I also gather the resistance of the rest of my circuit counts but I'm not sure where to measure that resistance across. A little fiddling with <a href="http://sim.okawa-denshi.jp/en/CRtool.php" rel="nofollow">this tool</a> gives me answers that look reasonable (500Hz = 330Ω/1uF) but I don't know enough to really know.</p>
<p>An example schematic showing where I measure the resistance of the existing circuit and where the low pass filter goes in the context of the rest would be exceedingly helpful.</p>
| Low pass audio filter design | 2010-12-20T14:48:25.000 |
8099 | |crystal| | <p>Intuitively, <em>I</em> would use the SLOWEST crystal that works for my application. You'll get less clock drift and circuit traces generally behave nicer at lower frequencies.</p>
<p>As an aside, if you want to do things every few milliseconds, you can do something along the lines of the following:</p>
<pre><code>Fosc = 25MHz.
T=1/Fosc = 40ns;
1ms/40ns = 25000 cycles/ms;
0xFFFF-25000=0x9E57;
on overflow TMR1: //assuming TMR1 is 16 bit and counts every clock cycle
doEveryMillisecond;
incrementMillisecondTimer;
TMR1 = 0x9E57;
</code></pre>
<p>Not sure what micro you're using but MPLAB has utilities to time how long events take, so you can use that to adjust the reset value of TMR1 to deal with any overhead and/or an inaccurate clock. Crystals might vary enough that this is infeasible in a production environment... not sure.</p>
| <p>I have seen questions like <a href="https://electronics.stackexchange.com/questions/5850/how-critical-are-uart-frequencies">this</a> that talk about selecting a crystal for UART and I have seen questions like <a href="https://electronics.stackexchange.com/questions/7800/real-time-clock-and-crystal-precision">this</a> that mention 32.768 kHz for RTC. But how do I decide the right crystal for my application.</p>
<p>At this point I am not sure what UART baud I will be using, but it will be one of the standard one. It would be nice to be able to get semi-accurate time in milliseconds, but not a requirement. Intuitively I think going with the fastest crystal that my micro can use will give me the most flexibility, but is there something I am missing? Is there a "general-purpose" frequency that people use?</p>
| How should I select my crystal frequency? | 2010-12-20T14:57:23.660 |
8103 | |arduino| | <p>Dave Jones did a <a href="http://www.eevblog.com/2009/11/21/eevblog-45-arduino-picaxe-and-idiot-assembler-programmers/" rel="nofollow">video blog</a> on the Arduino. If the link doesn't work search for the EEVBlog #45. </p>
| <p>I've played with AVRs before with my atmel development kit and have seen recently the use of Arduinos increasing. I have a few questions from users: </p>
<ol>
<li>Is it the same as using a microcontroller?</li>
<li>Are there any restrictions with the use of the Arduino instead of using the microcontroller?</li>
</ol>
<p>I am interested in moving to them but also which should i get as there are so many to choose from.</p>
| Arduino: is it worth it? | 2010-12-20T15:27:06.013 |
8112 | |power-supply|voltage-regulator| | <p>if you want an efficient solution, using a Buck Converter would be a smart choice. you can build it with discrete components (inductor, diode, capacitor and transistor) or you can use some IC. </p>
<p><a href="http://en.wikipedia.org/wiki/Buck_converter" rel="nofollow">http://en.wikipedia.org/wiki/Buck_converter</a> </p>
| <p>What's a good way to reduce the output from a 9V battery to the 1.8V to 5V required by an ATmega328 controller? The context is a small robotics platform with low power requirements (very slow movement).</p>
| How do I convert 9 V DC to 5 V? | 2010-12-20T19:10:45.260 |
8121 | |voltage-regulator| | <p>The <a href="http://www.fairchildsemi.com/ds/LM/LM7805.pdf" rel="noreferrer">Fairchild datasheet</a> says on page 23</p>
<blockquote>
2. C<sub>I</sub> is required if regulator is located an appreciable distance from power supply filter.
<br>
3. C<sub>O</sub> improves stability and transient response.
</blockquote>
<p>where C<sub>I</sub> is the input capacitor and C<sub>O</sub> is the output capacitor.</p>
<p>So depending on your circuit you have some freedom in picking C<sub>I</sub>.</p>
| <p>It says in the datasheet these values in this picture:
<img src="https://i.stack.imgur.com/awG8M.gif" alt="7805 1"></p>
<p>But I've also seen it with these values:<br>
<img src="https://i.stack.imgur.com/Wph1i.gif" alt="7805 2"></p>
<p>So what values should i use or doesn't it matter? And its for when its first starting.</p>
| Capacitor Sizes for 7805 Regulator | 2010-12-20T22:58:45.367 |
8128 | |transformer|debugging|fuses|rectifier| | <p>A 50VA transformer will take about 0.21 Amps when correctly loaded (VA / Input voltage)</p>
<p>So a fuse of about 1.5 x the input is suggested and should be Anti Surge (Usually marked T or TT - T stands for "träge" which is german for Lazy or slow) - so 315mA A/S or 400mA A/S </p>
<p>If your fuses are vaporized and cover insides with remains of the wire - This indicates a major short...</p>
<p>What type of transformer are you using - is it a toroidal - if so have you got a shorted turn (if you mount a toroidal transformer incorrectly you can add an extra winding which is shorted out - this is creates by mounting the transformer with a conductive clamp which is bolted down in the middle - if you are using a toroidal - try removing the clamp...)</p>
<p>It is possible that you have a faulty diode in your bridge - I have seen diodes that measure OK when tested with a meter, but when either loaded, or subjected to a higher voltage, break down and become shorts, or leak - the easiest way to prove is to replace ALL the diodes, as I have found if one is faulty, it usually subjects others in the bridge to stress, which may make them more likely fail, and for the cost of 4 diodes of 1N400X or 1N540X - I usually use 1N4007 or 1N5408...</p>
| <p>I recently made a voltage and current controlled supply from a kit I found. It worked for about 15 minutes and then fuses started popping. Unfortunately, I have no idea why, because power supply worked for some time fine then and there were no changes to (just voltmeter connected all the time to output) it when fuse problems started. </p>
<p>At first, I thought that some part overheated and malfunctioned, but everything felt cool. Next idea was that a piece of debris inside the box might have caused a short circuit somewhere. I carefully checked the box and didn't find anything which could have caused short circuit. </p>
<p>Next thought was that maybe IC died. I already asked about that <a href="https://electronics.stackexchange.com/q/8094/1240">here</a>, so I decided to separate circuit board and transformer and check transformer to make sure it was working correctly. So on one side I had PCB and on the other 50 VA transformer connected to a Graetz bridge rectifier. Here's the picture of the transformer part of the circuit.</p>
<p><img src="https://i.stack.imgur.com/loFcb.png" alt="transformer and rectifier"></p>
<p>I connected ends of the rectifier to my multimeter and powered on the transformer and got around 25 V, as expected. A minute or two later, fuse died again. To me this looked very strange, because the rectifier wasn't actually connected to anything. </p>
<p>Since I run out of required fuses, I decided to connect my multimeter in place of the fuse and see what's going on with current. At first, I connected it to 20 A range and saw that at the time I press the power switch, I get around 0.02 A. In less then a second, that falls to zero. I switched to milliamp scale and got same 20 mA. After power-cycling transformer again, the 200 mA fast multimeter fuse for milliamp scale died.</p>
<p>By this time I was left only with a 10 A fuse, so I decided to do some testing with it. Since the original recommended fuses were of 315 mA fast type, I decided to be extra careful. I checked insides of the box again, checked both switches, all wires and as far as I can see, everything is working correctly. I turned the transformer on with 10 A fuse and did some voltage measurements. I get around 27 V when the ends are serially connected and around 13.5 V when I'm using only one end of the transformer. When measuring DC voltage at the rectifier, I get around 25 V for both secondary coils and around 13 V for one secondary coil. I also get around 9 V AC at the rectifier for both secondary coils and around 3.5 V AC for single secondary coil. I also noticed that when power switch is in OFF position, I get around 3 V AC at the rectifier input and around 3 V DC at the rectified output. These only disappear when I pull the power plug.</p>
<p>After all this, I concluded that there must be something in the transformer/rectifier part of the circuit that is making fuses blow. Any ideas how to find out exactly what it is?</p>
<p>Also, is the behavior of the rectifier normal and should I change the switch to double pole switch which would control both power lines?</p>
<p><strong>EDIT 1</strong></p>
<p>I connected the PCB to the rectifier and turned it on with 10 A fuse. I'm running a small 9 V DC radio from the power source and it seems to be working correctly. Could it be that the recommended fuse current is wrong? The transformer's maximum output current is 2.1 A, so if I'm calculating correctly, maximum input current should be 230 mA. I used 315 mA fuses, so the should have survived full load on the transformer. IS there something I'm missing here?</p>
<p><strong>EDIT 2</strong> </p>
<p>Looks like the fuses could be blowing because of inrush current of the transformer. How would I solve that problem? One of the fuses I used and which blew was a slow acting fuse, so they aren't the solution.</p>
| Need help debugging my project: Fuses popping like crazy, but I can't find the reason why | 2010-12-21T01:00:35.257 |
8129 | |components| | <p><strong>TVS</strong>: Fails shorted in 90% of cases but can fail open due to extreme overheating (device can split into two pieces)</p>
| <p>How do components fail?</p>
<p>General rules with an answer per component type would be valuable.</p>
<p>We can work as a community to build up a single question that holds valuable information about how components fail.</p>
| How do components fail? | 2010-12-21T01:47:45.903 |
8132 | |prototyping| | <p>I use standard 0.1" pitch headers and then I connect everything via wire-wrap. That way I can modify if I make a mistake or if I want to change it up. </p>
<p>I typically connect one end to the board itself and then the other to some long pinned breakaway headers. That way I can remove the connections from a development board and plug into a completely different system in seconds.</p>
<p><a href="https://i.stack.imgur.com/AbLpI.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/AbLpI.jpg" alt="Wire Wrap Prototyping"></a></p>
<p>This does require you to purchase wire-wrap wire, a decent stripping tool, and a wire wrapping tool. If you look on eBay they're dirt cheap compared to what you can get them for new from Digikey (or the like)</p>
<p>I wrote an article and made a video on wire wrap for prototyping on <a href="https://www.circuitdojo.org/fundamentals/#wire-wrap" rel="nofollow noreferrer">Circuit Dojo</a>. Feel free to check it out.</p>
| <p>I am looking for connecters to connect two PCB boards together for prototyping. Can anyone recommend any models in particular.</p>
<p>Features I am looking for are decent price available from some where like Farnell or RS Components in Australia
3 wire mainly doesn't need speacilized tools to make the connects standard pin spacing for prototyping board
Also up to 10+ connections</p>
<p>I have looked my self but there is hundreds of models and it's hard to work out how they make there connects</p>
<p>Anyone recommend any models that they use? </p>
| Board to board connections | 2010-12-21T07:00:31.940 |
8141 | |microcontroller|uart| | <p>Looking at the datasheet: <a href="http://www.nxp.com/#/pip/pip=%5bpip=LPC1769_68_67_66_65_64_63,jp=Features%5d|pp=%5bt=pip,i=LPC1769_68_67_66_65_64_63%5d" rel="nofollow">LPC17xx</a> has support for 5 Bit data.</p>
<p>SiLabs 80C51F0XX has only 8 and 9 bit.</p>
| <p>I want to receive 5-bit serial words using a microcontroller's hardware UART at 45 Baud. This is the basic protocol for teletype machines. Since the baud rate is 45, I really want this done in hardware so that I am not spending all the processor time polling a pin, and for ease of programming. </p>
<p>Are there microcontrollers that can do 5-bit serial data in hardware? Is there a reasonable hardware/software implementation that won't tie up the processor?</p>
| Microcontroller support for Teletype | 2010-12-21T14:40:42.677 |
8145 | |level-shifting|obd| | <p>Maybe look at using an off the shelf chip solution such as the <a href="http://www.obd-ii.de/prodelm327.html" rel="nofollow">ELM327</a>. This looks like it will handle all of the various voltage and protocol issues.</p>
| <p>I've been tasked with interfacing with the on-board diagnostics of a vehicle. </p>
<p>Some systems use 7V signalling, some use 5V signalling, some signal up to the battery voltage (which can be as high as 28 V on some bigger vehicles). I need some way to handle these high voltage inputs which may exceed my microcontroller's 5V rating. I was thinking of an optoisolated system but communications need to be bidirectional and fast (100kbits second maximum). As it's OBD-II, I'll need two channels; some vehicles use transmit and receive channels, while others use one channel for both transmit and receive. Are there any options for me to consider?</p>
| How do I interface with OBD-II? | 2010-12-21T15:09:21.713 |
8149 | |fpga|intel-fpga| | <p><a href="http://users.ece.gatech.edu/~hamblen/book/bookse.htm">This</a> book is based on Altera hardware and development tools. You need the fourth edition for the DE1.</p>
| <p>I am getting a Cyclone II-based <a href="http://www.terasic.com.tw/cgi-bin/page/archive.pl?Language=English&No=83" rel="nofollow">Altera DE1</a> FPGA board to experiment with. I know a lot about programming, a bit about electronics and very little about FPGAs. What books or other resources would you recommend to someone like me to get started?</p>
| Getting started with Altera FPGAs | 2010-12-21T16:35:43.297 |
8152 | |pic|mplab| | <p>Thank you all for your kind help!</p>
<p>Maybe a part of the solution can be of general help:
I found out I had large constant arrays (I hadn't written the code myself..) and I drastically reduced the RAM need by putting them into Flash instad of RAM by using the "rom" keyword in their declaration.</p>
| <p>I am working with Invensense IMU3000 and a PIC18 microcontroller. I am migrating a library, written in MSVS2005, to MPLAB, doing the proper modifications to run on it.. the code itself provides just warnings, but when it comes to linking, I get this:</p>
<p>Error - section '.idata_dmpDefault.o' can not fit the section. Section '.idata_dmpDefault.o' length=0x000004b0</p>
<p>What does it mean?</p>
| MPLAB linking error | 2010-12-21T16:49:31.983 |
8158 | |multimeter|failure| | <p>I've had a similar problem years ago. What helped was <strong>disassembly and cleaning of the contacts below the rotating switch</strong>.</p>
<p>You will find little spring contacts assembled in cavities of the rotating plastic part and contacts on the PCB that the little spring contacts brush over. A bit like the wiper of a potentiometer. Ethanol or isopropyl alcohol (or contact spray) will likely help.</p>
<p>Seems like even the analog signals are routed along the contacts of the rotating switch, which sometimes gives not only complete open contacts but also resistance measurements that are just a bit too high, especially for the 200 Ohm range.</p>
| <p>I have a <a href="http://www.caltek.com.hk/cm1200.htm" rel="nofollow noreferrer">cheap handheld multimeter</a> that has stopped working. It basically behaves as if the leads weren't connected: the <code>Vdc</code> readout stays at zero, and the resistance readout stays at "1."</p>
<p><img src="https://i.stack.imgur.com/rRZvi.jpg" alt="enter image description here"></p>
<p>I've checked the battery and have tested the leads with a bench meter. Now, before I chuck the meter in the bin (it's long overdue an upgrade anyway), is there anything else relatively obvious that may be worth checking?</p>
| Failed multimeter | 2010-12-21T19:51:18.020 |
8176 | |power|usb|netduino| | <p>The Netduino requires power of 7.5-12v on its power connector. However, the Netduino can also pull it's power from the 5v USB connector. So yes, your IPhone wall charger should work just fine for you.</p>
| <p>I have a IPhone wall charger. Can I plug my netduino into it to power it via USB?</p>
| Netduino powerd by USB wall charger | 2010-12-22T04:50:26.150 |
8182 | |led|batteries| | <p>Take a peek at the <a href="http://data.energizer.com/PDFs/cr2032.pdf" rel="nofollow">pulsed characteristics for the CR2032</a>. This load may pull down the voltage to 2.3V-2.9V and IR is ~30Ω. Using <a href="http://data.energizer.com/PDFs/cr2032.pdf" rel="nofollow">the "Pulse" data in the 4th graph (bottom right)</a>: (2.4V-1.85V)/(20mA)=27.5Ω. Your milage may vary.</p>
<p>Also, looking at <a href="http://www.adafruit.com/datasheets/WP7113SRD-D.pdf" rel="nofollow">the "Spacial Distribution" graph in the LED datasheet</a>, you can see that its viewing angle is only about 20°. If you want it to look brighter despite poor viewing angle (I bet it is often non-ideal when all you're doing is "throwing" them on out-of-reach surfaces), look for an LED with a better viewing angle. While you're at it, you can get high-efficiency ones that only need a few mA for the same lumens. These are often in surface mount packages, so constructing a <em>throwie</em> would be quite different. Examples: <a href="http://www.lumex.com/specs/SSL-LX203CSRT.pdf" rel="nofollow">SSL-LX203CSRT</a>, <a href="http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=475-2820-1-ND" rel="nofollow">LR T68F-U1AA-1-1-Z</a>, <a href="http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=475-2835-6-ND" rel="nofollow">LY T68F-T2V2-35-1-Z</a>.</p>
| <p>I'm going to try to build some throwies soon and am ordering some LEDs and other needed things for the task.</p>
<p>It is my understanding that a CR2032 battery is 2.6-3.1 volts.</p>
<p>Well, I have <a href="http://www.adafruit.com/index.php?main_page=product_info&cPath=37&products_id=299" rel="noreferrer">these LEDs</a> picked out.</p>
<blockquote>
<p>660 nm wavelength</p>
<p>1.85-2.5V Forward Voltage, at 20mA current</p>
</blockquote>
<p>Would this be ok to use without any resistors? I'm ok if LED life is shortened, but I definitely don't want for the LED to just light up and then be burnt out a second later.</p>
| Will these LEDs work for throwies? | 2010-12-22T12:13:02.150 |
8199 | |serial|temperature|msp430|baudrate| | <p>So here's the answer:</p>
<p>The product has a 32 kHz crystal, and I had coded a routine to adjust the DCO frequency. The frequency adjustment used two timers, one from DCO and one from the 32kHz ACLK. It was driven by an interrupt off of capture/compare system, so that it could periodically recalibrate itself during operation.</p>
<p>Unfortunately, I inserted the initial calibration in the wrong part of my startup code, where interrupts were turned off. Therefore calibration didn't happen before the first use of the serial port, and initialization would hang waiting for a response on the serial port.</p>
<p>The DCO frequency starts at the factory calibrated value, which is why it was working at room temperature.</p>
<p>These plots tell the story:</p>
<p>First, the DCO-temperature curve:
<img src="https://i.stack.imgur.com/ZChOM.png" alt="alt text" /></p>
<p>Now the curve after calibration is actually working:
<img src="https://i.stack.imgur.com/VXpgD.png" alt="alt text" /></p>
| <p>I have a product using the MSP430 microprocessor, which has been selling for a couple years now. One of the MSP430's jobs is to communicate over async serial to a low-power radio.</p>
<p>With the onset of this winter, there has been an unacceptable failure rate (several percent) in cold temperature. Investigation has found that the serial communication with the radio is failing. The baudrate generator for the serial port is fed by SMCLK, which is divided from the MSP430's digitally-controlled oscillator (DCO).</p>
<p>Why is serial communication failing at low temperatures?</p>
<p>(Note: I have already solved the problem and will be posting the answer soon. Hint: it was a software bug.)</p>
| MSP430 serial communication failing in cold weather | 2010-12-23T05:37:28.453 |
8202 | |pcb| | <p>Back when we made our own PCBs, we used an HP2100, and printed on translucent acetates. The translucent ones are better because the toner grips it better. It was expensive at £500, but it's still producing perfect prints after 10 years!</p>
<p>It's worth getting a printer capable of 1200x1200 if you're doing SMD.</p>
| <p>could you please suggest printer for printer photomasks at home?
