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6959 | |decibel| | <p>Kellenjb's answer is excellent, I just wanted to add a webpage that gave me a "Ohhh" moment when I was reading about this -3db thing. Maybe it helps to visualize.</p>
<p>I read a <a href="http://www.electronics-tutorials.ws/filter/filter_4.html" rel="nofollow noreferrer">tutorial</a> on Band Pass filters which includes a great image of a Bode Plot. You can see the key image below. It nicely illustrates how signal attenuation varies depending on the frequencies. We see there is no phase shift at the center frequency, so we have complete signal transmission. However as we go out of the Pass Band, we get to a point where the Band Pass Filter shifts the signal to lag or lead the central frequency by 45 degrees, and we see our point of -3dB. </p>
<p>At this point, we can note that sin(45°) = \$1/\sqrt(2)\$</p>
<p>For me the visual below really helps to bring some sense into this seemingly arbitrary choice of \$1/\sqrt(2)\$.</p>
<p><a href="https://i.stack.imgur.com/KToEm.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/KToEm.gif" alt="Band Pass Signal Attenuation in regular plot and Bode plot"></a></p>
| <p>My oscilloscope has 100 MHz -3dB bandwidth. -3dB is 0.707 units (<span class="math-container">\$\sqrt{2} / 2\$</span>). What does this mean, why 70.7% attenuation? Is there any particular reason for this attenuation level?</p>
| What is the significance of -3 dB? | 2010-11-19T13:46:05.313 |
6963 | |arduino|voltage-regulator| | <p>No, you can't do that with an op amp. </p>
<p>Op-amps require power supplies. Many opamps have dropouts just like your 7805, so the output cannot quite reach the power rails. Others, called rail-to-rail opamps, can operate over the entire supply voltage. They're just drawn as triangles in some textbooks because it gets tedious to draw the power supplies every time (same with logic symbols).</p>
<p>Even if you could power an op-amp to beyond the rails, it's not advisable as a replacement for a 7805. Most opamps are low current (<20mA), and suitable only as precision voltage references.</p>
<p>Your options are, from easiest and cheapest to most difficult and expensive.:</p>
<ul>
<li>Tolerate the 4.8V and associated droop as the battery discharges (4.8V is a nominal value, not exact/constant). Many simple circuits can run off of 4.8V just as well as 5V.</li>
<li>Use to get a higher voltage battery pack or put more battery packs in series to raise the supply voltage.</li>
<li>Use a low dropout regulator[LDO] to regulate to a slightly lower voltage (3.3V, for example). 78XX isn't the only series of regulators! Many LDOs are available with dropout voltages of less than 0.2V.</li>
<li>Use a boost regulator.</li>
</ul>
<p>The final option uses switching of current through an inductor to generate voltages above the input. You will probably need a boost/buck regulator, since your input is so close to your output.</p>
| <p>I have a 4.8v battery pack and I made a simple power supply with a L7805CV voltage regulator, which has a 2v dropout. So I'm only getting like 3.5v out. Is it possible to throw an op-amp or something like that before the voltage regulator to make sure I get at least the 7v I need to achieve 5v on vout?</p>
<p>If not, what is best practice?</p>
| Can I use an amp before my voltage regulator to ensure I get 5v? | 2010-11-19T14:54:15.430 |
6972 | |peltier| | <p>Just obtained some today. The big problem is that they are a lot more fragile than most.
The ones used in Casio projectors are believed to be very efficient, possibly 1.3* better than units found in typical camping refrigerators.