Target is to have 0.1x0.1 features or better.</p>
<p>My tests shows that inkjet are pretty bad when working under 0.3x0.3.
So obviously, only lasers left.</p>
<p>Is 1200x1200 worth it? Any experience showing one models better than others? Any specific examples?</p>
| Suggest printer for printing photomasks for homemade PCBs | 2010-12-23T07:42:14.703 |
8205 | |microcontroller|power|relay|solid-state-relay| | <p>With the concerns you state, and especially with having the relay installed in a wall, I guess the answer is:</p>
<p>Don't.</p>
<p>You might add a fuse, but then, you'd have to find a rating in the relay's data sheet telling you if it is approved for usage with a fuse, and if so, what the fuse's rating would have to be. All in all, you would have to do the same qualification for the entire system (relay, fuse, type of outlet socket, possible loads) that the original vendor did for the combinaiton of the relay and fountain.</p>
<p>The relay will not limit the current (amps) to a level that is safe to itself. When overloaded, it will likely act like a short circuit for moderate overload conditions and will fail open (or explode, or burn) for severe or ongoing overload conditions.</p>
<p>The thing to remember is this: Once you exceed any of the ratings, the manufacturer won't guarantee anything they tell you in the data sheet any more and you are on your own.</p>
<p>Also, with having the relay installed in a wall where it can't really get rid of any heat it produces, I recommend using the derating curve for 60...70 °C, which tells you to rather not exceed 2...3 A.</p>
<p>A hacker's answer, however, is:</p>
<p>Yes, your setup might work, ...</p>
<p>... but you would have to make sure all is well and within the specified limits and characteristics.</p>
| <p>Had a quick question. I am using a <a href="http://www.crouzet-ssr.com/english/products/download/GA1GA8.pdf" rel="nofollow">Crouzet GA8-6D05</a> SSR to relay xmas lights for the holidays. I basically hacked an extension cord (120VAC US <1Amp) to do this. I am currently using a spliced extension cord to perform on and off operations via a micro controller.</p>
<p>During the summer, we commonly use this same outlet for a water fountain on our patio (also 120VAC US <1Amp). I was thinking to use the SSR mentioned above to switch the water fountain on and off also. I am thinking that the best way to make this work would be to hack the actual outlet. I already know that you can separate a two plug receptacle by cutting the metal plate which connects positive on one side and negative on the other.</p>
<p>My question is: What will happen to the SSR if the load exceeds more than the max 5 amps it is rated for? Will it blow up, start a fire, or just reject the call for the extra amps? I am concerned about fire hazards, not really concerned about the thing dieing necessarily. I worry about leaving this in the wall if I sell the house as I do not plan to use the outlet for anything more than what is stated above, but the next home owners may not follow directions.</p>
<p>Thanks in advance for your help!</p>
| What Happens When You Exceed a Solid State Relay's Max Amps? | 2010-12-23T08:26:20.833 |
8214 | |datasheet| | <p>XC was the designator used by Motorola for their pre-release parts (experimental?), generally parts were developed as XCxxxx then released as MCxxxx.</p>
| <p>Usually Google guides me to <a href="http://www.alldatasheet.com/" rel="nofollow">http://www.alldatasheet.com/</a> or a similar site when I'm looking for a datasheet, but no such luck this time. The <code>XC</code> prefix reminds me of Xicor, but after being directed by Google to the Intersil site I couldn't find it there either.<br>
Does anyone have a datasheet for the XC34064P?</p>
| Datasheet for XC34064P wanted | 2010-12-23T14:51:03.083 |
8216 | |led| | <p>I know the question specifies that LEDs are the required illuminating device, but if you want to scale things up a bit, you can make a very convincing flame effect with a yellow 25w GLS incandescent bulb and a standard fluorescent tube starter.</p>
<p>All you need to do, is connect the starter in series with the bulb, and it will happily flicker on and off indefinitely.</p>
<p>Connect a few bulbs, all with their own starters, and mix up the colours between yellow orange and red to make a nice warm fireglow effect.</p>
<p>Very simple, and few parts required!</p>
| <p>My wife bought these <strong>flameless candles</strong>. They have 3 LEDs in them that have a seemingly random flicker to them. (Get bright, fade out a bit, fade in a bit etc...). Since there are three when you see it through wax it looks like a flame flickering. Very cool.</p>
<p>I though it would be a fun project to get back into electronics. I am a computer engineer but I fell into software - so while I understand concepts and how things work, I have no clue how to start this unless I got a pic chip or whatever people use now.</p>
<p>Any suggestions? The simpler(cheaper) the better. I just need some general ideas to get me pointed in the right direction. What kind of circuits should I be looking at or does this need to be done with some kind of controller like a PIC?</p>
| LED Flame Emulation | 2010-12-23T15:26:36.023 |
8219 | |driver| | <p><strong>HOW TO FIGURE OUT THE PINNING</strong><br>
The connection for the filament are usually the two outer most pins, but in your case it looks like it is only the first and last pin. Check with an ohm-meter (should be something below 20ohm). The mesh gates are usually counting from one end and the multiplexed segments from the other.</p>
<p>When I salvage VFDs from DVD players and alike This works 90% of the time.</p>
<p>Connect +3.3v DC on one filament end and ground to the other. Use a current limiter and raise it slowly. If the filament start to glow the voltage is to high! The current should stabilize below 30mA depending on the VFD size (filament length) and voltage.</p>
<p>Connect +12v DC to a mesh-gate (start from one end) and +12v DC to a segment (start from the other end). Keep moving from pin to pin at the segment end to see if some segments light up. I usually use a 1K series resistor to limit the current if I should hit any ground pin. If nothing happend, move to the next the mesh-gate and repeat.</p>
<p>If nothing shows, try to increase the voltage on the filament a bit (it should not show any signs of glowing!) or the gate and segment voltage (segment and mesh-gate should be the same voltage).</p>
<p><strong>HOW TO DRIVE</strong><br>
Now when you know how your VFD should be connected you need to drive the mesh-gate and then each segment with the +12. Then change mesh gate and then drive the next segments. Repeat thisat 50 or 100 times a second to get a steady display without flickering.</p>
<p>Since your controller propably use 3.3v or 5v you nedd to either use a Step-Up or Booster to convert the power to 12v (or just use an external 12v power). Use a PNP transistors for each segment and mesh-gate to turn on +12v</p>
<p>This was some image I found on Google that shows how to drive one segment/gate (why draw one identical if someone else already done it, it's a quite standard solution)
<a href="https://i.stack.imgur.com/PXcEB.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/PXcEB.jpg" alt="Schema"></a></p>
<p>The first transistor is a level-shifter to drive the second transistor, the driver transistor. However, the "driver" transistor can be a very small one, there isn't many uA on that line. Connect the segment/gate to the "Out" terminal.</p>
| <p>In a box with old components I found a 16 character, 19-segment Futaba VFD:</p>
<p><img src="https://i.stack.imgur.com/JOYs3.jpg" alt="alt text" /></p>
<p>I would like to use it for "something" but I haven't the foggiest how to drive such a display. Even the filament is an unknown factor to me. The device dates at least from the early '90s. I guess at that time there were drivers for it, but I don't know if this kind of display is still being designed-in. Information about a driver would be nice, as would some schematic about the whole. (For example: What voltage does the filament require with respect to the driver voltages?)</p>
| Help wanted with vacuum fluorescent display (VFD) | 2010-12-23T16:21:20.967 |
8231 | |fpga|programmable-logic| | <p>A good "rule-of-thumb" list would go something like this:</p>
<ul>
<li><strong>PAL/PLA/GAL:</strong> Used in place of discrete IC logic gates on a PCB</li>
<li><strong>CPLD:</strong> Used where complex, nonDSP, and possibly time-critical tasks are required (loading boot code onto an FPGA from memory, LUT sinewave generator for DAC, etc)</li>
<li><strong>FPGA:</strong> Used when time critical, multiplication, or DSP capability is required (FIR Filters, FFTs, etc)</li>
<li><strong>FPGA with hard MCU:</strong> Used when FPGA functionality is required and peripherals on the FPGA must be accesed (temp sensors) or to allow a less-time-sensitive task to be implimented in C rather than VHDL for simplicity (UART/serial port functionality, PCB housekeeping, etc)</li>
</ul>
| <p>Programmable logic can be implemented in your widget in many different spectrums, from burning a few gates or using a MUX to the latest FPGA with built-in microcontroller and IO peripherals, not to mention ARM's <a href="http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0190b/index.html" rel="nofollow">PrimeCell GPIO</a> or <a href="http://www.actel.com/products/smartfusion/default.aspx" rel="nofollow">other, more specific examples</a>. <strong>For what applications are the various levels of programmable logic device complexity used?</strong> Although the grouping appear to blend together near the extremes of <a href="http://en.wikipedia.org/wiki/Programmable_logic_device" rel="nofollow">their definitions</a>, I think this is an acceptable list:</p>
<ol>
<li><em><strong><a href="http://en.wikipedia.org/wiki/Programmable_array_logic#Output_logic" rel="nofollow">PAL/PLA</a>/<a href="http://en.wikipedia.org/wiki/Generic_array_logic" rel="nofollow">GAL</a></strong>: Programmable Logic Array;</em> appear to be listed as <em>'Embedded - PLDs'</em> at Digikey, covering asynchronous 10/8 I/O (<a href="http://www.atmel.com/dyn/resources/prod_documents/DOC0425.PDF" rel="nofollow">ATF16V8C</a>) to 50MHz, 192 macrocell, (<a href="http://media.digikey.com/pdf/Data%20Sheets/Cypress%20PDFs/CY7C341B.pdf" rel="nofollow">CY7C341B</a>), and are mostly reprogrammable.</li>
<li><em><strong><a href="http://en.wikipedia.org/wiki/CPLD" rel="nofollow">CPLD</a></strong>: Complex Programmable Logic Device;</em> Digikey lists them as such, available in 7.5ns 10 I/O (<a href="http://www.atmel.com/dyn/resources/prod_documents/doc0776.pdf" rel="nofollow">ATF750C</a>) to 233 MHz, 428 I/O "CPLDs at FPGA Densities" (<a href="http://download.cypress.com.edgesuite.net/design_resources/datasheets/contents/cy39030v_8.pdf" rel="nofollow">CY39100V484B</a>).</li>
<li><em><strong><a href="http://en.wikipedia.org/wiki/Field-programmable_gate_array" rel="nofollow">FPGA</a></strong>: Field-Programmable Gate Array;</em> available in 58 I/O (<a href="http://media.digikey.com/pdf/Data%20Sheets/Xilinx%20PDFs/XC2000%20Families.pdf" rel="nofollow">XC2064</a>) to 1023 I/O BGA beasts (<a href="http://www.altera.com/literature/hb/stx/stratix_section_1_vol_1.pdf" rel="nofollow">EP1S80F1508C7N</a>).</li>
<li><em><strong><a href="http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2556750" rel="nofollow">FPGA with hard MCU</a></strong>: this is when an MCU is physically laid out in the FPGA IC, not emulated.</em></li>
</ol>
<p>Wikipedia quote:</p>
<blockquote>
<p>The difference between FPGAs and CPLDs is that FPGAs are internally based on Look-up tables (LUTs) whereas CPLDs form the logic functions with sea-of-gates (e.g. sum of products). CPLDs are meant for simpler designs while FPGAs are meant for more complex designs. In general, CPLDs are a good choice for wide combinational logic applications while FPGAs are more suitable for large state machines (i.e. microprocessors).</p>
</blockquote>
<p>This doesn't explain the difference between using <a href="http://download.cypress.com.edgesuite.net/design_resources/datasheets/contents/cy39030v_8.pdf" rel="nofollow">a 233 MHz, 400 I/O CPLD</a> and a <a href="http://www.altera.com/literature/hb/cyc3/cyc3_ciii51001.pdf" rel="nofollow">comparable FPGA</a>; or between a <a href="http://media.digikey.com/pdf/Data%20Sheets/Cypress%20PDFs/CY7C341B.pdf" rel="nofollow">192 macrocell PLD</a> and a <a href="http://www.altera.com/literature/hb/max2/max2_mii5v1_01.pdf" rel="nofollow">comparable CPLD</a>. I can't grep reliable guidelines by which to narrow design options. Note that I don't currently have a specific application in mind, but have often wondered, "what would I use to do that?"</p>
<p><em>I've received excellent advice <a href="http://chat.stackexchange.com/">off-site</a> regarding specific requirements, but still think this question could benefit from some examples showing preference over one family of PLDs when another may have appeared to be equally or more suitable.</em></p>
| What are programmable logic ICs of different complexity used for? | 2010-12-24T00:12:27.117 |
8244 | |phototransistor| | <p>You'll want a PIN photodiode. The Osram BPW34 may be a good starting point.</p>
| <p>Where is photodiode in the CD/DVD drives?
What is his frequency response & sensetivity usuallY?</p>
<p>I am going to try laser data transfer, but finding decent photodiode is my weak point.</p>
| Where is photodiode in the CD/DVD drives? | 2010-12-24T10:02:23.207 |
8250 | |pcb|ethernet|layout| | <p>My understanding is you should NOT have a ground plane between the RJ-45 and XFMR due to the need for electrical isolation. Ethernet is supposed to withstand 1500V (lightning protection). The XFMR is rated to withstand 1500V (there's a split ground plane under the XFRM between digital GND and chassis GND). Chassis ground is stripped away from the ethernet traces on the cable-side for creepage/clearance.</p>
<p>Another reason is the XFMR has a common-mode choke to attenuate noise on both diff pairs (before the signal exits the board onto the cable, which makes a great antenna). You don't want digital ground plane underneath because the diff pairs will pick up more noise and cause you to fail </p>
<p>Here's the hard thing to understand. On a PCB, differential traces couple mainly to the reference ground plane and there is NOT much common mode rejection because crosstalk does not affect both traces equally. Most of the return current returns on the reference plane.</p>
<p>If a twisted-pair cable, the differential pairs have near 100% coupling with each other and therefore have extremely good common-mode rejection. The return current for one trace is on the other trace and vice versa.</p>
| <p>I'm working on a DC jack powered Ethernet design and I've downloaded many Ethernet Layout guidelines from many semi vendors with varying recommendations. I've read app notes recommending almost every possible termination resistor position, for example. Placing termination resistors at the PHY, at the Magnetics, the TX at the PHY and the RX at the magnetics, and visa versa. The most popular seem to be at the PHY, and this seems to make the most sense. Ethernet uses balanced differential pairs, which are typically terminated at the extremes to filter any common mode noise injected into the transmission lines, and the RX / TX traces on the board constitute part of the transmission line (these are being run at 100 ohm impedance to match CAT5 cable impedance).</p>
<p>The other controversy here is what to do with the ground plane. If this wasn't a DC jack powered app my life would be easier. Many app notes recommend no ground plane under the magnetics (which are built into the RJ45 connector in my case) to avoid coupling into the ground plane. But... that is exactly what I want. Better coupling into the ground plane then into the conformity testing antenna! A ground plane under the jack will help close the metal enclosure around the rest of the connector. I've read at least one example of anecdotal evidence on the net claiming better radiation performance with a solid ground plane in a DC jack application as opposed to a separate isolated Ethernet plane tied in with caps. So... I think I'm going to keep a solid plane under the RJ45 jack. </p>
<p>Some papers also recommend no plane under the RX / TX pairs. I can't make my mind up about this. I want to avoid coupling any ground noise into the RX and TX pairs but my experience seems to be any ground plane splitting / opening is usually based on hocus pocus type thinking instead of sound physics.</p>
<p>Does anyone here have any experience or suggestions related to Ethernet layout, specifically with regard to the RX / TX termination resistor placement and whether or not to use a ground plane under the RJ45 connector (with magnetics) as well as under the TX / RX pairs? Any suggestions greatly appreciated.</p>
| Ethernet Layout Guidelines | 2010-12-24T15:57:51.903 |
8251 | |pinout| | <p>The reason is that arranging the pins in a logical order is way down on the priority list of a chip company. Most designers they care about (which generally does not include hobby robotic people) will use a CAD package that has the pinout in some library, so they don't care either. So other factors, like efficient layout of the chip die, are more important.</p>
<p>Note that for some pins chip manufacturers do care:</p>
<ul>
<li>balanced pairs (ethernet, USB) are next or close</li>
<li>the xtal connections are close (with a ground pin nearby, but not on some PICs..)</li>
<li>ground and power pins are next or close, so a decoupling cap can be added close to the pins</li>
</ul>
<p>I remember 30 or so years ago I tried to make a single-sided Z80 computer PCB. I got most lines routed, but those silly data bus pins made it impossible.</p>
| <p>I am working as a winter intern at a robotics company. My job is to assist the lead embedded developer in... whatever he wants my assistance in. </p>
<p>About a week back, I was handed a NXP blueboard with LPC2148 on it. Although I loved the more processing power (compared to the ATmega32s I had been working on), I found something very odd about the ARM7 based controller. If you look at the pinout here</p>
<p><a href="https://i.stack.imgur.com/VlhM9.jpg" rel="nofollow noreferrer" title="LPC2148 pinout"><img src="https://i.stack.imgur.com/VlhM9.jpg" alt="LPC2148 pinout" title="LPC2148 pinout"></a></p>
<p>you would notice that the port pins are just all over the place. In the AVR series everything is arranged cleanly with all the port pins together. Why is it not so in the LPC21xx? I cannot find any logic at all, they are not arranged by pin number or by functionality (like all the JTAG pins together). It seems like the designers just stacked the pins in a random form. </p>
<p>Can any body please explain the reason behind this?</p>
| Why are the pinouts of LPC21xx all over the place? | 2010-12-24T15:59:53.710 |
8253 | |operational-amplifier| | <p>In many cases I've seen in online electronics forums, the 741 is designed in by beginners who just don't know of any other opamps. They may have read about it in a textbook or seen it in another old design and assumed it was a reasonable choice. Once they learn that LM324, etc. is readily available, cheap and easier to use, they'll normally switch.</p>
<p>The other big reason already stated is legacy designs. Something works, is still in production, and there's no compelling reason to change it. If you've been selling a product for 30 years and you won't run out of parts, and you won't make any more money by changing to a newer opamp, they why change?</p>
| <p>OK, so the uA741 is 42 years old now. For its time it may have been a great opamp; the requirements weren't as high as today, and there was far less competition. But I was wondering what's the 741's appeal today. </p>
<blockquote>
<ul>
<li>it's slow. GBW 1MHz, slew rate < 0.5 V/us </li>
<li>it's not low power, nor low voltage </li>
<li>it doesn't have low bias current FET inputs </li>
<li>it doesn't have rail-to-rail inputs or outputs </li>
<li>it's not low noise </li>
<li>many more modern opamps have comparable price </li>
</ul>
</blockquote>
<p>Why is the 741 still used today?</p>
| What's the uA741's appeal? | 2010-12-24T16:37:23.803 |
8264 | |microcontroller|sata| | <p>Think twice: You will also need a File System for large disks, and FAT32 has some design limits, esp. that Files must be < 4GB. Ohter file systems are much harder to implement on a µC. In most cases its easier to use a SD card, as it supports SPI.</p>
| <p>Are there any micro-controllers which support writing data to large sized SATA disks?</p>
| Micro Controllers Supporting SATA | 2010-12-24T20:09:41.653 |
8271 | |rf|oscilloscope| | <p>A sampling scope can indeed make a good spectrum analyzer. The three main limitations are in the areas of span width, dynamic range, and spur rejection. </p>
<p>The span width of a modern sampling instrument is usually constrained by the sample clock rate and/or various throughput limitations of its baseband FFT pipeline. Meanwhile, its dynamic range is lower than that of a classical spectrum analyzer because the front-end sampler 'sees' the whole DC-to-daylight spectrum worth of noise. The instrument folds the noise at every harmonic of the sampling clock, so noise and signals near all of the resulting aliases are visible at once. </p>
<p>Using a sampling front end with an FFT baseband analyzer section is not a new idea -- check out the <a href="http://cp.literature.agilent.com/litweb/pdf/5091-0791E.pdf" rel="nofollow">HP 71500A</a>, and its main module, the <a href="http://www.home.agilent.com/upload/cmc_upload/All/Product_Note_70820_1.pdf" rel="nofollow">70820A</a> introduced circa 1992. (Large .PDFs but worth the wait.) This 'microwave transition analyzer' was a bit too far ahead of its time due to the wimpy processing power available, but the concept is very sound, and it can be implemented very economically compared to a traditional microwave spectrum analyzer.</p>
| <p>I'm interested in measuring the spectral amplitudes / frequency content of RF frequencies up to <strong>30 GHz</strong>. This can be done using a digital sampling oscilloscope <em>(I'll call it a SO)</em> with FFT or a digital spectrum analyzer <em>(SA)</em> [or a fantastic digital storage 'scope, noted below]. <a href="http://www.cbtricks.com/miscellaneous/tech_publications/scope/sampling.pdf" rel="nofollow">As I understand it</a>, a <em>SO</em> samples the signals directly with known sample jitter, then recreates the signal using regression. A <em>SA</em>, on the other hand, first downconverts the high-frequency signal with a mixer, then samples. It would seem that a <em>SA</em> should deliver greater frequency resolution given comparable ADC sampling rates to the sampling oscilloscope.</p>
<p><em><strong>What are the limits of functionality of each type? How is one better than the other at spectral analysis?</strong> (They both rely on the FFT, right?) What makes either expensive?</em></p>
<p><em>Unrelated POIs: <a href="http://www.home.agilent.com/agilent/product.jspx?nid=-34363.937136.00&cc=CA&lc=eng" rel="nofollow">32 GHz Agilent</a>, <a href="http://www.lecroy.com/Oscilloscope/OscilloscopeSeries.aspx?mseries=329&capid=102&mid=504" rel="nofollow">120 GS/s Lecroy</a>, <a href="http://www.tek.com/products/oscilloscopes/dpo70000_dsa70000/" rel="nofollow">100 GS/s Tek</a>, <a href="http://ece.nsit.ac.in/website/eclub/projects/gba.pdf" rel="nofollow">Gameboy SA</a>.</em><br>
<strong><em>edit:</strong> There seems to be some confusion between digital storage 'scopes (DSOs) and digital sampling oscilloscopes (what I called SOs) -- they are not the same, although they both sample digitally. I've also updated the question.</em></p>
| What are the functional differences between a digital sampling 'scope and a digital spectrum analyzer? | 2010-12-25T01:51:34.880 |
8273 | |embedded|freescale| | <p>The datasheet makes it sound like you need to disconnect the on-chip debugger from port DD before you can use it as a normal port.</p>
<blockquote>
<h2>26.4 Functional Description</h2>
<h3>26.4.1 Overview</h3>
<p>[...]</p>
<p>In single-chip mode, all pins are configured as digital I/O by default, except for debug data pins (DDATA[3:0]) and processor status pins (PST[3:0]). These pins are configured for their primary functions by default in all modes.</p>
</blockquote>
<p>— <em><a href="http://cache.freescale.com/files/32bit/doc/ref_manual/MCF5282UM.pdf?pspll=1" rel="nofollow noreferrer">MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3</a>, § 26, p. 27</em></p>
<p>In most MCUs I've used, alternate functions usually override GPIOs, which has the lowest priority.</p>
| <p>I’ve got a MCF5282 that I’m trying to use PDD4 as a GPIO on. In my setup code, I’ve got:</p>
<pre><code>MCF5282_GPIO_DDRDD = 0x10; /* cs on dd4. */
MCF5282_GPIO_PORTDD = 0x10; /* active-low. */
</code></pre>
<p>And in my main loop, I’ve got:</p>
<pre><code>for( mainloop_cnt = 0; true; mainloop_cnt++ )
{
MCF5282_GPIO_PORTDD = (mainloop_cnt & 0x10);
/* other stuff. */
}
</code></pre>
<p>Which should give me a nice square wave on the oscilloscope, but the port doesn’t seem to be doing as I say. Am I missing some setup steps? I can’t find anything in the 5282 manual about a “Port DD pin-assignment register” to repurpose it from its “primary” role as DDATA.</p>
| Using Port DD as GPIO on MCF5282 | 2010-12-25T02:07:49.320 |
8280 | |rf|emc| | <p>To filter high frequency noise. Inductors' windings are capacitive at high frequency so they are effectively useless. If you're worried about your circuit affecting other circuits (or being affected by them), I would only filter the I/O and power entry to your module, so that conducted noise doesn't leave your module on the I/O and power lines, which can act like antennas and radiate the noise, or pick up noise from other modules. The other use, inside a module, is for sharing a voltage rail with sensitive analog components, such as an ADC with a micro. In the case of your PIC, it usually doesn't need such a thing.</p>
| <p>In a lot of circuits, I've seen ferrite beads on the Vdd lines to microcontrollers. For my high speed dsPIC33F (80 MHz, 40 MIPS) microcontroller, should I have ferrite beads on the Vdd lines or should I not bother? The datasheet doesn't suggest using them. I'd like to limit EMI/RF interference, as the module will be used on a model plane and this type of interference could cause problems for the onboard radios.</p>
| When is it appropriate to use ferrite beads? | 2010-12-25T13:13:15.893 |
8282 | |switches|input| | <p>It's a <strong>rotary encoder</strong>. It has two outputs giving pulses in quadrature (see image), as to determine the way it's rotated. </p>
<p><img src="https://i.stack.imgur.com/jZpGM.gif" alt="enter image description here"></p>
<p>In the image you can see that the level of the B channel is low on the rising edge of the A channel if the knob is rotated clockwise, but high if rotated counterclockwise.<br>
Differences in models are the number of pulses per rotation, often between 15 and 20, and the number of channels. More than 2 channels are used to obtain the absolute position of the knob. E.g. 10 channels give 1024 unique codes per rotation. Gray coding is used.<br>
<strong>edit</strong><br>
Another parameter is the detent. Detents are click-positions, which require a certain momentum to overcome. Some models have 2 detents per pulse, others don't have detents and rotate rather smoothly, so that it feels like a potmeter without stops.</p>
<hr>
<p><strong>Further reading</strong><br>
"Control Shaft Encoders" \$-\$ Circuit Cellar issue 250, May 2011, p.28 ff</p>
| <p>for my current project I'm planning to use an input "device" like this in the photo (don't know its real name):</p>
<p><img src="https://i.stack.imgur.com/MztUQ.jpg" alt="alt text"></p>
<p>It is used in a lot of musical instruments and it is like a potentiometer that can be rotated as many times as you want. I think it isn't read like an analog value.
Can someone give me some hints?</p>
<p>Thank you very much.</p>
| How to implement a "rotary switch" like in audio equipment? | 2010-12-25T14:54:08.357 |
8291 | |soldering| | <p>I don't think the temperature matters much, just that you get the material you are soldering to hot. Once the material is hot, allow the solder to flow from the heated material to your soldering iron. If you are getting big beads of solder on your soldering iron, you are doing things backwards. Make sure to move your soldering Iron away from the solder as it flows. </p>
<p>If your not able to maintain a hot temperature on the object being soldered to, then you may want to try either a larger tip, and or a higher temperature.</p>
| <p>I've got a Weller soldering station with settable temperature and interchangeable tips.</p>
<p>Is there a table or general guidelines for temperatures and tips for different soldering tasks, such as:</p>
<ul>
<li>wire-wire, thick</li>
<li>wire-wire, 20 gauge</li>
<li>wire to PC board</li>
<li>through-hole chip on PC board</li>
</ul>
| soldering temperature/tip guides? | 2010-12-25T23:47:43.217 |
8295 | |pwm|fan| | <p>From fan pulse signal (tachometer) convert to speed by measuring the frequency of the tachometer which 1 full rotation of fan represent 2 pulse signal. Thus, for a minute times with 60 seconds.</p>
<p>Fan speed in RPM:</p>
<p>$$RPM = \frac{freq}{2}*60$$</p>
| <p>I have a 3-pin 12 V computer fan and I want to interpret its speed sensor output. At the yellow wire I get something that looks like pulse-with modulation. How would I interpret the output without actually connecting the fan to a computer?</p>
| How to interpret the output of a 3-pin computer fan speed sensor? | 2010-12-26T01:41:15.463 |
8311 | |development|ide|beagleboard| | <p>I tried Meego and Angstrom, and settled on Angstrom. It's far easier to make it work, and very stable. The Meego port for beagleboard, on the other hand, had many glitches. I didn't test the other OSes, but I'd say Angstrom seems to be the best choice for both community support and stability.</p>
<p>To install the OS is quite simple: you download an OS image to an SD card and make some changes in the bootloader to make it boot from the SD. There are some ready-made OS images at the Angstrom website, along with recipes to install it on the SD. Basically you'll create two partitions: a smaller FAT for the boot and kernel, and the other for the root filesystem containing everything else. Here's one site containing instructions for SD boot:
<a href="http://www.xora.org.uk/2009/08/14/omap3-sd-booting/" rel="nofollow">http://www.xora.org.uk/2009/08/14/omap3-sd-booting/</a></p>
<p>You could also make it boot from the NAND flash, but I'd recommend to save this option for later when you're more comfortable with the device. Since the NAND is limited, you'll need to create a custom image using bitbake to make it fit, that's the kind of work you won't want to do right now.</p>
<p>About debugging, the best way is for you to buy an ethernet-to-usb interface + usb hub. Then you run gdbserver in your beagleboard and can use any gdb-compatible debugging IDE at your PC (I use Eclipse CDT).</p>
<p>For the camera interface, the easiest way would be to use the GPIO pins at the expansion connector; the drawback is that you may have a limited frame rate due to the bandwidth limitation, and also yo'll make the processor busy while transfering the image; on the other hand the GPIO is so flexible that you probably won't need any additional circuit to connect them - provided their voltage is compatible (the GPIO works at 1.8 V). There can be other ways if you want a higher frame rate and need the processor available for other parallel tasks, but I'd recommend to leave that for a second round of design.</p>
| <p>How can I easily start off professional development with the BeagleBoard XM?</p>
<ol>
<li><p>Which OS should I work with? .. my choices include:</p>
<ul>
<li>Ubuntu</li>
<li>Android</li>
<li>MeeGo</li>
<li>WinCE</li>
<li>QNX</li>
<li>Angstrom (preinstalled)</li>
<li>Symbian</li>
<li>Gentoo</li>
</ul></li>
<li><p>How do I install an OS onto the board?</p></li>
<li><p>Which IDE do I use?</p></li>
<li><p>How do I debug or run my code on the target?</p></li>
</ol>
<p>I bought a brand new Beagleboard XM to interface to a <a href="http://www.ovt.com/products/sensor.php?id=65" rel="nofollow">camera module</a>, capture video and do some image processing. The camera uses an 8-bit parallel port interface to transfer images. </p>
<p>What do you recommend?</p>
| Recommended first steps with the BeagleBoard | 2010-12-26T16:23:24.917 |
8314 | |frequency-measurement| | <p>I had two fleeting thoughts: </p>
<ol>
<li><p>One could use a <a href="http://en.wikipedia.org/wiki/Audio_crossover" rel="nofollow">crossover</a>, which is an implementation of several bandpass filters, followed by power measurement in order to obtain a rough power spectral density. The highest frequency pass-band achieving a threshold would indicate maximum significant input frequency. If each crossover channel were input to trigger/comparator interrupt pins, some <a href="http://hackaday.com/2010/11/09/debounce-code-one-post-to-rule-them-all/" rel="nofollow">good debounce code</a> may be able to take care of the rest. The crossover could be as simple as an array of diode detectors with RC filtering.