You may be able to use one of these as part of a stack.</p>
| <p>I have a thin 2x2 mm surface that I'm trying to cool by 5-10 degrees Celsius in 1 second or less. Some very rough back-of-the-envelope calculations reveal that I need to remove ~50 mJ of energy to do this.</p>
<p>I've been thinking of using a Peltier module, but have no real experience with TECs, and therefore don't know exactly what to look for in terms of specs. The speed of the temperature change is my primary consideration. My questions:</p>
<ol>
<li><p>Are there any manufacturers that sell very small Peltier modules that would roughly match my specifications, in prototyping quantities?</p></li>
<li><p>Are there any further considerations that I've missed?</p></li>
</ol>
| Is it possible to obtain very small Peltier modules with fast response times? | 2010-11-19T17:38:01.293 |
6973 | |led|timer|netduino|blink| | <p>Since you have a microcontroller around for switching the signal on and off it makes sense to let it do the dirty work as well. I'm not acquainted with Netduino, but I see that it's an ARM7 running at 48MHz, which makes it more than powerful enough for this. Set a timer to a 13\$\mu\$s period, and let it toggle an I/O pin on each timeout. The signal's period is then 26\$\mu\$s, giving a frequency of 38.5kHz with only 0.1% error. Duty cycle will be 50%.</p>
| <p>Several other questions are posted about methods for flashing an LED, but one additional requirement I have is the ability to turn the circuit on or off with a micro controller (Netduino, 3.3v). <a href="http://www.reconnsworld.com/ir_ultrasonic_555timer40khzir.html" rel="nofollow">This schematic</a> is very close.</p>
<p>What changes would be necessary to achieve 38.5kHz? Also, how could I make an additional adjustment to start or stop the circuit via a pin on the Netduino?</p>
| Create a circuit that can flash IR LEDs at 38.5kHz and be turned on or off by microprocessor | 2010-11-19T18:32:20.713 |
6977 | |temperature|integrated-circuit| | <p>Other than the physical aspects of cold silicon, -40/85C tends to fit the most stringent conditions that most folks would need (commercial/industrial). </p>
<p>Practically, characterizing a device is a very time consuming process because it requires test fixtures and other equipment capable of the temperature range. It's not about buying a better freezer since many devices are characterized using the same test equipment used for production testing. The fun part is collecting and parsing the characterization data just to realize that the test fixture froze over and started collecting garbage data.</p>
| <p>Most devices seem to be characterised over -40°C to ≥85°C. What limits them to cold temperatures? Can an IC be damaged by keeping it too cold? Does this apply to other devices, e.g. diodes, transistors?</p>
| What prevents semiconductors working below -40°C or so? | 2010-11-19T21:08:33.783 |
6983 | |soldering| | <p><strong>PCB Manufacturing</strong></p>
<p>If you are manufacturing the pcb in house it may be a little difficult to do. Preferably you really need to have plated holes and soldermask. The plated holes are a must as the center pad is usually for thermal purposes and must have a good thermal connection to your ground plane. This means you will have to have several of them across this center pad. There are some via techniques that you can use at home that will work, but I do not have any experience with them. You can get away with no soldermask, but it makes life much easier.</p>
<p><strong>The Footprint</strong></p>
<p>There are 2 things you can do to make your soldering life easier while making the footprint. The first is to extend your pads out long enough that you can stick a soldering iron to it. The second is to round the corners of the pads on the inside of the chip. Typically I see students have issues with solder liking to bridge from the center pad to the others. They have found that rounding the back corners has extremely helped prevent this.</p>
<p><strong>Time to Solder</strong></p>
<ul>
<li>Apply flux.</li>
<li>Place your IC.</li>
<li>Tack 1 pin on each corner down by pushing solder into the pad along your extended pad.</li>
<li>Flip your board over and apply solder to all of your vias. Make sure you get it nice and hot first, it will take it a bit longer for the heat to transfer to the IC. You want the IC to be hot when solder gets to it. This is a bit hard to tell so you will just have to do some guess work. You have put enough solder down when your vias becomes completely filled with solder.</li>
<li>Flip it back over and continue soldering all other pads with the method of pushing the solder into the pad.</li>
<li>Check the board and your done.</li>
</ul>
| <p>Is it possible to hand solder a DFN package? It's leadless, so it could be tricky. I can't find any videos on YouTube about it, so I'm sort of thinking it as difficult, if not impossible.</p>
| Is Hand Soldering a DFN Package Possible? | 2010-11-19T22:49:00.757 |
6984 | |computers| | <p>If a small form-factor is really important, <a href="http://gumstix.com" rel="nofollow">Gumstix</a> will win. They're a little more expensive, but they're tiny. They run Linux, and they have a wireless module.</p>
| <p>I am researching some embedded applications that will leverage the use of a single-board computer (SBC). I am looking for a SBC that has a very small form factor, supports wireless networking, and can boot from a memory chip or USB memory stick. Does anyone have experience with something like this and can recommend a manufacturer to use?</p>
| Single-board computer | 2010-11-19T22:52:12.627 |
6986 | |clock|flipflop| | <p>A latch may guarantee that if the clock input has a rising edge and remains high for at least Twidth, and the data input is high at least Tsetup before a rising clock edge and remains high for at least Thold after, then within Tpd the output of the latch will be high and remain so until the next rising clock edge. That does not mean, however, that the output of the latch will never change at a time more than Tpd removed from a rising clock edge.</p>
<p>In an ideal world, if a latching circuit receives a stimulus which may or may not cause it to change state, one of two things would always happen:</p>
<ol>
<li>The stimulus will visibly change the latch state immediately; the latch will remain in that particular changed state until the next stimulus.
<li>The stimulus will not change the latch state at all; the latch state will remain unchanged until the next stimulus.
</ol>
<p>Unfortunately, there's another possibility:</p>
<ol>
<li>The latch state may be changed in a way that is not by immediately or fully apparent for some time; the visible state may change at some arbitrary future time, unless a "clean" stimulus puts the latch into a known state.
</ol>
<p>To use a crude physical analogy, if a standing bowling pin is hit soundly, it will fall over immediately. If it's hit very weakly, it may be nudged slightly off vertical, but will quickly return to standing firmly. If it's hit somewhere in the middle, though, it may wobble around awhile before either returning to a steady upright state or toppling over. It may not be apparent for a over a second what the pin would end up doing if left undisturbed. The worst-case time to determine if a pin has been hit hard enough to topple it may far exceed the time that would be required to determine a clean hit or miss.</p>
<p>The closer a latch's stimulus is to one which would either almost or barely cause it to permanently change state, the longer it may take the latch to produce a cleanly-resolved output. </p>
<p>It would seem like it would be possible to design a latching circuit with a three-phase output, where the three phases were "high", "low", and "wobbly", and have downstream circuitry wait for the latch to produce a clean output before using the output value. Unfortunately--returning to the bowling analogy--while it may be possible to tell that a pin has fallen over sufficiently that it's not going to right itself, and it may be possible to tell that a pin has sufficiently stabilized that it's not going to fall unless it's hit again, there no clear and unambiguous way of establishing the moment where the pin's outcome becomes certain. No matter what one does, there will always be a theoretically-possible "trouble case". The best one can do, oftentimes, is let the pin sweeper come in and reset the state of the system, and hope there's no disagreement about whether the pin should be counted as having fallen before the pinsweeper got it.</p>
| <p>im having some trouble finding an example of the time-instability that motivates the flip-flop. wherever i look, the explanations are awfully airy-fairy (or at least my understanding is). for example, <a href="http://wearcam.org/ece385/lectureflipflops/flipflops/" rel="nofollow">here</a> they explain that there can be instability if the clock pulse is sampling from combinational circuits. im looking for a concrete example of such instability (i need these things explained to me like im a six-year-old kid), not just saying "things can be unstable". if i wrote in a maths exam "the given implication can be problematic" without providing a counter example i wouldnt get half a mark, and by the same token if i were authoring an article that discusses motivating flip-flops i would see it essential to "prove" their necessity.</p>
<p>my problem is that if i have worked out that if the [maximum] propogation delay for a given circuit, i dont need to wait for a clock pulse edge, i can just sample the output after that amount of time. meaning, even with a flip-flop i have to work out my clock-pulse speed, so why go to all the trouble of having 2 latches when i know that the desired ouput will exist after 1 pulse-length of time?</p>
<p>so if i had many different circuits that relied on each others output, instead of flip-flopping them all, i would just activate them in the relevant order according to a clock-pulse. im obviously missing something simple here because as far as i can see the flip-flop functioning to save from instability isnt necessary...</p>
<p>the JK flip-flop is a nice way to "regulate" the ouput because it solves an altogether different problem, that when j=k=1 the toggle that the JK latch would otherwise perform for the entire cycle that the clock-pulse is 1, happens only once, which means the final output is deterministic - as opposed to undefined. although that doesnt explain why its necessary on a D latch and an RS latch.</p>
<p>on that note, ill add a second question. whats the use of the JK latch/flip-flop? it seems to be introduced in many texts as an improvement on the RS latch, because of the problematic s=r=1 situation and resulting race condition. however if we setup the RS in a flip flop, we provide ourselves with a better alternative to the JK flip-flop: this acts like an RS latch but when r=s=1 on the clock's rising edge both Q and Q' are 0, and on the falling edge theres no change in the slave latch. so the problematic situation of r=s=1 becomes stable. the only advantage JK has over this setup is that r=s=1 actually provides a new functionality of toggle, im not sure if thats a desired thing or not...</p>
<p>hoping for some insight...</p>
| master-slave flip-flops | 2010-11-19T23:05:16.490 |