Circuit complexity would be dependent on the bandwidth and resolution of the crossover. I'm sure we've all <em>ooo'd</em> & <em>aaw'd</em> at quality audio crossovers; diode detectors are very simple; RF range adds complications, but can use diode detectors as well. </p></li>
<li><p>One could <a href="http://en.wikipedia.org/wiki/Frequency_mixer" rel="nofollow">mix down</a> the input frequency, followed by a LPF. Using a continous LO frequency, start at some minimum (~kHz) and increasing to a maximum expected frequency (20 kHz for audio), one could setup a trigger based on a threshold DC or low frequency output, or just record and compare over the entire range. I've never looked for a low frequency mixer, but it would be simple to make a crude one (diode bridge; Gilbert cell); RF mixer ICs are available.</p></li>
</ol>
<p>Both of these methods are inferior to oversampling, but much more fun. There are frequency-to-voltage conversion ICs <em>(DigiKey: PMIC - V/F and F/V Converters, <a href="http://dkc3.digikey.com/CA/images/datasheet.gif" rel="nofollow">1MHz max</a>)</em>.</p>
| <p>As a follow up to this question: <a href="https://electronics.stackexchange.com/questions/8284/how-to-sample-audio-at-nyquist-frequency-with-msp430f5438">How to sample audio at Nyquist frequency with MSP430F5438?</a></p>
<p>What type of circuit would I use to generate something that a microcontroller could use to determine the max frequency of an input? I was thinking it would preferably provide a voltage that is lineally related to the frequency.</p>
<p>The information provided by the frequency detector could then be used by the microcontroller to know what frequency it needed to be sampled at.</p>
<p>Is there any ICs that do this? or any circuit that will do this?</p>
| Analog Max Frequency Detector Circuit | 2010-12-26T20:02:14.230 |
8319 | |pcb| | <p>I would propose designing your enclosure so that the board is seated in a groove on one end, and has a plastic leaf spring-like catch on the opposite side. Gently pull back on the catch and then lift out the board when you need to remove it.</p>
<p>I'm coming from this standpoint since I have a 3D printer and can print pretty much whatever I need to fit around PCBs, but even if you don't have access to one, services like Ponoko and Shapeways can help you out.</p>
| <p>My project Super OSD fits on a PCB with dimensions of approximately 40mm x 70mm. It's very space constrained and I can't expand the PCB too much. How should I approach this problem? I realise it's not strictly electronics, but it is a problem many have presumably solved before. I first considered screws but I didn't find any ones small enough - I need to go as small, or smaller than 4mm diameter. I was thinking of using heatshrink to keep the module secure if screws were not an option. Any opinions?</p>
| Mounting my PCB project | 2010-12-26T23:00:41.000 |
8325 | |power|batteries| | <p>The best way is to buy cheap made-in-China Li-ion batteries and remove the upper section which shows three terminals; there you will get two terminals which you can connect in series.<br>
You can charge them individually with any mobile charger.</p>
| <p>I Am currently looking for battery suggestions for use in one of my projects. My projects current consumption (calculated) is</p>
<ul>
<li>360mA for the main rotor 2.5A stall Link (my exact part RK370SD-4045)</li>
<li>400mA for the Mbed uC</li>
<li>tail motor ? unknown specs, N30 is the only part reference</li>
<li>3x servos <a href="http://www.e-fliterc.com/Products/Default.aspx?ProdID=EFLRS75">Link</a> unknown mA </li>
<li>sensor 100mA or less</li>
</ul>
<p>Voltage has to be 7.2V to 12V</p>
<p>What I would like to know is what are the pros and cons of each battery? This <a href="http://batteryuniversity.com/learn/article/whats_the_best_battery">link</a> gives some great info but i want real world recommendations and things I should look out for and any other pertinent information when selecting my new battery.</p>
<p>Currently I have looked for batteries and have come to this conclusion, Lead Acid batteries are not a choice in this project, which leaves me with Li-ion batteries, Li-Po, Nimh, NiCd. The original battery was a 9.6V 650mAh Nimh battery and the helicopter had about 20 mins of flight time with the original equipment.</p>
| What type of battery to use? | 2010-12-27T08:43:49.423 |
8327 | |power|voltage-regulator| | <p>A UBEC (Ultimate Battery Elimination Circuit) is basically a step-down voltage regulator. I feel that the jargon deserves a bit of explanation and history, so here goes:</p>
<p>In hobbyist grade remote control cars/planes/boats/etc. the electronics (receiver, speed controller, servos) need a power source. With engine powered craft, a small 6V battery pack was used to power the electronics. When electric motors became more popular, people wanted to use the large motor battery packs to power the low-power electronics. Typically, the electronic speed controller absorbed this function, and it became known as a Battery Elimination Circuit (BEC). With battery packs usually in the 9V-11V range, the electronics would probably need 5-6V to be happy. </p>
<p>Evidently there has been a push to use higher voltage battery packs (10V-25V), probably to take advantage of the brush-less motors. As a result, if the servos draw any appreciable current, a linear regulator would burn a lot of power. Obviously, when your flight/driving time is based on how efficiently you use your battery, a linear regulator is not what you want. Ultimate Battery Elimination Circuits are basically separate regulators (usually switch-mode) that deliver 5V-6V at hopefully high efficiency.</p>
<p>Now for the comparison. Your parts basically have two different end-use requirements. The Dimension Engineering product tries to match the form factor of a common linear regulator (7805). It would probably integrate better with any finished PCB you would make, and has a metal shell which hopefully shields EMI. The Hobbywing regulator is a more cost-conscious physical design, with a bit better efficiency spec. Honestly they're pretty much the same thing, so you could probably go with the cheaper one (Hobbywing).</p>
| <p>I want to regulate the voltage from a battery down to 5v to power an Arduino and a Wi-Fi webcam. I’m not too keen on a linear regulator as a lot of power is wasted, so that’s led me to look at switching regulators. I’ve also stumbled on UBECs, which seem to do a similar thing.</p>
<p>The two components I am looking at are these:</p>
<ul>
<li><a href="http://www.technobotsonline.com/switching-5v-regulator-1a.html" rel="noreferrer">Dimension Engineering Switching 5V Regulator 1A</a></li>
<li><a href="http://www.giantcod.co.uk/hobbywing-3amp-ubec-p-402342.html" rel="noreferrer">Hobbywing 3amp UBEC</a></li>
</ul>
<p>What's the main difference between these? Is either one more suitable for my purposes? My load will be under 1A.</p>
| What's the difference between a "Switching Regulator" and a "UBEC" | 2010-12-27T10:45:50.427 |
8337 | |power| | <p><img src="https://i.stack.imgur.com/uQKpb.jpg" alt="alt text"></p>
| <p>I found a website recently about harvesting energy from the air, and I am wondering if someone could tell me why the following wouldn't work?</p>
<p>Their "generator" is supposed to make electricity from the ionosphere (not UV, X-Ray, etc). Some claim it can knock out your electric bill totally (a bigger version, not this example). From what I understand, this is possible (it was discovered by Nikola Tesla), however this diagram doesn't look like it would work. Any help would be appreciated.</p>
<p><strong>An example from the website:</strong></p>
<p>You need:</p>
<ul>
<li>(4) 1N34 germanium diodes</li>
<li>(2) 100 µF 50 V electrolytic capacitors</li>
<li>0.2 µF 50 V ceramic capacitors</li>
</ul>
<p>Here is the electrical diagram they provide:</p>
<p><img src="https://i.stack.imgur.com/21Q4R.png" alt="Diagram of generator"></p>
<p>And they claimed to power a cell phone with it. I am not sure what kind of antenna to use.</p>
<p>While this seems like a sham, I just found this website recently and am looking for more info on the physics behind it.</p>
<p>Perhaps Teslo's patent explains things better, so here it is: <a href="https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B6Qd42rbY4FvYTdlN2E2MDctN2VhZi00YWYxLThkNTQtMzhiMzllY2E2ODk5&hl=en" rel="nofollow noreferrer">Patent 685958.pdf</a></p>
<p><strong>Found something:</strong> Here is a page that explains it.
<a href="http://www.nuenergy.org/alt/tesla_energy.htm" rel="nofollow noreferrer">Nikola Tesla free energy: unraveling Greatest Secret</a></p>
| Can you harvest electrical energy from the air? | 2010-12-27T16:18:31.113 |
8345 | |batteries|wire|resistance| | <p>You have to <em>make</em> that it's not too high. Work backwards from the receiver's specifications and see what cable the system can afford. You need to know the minimum operating voltage of the receiver, as well as its maximum current.</p>
<p>The AA batteries are probably not a good idea. Rechargeables like NiMH have a low 1.2 V rating, so you don't want to get that even lower. Alkaline cell energy is around a 1000 times more expensive than electricity from the wall. Use a 3 V wall wart instead, and you won't have to worry about sagging voltage. </p>
<p>Say the receiver's minimum operating voltage is 2.7 V, and that it uses maximum 100 mA. Then this 100 mA may drop maximum 300 mV (provided the wall wart effectively outputs 3.0 V). Ohm's Law says a maximum wire resistance of 3 \$\Omega\$ is allowed. </p>
<p>Copper has a resistivity of 16.8 m\$\Omega\$ \$\cdot\$ mm\$^2\$ / m, and we have 20 m to and fro, that's 336 m\$\Omega\$ \$\cdot\$ mm\$^2\$, then a cross section of (336 m\$\Omega\$ / 3 \$\Omega\$) \$\cdot\$ mm\$^2\$ = 0.112 mm\$^2\$ is the minimum required. That's bit less than <strong>0.4 mm diameter</strong>. That's all non-USAers need to know. USAmericans still have to <a href="http://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes" rel="nofollow">lookup in a table</a> what AWG value this is, or calculate it (involves a couple of logarithms). </p>
<p>Everything in one formula: </p>
<p>\$ d = 2 \sqrt{\dfrac{2 L \cdot I \cdot 16.8 m\Omega \text{ } mm^2 / m}{\pi \Delta V}} \$</p>
<p>where</p>
<p>\$ d \$ = minimum wire diameter<br>
\$ L \$ = cable length<br>
\$ I \$ = maximum current<br>
\$ \Delta V \$ = maximum allowed voltage drop.</p>
| <p>I have a wireless security system at home, and the wireless node is too far from the receiver. I was thinking that I could splice about 10 extra meters of wire into the existing line to move the node close enough to the receiver.</p>
<p>From my university days, I remember the I = V / R equation, meaning that with a fixed voltage (from the two AA batteries), if I increase the resistance, the current that gets through will be smaller - possibly not enough to power the wireless node.</p>
<p><strong>How do I determine the resistance of the wire? Is there a standard calculation I can use?</strong></p>
<p>I haven't picked up the wire yet, so I can use another type of wire and a small gauge if that would help.</p>
| is the resistance in ten meters of copper wire too high to use in a circuit powered by AA batteries? | 2010-12-27T18:37:19.517 |
8355 | |resistors|current|function-generator| | <p>This comes down to a simple i=v/r. There are 2 things you will most likely need to worry about assuming you aren't at very high frequencies:</p>
<ol>
<li>What is the max current your function generator can output?</li>
<li>Is your load frequency dependent.</li>
</ol>
<p>For point 1, you just need to check to see if you are hitting a current limit.</p>
<p>For point 2, if your circuit is frequency dependent (has capacitance and/or inductance) then with a fixed voltage, the magnitude of your resistance, and thus your current, will change with frequency.</p>
| <p>I couldn't find an equation for this on Google/Wikipedia, but does the frequency of a function generator (we'll say that it's a sine wave) impact the current output. Example, if I had a 5 volt source and applied it to a 10 ohm load at 50Hz what would be the current seen by the load?</p>
<p>Thanks,</p>
| Calculate Current out of Function Generator | 2010-12-27T21:20:48.743 |
8365 | |arm| | <p>As to why the board will cost 200 USD + when the chip is only 15 USD I can give you an answer: You need to check out the other required components:
* OMAP: Alright, you'll certainly need that, but how can I power it?
* PMIC: Power Management IC, alright, now I have my required 4 voltages, now for some memory
* SDRAM: Depending on what you will need, you need an appropriate amount of SDRAM
* NAND flash: Definitely you want some non-volatile memory
* SD card: Maybe some exchangeable memory
* Connectors: Count in the cost for connectors for USB, LAN, eventually you want WLAN Bluetooth or GPS</p>
<p>Alright, now you have the components, but where do you put them on. Designing such a system usually leads to 10 or 12 layer PCBs, eventually including micro-vias, which are not cheap themselves.</p>
<p>Finally, add testing and bring-up of the board, account for a few prototypes before the production can actually start and you have your USD 200 :)</p>
| <p>Where can one find information on how to put together a minimal linux bootable board based on the cortex A family (like the beagleboard)? Programming information is plentyfull, but hardware knowledge appear more arcane. I'm especially curious about:</p>
<ul>
<li>What external components are needed and why.</li>
<li>Why dev boards seems to end up around 200$, even though I could get an omap3517 for 15$?</li>
<li>What kind of equipment is needed to create prototypes around a chip such as the omap3517?</li>
</ul>
| Beginning arm cortex Ax hardware development | 2010-12-28T00:29:33.237 |
8374 | |infrared|motion|laser|range-detector| | <p>Your requirements:</p>
<ul>
<li><strong>line-of-sight activation</strong>: this means focusing lenses & apertures for LEDs, or a laser.</li>
<li><strong>self-contained unit</strong>: this means it must register a reflection from a variety of surfaces.</li>
<li><strong>low power</strong>: doesn't really limit implementations, but puts some design constraints on them.</li>
</ul>
<p>There are two options:</p>
<ol>
<li><strong>Infrared emitter and detector package</strong>, like the <a href="http://www.ladyada.net/media/sensors/PNA4602.pdf" rel="nofollow noreferrer">one linked</a> in <a href="https://electronics.stackexchange.com/questions/8374/best-way-of-making-a-trip-wire-type-device/8395#8395">Matt's answer</a>, but with a <a href="http://www.dialight.com/Assets/Brochures_And_Catalogs/Illumination/MDEXLUMADBOGD.pdf" rel="nofollow noreferrer">focusing lens</a> or aperture or a small viewing angle.
<ul>
<li>Focusing lens, aperture, or small viewing angle is required to maintain directionality.</li>
<li>Focusing lens or aperture would be a pain in the butt, and could only be tuned for certain distance ranges.</li>
<li>Viewing angles as low as 6<sup>o</sup> are available. Geometry will tell you what kind of directionality this gives you at a distance. <br><br></li>
</ul></li>
<li><strong>Laser and photodiode</strong>: Lasers are available with focusing lens and aperture <a href="http://www.dealextreme.com/details.dx/sku.13378" rel="nofollow noreferrer">for less than $5 each</a>; photodiodes are <a href="http://ca.mouser.com/ProductDetail/TAOS/TSL252R-LF/?qs=sGAEpiMZZMtWNtIk7yMEscFVjdrg3sSauchWfwSrPGg%3d" rel="nofollow noreferrer">about the same</a>. I would use a visible one to make aiming it easier (but require bandpass filtering around carrier frequency to filter out ambient), but it's up to you: there are IR and <sup>(expensive!)</sup> UV laser diodes. It may take a bit of experimentation to develop an algorithm that filters out ambient effectively and detects weak reflections. <a href="http://www.lucidscience.com/pro-laser%20spy%20device-1.aspx" rel="nofollow noreferrer">This guy</a> did something like it. Note that some surfaces will simply gobble up a visible beam (eg. flat black).</li>
</ol>
<p>For <strong>low power operation</strong>, use sleep modes, pull-up PMOS FETs for <em>always-on</em> devices, including voltage divider branches (stop current drain when controller is <em>off</em>), and activate the sensor intermittently. It doesn't sound like it needs to capture any fast single-shot events; going with 20km/h and 10cm objects, a 0<sup>o</sup> (perfect line) detector would get <strong>18ms</strong> to react, or just over 55Hz. You could wake-up every 10-15ms, check the <em>line-of-sight</em> a few times, then go back to sleep. With a switching (or <a href="https://electronics.stackexchange.com/questions/8112/how-do-i-convert-9-v-dc-to-5-v/8118#8118">no</a>) regulator and some intelligent power budgeting in the design phase, you'll easily get this to run for days on AAs.</p>
| <p>I'm wanting to make a type of electronic "trip wire". </p>
<p>My basic idea is to have like a laser and basically when the laser is interrupted then it sends some signal to a microprocessor. </p>
<p>I'm not tied to a laser but it was the first thing that comes to mind. The attributes it needs to have is it needs to be only like a "wire"(as in, it doesn't detect motion anywhere but head on) and it needs to be low power(like run for a few days at least off of 2 AAs). Also, an actual wire is out of the question because it needs to be capable of being "reset" after a certain time out(of say 1 second or so) The range it needs to work with is only 5 or 10 feet though. Also, it's not possible to have two parts to this device like a typical laser-photodiode setup. This needs to be contained all in one (preferably small) package. </p>
<p>What is my best bet with this? I was thinking maybe super-sonic sound like <a href="http://www.sparkfun.com/products/639">this</a> but I think there would probably be a better way. </p>
<p>So basically what I have in mind for the device is like when you first set it up, you "calibrate" it for a certain distance. So for instance if there is a wall five feet in front of it, then this device would work if there was anything that came head-on with it in 5 feet. And etc. </p>
| Best way of making a trip-wire type device? | 2010-12-28T06:18:05.367 |
8376 | |signal|tv| | <p>Almost any FPGA evaluation board of the last 6 years vintage will give you an ability to generate clock signals of varied frequency using PLL multipliers and dividers; they probably have too much jitter for radio transmission carrier frequencies, but are fine for modulation. And you can make actual test pictures using the fpga logic. A resistive ladder DAC, or just a few resistors from various outputs to give you two video levels and a sync pulse can be used. You will want to take the input impedance of the video transmitter (probably 75 ohms, but you can test it by making a resistive divider with it as the lower leg) into account when designing these. </p>
<p>Since you have a scope available, you may do better to use that to measure the voltage for various modulation frequencies and plot a transfer function rather than to rely on a test that also depends on the bandwidth of your display (which if LCD is going to be sampled and then pixelated itself). </p>
<p>You may well have a video audio gain control to contend with, so you might want to make a circuit which generates a few cycles of a reference wave at low frequency (say 500 KHz or 1 MHz) and then skips up to a test frequency you control with DIP switches on the board, and outputs that for a half line of video or so, and then goes back to the low frequency. What you will do is measure the amplitude of the high frequency signal in comparison to that of the low frequency reference, which is there to set the AGC level. Doing this with square waves you will probably see a rounded off leading edge of the pulses, but the low frequency one will get to a flat top. The high frequency one will at some frequency never get beyond the rounded portion, and then start not even completing the rise.</p>
<p>If your scope has good measurement cursors, you might also simply be able to measure the rise time of the low frequency square wave until it reaches its full excursion, and calculate the bandwidth from that. </p>
| <p>I need to test the bandwidth of a variety of video transmitters to figure out the maximum resolution I can safely output without losing detail. To this end, I came up with a solution using a TV pattern generator to generate a proper PAL or NTSC video signal with colour bars or with just blackness, and a 10 MHz signal generator, to generate a pixel clock. However, the 10 MHz signal generator is too expensive for a student like me - about £300 here. The TV pattern generator is only £75, which I can afford. I need a way to generate an adjustable square wave signal from 5 MHz to about 12 MHz, synchronised with a video signal. The frequency doesn't have to be precise, because I can verify it with an oscilloscope. I just need to see the point at which a typical video TX can handle no more pixels, because I have the opportunity to make a high resolution on screen display - but it doesn't matter if no-one can see the pixels!</p>
| Testing a video transmitter for video bandwidth | 2010-12-28T10:35:47.083 |
8387 | |operational-amplifier| | <p>Your first image has an implicit positive and negative power supply, which allows the output to swing above and below the reference voltage (ground). If you assume an ideal op-amp (usually reasonable for these circuits), then the inverting output is a virtual ground - it is driven to the same voltage as the non-inverting input. The current through the feedback resistor (Rf) must be equal to the sum of the currents flowing through the input resistors (R0, R1, Rn...).</p>
<blockquote>
<p>\$ \dfrac{V_0 - V_{ref}}{R_0} + \dfrac{V_1 - V_{ref}}{R_1} + \dfrac{V_2 - V_{ref}}{R_2} = \dfrac{V_{ref} - V_{out}}{R_f} \$</p>
</blockquote>
<p>To make the math easy, lets make Rin=R0=R1=R2. The output voltage becomes:</p>
<blockquote>
<p>\$ V_{out} = \dfrac{-R_f (V_0 + V_1 + V_2 - 3 \cdot V_{ref})}{R_{in}} + V_{ref} \$</p>
</blockquote>
<p>In the first example, Vref=Ground=0V, which simplifies the equations a bit. If (V0+V1+V2) > 0, then Vout will be negative. If Vout can't be negative, due to a lack of a negative rail or negative voltage headroom, then the circuit stops functioning as intended.</p>
<p>Nothing explicity requires you to have a negative rail, and single-supply operation is usually desirable for its simplicity. In order to get the expected signal swing, you need to set Vref to some value between VDD and Ground. A pair of resistors acting as a voltage divider will work, or a poteniometer would allow you to adjust the reference voltage.</p>
<p>In the context of <a href="https://electronics.stackexchange.com/q/3105/638">this question</a>, the object was to measure voltages that were always below your ground reference, without having a negative power supply. In that case, a reference voltage of 0 would be OK because the output voltage would never need to swing below the negative rail.</p>
| <p>Reading questions on converting negative voltages to positive ones it has left me with a question that I can't seem to work out. The circuit looks like this:<br>
<img src="https://i.stack.imgur.com/8LbjM.gif" alt="Op Amp Adder"></p>
<p>But you only have the one going to the inverting input. My question is: </p>
<blockquote>
<p>When inputting a positive voltage it doesn't change/very slightly change. So do you have to implement something else for when the voltage is positive? </p>
</blockquote>
<p>EDIT:
Image borrowed from Kortuk's answer <a href="https://electronics.stackexchange.com/questions/3105/how-do-i-measure-a-negative-voltage-with-a-adc/3109#3109">here</a> </p>
<pre><code> R
___
.------|___|----.
| |
| |
| |
| VCC |
| + |
R | | |
___ | |\| |
Input -|___|----------o-------|-\ | Output
| >----o----
.------|+/
| |/|
| |
=== ===
GND GND
</code></pre>
| Op amp Adder circuit and positive voltages | 2010-12-28T21:21:41.943 |
8402 | |power|power-supply|usb| | <p>The <a href="http://www.usb.org/developers/docs/usb_20_081810.zip" rel="nofollow">USB spec</a> allows any device to draw 100mA from a port. No communication with the host is required. </p>
<p>However, 500mA is available by communicating with the host unless you're plugged into an unpowered hub. Many computers allow you to draw this 500mA without properly requesting it. </p>
<p>If this is a personal project, put a 10 ohm power resistor across the terminals of your USB port and see how much the voltage drops. If it works, you're golden. Just remember that it might not work if you plug it into a different computer.</p>
<p>If this is something you want to distribute, you'll have to tell the host that you want 500mA. If you don't have a micro on the project that can handle this task, the easiest way to do this is to put the cheapest USB hub controller IC you can find on the board, and configure it to do the communication. The TI TUSB2036 is about $3, and just requires you to pull a pin high (Or low, I can't remember) to get the 500mA.</p>
<p>I think you'll want the 500mA to get a decent audio volume. I don't know about the 50 ohm speaker you have, but in general, your power is limited to Vrms^2/R. A pair of 50 ohm speakers operating from 0V to 5V will draw .125W (assuming 100% efficiency). That's hardly better than the stock speakers. Four 8-ohm speakers will bring you up to a more respectable 1.5W of power, which is well under your 2.5W allowable power from the USB port. </p>
<p>If you're operating on a device which has a FireWire (IEEE 1394) port, you might consider using that as it has much more power available (Up to tens of amps, but possibly less. <a href="http://support.apple.com/kb/HT2952" rel="nofollow">Apple products</a> guarantee that there's a minimum of 7W available, but the spec allows for as much as 45W of power to be delivered. </p>
| <p>I'm trying to build a stereo speaker system for use on a laptop. I want to keep it as simple as possible, so I'm thinking of using laptop's audio output to for the audio signal and a USB port for power.</p>
<p>As far as I know, each port should be able to provide 100 mA for devices. Is there any need to signal to the computer that I'm going to try to draw 100 mA, or is it acceptable to just connect the device?</p>
<p>Also, how stabilized and filtered is USB power? I'm thinking of using <a href="http://www.quasarelectronics.com/kit-files/datasheets/tda7053a.pdf" rel="nofollow">TDA7053A</a> to drive the speakers and its minimum voltage is 4.5 V. If that doesn't work, I'd use two <a href="http://kitsrus.com/projects/tda7052.pdf" rel="nofollow">TDA7052</a> amplifiers, but I'd like to keep number of parts as low as possible.</p>
<p>As for power consumption, I already have a small radio which uses one 50 Ω speaker and a TDA7052 and it uses at most 25 mA, so even with two of those speakers, I should have lots of power to spare with a maximum supply current of 100 mA.</p>
| What's needed to get 100 mA from a USB port? | 2010-12-29T13:54:21.740 |
8405 | |power|rf|noise|wall-wart| | <p>Simple, cheap and most cleanest solution:</p>
<p>Use lm7805/LM2941/LP2985/ any other linear regulator, low-drop are better.</p>
<p>There are many ultra low drop LDO that even don't need to adjust source voltage if it is already 5.2-5.3v.
In other case adjust voltage to 5.5-7v according to linear regulator requirements.
To adjust voltage change zener inside AC-DC circuit.</p>
<p>Most of cheap "power usb adapter"s from China can be converted in this way.</p>
| <p><strong>Assumption:</strong> I <em>think</em> it's generally true that commercially available AC/DC wall-worts can be expected to be pretty noisy (e.g. you can't count on much better than 5% stability).</p>
<p><strong>Background:</strong> I'm dorking around with an RF application right now, and I hypothesize that some significant subset of my headaches is coming from powering my RF receiver with 5VDC coming directly from an AC/DC wall-wart (i.e. no RF choke, no regulator, nothing).</p>
<p><strong>Question:</strong> What's the simplest way (e.g. fewest parts) and cheapest mechanism for converting the "angry" 5VDC off a wall-wort into a "happy" 5VDC for my RF receiver? I think the other subsystems are more tolerant to noisy power. </p>
<p><strong>Aside:</strong> I wish I could give more definitive characterization of the noise coming out of the wall-wart, but sadly I am sans o-scope.</p>
<p><strong>Edit1:</strong> In response to the request for more detail on parts being used:</p>
<ul>
<li><a href="http://www.powerconversion.com/assets/dch3_ds_1222495015.pdf" rel="noreferrer">Wall-Wart</a></li>
<li><a href="http://www.sparkfun.com/datasheets/Wireless/General/MO-RXLC-A%20data%20sheet.pdf" rel="noreferrer">RF Receiver</a></li>
</ul>
| Advice on cleaning up 5VDC from a wall-wart | 2010-12-29T15:19:37.840 |
8406 | |i2c|atmega| | <p><strong>Theoretically</strong></p>
<p>I2C and SMBUS are essentially compatible as long as you are operating at 100kHz bus speed. The datasheet on page 15 (7.4.3.1.1) suggests to read a register you (as a master) have to do:</p>
<pre><code>Start
SLA+W (slave acks)
Command (slave acks)
Repeated Start
SLA+R (slave acks)
READ data byte low (you ack)
READ data byte high (you ack)
READ PEC (you ack)
STOP
</code></pre>
<p>The appropriate SLA is 0x5A. Just like with I2C, you will need pullup resistors on the SCK and SDA lines (3.3kOhm should be fine). Command value will depend on what you are trying to do as described on page 16 (7.4.6).</p>
<p><strong>Reality (?)</strong></p>
<p>However, there is a paragraph (7.4.1) on page 13 that says:</p>
<blockquote>
<p>In order to provide access to any
device or to assign an address to a SD
before it is connected to the bus
system, the communication must start
with zero SA followed by low RWB bit.
<strong>When this command is sent from the MD,
the MLX90614 will always respond and
will ignore the internal chip code
information.</strong></p>
</blockquote>
<p>... now that is a vague description of a specialization of the protocol at best, but it appears to be what the github code is exploiting.</p>
<p>If one is to believe the github code, it is actually illustrating an undocumented protocol behavior. Namely:</p>
<pre><code>START
SLA(0)+W (slave acks)
Command(7) (slave acks) (writes to the RAM read-address register the value 7 = TOBJ1?)
STOP
START
SLA(0)+R (slave acks)
READ low byte (master acks)
READ high byte (master acks)
READ pec (master nacks)
STOP
</code></pre>
<p>I've seen this "flavor" of I2C interaction before, but I'm with you that it's not described that way in the datasheet.</p>
<p><strong>Sidenote on PEC</strong></p>
<p>As for "how you generate the PEC" it's described on page 14 at the bottom of the page:</p>
<blockquote>
<p>The PEC calculation includes all bits
except the START, REPEATED START,
STOP, ACK, and NACK bits. The PEC is a
CRC-8 with polynomial X8+X2+X1+1. The
Most Significant Bit of every byte is
transferred first.</p>
</blockquote>
<p>Basically it's CRC-8-CCITT (see <a href="http://en.wikipedia.org/wiki/Cyclic_redundancy_check" rel="nofollow">wikipedia</a>) - implementations exist, just google for it, or post a separate question about CRC...</p>
| <p>I am trying to use a Melexis <a href="http://www.melexis.com/Infrared-Thermometer-Sensors/Infrared-Thermometer-Sensors/MLX90614-615.aspx" rel="nofollow">MLX90614</a> with Atmega8. I have failed in all my attempts till now. I tried sending this sequence </p>
<pre><code>slave address(as 0x00 and 0x5A) --> opcode to read SMBus address
--> data byte high --> data byte low
</code></pre>
<p>I get a slave address NACK for both SMBus addresses. Is it because I am using an I2C library? I understand we have to give a PEC also, but as the Slave address is NACK'd I don't think the sensor is responding to my commands. I tried using the write opcode and got ACK's for that. So the communication is ok. Can anyone tell me what kind of problem may be here?</p>
<p>Also how would one generate a PEC for SMBus protocol?</p>
<p>I looked at <a href="https://github.com/a1ronzo/SparkFun-IR-Evaluation-Board/blob/master/IR_eval/main.c" rel="nofollow">this code</a> and it just sends 0x00 and 0x07 over i2c to fetch two bytes of temperature. How can that be possible? In the datasheet it is specifically mentioned how to read one word and how to write one word. How can this be bypassed?</p>
| Using MLX90614 OR is I2C and SMBus compatible? | 2010-12-29T15:38:46.990 |
8409 | |relay| | <p>If money is no object, then the first thing I go to is a solid state relay (SSR), instead of the mechanical switch variety. I've had to switch 120VAC with a DC control voltage many times in the past, and I've alwyas started with Crydom SSRs. SSRs make interfacing with AC voltage really, really simple. Crydom has <a href="http://www.alliedelec.com/Search/SearchResults.aspx?N=0&Ntk=Primary&Ntt=Crydom&gclid=CL3GjvyQlKYCFQYnbAodVC_goQ" rel="nofollow">several models</a> that can switch 230VAC.</p>
<p>That said, everything I have used them in is for prototype and R&D automation. It would be interesting to hear how others here feel about it.</p>
| <p><br>
I am thinking of starting a project where I will need to interface a microcontroller output and mains for a lighting system. My question is about relays. I have found this <a href="http://www.rapidonline.com/netalogue/specs/60-2008.pdf">one</a>. And I am wondering will it be ok to put 230v through the switch of the relay? Also what am I looking for in the data sheet to tell me what is the maximum voltage that the switch will take?</p>
| Interfacing microcontroller and mains via a relay | 2010-12-29T16:39:15.510 |
8418 | |pcb|current| | <p>I remember having seen this nomogram in <a href="https://electronics.stackexchange.com/a/5405/4950">another answer</a>: </p>
<p><img src="https://i.stack.imgur.com/Yyekj.png" alt="enter image description here"></p>
<p>Select 2.5A on the vertical axis of the top graph. Move to the line indicating the allowed temperature rise. Move downward to the PCB's copper thickness in the bottom graph. This intersection gives you the required width on the vertical axis.</p>
| <p>I need a trace on my PCB to carry up to 2.5 amps (average) current, with 5-6 amp spikes (it's going to a switch mode power supply.) How wide should the traces be? I've got a trade off between reliability and size, as the product is space constrained. Any tips would be appreciated. </p>
| Sizing a trace on a PCB to carry 2.5 amps | 2010-12-30T03:53:52.817 |
8421 | |light|flash| | <p>I was able to achieve a rapidly flashing fluorescent light during a stage talent show using a light dimmer. You can buy one that goes in a wall socket if that's what you need. At around 35% - 40% power there will be a certain moment where it just flashes extremely fast, any % other than that it will just emit less or more light, depending on the %.</p>
<p>This is actually not very safe and I don't have any idea what long-term impact it may have on the ballast or the actual tube, but for me, it worked.</p>
| <p>Is it possible to build a circuit to make a fluorescent tube flash on and off for use as a lighting effect? If so, how?</p>
<p>Also, if the above is possible, can it be used to flash more than one tube at a time without having to repeat the control circuitry for each tube?</p>
| Flash a fluorescent tube | 2010-12-30T09:29:30.277 |
8425 | |power|sd| | <p>In addition to the other answers:
Newer cards might support flushing the cache of the SD card and/or signalizing to the SD card that the host wants to power off. This is described in Part 1 of the Physical Layer Simplified Specification <a href="https://www.sdcard.org/downloads/pls/" rel="nofollow noreferrer">SD Card Specification</a> (V8.00):</p>
<p>Chapter "4.17 Cache"/"5.8.2 Performance Enhancement Function" and "5.8.1. Power Management Function" ("Power Off Notification").</p>
<p>However, as far as I know, these functions are not supported in SPI mode, which is probably what you use. :(</p>
| <p>I am working on a device that uses the Microchip MDDFS library to store data to an SD card. The logger will log data at a maximum rate of 1 entry (56bytes) every minute. The problem is the device may lose power at any time, potentially in the middle of a write sequence. I am wondering what is the best way to protect my data against corruption. I have found that if the file is open when the power is lost, all data that was written to the file after the last file-close is lost. I don't know if the same holds true if power is lost in the middle of the write sequence. </p>
<p>Since the write procedure doesn't happen very frequently I could open the file, write the data, and then close the file, every time data is logged. Would this approach damage the sd card over time? </p>
<p>Another approach could be to keep the file open but after every 10 or 50 writes I could close the file and then re-open it.</p>
<p>I could also buffer data in memory, then flush the data occasionally maybe after a kbyte or so. </p>
<p>The last idea I had was, in my circuit, I could add a large capacitor that would provide power to my pic/sd card long enough after the power is disconnected to quickly close the file. The problem with this approach is that the time it takes to close the file and/or save data is very inconsistent. From my understanding, this time can very depending on the current place in a flash page that the file is in.</p>
<p>Anyways, what would you guys suggest?</p>
| How do I protect SD card against unexpected power failures? | 2010-12-30T12:58:28.793 |
8427 | |storage|workbench| | <p>I cut PVC pipe that is 1/2" to 3" width into lengths from 4" to 12". I take each electrical cord and put the two ends together, then fold the remaining loop in half as many times as the PVC pipe in which they are to be placed will allow (once or twice). This way, I see both ends, and the cords which are inside the PVC pipes never become tangled. You can stack the PVC pipes and mark them as to their length, if need be.</p>
<p>If I have a really long cord, I use a wider PVC pipe and thread one end of the cord through the middle and then back through the outside, over and over again until the cord becomes short enough to use easily, unwinding however much cord is needed for any specific job at hand. The cord ends are, in this case, at opposite ends of the PVC pipe.</p>
| <p>One thing that it seems I have many of are cords and connector/patch cables.</p>
<p>I don't want to throw out all of them, but am looking for useful storage tips?</p>
<p>Most are under 6 foot / 2 metres long, they are the usual assortment of TV cable, stereo-cable, serial cable, ethernet, 12-volt power, etc.</p>
<p>Looking for some way to store them efficiently, while I can still see both ends. Coiling is a possibility, but then there's just a stack of circles that I have to dig through.</p>
<p>Ideally, some sort of hanging method, that has them semi-secur, but still accessable/visible.</p>
<p>How do you store all those cables? (and hope this is Electronics-enough!)</p>
| How to store all those spare cables and connector cords? | 2010-12-30T14:25:54.503 |
8428 | |microcontroller|serial|uart|ftdi|reverse-engineering| | <p>This may be a time when scrounging the resources to buy an inexpensive USB-based logic analyzer is the right answer. I recently acquired a <a href="http://www.usbee.com/sx.html" rel="nofollow">USBee SX</a> and have been very pleased. Out of the box, it can decode serial on multiple (TTL level only) lines, and keep it all synchronized to well better than single bit time.</p>
<p>It has no internal RAM, so it pushes all the data it samples up the USB. That has a couple of advantages, and at least one disadvantage. A big advantage is price. There's hardly anything inside the USBee SX between your signals and the USB, so it doesn't have to cost many arms and legs. The biggest advantage is capture depth. You are limited only by the storage on the PC. If you need a one hour capture to catch an elusive timing window bug, it can do that.</p>
<p>A disadvantage is that the top sample rate is limited so that all sample can be fed up the USB. This makes it less useful for high-end digital logic, but for serial communications protocols that really isn't a big deal.</p>
<p>The SX lists for about US$170. At that price it doesn't have to save your company very many hours to pay off....</p>
<p>It certainly isn't the only example of the breed, but it is the only one I've personally used.</p>
| <p>First this is the setup:
<img src="https://i.stack.imgur.com/81rsE.png" alt="Two serial devices talking to each other, plus two FT232RL with Rx pins connected to each device's Tx lines">
(please note that one of the grounds is not connected, both FTDIs working properly)</p>
<p>Now, I have used PuTTY to look at these two serial streams, both exchanging data at 9600 bauds, but my problem is logging the activity time-wise.</p>
<p>I've also tried some serial monitors that I found on the tubes, but the time resolution is in seconds.</p>
<p><strong>Is there a tool for monitoring these two streams at the same time?</strong> If there is not, I should program one myself in Processing (it will take less time in this language I suppose).</p>
<p>PS: the ultimate goal of this is to replace the remote device (an actual wired remote) with a little MCU like the ATtiny85 or ATtiny2313 with a simulated input.</p>
<p>PS2: I only have these two FTDIs, an analog oscilloscope and a multimeter.</p>
| Monitoring two serial lines at the same time | 2010-12-30T14:41:07.950 |
8440 | |fuse-bits| | <p>It's an irreversible part of the chip which is "burnt" out (without causing damage to the rest of the chip) and is usually a single configuration bit. The bit (and subsequent bits) might control something like software version, or whether the Xbox supports 1080p, or whether you can play certain region discs... Pretty much anything you can imagine. Like a one time programmable read only memory. They are a concern because it effectively allows a manufacturer to obsolete a product remotely without any consent from the owner.</p>
<p>That's the paranoid view, anyway. </p>
| <p>I heard in a recent presentation that the XBox 360 uses an <strong>eFuse</strong> to prevent users from reverting back to prior boot/firmware image. What is an eFuse and how do they work?</p>
| What is an eFuse | 2010-12-30T18:39:04.110 |
8462 | |audio|operational-amplifier| | <p>TI has <a href="http://focus.ti.com/en/download/aap/selectiontools/audio/tool.htm" rel="nofollow">this tool to help you choose one</a> and has a <a href="http://focus.ti.com/lit/sl/slyy013e/slyy013e.pdf" rel="nofollow">selector guide</a>. And as pointed out by @Fizz, this isn't special for TI.</p>
| <p>I understand that the <a href="http://www.onsemi.com/pub_link/Collateral/NE5532-D.PDF">NE5532</a> is an evergreen in audio applications. Which other op-amps would you consider for preamp, filter and other high fidelity audio applications?</p>
| Which op-amp for audio? | 2010-12-31T14:12:53.727 |
8464 | |fpga| | <p>It's true that the power estimation tools made by the vendors are the best tool to get information.</p>
<p>However, to get a feelinig, A "full" Altera Cyclone 3 I have recently encountered uses something like 0.8 A on the 1.2 V rail and not much (1...50 mA) on its 3.3 V and 2.5 V rails. It totals to a bit more than 1 W when running.</p>
<p>Since the 3.3 V rail is pretty much just used for the IOs, the FPGA will draw whatever the connected circuitry requires from this supply rail.</p>
| <p>I'm in the R&D stages of a V4 of my project, which may replace the high-speed DSP with an FPGA.</p>
<p>I was looking at this FPGA, because it is cheap: XC3S50A (about £6.50/each.) I think I can probably fit the project onto there, with one concern. I can't find anywhere in the datasheet about how much current it will consume. Is it a fixed amount, or does it vary, depending on how much logic I am using? Is there a quiescent current draw by it, when no logic is in use? What about the current draw by its clocks/PLLs? I've looked through the datasheet - it has many characteristics, but these ones in particular don't seem to be mentioned.</p>
| How much current does an FPGA consume, anyway? | 2010-12-31T15:05:18.707 |
8469 | |fpga| | <p>An FPGA is really not the right device to do this sort of task. There are CPUs with all the required peripherals to do the job (e.g.LPC2478) which will be cheaper and draw a ton less power.