6992 | |555|power-supply| | <p>You want a low-going "power good" to temporarily turn off the supply.</p>
<p>This circuit will do what you want. Choose R and C to get your desired delay.</p>
<p>Edit: there should probably be a resistor between the PNP base and NPN collector instead of a direct connection as shown.</p>
<p><img src="https://i.stack.imgur.com/kEeCM.jpg" alt="alt text"></p>
| <p>I am designing a circuit which may fail to start up. It has a power good output which is high when the supply is working. When the power good output goes low, the circuit has failed to start oscillating properly, and needs to be restarted. I thought about using a 555 timer but couldn't figure out how to make the output stay high when the input signal was low. Any ideas?</p>
<p>The circuit must do this because it fails to start under high current set points. It drives an LED. The idea is at higher currents the output folds back, but doesn't require an actual restart of the circuit to get it working again, and the fold-back mechanism makes the LED blink on and off.</p>
<p>Here's an image to show what I mean. Green shows the LED current. It has been set too high and the supply's overvoltage protection circuit kicks in to prevent more than 4.7V being applied across the LED (to prevent breakdown of the LED if in reverse.) The blue trace represents the power good output. During the oscillations the supply is outputting correctly, so it is high. It drops low after the oscillations stop. A short delay after it drops low, I need the supply to reset and try again - this would be accomplished by turning the supply controller IC on and off.</p>
<p><img src="https://i.stack.imgur.com/IEFlY.png" alt="alt text"></p>
| Power cycling circuit | 2010-11-20T00:05:16.837 |
7003 | |pcb|pcb-fabrication|pcb-design| | <p>I wasn't getting reliable results ironing on toner transfer. I modded an old waffle iron - named the <a href="http://www.ka6wke.net/finished-projects/pcb-press" rel="nofollow">PCB Press</a>. I like the ability to produce a prototype board at home in under an hour. If I need something of professional quality I send the tested proto out to fab house. </p>
| <p>I have finally built up a lab to design electronics in. I have quite a few designs I would like to test. I have tried the printer toner/iron technique a few times but have found that I cannot create small pitch sizes as they tear off while removing the printer paper. A few people have mentioned that this is due to using a Samsung laserjet versus a HP.</p>
<p>I am wondering what methods you use to develop PCBs for one-offs in your lab or at home (like me). I am trying to fast track a move to SMT/SMD components and would like some tips from seasoned experts on the best PCB creation methods to test board concepts before sending them off to a PCB MFG. I would like something that balances cost, time, and beauty of the finished product geared towards a hobbyist (at this point) and geared towards SMT/SMD components.</p>
<p>Please include pics/documentation of your preferred method. Thank you in advance for your post.</p>
| Best One-Off DIY PCB Creation Technique | 2010-11-20T07:12:31.967 |
7005 | |arduino|led|driver| | <p>There are plenty of options for "ULN2803A"
<a href="http://ciiva.com/CloudSearch/SearchComponent?searchCondition=ULN2803A" rel="nofollow noreferrer">http://ciiva.com/CloudSearch/SearchComponent?searchCondition=ULN2803A</a></p>
<p>And for each "ULN2803A", you can find their alternatives on <a href="http://ciiva.com" rel="nofollow noreferrer">Ciiva</a>
E.g,
<a href="http://ciiva.com/CloudSearch/Component/997843/stmicroelectronics-uln2803a" rel="nofollow noreferrer">http://ciiva.com/CloudSearch/Component/997843/stmicroelectronics-uln2803a</a>
<img src="https://i.stack.imgur.com/6xjwE.jpg" alt="enter image description here"></p>
| <p>I moved my Arduino-logic-level-5V-to-12V-LED strip circuit off project board and onto Veroboard and I'm very proud to say everything worked first time:</p>
<p><img src="https://i.stack.imgur.com/KYgSl.jpg" alt="alt text"></p>
<p>(I'm not at all proud of the soldering job, so you don't get to see that.)</p>
<p>So this is the point where you all tell me I can replace the whole shebang with a $0.65 IC. The LED strips pull a few hundred mA per channel and I want to drive them off the Arduino's PWM pins. I've found the <a href="http://www.datasheetcatalog.org/datasheet2/5/0w2oz7jig6lt2chlgy7joisuwipy.pdf" rel="nofollow noreferrer">ULN2803A</a>, but that's 8 Darlington Pair array in a DIP18 package, I want a 3 or 4 Darlington Pair array in a DIP8 or thereabouts. <a href="https://electronics.stackexchange.com/questions/6145/using-an-uln2803-with-netduino">This question</a> might actually contain the answer I'm looking for, but I don't know enough to even work that out.</p>
<p>Secondary question: how do you even know things like the ULN2803A exist? I happened upon it randomly and from there I worked out that "transistor array" was the search term I wanted. But aside from simply hanging around here, how does one answer the question, "What IC can I buy that will replace this portion of this circuit?"</p>