If you want to do it with an FPGA as a learning excercise, I'd suggest you break the task down and start off By making your life easier by preprocessing the book content on a PC into a file format that is easier to display than PDF, e.g. uncompressed bitmap or run length coded bitmaps. And start off using a simple block-oriented filesystem, as doing FAT stuff on an FPGA will be quite complicated.
That way you should be able to get something working reasonably quickly, then look at doing more complex stuff like other file format etc. later. If you start off trying to do it all, there is a high chance you will spend a ton of time and have nothing working to show for it when you get bored or run out of time.
At some point you definitely will need to using be using a CPU, either external or on the FPGA. </p>
| <p>I am a newbie in FPGA world, working out on Verilog these days. I have thought of a couple of Projects for my FinalYearProject at my college. One of them is Handheld Ebook Reader. Well, I will workout the other things required, what i am most concerned about is, How am i going to read a pdf file through FPGA.</p>
<p>Well, in the project, i will be interfacing a MicroSD card module with FPGA, the FPGA would read the file from pdf and would display it on LCD, interfacing with LCD wouldnt be a big problem as i have got a couple of good resources for that, interfacing the memory card module too. But the thought that has been troubling me in choosing this project is, how am I going to read PDF. I may work on the pdf which has texts only, i wont work on images, on the other hand if i plan to work on images as well, i will have to do a lot of work for several tasks, say for zooming in and others.
Kindly help me on this.
Plus, i am pretty keen about this task. Kindly tell me if this can be done more easily with microcontroller. I have a little bit of experience working with them.</p>
| Reading PDF through FPGA | 2010-12-31T18:18:28.730 |
8480 | |arduino|spi|datasheet| | <p>That's because it's in the datasheet in hex. :-) Page 7, table 2. I'd have written the define as <code>#define OP_SHUTDOWN 0x0C</code> to be consistent with the datasheet…</p>
| <p>I Have started making my 1st PCB, as per my other question <a href="https://electronics.stackexchange.com/questions/8453/is-my-schematic-correct-max7219cng-tips-for-etching">(Located Here)</a> and have been looking at the datasheet for the <a href="http://datasheets.maxim-ic.com/en/ds/MAX7219-MAX7221.pdf" rel="nofollow noreferrer">MAX7219CNG</a> and studying the library to run it on an Arduino <a href="http://www.wayoda.org/arduino/ledcontrol/index.html" rel="nofollow noreferrer">(Located Here)</a></p>
<p>Now my question is from what I can see in the library, there is a method called spiTransfer that sends the data to the IC to turn on and off the various LEDs. This is done by shifting data containing opcode and data bits. The opcodes are at the top of the .cpp file. For example
<code>#define OP_SHUTDOWN 12</code> </p>
<p>I can't find where the related information is in the datasheet to say that 12 = Shutdown.</p>
<p>Am i reading the datasheet wrong or understanding the library wrong. I want to learn how to read a datasheet and implement code to run an IC with out relying on code written by others.</p>
<p>And guidance would be great thanks</p>
| Help understanding SPI and Arduino | 2011-01-01T12:35:19.430 |
8485 | |avr|c|avr-gcc| | <p>There are many benefits to inline functions over preprocessor macros:</p>
<ul>
<li><strong>Type checking</strong>. The compiler will complain if the arguments are of incorrect type.</li>
<li><p>No risk of <strong>multiple evaluation</strong>: macros can be dangerous when the argument is an expression, consider:</p>
<pre><code>#include <stdio.h>
#define square(n) ((n)*(n))
int main(void)
{
int x, i = 0;
while (i < 10) {
x = square(i++);
printf("%d\r\n", x);
}
return 0;
}
</code></pre></li>
<li>Can include <strong>multiple lines</strong> of code without trailing backlashes.</li>
<li>Inline functions have their <strong>own scope for variables</strong> and they can <strong>return a value</strong>.</li>
</ul>
<p>Macros can be useful e.g. when concatenating tokens into code, so as to simplify some complex declarations.</p>
<p><em>Consider macros as just a dumb text replacement functionality.</em> A good rule of thumb is to <strong>avoid function-like macros, unless there is no other viable solution</strong>.</p>
<p>It is a common misconception that inlining always equals faster code. Keep in mind, that <em>every inlined call from more than one place adds up to code size</em>. <a href="http://en.wikipedia.org/wiki/Optimization_%28computer_science%29#When_to_optimize">Premature optimization</a> is not a virtue, even when working with the constrained resources of a microcontroller.</p>
<p>GCC interprets the <code>inline</code> keyword as a mere hint. There is no guarantee thet the function will actually be inlined. To have GCC inline your function regardless of optimization level, declare the function with the <code>always_inline</code> attribute:</p>
<pre><code>void function() __attribute__((always_inline));
</code></pre>
| <p>I have been doing my first serious work of programming these days. I have been exposed to a lot of code by different developers. One thing I find confusing is how do these developers decide when to use a macro definition and when to use a inline function. Both have essentially the same function, they place a certain code at the place they are called from. So is there some logic for selection or is it just at the whimsy of the developer?</p>
<p>(I am here talking about macros for functions and not constants).</p>
| Macros V/S inline functions while programming for avr-gcc | 2011-01-01T16:31:50.133 |
8489 | |checklist| | <p>A DVT should cover everything you promise to your customer in the data sheet. Ideally, you also have made a spec long before you've written the data sheet, and the spec may even have more details than the data sheet because you don't want all the little things to be published.</p>
<p>When you do the DVT, you test each and every parameter you specified before or while you designed the gadget. It's as simple (and as much work) as this.</p>
| <p>Despite doing a Google search and finding <a href="http://www.avanthon.com/dvt_checklist.php" rel="nofollow">this from Avanthon Engineering</a> (link now dead, see <a href="https://web.archive.org/web/20060616183148/http://avanthon.com/dvt_checklist.php" rel="nofollow">archive.org</a>), I haven't found a good checklist. Theirs is more for board bring up than making sure a design really works before it goes to production. I'm thinking of checks such as</p>
<ul>
<li>Check at high/low voltage</li>
<li>Check at high/low temperature</li>
<li>Check more than one unit</li>
<li>Check signal integrity on clocks and other critical signals</li>
</ul>
<p>In this case the design is an analog one. But since I mainly do digital designs, suggestions there are welcome. I have a mental checklist, but I'm sure I could use a written one.</p>
| What should be on a DVT (Design Verification Test) checklist? | 2011-01-01T20:44:44.243 |
8490 | |wiring| | <p>Mini-Circuits has a detailed page dedicated to exactly this question, including an example photo.</p>
<p><a href="https://blog.minicircuits.com/soldering-turret-terminal-pins-on-zx-series-models/" rel="nofollow noreferrer">https://blog.minicircuits.com/soldering-turret-terminal-pins-on-zx-series-models/</a></p>
<p>Wrap the wire into position first, then solder.</p>
<p>For prototyping, you might be OK with a test hook, alligator clip, etc. (Short circuits to ground should be avoided.)</p>
<p>There are no "proper" pluggable connectors that are intended to mate with these turret terminals.</p>
<p>If you're not experienced with soldering, can you find a local friend / colleague / teacher to help you solder this joint?</p>
<p>You don't want to damage your relatively expensive Mini-Circuits amplifiers or similar modules with excessive heat or by breaking off the power pin.</p>
<p>Personally, I would use very flexible silicone-insulated wire, as it's generally just very nice, and will avoid mechanical stress on the turret pin.</p>
| <p>I'm using several pieces of equipment from Minicircuits, namely an amplifier and a bias-T. Each of them have a strange power connector - it looks like a small metal post with a disk on the top, or a bare wire that sticks out of insulation. See example image below:</p>
<p><img src="https://i.stack.imgur.com/kfJ4o.png" alt="enter image description here"></p>
<p>I'd like to find cables that properly attach to this. Any input?</p>
| What type of cable do I use to connect to the power pins on RF equipment? | 2011-01-02T03:01:21.450 |
8493 | |pins|cpu| | <p>Your question can be easily answered with a continuity tester (which most voltmeters have).
The below pinout is for an i3-540 (LGA1156). I connected one voltmeter probe to the jtag pad on the underside of the processor. Then I swept the other voltmeter probe across the top side of the processor until the voltmeter registered a continuity.</p>
<p>TOP SIDE OF PROCESSOR:</p>
<pre>
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 |
| |AL31* |BPM4 |BPM1 |BPM0 | |AL31* |TDO |TRST |PRDY |TAPPWRGD|AL31 | |
| | |BPM6 |BPM7 |AL31 | |TCK |TDI |PREQ | | | | |
| | |BPM5 |BPM3 |BPM2 |TMS | | | | | | | |
</pre>
<p>*Connected to BLCK_ITP# (useless since shorted)
AL31 refers to Vss</p>
<p>CPU IS UPSIDE DOWN
(ie Intel Made in Malaysia and S/n Upside down)</p>
<p>I will be interested if you could find the pinout for the i7 or perhaps we could reverse engineer the Intel JTAG protocol.</p>
| <p>Here is a core i7 cpu</p>
<p><img src="https://i.stack.imgur.com/PCLmp.jpg" alt="i7"></p>
<p>It has some contact pads on the top side, some grouped in 4 or 6 and two big groups.
Is there a pinout of these pads? Where are the JTAG connection pins?</p>
| What is a pinout of TOP side of Intel Core i7? | 2011-01-02T05:12:04.740 |
8496 | |layout|pcb-design| | <p>Sometimes. On the TDA89xx, the recommended layout has traces routed through the NC pins.</p>
| <p>Several ICs are manufactured in packages with more pins than it supports. For example, the LM317 in an SO8 package has 4 V<sub>OUT</sub> pins and 2 N/C <em>(no connection)</em> pins. I often want to run traces through N/C pins to ease routing, but wonder if it would make them give up the ghost. <strong><em>If it exists, what is the standard or rule by which manufacturers follow concerning the electrical characteristics of N/C pins?</strong> Or do I have to scour the datasheet / do my own testing every time?</em></p>
<p><img src="https://i.stack.imgur.com/sNEvm.png" alt="LM317 SO8 pinout"></p>
| Can I run traces through "No Connection" pins? | 2011-01-02T09:59:33.157 |
8506 | |power|video|multiplexer|ntsc| | <p>How did you get your Nintendo to display on a TV without baseband inputs? You used an <a href="http://rads.stackoverflow.com/amzn/click/B0014KKV7W" rel="nofollow">RF modulator</a>.</p>
<p>So set up an RF modulator at the camera, then the normal DC block capacitor will work.</p>
<p>It shouldn't be too hard to find an NTSC demodulator for the other end.</p>
| <p>I've got a few NTSC security cameras I'd like to set up around the perimeter of the house. They output standard NTSC video and require 12V for power. I was hoping to power them and take video off the same cable, but I haven't been able to figure out a slick way to do it yet. Structured cable isn't all that expensive but if I could stick with standard RG59 or RG136 I think that'd be best.</p>
<p>Unfortunately it's not like injecting power into RF signals; NTSC video sits around 1Vp-p and has high frequency components to it so it's not as simple as just using a DC blocking cap. Has anyone done something like this before and what kind of success have you had?</p>
| slick way of muxing power+NTSC video over RG59/RG136? | 2011-01-02T19:07:05.157 |
8511 | |microcontroller|lcd| | <p>Perhaps you could use a "programmable display pushbutton" as a combined display and user interface.</p>
<p><a href="http://www.sparkfun.com/search/results?term=screenkey&what=products" rel="nofollow">http://www.sparkfun.com/search/results?term=screenkey&what=products</a></p>
<p><a href="http://www.nkksmartswitch.com/" rel="nofollow">http://www.nkksmartswitch.com/</a></p>
<p><a href="http://www.nkkswitches.com/SmartSwitch-Development-Tools.aspx" rel="nofollow">http://www.nkkswitches.com/SmartSwitch-Development-Tools.aspx</a></p>
<p>They are extremely small.
They can be programmed with 4 wire SPI.
Alas, they are not exactly what I would call "cheap".
Still, fulfilling 2 out of 3 wishes is pretty good ...</p>
| <p>What cheap LCD pixel displays are available which are 1" or smaller which could be interfaced to a microcontroller? (AVR, PIC24, etc.)</p>
<p>I'd like to make an interactive keyfob.</p>
<p>The important factor is small size, 1.5"^2 maximum. </p>
<p>I've seen small colour displays in LCD keychains which look ideal - but, it looks as though they use some custom controller logic which only talks USB.</p>
<p><img src="https://i.stack.imgur.com/0bJRW.jpg" width="200">
<img src="https://i.stack.imgur.com/jViqT.jpg" width="200"></p>
<p>Something like these 16x16 monochrome LCDs would be ok, if I could find a display controllable with SPI (this device has a custom epoxied blob).</p>
<p><a href="http://img.skitch.com/20090406-8dargu3hrnwdnfpgdu35k3tu78.jpg" rel="nofollow noreferrer">http://img.skitch.com/20090406-8dargu3hrnwdnfpgdu35k3tu78.jpg</a></p>
<p>Any ideas?</p>
| Cheap 1" LCD suitable for use with microcontroller? | 2011-01-03T00:42:14.350 |
8515 | |dc|ac| | <p>This circuit will do what you want (for a literal interpretation of the question):</p>
<p><img src="https://i.stack.imgur.com/vXExQ.jpg" alt="alt text"></p>
| <p>I got an electrical engineering degree 15 years ago that I barely use. Although I bought a fairly fancy multimeter, I will freely admit to having only a vague recollection of what I did back then... which was mostly discrete math and signal processing (as opposed to circuits).</p>
<p>A friend of mine who has a lot more real-world "electrician" experience was trying to figure out what was wrong with some cameras he owned. They were powered by cheap wall-warts and failing. We were trying to check these power supplies to make sure they were working, as we didn't know if the problem was with the power or the camera. Sure enough, some of the supplies were dead.</p>
<p>We tried to substitute in some switchable supplies to get them working. In the process, I noted with the multimeter that the polarity was different on the switchable supply from the adapters we were trying to replace. As we were plugging in these 2-prong plugs haphazardly into 3-prong outlets, I wondered out loud if we might have the plugs in upside-down.</p>
<p>He looked at me condescendingly and said <i>"Oh, I see. You have a degree in this, do you?"</i></p>
<p>Well firstly, it's been 15 years, and secondly...while he may know a lot about being an electrician I know about the diode bridge inside the stupid wall wart. And yes, diodes can tell the difference between electron source and electron sink. But if the power is an AC sine wave then it spends as much time in an up cycle as down cycle and so the decision about polarity is in the circuit post-rectification, etc.</p>
<p>(So it was; to change the polarity on the adapter you just changed the terminals on the plug once it had been converted to DC, not before. Fine.)</p>
<p>But the hypothetical question kept nagging me. Given that one of the terminals is ostensibly true ground, would it be <i>possible</i> to build an AC/DC converter whose DC polarity would flip based on which way you plugged it in (and I'm talking about no connection to 3rd prong)? Do such things exist?</p>
| Can a 2-prong AC/DC converter switch polarity based on inverting the plug? | 2011-01-03T01:34:21.717 |
8518 | |ram| | <p>Dallas also did a unit with a real time clock.</p>
<p>What you have is several parts in one package.</p>
<ol>
<li>Lithium battery (or Cell) - Non rechargeable - Not designed to be recharged</li>
<li>SDRAM ic (or Real time Clock IC with SDRAM - External xtal)</li>
<li>Power control IC - e.g. DS1210 - this switches from external to internal battery, and disables the write control signal when external supply falls.</li>
</ol>
<p>The RTC versions had visible terminal for the battery, which if you were careful you could remove (Damaging the Package) and replace with another cell/battery or cell/battery holder.</p>
<p>The one shown in your link was made in 1996 - and is now about 14 years old. - the internal battery will be dead as even if it was not used - it would be past it's shelf life. It could be used as a SDRAM but would not hold data when power is removed.</p>
| <p>The DALLAS DS1220ABs that I have were mostly manufactured in 1992 and 1993, I have a bunch of pulls. The datasheet speaks of a "lithium" battery inside (not "lithium-ion"). Do people here think that applying GND and VCC would recharge the "lithium" battery inside to make these chips quite usable, or is that just not the way it works? </p>
<p>(for e.g. <a href="http://cgi.ebay.com/Dallas-DS1220AB-200-16K-NonVolatile-SRAM-/170576839051" rel="nofollow">http://cgi.ebay.com/Dallas-DS1220AB-200-16K-NonVolatile-SRAM-/170576839051</a>)</p>
| DALLAS DS1220AB Non-volatile SRAM from 20 years ago --- reusable? | 2011-01-03T02:23:54.557 |
8530 | |fpga|xilinx|spartan| | <p>Your absolute references will be the <a href="http://www.xilinx.com/support/documentation/spartan-6.htm" rel="nofollow">Spartan 6 user guides</a>. For instance, the Clocking Resources guide (UG382) covers how to configure the DCMs. For examples of how the actual code looks, ISE has a database of them. Open Language Templates (the lightbulb in the toolbar), then look in language (VHDL or Verilog) -> Device Primitive Instantiation -> chip family (Spartan-6) -> Clock Components. </p>
<p>Details specific to your board are available from Digilent, in particular you'll want the UCF (which names all the IOs) and the reference manual (which explains the peripheral circuitry).</p>
<p>The general structure of your language, including how to make a component, is probably better picked up from books and examples. I haven't used Verilog so don't have any specific suggestions. Still, the templates include snippets of various generic contructs as well.</p>
| <p>Well this is a continuation of my question on FPGA over <a href="https://electronics.stackexchange.com/questions/5435/fpga-development-kit-for-beginners-spartan6-or-spartan3">here</a>.</p>
<p>I finally selected a <a href="http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,400,836&Prod=ATLYS" rel="nofollow noreferrer">Digilent Atlys</a> with a Spartan 6 FPGA, I don't have any prior experience of FPGA's although I have done some amount of work with micro-controllers.</p>
<p>I spent the last few days reading through data sheets of the FPGA, and I think it would be a good choice to start off with Verilog. I couldn't find any code examples though and even the data sheets are not newbie friendly. </p>
<p>I want to do some hand's on programming, simulation, synthesis now and this is what I want to do</p>
<ol>
<li><p>Generate an odd frequency, say 54Mhz from the FPGA (it runs on a 100Mhz clock) and route it to one of the pins. I would probably have to use the DCM or PLL for this, but no idea how to start here?</p></li>
<li><p>Implement some sort of I2C read write from the FPGA.</p></li>
</ol>
<p>What I'm looking for is a reference, possibly an online one or a book that gives me code examples and description of each of the hardware components available inside the FPGA, like DCM's, slices, clb's etc.</p>
<p>I guess that should get me started into the world of FPGA's.</p>
| FPGA, first steps | 2011-01-03T09:35:07.073 |
8534 | |oscilloscope| | <p>Use step down transformer and reduce the amplitude depends upon the oscilloscope specification say 12 v. And then you can measure and analyse those input. The values you can manipulate from transformation ratio of transformer.</p>
<p>i.e. transformer ratio K = voltage at secondary / voltage at primary. </p>
| <p>this is a noob question but here it is:<br>
How can i connect an osciloscope to the 230V mains power line to see the voltage sine wave ? <br>
- what schematic do i need<br>
- how safe is it ?</p>
| Connect 230V AC 50Hz to oscilloscope | 2011-01-03T11:44:13.707 |
8565 | |oscilloscope|frequency-measurement|bandwidth| | <p>The bandwidth and the sample rate normally should be 4 to 5 times the maximum frequency you want to measure. But be aware that if your input signal is not a pure sine wave, as in your case the square wave, it also contains harmonics with much higher frequencies. For an accurate measurement you have to cover at least the first of these harmonics.</p>
<p>At the frequency of the maximum bandwidth (here 10 MHz) a sine wave of this frequency is attenuated by 3dB by the analog frontend of the scope. This means it is measured at only 70% of its real value. The sample rate specifies how many measurements are done by the scope per second i.e. how accurate the form of the signal is acquired (50 MS/s equals 5 measurements per cycle on a 10 MHz signal).</p>
<p>Now think about what your scope is seeing with the input signal heavy attenuated (due to the too low bandwith) and with only 5 samples per cycle (due to the sampling rate).</p>
| <p>This question popped up to me a few moments ago.
I was measuring what is intended to be a 50Mhz square wave of level 0 to 2.5, however what I saw on the screen is a sine wave that was centered around 1.2V and level of 0.5 to 2.0V, the frequency was 4MHz.</p>
<p>I checked up my oscilloscopes datasheet and it showed that the bandwidth was 10MHz with a sampling rate of 50 MS/s. </p>
<p>I'm wondering what these figures are all about. </p>
<ul>
<li>Are they a measure of the upper
frequency limit an oscilloscope can
measure? </li>
<li>Is this oscilloscope capable
of measuring 50Mhz at all?</li>
</ul>
| Oscilloscope Bandwidth, what's it all about? | 2011-01-04T07:27:38.357 |
8569 | |servo|remote-control|reliability| | <p>Get the most reliable servos (and other gear) you can in the first place and over spec the servos and their attachments greatly so any mechanical stickyness can be forced out of the way.</p>
<p>If you are still not convinced that you have enough reliability, then look into how commercial airliners get higher reliability:</p>
<ul>
<li>Have multiple batteries, all of them feeding the bus though diodes, so that if one battery craps out it will not bring down the others.</li>
<li>Split control surfaces and use independent servos to control each, mixed so each control surface is held below 25% authority in normal operations, that way you can count on being able to counter a stuck surface with the one left operational, just by switching off the excursion limit and accepting a lot of drag.</li>
<li>Fuse each servo at the central controller, so it cannot bring down the power bus if it shorts out.</li>
<li>Use servos which can report back their position and other data, like motor current like: <a href="http://www.openservo.com/" rel="nofollow">http://www.openservo.com/</a> so the flight controller can detect stuck servos and try to fix the problem or at least let you know.</li>
<li>Run all servos from a controller that is able to power down individual servos, so if one servo goes nuts, then it can be turned off and allowed to weather vane.</li>
<li>Stick a complete autopilot with GPS and IMU in the plane (see: ArduPilot), to take it back to the launch site, if the radio craps out.</li>
</ul>
<p>In the end I doubt any of those enhancements would do a lot of good in practice as all the redundancy will also add complexity and thus new sources of errors, just look at all the problems Airbus had getting their flight systems debugged.</p>
<p>... but I bet a whole lot of fun could be had building all of that redundancy.</p>
| <p>I am building an RC aircraft, 10kg weight range.
It is supposed to perform long flights (20km+), so reliability is my main concern, mainly on servos controlling Flight control surfaces.</p>
<p>How reliability is maintained on RC planes?</p>
<p>I am afraid if any flight control surface servo would be jammed while manouvering, crash would be quite horrible :-)</p>
| Reliability of servos | 2011-01-04T09:20:40.460 |
8575 | |iphone|android|touchscreen| | <p>Travis, sampling rate is important, but the other things are important too. Thats the really answer about the great experience on iDevices. The full sum is well balanced: touchscreen tech (for sensitiviy) + controller inteface (sampling rate and signal integrity for multitouch) + GPU (for smooth scrolling hardware acceleration) + tuned firmware tighly coupled. You can check the products that Cypress or ATMEL offer to get more info about the challenges on build touchscreens controllers.</p>
| <p>Who makes the touch screens for the iPhone or Android devices? Specifically I'm wondering what the sampling rate is for dragging, etc. that gives these devices such smooth touch and drag performance.</p>
<p>Also is there a common standard of measurement for touch screen performance? How do you quantify a touch screens drag performance?</p>
| Touchscreen Performance (iPhone, iPad, Android, Nexus S, etc.) | 2011-01-04T15:29:09.640 |
8580 | |microcontroller|pic|power-supply| | <p>How stable is the power supply's output when you connect it a volt-meter (multimeter)? Is it quite close (less than 10% error) to the nominal value? (e.g. 5.06V for a 5V supply is good)</p>
<p>One potential addition source for glitches caused by the power supply, would be if the power transformer's output voltage is too close to the necessary input voltage of the linear regulator. For example the 7805 linear regulator requires an input voltage of 2 volts higher than the output (i.e. 7V input), and I like to add 1V as a margin of tolerance to make it more reliable. Adding the voltage drop of the (diode) bridge rectifier (1.4V), you want 9.4V peak-peak Vac from the power transformer. That works out to around 9.4 / sqrt(2) = 6.6 or 7Vrms AC.</p>
<p>So a 6Vrms rated transformer would work most of the time, but does not have much (sufficient?) margin of tolerance (AC mains may vary by 10% from nominal value, e.g 108-132 for 120Vac) to withstand potential AC main voltage drops. </p>
<p>Ref: <a href="http://knol.google.com/k/electronic-circuits-design-for-beginners-chapter-1#" rel="nofollow">Electronic Circuits Design For Beginners - Chapter 1</a></p>
| <p>I've been playing around with PIC microcontrollers for a while now, and have had a fair bit of success, however I sometimes get unexplained resets and sometimes need to cycle the power a few times to get my device to start working.</p>
<p>I think this is down to my simplistic PSU.</p>
<p>I normally throw together a mains transformer, bridge rectifier, linear regulator and a few capacitors.</p>
<p>Does anyone have a circuit diagram of a better more efficient PSU that is easy to build on stripboard and doesn't cost too much?</p>
| A better power supply for microcontroller circuits | 2011-01-04T16:32:35.820 |
8582 | |breadboard|pcb-design| | <p>Filling in the data Pololu seems to be using:</p>
<p>1.</p>
<div class="s-table-container">
<table class="s-table">
<thead>
<tr>
<th>BB</th>
<th>A</th>
<th>B</th>
<th>C</th>
<th>D</th>
<th>E</th>
<th>1</th>
<th>2</th>
<th>3</th>
<th>4</th>
<th>R4</th>
</tr>
</thead>
<tbody>
<tr>
<td>Pololu</td>
<td>-</td>
<td>.1</td>
<td>.4</td>
<td>.3</td>
<td>.26</td>
<td>?</td>
<td>.4</td>
<td>.2</td>
<td>-</td>
<td>-</td>
</tr>
</tbody>
</table>
</div>
<ol start="2">
<li><p>No</p>
</li>
<li><p>PMP</p>
</li>
<li><p>30 pairs of 5-pin rows, and 10 5x2 power blocks.</p>
</li>
<li><p>The power rails and the rows in the middle section is not aligned, and measurement 1 is not detailed. Also E is not .3 inches.</p>
</li>
</ol>
<p><a href="https://www.pololu.com/product/4000#lightbox-picture0J10627" rel="nofollow noreferrer">https://www.pololu.com/product/4000#lightbox-picture0J10627</a></p>
| <p>I'm working on a development board which will mount on a solderless breadboard. It uses a 100 pin TQFP IC and Ethernet jack, among other things, so it would be a nightmare to get it to fit on a single section of breadboard at only 1.1" wide, and I'd like it to be big enough for users to make some edits. I'd also like to be able to plug into power distribution rails on the breadboard (like the <a href="http://www.sparkfun.com/products/114" rel="noreferrer">Sparkfun Breadboard Power Supply</a>). </p>
<p>However, after comparing my breadboard with a few friends and coworkers, I see that there are a number of differences in layout. I hope that I can accommodate some if not all of these differences by including multiple places to mount the headers for various breadboards. </p>
<p>Here's a dimensioned diagram so we're all on the same page. Imagine that there are two full strips side by side (one mostly off to the left), with power rails on both sides.</p>
<p><img src="https://i.stack.imgur.com/C3Sip.png" alt="breadboard diagram">
[Whoops! I forgot the horizontal dimension between B and C. Let's call it E, since I don't have the source for this image anymore.]</p>
<p><strong>1.</strong> What are the dimensions of popular, currently manufactured/used breadboards?<br>
In addition to the measurements in the diagram I'd like to know the following:<br>
<strong>2.</strong> Is there an electrical discontinuity between the top and of the power rails? (If so, is measurement '3' different at this location?)<br>
<strong>3.</strong> What is the configuration of the breadboard? Using the convention that P is a two-column power strip and M is a middle section (rows of connections with a gap for DIP ICs in the center), my breadboard looks like: PMPPMPPMP<br>
<strong>4.</strong> How many rows are in the breadboard middle section and power sections? Mine has 64 pairs of 5-pin rows in the middle and 10 5x2 blocks.<br>
<strong>5.</strong> Any other discrepancies I missed which would affect PCB layout?</p>
| Breadboard Dimensions for making DIP PCB | 2011-01-04T17:45:53.107 |
8589 | |switches|development|configuration|jumper|tutorial| | <p>Solder pads are out. Just say NO. You absolutely do not want to force anyone to use a soldering iron in order to be able to use your board, EVEN IF they are good with a soldering iron.</p>
<p>The EEPROM/FET idea is also not a good idea, because it is not readily observable. What is the state of that FET? You need a SW suite to find out, and maybe that is not enough: what if something funky happened between what you told SW you wanted and what actually happened at the FET?</p>
<p>So your choices are DIP switches or pins and jumpers. You could also do pins with a wire wrap gun. I would slightly prefer the DIP, but take your pick. Any of these three is miles better than solder/SW.</p>
| <p>I'm working on a development board, and need to let users set some configurations.</p>
<p>It will be used by students and engineers who are trying to build circuits on a breadboard; I'm not dealing with consumers. Usually, the settings will stay the same, but it's possible that every new project could use a different configuration.</p>
<p>I will be dedicating some pins to interfaces like USB and Ethernet, but I'd like to give users the option of using those pins for a different purpose. Some kind of configuration will be required. The options I've considered so far are:</p>
<h1>Solder bridges:</h1>
<p><img src="https://i.stack.imgur.com/iCzRd.jpg" alt="0-ohm resistor" /><br />
Either 0603 resistor packages to allow 0-ohm resistors to be used, or nearby pads for a solder blob.<br />
Pros:</p>
<ul>
<li>Cheapest option possible</li>
<li>Smallest PCB area required</li>
<li>No accidental changes</li>
<li>Customizable by soldering directly to pad</li>
</ul>
<p>Cons:</p>
<ul>
<li>Requires soldering iron to make changes</li>
<li>Possible to damage board with repeated soldering/desoldering</li>
<li>0-ohm resistors require having those parts on hand.</li>
</ul>
<h1>DIP switches:</h1>
<p><img src="https://i.stack.imgur.com/dOdih.jpg" alt="alt text" /><br />
Tiny mechanical switches in an IC package.</p>
<p>Pros:</p>
<ul>
<li>Easiest to change</li>
<li>Fairly durable</li>
</ul>
<p>Cons:</p>
<ul>
<li>Most expensive option by far</li>
<li>Might be changed by accident</li>
<li>Large area on PCB</li>
<li>Lowest current of the options</li>
<li>Hard to make changes to PCB</li>
</ul>
<h1>Pin Jumpers</h1>
<p><img src="https://i.stack.imgur.com/1UvBl.jpg" alt="pin jumper for IDE hard drive" /><br />
Removable Jumpers for .1" headers like those found on PC motherboards and drives.</p>
<p>Pros:</p>
<ul>
<li>Less expensive than DIP switches</li>
<li>Easy to make changes to PCB</li>
<li>Good balance between easy-to-change and semi-permanent</li>
<li>Easy to see configuration</li>
</ul>
<p>Cons:</p>
<ul>
<li>Large PCB area required</li>
<li>Tallest profile; usually .5" or so required vertically</li>
<li>Jumpers might be lost</li>
</ul>
<h1>Electronic Bus Switching</h1>
<p><img src="https://i.stack.imgur.com/cnjVT.jpg" alt="TI SN74CBT3384ADBQR" /><br />
Use FETs or a bus switching IC like the TI 74CBT series, and control with an EEPROM/microcontroller. Suggested by <a href="https://electronics.stackexchange.com/questions/8589/8593#8593">Brian Carlton</a>.</p>
<p>Pros:</p>
<ul>
<li>Small PCB area</li>
<li>Configurable in software</li>
<li>Can put both to High-Z or connected</li>
</ul>
<p>Cons:</p>
<ul>
<li>Requires another couple ICs; medium cost.</li>
<li>Less current than other options</li>
<li>Has real resistance</li>
<li>Can now confuse hardware bugs with software bugs and vice versa</li>
</ul>
<p>The solder bridge option makes me worry about weakening the pad with repeated resoldering and delaminating it from the PCB. How many times can a good soldering tech change a part on 1-ounce copper with an ENIG finish? Would covering the edges of the pad with soldermask and adding thermal reliefs (for adhesion, not heatsinking) on several sides of the pad increase the durability?</p>
<p>Am I missing anything? What configuration methods do you like to use on a dev board?</p>
| Choosing Configuration Jumpers - Solder bridges, 0-ohm resistors, DIP switches, pin jumpers | 2011-01-04T18:50:22.217 |
8603 | |cmos|vlsi| | <p>According to <a href="http://www.ece.ucsb.edu/bears/class/ece224a/Harris_logical_effort.pdf" rel="nofollow noreferrer">David Harris's presentation for eve224a course:</a> (slides 6-11 and 47)</p>
<blockquote>
<p>Delay d = f+p = g*h+p</p>
</blockquote>
<p>Where <em>d</em> is process-independent delay, <em>f</em> is effort delay (stage effect), p is parasitic delay, <em>g</em> is logical effort, <em>h</em> is electrical effort (fanout; h = C_out/C_in)</p>
<p>In the <a href="http://en.wikipedia.org/wiki/Logical_effort" rel="nofollow noreferrer">Wikipedia article "Logical Effort"</a> there are some examples too:</p>
<blockquote>
<p>Delay in an inverter. By definition, the logical effort g of an inverter is 1</p>
<p>Delay in NAND and NOR gates. The logical effort of a two-input NAND gate is calculated to be g = 4/3</p>
</blockquote>
<p>For NOT gate with FO1 (driving the same NOT gate):</p>
<p>g=1; h=1; p=1; so d = 1*1 + 1 = 2</p>
<p>For NOT gate with FO4 (the FO4 metric itself):</p>
<p>g=1; h=4 (Cout is 4 times more than Cin); p=1 so d = 1*4+1 =5 (the same result is at page 20 of books "Logical Effort: Designing Fast CMOS Circuits", draft from 1998)</p>
<p>1 FO4 delay is equal to 5 process-independent units (defined by harris, slide 6)</p>
<p>For NAND gate with two inputs (p=2) which drives the same:</p>
<p>g=4/3; h=1; p=2; d= 4/3 * 1 + 2 = 10/3 = 3,3 (a 1.5 times slower than NOT with FO1, but faster than NOT FO4)</p>
<p>For NAND gate asked by me - 2 inputs which drives 3 same NANDs:</p>
<p>g=4/3; h=3; p=2; d= (some magic inside) 4/3 * 3 + 2 = 6</p>
<p>So</p>
<p>Delay of 1 FO4 gate is equal to 5/6 delay of NAND (2-in, 3 FO).</p>
<p>The last problem is to convert chain delay of 18 NANDs to chain delay of FO4. (slide 41 of harris)</p>
<p>Hmm.. seems I need only to multiply 18 NANDs delay with 6/5... 21,6 FO4.</p>
<p>Thanks!</p>
| <p>This question is about gate delay in VLSI (microchips). (Yes, it is a CMOS)</p>
<p>Every digital chip consists of 2 kinds of elements, Register Logic (trigger or latch stations) and combination logic (between the registers, does the actual computation). Most chips can be expressed as <a href="http://en.wikipedia.org/wiki/Register_transfer_level" rel="nofollow">http://en.wikipedia.org/wiki/Register_transfer_level</a> which describes logic and registers.</p>
<p>The maximal clock frequency of microchip is determined (limited) by the delay of the slowest combination path. This delay depends from kind of elements, used in it.</p>
<p>The most popular metric of this critical delay is FO4 <a href="http://en.wikipedia.org/wiki/FO4" rel="nofollow">http://en.wikipedia.org/wiki/FO4</a> or Fan-out of 4:</p>
<blockquote>
<p>process independent delay metric used in digital CMOS technologies.</p>
</blockquote>
<p>It is counted as chain of length N of NOT gates. Each gate have output power enough to drive 4-fold more powerful inverter (according to wiki). I get this metric as tree of inverters with N levels, where each inverter drives 4 same inverters. Tree looks like <a href="http://www.mathworks.com/help/toolbox/wavelet/ug/wptreed2.gif" rel="nofollow">http://www.mathworks.com/help/toolbox/wavelet/ug/wptreed2.gif</a> but with NOT gates (transistors) at nodes. (better description is at <a href="http://www.realworldtech.com/page.cfm?ArticleID=RWT081502231107" rel="nofollow">http://www.realworldtech.com/page.cfm?ArticleID=RWT081502231107</a> )</p>
<p>So, the any modern processor have a metric FO4, which can be equal to 14, or 20 or 40. If the processor have small FO4, it can have more frequency, than a processor with large FO4 at the same silicon technology.</p>
<p>I have a metric for critical path of some chip, expressed in terms of fan-in-2 and fan-out-3:</p>
<p>18 fan-in-2 fan-out-3 NAND gates</p>
<p><em>How can I convert this to FO4? (Fan-out of 4)</em></p>
<p>I want to compare this chip with modern CPUs. FO4 will give me a clear way to check, how fast the chip can be on technology of modern CPU.</p>
<p><em>Update:</em> There is a <a href="http://books.google.com/books?id=oDWRAxCU-g8C&pg=PA175&lpg=PA175&dq=%22fan-in-2%22+fan-out-2" rel="nofollow">book which says</a>:</p>
<blockquote>
<p>This fan-out-of-four (FO4) inverter delay, t_4, is a good estimate of the delay of typical logic gate (fan-in=2) driving a typical load (fan-out=2) over relatively short wires.</p>
</blockquote>
<p>So, Fan-in=2 and Fan-out=3 is close to 2/2 or to FO4. For the first estimation I will use this 18 fi2/fo3 as equal to 18 FO4.</p>
| Convert fan-in-2 fan-out-3 NAND gates to FO4 | 2011-01-05T03:30:47.497 |
8608 | |lcd|interface|parallel| | <p>You can do this without issue.</p>
<p>However, you want to use the <em>Upper</em> (e.g. MSBs) of the digital output, discard the least significant bits. Otherwise, you will get all sorts of interesting effects.<br>
(for instance, a gradient would be "Multiplied", in that a simple span from black to red would repeat twice, provided you're discarding the MSB of the signal).</p>
<p>I currently have a similar project, which uses a 16 bit graphics controller, with a 18 bit LCD. In this case, you connect the 16 bit interface to the MSBs of the LCD, and ground the additional LSBs. What you are proposing is simply the inverse.</p>
<hr>
<p>Note: I've always thought of the MSBs as being "Upper" - This may simply be a terminology disconnect. Anyways, MSB and LSB are a far better way to describe the bus.</p>
| <p>I might not be able to find an LCD with a 24 bit parallel interface, which is what my controller requires. I have seen 18 bit parallel interfaces, though. I assume that I could really just use the lower 6 bits of each color and not use the other two bits per color channel. All I would have to do is make sure that my color palettes are adjusted accordingly, right?</p>
| LCD parallel interfaces | 2011-01-05T06:11:19.933 |
8610 | |power|audio|transistors|amplifier|repair| | <p>1 bank of 6 at a time ok.