| Can I replace this circuit with an IC? | 2010-11-20T09:11:18.217 |
7011 | |pcb|surface-mount|layout|pad| | <p>As Leon noted, 90<sup>o</sup> corners are undesirable because they heat up faster. </p>
<p>Another downside even if you're not doing reflow work is that the corners are the first thing to lift if you abuse the board during rework, just like the corners of a sticker are the easiest and first things to peel up.</p>
<p>However, I route at 45 degree angles, so an octagon is a better shape than a round pad. It minimizes the space required of the trace around the pad, while simultaneously maximizing the area of said pad for soldering strength, board-to-copper adhesion, and heat dissipation. Here's a diagram in hopes that it will help you see why.The diagram is for a through-hole component, but the same logic applies to SMDs. </p>
<p><img src="https://i.stack.imgur.com/cH8hd.png" alt="trace rounding octagon at even spacing"></p>
<p>The 135<sup>o</sup> angles are better than 90<sup>o</sup>; but I'm not convinced that going to fully rounded corners is significantly better than 135<sup>o</sup>. Also, (insignificantly)I like the uniform look that octagonal pads and 45 degree routing produces; I think round pads look out of place.</p>
| <p>I'm learning to layout PCBs and lately I came across practice that made me curious. The chip passives' pads are etched with oblong / rounded shape, instead of rectangular shape that is used in all example libraries and even the <a href="http://landpatterns.ipc.org/default.asp" rel="noreferrer" title="IPC-7351B standard">IPC-7351B standard</a> (you can download LP Viewer for free registration and see for yourself). Here are the examples (I marked the interesting pads with yellow):</p>
<ul>
<li><p><a href="http://beagleboard.org/" rel="noreferrer" title="Beagle Board">Beagle Board</a>:
<img src="https://i.stack.imgur.com/DGAsA.png" alt="Beagle Board"></p></li>
<li><p><a href="http://arduino.cc/en/Main/ArduinoBoardMega2560" rel="noreferrer" title="Arduino Mega">Arduino Mega</a>:
<img src="https://i.stack.imgur.com/56kul.png" alt="Arduino Mega"></p></li>
</ul>
<p><strong>The question is: what are these rounded pads good for? Should I use them instead of rectangular ones to make my board look more "pro"?</strong> </p>
<p>My first thought was that it might be because it might be better for reflow soldering, but I'm bit puzzled about that reasoning. The one advantage I see with these is more routing space around such rounded pad (no "sharp" edges).</p>
| Using oblong / rounded surface mounted pads for chip resistors, capacitors and inductors | 2010-11-20T12:39:03.803 |
7012 | |cooling| | <p>Just like cooling mosfets, you bolt them to a heatsink with some form of thermal paste that does not conduct electricity. The bigger the heatsink, the better.
All thermal paste does is it fills in all the little holes and dents in the surface of the heatsink, and the component, thermal paste is thermal paste regardless of what application it is used for. Yes thermal paste used in computers would be good to use. </p>
<p>(If someone disagrees with me, say why you do, not just that you do.)</p>
| <p>I've read <a href="https://electronics.stackexchange.com/q/6583/1240">this</a> question and in its comments it is said:</p>
<blockquote>
<p>LDO and IC heatsinks will generally
have a very different answer then
computer motherboard heat sink. This
question really doesn't belong here</p>
</blockquote>
<p>What I'm asking is how to use coolers with IC packages. For example let's say I have a device in TO220 package which according to my calculations needs cooling. How would I cool it? Most obvious answer is of course using a cooler, but that part isn't very clear to me.</p>
<p>I've seen that sometimes heatsink is directly connected to the package by a screw but sometimes insulator is used to prevent direct contact between screw and package. Some other times, heat conductive insulator is used together with insulator for screw to prevent direct contact between package and heatsink. </p>
<p>Sometimes silicon paste is used and sometimes it isn't. How would I determine when it is needed and when it isn't needed? My experience with computers tells me to always use it.</p>
<p>I've also seen silicon pastes marketed as for use in electronics. How are they different that ones used in computers? Would thermal pastes for computers work well with ICs? </p>
| How to cool ICs? | 2010-11-20T12:42:59.730 |
7016 | |pic|sensor|music|midi| | <p>There are multiple ways of doing it. I will explain one design that's very cost effective and quite ingenious. It's the design of <a href="http://www.rogerlinndesign.com/linnstrument.html" rel="nofollow noreferrer">LinnStrument</a>. You can have a look at its <a href="http://www.slideshare.net/gbevin/linnstrument-the-ultimate-opensource-hacker-instrument/12" rel="nofollow noreferrer">sensor board</a>. Since I didn't do the sensor design, nor do I own a LinnStrument, the below is all a result of reverse-engineering and may not match the original design. Certainly the mechanical and material choices don't.</p>
<p>TL;DR: It's possible to scan a LinnStrument sensor plane using nothing but MCU pins and a resistor per column. No external op-amps nor multiplexers are needed.</p>
<h1>Mechanical</h1>
<p>The sensor board uses a piezoresistive material such as <a href="http://www.adafruit.com/product/1361" rel="nofollow noreferrer">Velostat</a>. Such material decreases its bulk resistance with increasing pressure. The strips of the material are laid in a grid, and scanned to measure the pressure and position within each cell. I'll elaborate on that below.</p>
<p>A prototype design might look as follows, going top-to-bottom:</p>
<ol>
<li>adhesive plastic foil cover (large adhesive sheet),</li>
<li>column strips,</li>
<li>double-sided adhesive sheet with large holes cut out at each row-column intersection, to provide an air-gap between rows and columns,</li>
<li>row strips,</li>
<li>a non-conductive base plate (say an acrylic sheet) covered with double-sided adhesive. The base plate should offer a 1/2-3/4 inch margin around the grid, so that the terminations can be properly retained without stressing the rows and columns.</li>
</ol>
<p>A sheet of thin silicone can be installed on top of this sensor assembly, for a softer feel.</p>
<p>The intersection of each row and column is called a cell.</p>
<p>When assembling, it's fairly important that the columns stick well to the top foil cover, and that the rows stick well to the base plate. This ensures that the air gap will not be prematurely bridged. Thus you should assemble (1)+(2) and (4)+(5) separately, then install the (3) on either one, and then sandwich it up.</p>
<p>If you wish the cells to feel springy and somewhat "weird", you can leave the air-gap enclosed, with air trapped inside. Alternatively, you can cut a small central hole through each cell in the (4)+(5) assembly, prior to sandwiching it with the rest of the sensor. This vents the air gap and offers a different feel.</p>
<p>A half inch on either end of each row and column strip should protrude from this sandwich. Copper tape with conductive adhesive is used to get connections to the ends of each row and column strip. Make sure that you solder connecting wires to the copper tape <em>before</em> you attach them to Velostat. Velostat has <strong>very low melting point</strong>. You will ruin your painstakingly assembled sensor assembly if you forget that (yeah, I know from first-hand experience).</p>
<p>When mounting the row- and column-strips, it's important to slightly pretension them, so that they are perfectly flat when applied to the adhesives.</p>
<p>As far as I can tell, that's more-or-less Roger Linn's design, inasmuch as the sensor board's picture and the <a href="https://github.com/rogerlinndesign/linnstrument-firmware" rel="nofollow noreferrer">firmware</a> can be used for reference.</p>
<p>With ample experimentation, you should be able to get to <em>cut</em> the Velostat strips using <a href="http://us.cricut.com/home/" rel="nofollow noreferrer">Cricut</a>, <em>while</em> already laminated to either the cover or the base plate. After cutting, you can peel off the thin isolation strips between the rows/columns. This would be useful if you wanted to have a more accurate sensor without swearing each time a column or row stuck down to the adhesive before you got it properly positioned :)</p>
<h2>Limitations</h2>
<p>When you actuate four corners of any rectangle on the sensor plane, you short two rows and two columns, and thus effectively take them offline and unusable for other measurements.</p>
<p>To overcome this limitation would require to inter-row pick-offs (connection points) on every column, not only at the ends of each column. For a 4 row matrix, you'd need 5 connections on each column - on each end, and between each row. This would complicate the design.</p>
<h2>References</h2>
<p>A basic, single-cell design for Z-axis sensing can be seen <a href="http://iainmccurdy.org/diy/forcesensorlowprofile/" rel="nofollow noreferrer">here</a>. Since it has a single Velostat square without separate row/column pick-offs, it can't sense the pressure position. A simple modification to this FSR would be to attach narrow column pick-offs along the Top/Bottom edges on the front face, and along the Left/Right edges on the back face. It'd allow read-out of X, Y and Z values.</p>
<h1>Scanning</h1>
<h2>Z (pressure) detection</h2>
<ol>
<li>Both ends of one row are grounded.</li>
<li>Both ends of one column are attached to the same A/D channel input and a pull-up (divider) resistor. The resistor forms the upper half of a voltage divider, the bottom half is the pressure-sensitive resistance between the row and the column. The sensitivity of each grid position is different, so there needs to be a per-position multiplier applied to normalize the reading.</li>