Bias not affected significantly.
10-15 mA plausible.</p>
| <p>A question concerning my current repair project of an audio amp that uses big (600 W) but otherwise rather classic complementary output stages:</p>
<p>I assume when testing an audio power amp with 6 pairs of paralleled npn/pnp transistors, it is o.k. to assemble just 1 pair while testing as long as you have no significant output load connected. The advantage would be that, while testing, I would not blow as many of the precius MJ15022/23 transistors I have available as spare parts.</p>
<p>In what ways (if any) will the bias current circuit be affected?</p>
<p>Any problems I may not have considered but may be important for this repair technique?</p>
<p>Any other really good tricks for fixing big amps?</p>
<p>Once I am closer to finishing the repair: Does 10...15 mA of bias current per transitor branch sound like a good number to you?</p>
| Testing an Audio Power Amp with Paralleled Transistors | 2011-01-05T10:43:25.527 |
8620 | |switch-mode-power-supply|buck| | <p>A buck duty cycle is fundamentally defined by Vout / Vin. If you have 12V in and 5V out, 5 / 12 ~= 0.416 which is 41.6 percent.</p>
<p>The error amplifier compares a sample of the output voltage (usually with some frequency compensation) to a fixed, precise reference voltage. This is what is referred to as the error signal.</p>
<p>If the output voltage goes high for some reason, the error signal will cause the PWM to reduce duty cycle in an attempt to bring the error to zero.</p>
<p>If the output voltage goes low for some reason, the error signal will cause the PWM to increase duty cycle in an attempt to bring the error to zero.</p>
<p>If the output voltage matches the reference voltage, the duty cycle will be as per the above formula (which is a first-order approximation; losses and delays will add some extra duty cycle to the result.)</p>
| <p>According to <a href="http://www.ecircuitcenter.com/Circuits/smps_buck_vm1/smps_buck_vm1.htm" rel="nofollow noreferrer">this site</a> in a buck converter with voltage mode control the duty cycle is set directly by comparing a voltage ramp to an error voltage. I agree with that. But this is where my headache starts:</p>
<blockquote>
<p>If Vo < Vref, then Ierr is positive - increase V(10) and the PWM duty cycle.</p>
<p>If Vo > Vref, then Ierr is negative - decrease V(10) and the PWM duty cycle.</p>
<p>If Vo ~ Vref, then Ierr is close to zero - maintain V(10) and the PWM duty cycle</p>
</blockquote>
<p>where Vo is the output voltage and Vref is the reference voltage. Well, the first two lines are ok for me, but i can't imagine how the duty cycle is maintained, when Vo ~ Vref.</p>
<p>My assumption here is, that when Vo ~ Vref holds, then the duty cycle should be set to 50% and <strong>not</strong> maintained. Or am i missing something here?</p>
<p>Regards</p>
<p>Macs</p>
| Buck converter with feedback loop | 2011-01-05T15:47:10.200 |
8621 | |prototyping|breadboard| | <p>I have friends who have permanently-constructed projects using breadboards.</p>
<p>In this case, it was a audio crossover, and it had been assembed on a solderless breadboard, the wires were given some additional retension by being glopped down with hot-glue, and the whole thing was stuck in an enclosure, and then used for <em>years</em> without issue.</p>
| <p>In school, I was told not to leave components in a breadboard for extended periods of time. However, this length of time was never quantified. The reasoning was that the contacts would eventually lose their "springiness"; at some point later in time, you'd be debugging issues with a circuit, only to find out that the contacts were bad.</p>
<p>I have no idea if this is really true, or if breadboards are now made so well that it's not an issue. I have some nice ones, but in the end they seem to use the same narrow white piece that everyone else uses.</p>
<p>I've got some prototypes put together that I don't want to take apart yet, and I also don't know when I'll get back to it. My mbed board has now taken a back seat to the Netduino that I just received. :)</p>
| How long can I leave components in a breadboard? | 2011-01-05T15:54:07.423 |
8632 | |surface-mount|resistors| | <p>My fifty cents to Nick T's answer.</p>
<p>For <a href="https://en.wikipedia.org/wiki/Resistor#Thick_and_thin_film" rel="nofollow noreferrer">thin film resistors</a>, after metal deposition (and before trimming) the foil undergoes photo-etching (an important manufacturing step):</p>
<blockquote>
<p>the surface is coated with a photo-sensitive material, then covered
by a pattern film, irradiated with ultraviolet light, and then the
exposed photo-sensitive coating is developed, and underlying thin film
is etched away.</p>
</blockquote>
| <p>I'm using some 0.1% precision 10k and 150k resistors. They are thin film 0603 surface mount. For a lot more, there are also thick film types. Fundamentally and practically, what is the difference between these two? </p>
<p><a href="http://uk.farnell.com/panasonic-electronic-components/era3arw103p/resistor-10k-0-05-0603-0-125w/dp/1688472RL">Thin film example</a></p>
<p><a href="http://uk.farnell.com/panasonic-electronic-components/erj3rbd1002v/res-thick-film-10k-0-5-50v-0603/dp/2379939">Thick film example</a></p>
| Difference between thin film and thick film precision surface mount resistors | 2011-01-05T19:54:49.863 |
8633 | |calibration| | <p>You can calibrate out:</p>
<ul>
<li>Manufacturing tolerance [2] [3], (+/- 1*%) = can be calibrated</li>
<li>Solder heat [2] [3], resistance change due to soldering (+/- 0.2* to 1%) = can be calibrated</li>
</ul>
<p>But do not forget about all the other tolerances:</p>
<ul>
<li>TCR [2][3], temperature coefficient resistance (+/- 50 to 100* ppm/C)</li>
<li>VCR [2], voltage coefficient resistance (+/- 25* ppm/V)</li>
<li>Environmental factors, resistance change during lifetime (<=+/- 3%* at 155 C, 225 000 h) [2] [3] [4]</li>
</ul>
<p>* Note that all values can differ between resistor brands and products.</p>
<p>[1] <a href="https://www.vishay.com/docs/28809/driftcalculation.pdf" rel="nofollow noreferrer">https://www.vishay.com/docs/28809/driftcalculation.pdf</a> </p>
<p>[2] <a href="https://www.digikey.se/sv/ptm/v/vishay-beyschlag/mm-hv-high-voltage-thin-film-melf-resistors/tutorial" rel="nofollow noreferrer">https://www.digikey.se/sv/ptm/v/vishay-beyschlag/mm-hv-high-voltage-thin-film-melf-resistors/tutorial</a></p>
<p>[3] <a href="https://industrial.panasonic.com/cdbs/www-data/pdf/RDA0000/AOA0000C304.pdf" rel="nofollow noreferrer">https://industrial.panasonic.com/cdbs/www-data/pdf/RDA0000/AOA0000C304.pdf</a></p>
<p>[4] MIL-STD R-10509</p>
| <p>At the moment, I use 0.1% resistors to get accurate voltage measurement through a voltage divider. However, the cost is high, so I was thinking of using 0.5% or 1% resistors and calibrating out the error in software by using a precision voltage reference during production. Has anyone done this successfully? What pitfalls might I encounter?</p>
| How viable is it to just use 1% resistors and calibrate out the error? | 2011-01-05T20:03:07.177 |
8645 | |rf|simulation| | <p>You can sign up for CENOS 3D Antenna Design Simulation software Beta version for free here: <a href="https://www.cenos-platform.com/antenna-design" rel="nofollow noreferrer">https://www.cenos-platform.com/antenna-design</a></p>
<p>Disclosure: I am Head of Marketing at CENOS.</p>
| <p>What free tools are there to simulate RF circuits?</p>
| Free RF Simulation Software | 2011-01-06T08:04:55.237 |
8656 | |bjt|spice|emitter-follower| | <p>So if I am decoding your netlist correctly, you have the circuit on the upper left. The reason the output doesn't go below zero is that the thing pulling down on the output is connected to ground.</p>
<p>One solution is shown in "A", which is to have the pulldown pull from -15V instead of 0V.</p>
<p>Another solution is shown in "B", which is to replace the pulldown with a PNP transistor. This wastes less power, because there isn't the 3.3k resistor always dissipating. Class-B amplifiers form the basis of most audio amplifiers and op-amp output stages.</p>
<p><img src="https://i.stack.imgur.com/TNg7U.png" alt="alt text"></p>
| <p>I cannot afford a function generator and oscope right now, so I'm trying to learn analog electronics with Spice (MacSpice, to be specific). Below is the Spice model for a simple emitter-follower circuit. Vcc is 15V, and the input at the base is a 5V 60Hz sine wave with a 0V DC offset. R1 sits between the transistor base and the sine input, and R2 sits between the transistor emitter and ground.</p>
<p>The output at the emitter has me a bit puzzled and I would appreciate it if anyone has an explanation for the behavior.</p>
<pre><code>* Simple Emitter Follower
Vcc 3 0 DC 15
Vin 1 0 SIN(0 5 60) dc 0
R1 1 2 270
R2 4 0 3.3k
Q1 3 2 4 generic
.model generic npn
.control
tran 1ms 60ms
plot v(1) v(4)
.endc
.end
</code></pre>
<p>The output of the transient analysis plot command is below.</p>
<p><img src="https://i.stack.imgur.com/br8vj.png" alt="alt text"></p>
<p>I was surprised by this output. As expected, there is a slight voltage drop in the amplitude due to the base-emitter junction of the NPN. However, the output is clipped and does not swing below zero. What would I need to do to catch the negative part of the sine wave?</p>
| Emitter Follower Output | 2011-01-06T16:51:39.887 |
8662 | |pic|microchip|library|matrix| | <p>If you're just using simple, fixed size matrices like 2x2 or 3x3 affine transforms, it's not <a href="http://local.wasp.uwa.edu.au/~pbourke/miscellaneous/determinant/" rel="nofollow">very difficult to implement them yourself</a>. That link shows how to compute the determinant and inverse of a matrix. Multiplication, addition, etc. are much easier. In fact, the Cairo source code, a drawing library, has GPL/LGPL/MPL licensed code for dealing with matrices (2D affine only): <a href="http://cgit.freedesktop.org/cairo/tree/src/cairo-matrix.c" rel="nofollow">cairo-matrix.c</a></p>
| <p>I'm using a Microchip PIC18 and I need to use matrices in my code. I know DSPIC do have matrix libraries, that simplifies the implementation.
Does anybody know whether any is available also for the 18 family (my present PIC18 embeds an hw multiplier)?</p>
<p>Thank you all!</p>
| Microchip PIC18 matrix routines | 2011-01-06T18:07:51.303 |
8672 | |power|ac|opto-isolator|zero-crossing| | <ul>
<li>It is possible to make a ZCS in < 1mA.</li>
<li>You need to buffer with an external supply.</li>
<li>Leakage to ground is < 1µA</li>
<li>Safety Agencies require it to be < 500µA.</li>
<li>External wiring shows connect to Line and ground only...</li>
<li>Neutral is not required but may be used instead.</li>
</ul>
<p>All passive parts must be rated for 1.5kV. Any small signal silicon bridge will do. Schottky diode powers the Schmitt inverter to provide noise free hysteresis. Input cap and ferrite bead to inverter input will assist with RF rejection.. 100pF without phase shift.</p>
<ul>
<li>Use trailing edge of +ve ZCS pulse to activate a pulse to Triacs or latches as the pulse staarts before zero and finishes after zero V. Pulse width depends on resitor ratio and Zener voltage for chip or use 3V white or blue, LED 3mm or 5mm. It will not illuminate much , just a cheap zener.<img src="https://i.stack.imgur.com/syqNi.png" alt="enter image description here" /></li>
</ul>
<p>If target device is grounded to AC ground, you must use a simple signal pulse transformer or OptoIsolator with different bridge divider resistors and no inverter then.Bridge to opto darlington directly with ceramic input current limiting resistor.</p>
| <p>I'm designing a digital phase-controlled light dimmer, and I need a zero-crossing detector circuit. From what I've read, it's a bad idea to wire the AC main directly to the microcontroller through a resistor, and folks have suggested using optoisolation instead. However, I don't know how the circuit actually falls together.</p>
<p>It would seem elegant to me if the zero cross circiut's output is a 5V logic pulse for use as a rising-edge interrupt. But I'm not married to that idea if some other output is easier to use.</p>
<pre><code>Input: 120V AC @ 60 Hz
Output: 5V pulse at zero crossing
</code></pre>
<p>Interesting related post, with not enough detail for me: <a href="https://electronics.stackexchange.com/questions/4679/detecting-zero-cross-in-ac">detecting zero cross in ac?</a></p>
| 120VAC 60Hz Zero Cross Detector | 2011-01-06T21:34:41.623 |
8678 | |prototyping|safety|ac|high-voltage| | <p>If you make it plug in and not hardwired you can prototype anything. If you want to sell it you will need to have your device meet ul or some other governing body that oversees your perticular type of electrical device.</p>
| <p>I'm planning to build a digitally-controlled light dimmer circuit. I'm not trained in electrical engineering, and I don't want to do something that an electrician would immediately recognize as dangerous and stupid.</p>
<p>Please suggest a reasonable home set up for prototyping circuits involving 120V AC power.</p>
| Basic Training for working with 120V AC | 2011-01-06T23:20:19.363 |
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