</ol>
<p>Once you've detected a touch within a cell, you can do more: you can detect the <em>position</em> of the press within the cell. Thus you can do pitch bending and texture modulation.</p>
<h2>X position within the cell</h2>
<ol>
<li>The ends of one row are connected to 0V and VCC, forming a position-to-voltage converter.</li>
<li>Both ends of one column are connected to the same A/D channel.</li>
</ol>
<h2>Y position with the cell</h2>
<ol>
<li>The ends of one column are connected to 0V and VCC, forming a position-to-voltage converter.</li>
<li>Both ends of one row are connected to the same A/D channel.</li>
</ol>
<h2>How to do it on the cheap?</h2>
<p>The sensor surface itself can be assembled for under $100 in materials, much less if you aim for a small surface. The most important tools that you'll need are an X-acto knife with <em>sharp</em> blades for it, and a steel ruler to cut the materials. Some experimentation on a single cell is necessary to evaluate the particular materials used.</p>
<p>An ingenious way of scanning such grid without need for any signal conditioning is given below. This is a simplification over the original design, which uses analog switches and some signal conditioning. It still performs adequately and has the advantage of requiring no components external to the MCU, save for a few resistors. The assumption is that rows are physically no shorter than columns - this helps with the accuracy of Z sensing. You can of course play it in any orientation you wish.</p>
<p>All we need to interface to the sensor surface are the GPIO pins: no external switches needed!</p>
<p>The sensor performs adequately even if you connect the A/D channel to only one end of a row or column, and leave the other end floating. This allows us to use the pin multiplexer functionality present in most any MCU with analog inputs.</p>
<p>The sensing of one cell operates as follows, with all other pins set as inputs:</p>
<ol>
<li>Z: both ends of the row to 0V; one end of the column to A/D and pull-up.</li>
<li>X: one end of the row to 0V, another end to VCC; one end of the column to A/D.</li>
<li>Y: one end of the column to 0V, another end to VCC; one end of the row to A/D.</li>
</ol>
<p>Suppose we have a 4x4 grid and 8+8+4 GPIO pins, 8 of which can perform A/D conversion. The sensor grid has 16 direct connections to GPIO: two ends of each of 4 rows and columns. Let's label the ends of rows as 0L, 0R through 3L, 3R, for left and right ends of rows 0 through 3 respectively. Let's label the ends of columns as 0T, 0B through 3T, 3B, for top and bottom ends of columns 0 through 3, respectively.</p>
<ol>
<li>The <em>r</em>L and <em>c</em>T ends go to GPIO pins that can double as A/D inputs.</li>
<li>The <em>r</em>R and <em>c</em>B ends go to regular GPIO pins.</li>
<li>Each <em>c</em>T is connected via a pull-up resistor to another GPIO pin, we can call those pins <em>c</em>D.</li>
</ol>
<p>The sensing of a cell with given <em>r</em>ow and <em>c</em>olumn is then achieved by simple reconfiguring of GPIOs. The trick is to realize that any GPIO configured as <em>input</em> is effectively <em>disconnected</em>.</p>
<ol>
<li><p><strong>Z</strong></p>
<ul>
<li><em>r</em>L and <em>r</em>R set as output, driven to 0.</li>
<li><em>c</em>B set as input.</li>
<li><em>c</em>T set as A/D input.</li>
<li><em>c</em>D set as output and driven to 1. This connects the top half of the voltage divider to the cell.</li>
<li>All others set as inputs.</li>
<li>The A/D value is proportional to Z force, with different scale for each cell.</li>
<li>Once a given cell is classified as "touched", you can then also obtains its X and Y value.</li>
</ul></li>
<li><p><strong>X</strong></p>
<ul>
<li><em>r</em>L set as output, driven to 0.</li>
<li><em>r</em>R set as output, driven to 1.</li>
<li><em>c</em>B set as input.</li>
<li><em>c</em>T set as A/D input.</li>
<li>All others set as inputs.</li>
<li>The A/D value is proportional to the X position.</li>
</ul></li>
<li><p><strong>Y</strong></p>
<ul>
<li><em>c</em>B set as output, driven to 0.</li>
<li><em>c</em>T set as output, driven to 1.</li>
<li><em>r</em>L set as input.</li>
<li><em>r</em>R set as A/D input.</li>
<li>All others set as inputs.</li>
<li>The A/D value is proportional to the Y position.</li>
</ul></li>
</ol>
<p>There is some logic involved in tracking a touch as it moves between cells, but this can be ignored if the sensor is designed with wide large cells - say 1x1 inch.</p>
<p>All GPIO pins should be configured for high-current drive mode, to lower their impedance and improve the sensitivity.</p>
<p><img src="https://i.stack.imgur.com/edDm9.png" alt="schematic"></p>
<p><sup><a href="/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fedDm9.png">simulate this circuit</a> – Schematic created using <a href="https://www.circuitlab.com/" rel="nofollow">CircuitLab</a></sup></p>
<p><img src="https://i.stack.imgur.com/ukxUj.png" alt="schematic"></p>
<p><sup><a href="/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fukxUj.png">simulate this circuit</a></sup></p>
<h2>In Closing</h2>
<p>As you can tell, I've decided to make one for myself for less than $1.5k sticker price, and have some fun while doing it :)</p>
<p>If your student wished to leverage LinnStrument's open-source firmware with minimal changes, then the design could be based on <a href="http://arduino.cc/en/Main/arduinoBoardDue" rel="nofollow noreferrer">Arduino Due</a>, with some external analog switches and an external 12-bit A/D converter. The original design uses <a href="http://www.ti.com/product/ads7883" rel="nofollow noreferrer">ADS7883</a>, but it's a simple change to just one function to use another converter. The source code should be portable to most any platform with a C++ compiler, as long as it's fast enough.</p>
| <p>One of my students are planning to make a simple musical keyboard with PIC microcontrolers, using MIDI output.</p>
<p>The main problem now is about the pressure/force sensor. I've found a good alternative in this question about <a href="https://electronics.stackexchange.com/q/6621/1757">flexiforce</a>.</p>
<p>I'm wondering if there is a simpler sensor alternative, without ampops, to be used in AD input.</p>
<p>Thanks.</p>
| Pressure/Force sensor | 2010-11-20T13:20:32.020 |
7018 | |power-supply|transistor-array| | <p>Just because two different supplies both have a terminal labeled 'ground' doesn't necessarily mean that those nodes are at the same voltage. In fact, if you have two supplies that have isolated output, you could have almost any potential between their ground lugs, unless you strap them together. You could find a DC offset or even significant AC between the grounds of two isolated supplies. To establish a proper relative voltage levels within your system, each component needs to have a common voltage reference, and usually that's the ground node, so you connect them for that purpose.</p>
| <p><br>
The other day I was playing with a ULN2803a and a stepper motor. I spent ages trying to work out why it wasn't working and why i was reading ~14V as an output on the PIC I was using. So why did I have to connect the 0V of both supplies together?<br>
Thanks in Advance,<br>
Dean </p>
| Why do 0v have to be connected when using two power supplies and ULN2803A? | 2010-11-20T14:33:46.863 |
7028 | |noise| | <p>From a quick look at the two datasheets:</p>
<ul>
<li><p>You should <em>expect</em> the 2981 to have very sensitive inputs - these are voltage driven logic inputs, which take a few hundred uA max to turn them on. They're expecting to be driven by a source which is confident about what voltage it's driving. If you disconnect them, you can expect them to wander around.</p></li>
<li><p>The segment outputs of the 7219 are current source outputs, which are expecting to supply current (mA) to the anode of an LED - instead you've connected them to a high-impedance input which basically draws no current at all.</p></li>
</ul>
<p>I'm not really clear what the 2981 is bringing to the party here, but I guess you want more segment drive. If that's the case, you should convert the SEGx current outputs to voltage outputs, by arranging a pull-down resistor on each one. You will need to chose the current programming for the SEGx drives, and the resistor value, to give you sensible input voltages for the 2981.</p>
| <p>I'm playing with <a href="http://www.allegromicro.com/en/Products/Part_Numbers/2981/2981.pdf" rel="nofollow noreferrer">UDN2981 source driver IC</a>. But its inputs are so sensitive that the noise collected by connector wire switches them on. A simple touch is enough to set it on, but actually I don't want to make a touch sensor :)</p>
<p>I tried using pulldown resistors, but only under 1K worked successfully in all conditions, which is too small for pulldown, I think. </p>
<p>Are there other tricks to avoid false switching?</p>
<p>EDIT: added schematic
<img src="https://i.stack.imgur.com/t3lh5.png" alt="alt text"></p>
<p>It should display 3
<img src="https://i.stack.imgur.com/1XFa1.jpg" alt="alt text"></p>
| How to avoid input noise? | 2010-11-20T20:30:08.177 |
7033 | |transformer| | <p>A transformer secondary can be approximately modeled as a <a href="https://secure.wikimedia.org/wikipedia/en/wiki/Th%C3%A9venin%27s_theorem" rel="nofollow">Thevenin equivalent voltage source</a>. Like any real-world source, it has output impedance, and since it's a passive device, that impedance is essentially fixed. This means that the more current you draw, the lower the voltage gets.</p>
<p>(More experienced engineers than I will have to speak as to the physical nature of the output impedance; it's obviously some combination of the windings' resistance and the transformer secondary's impedance at the line frequency, but the inductance of a transformer is also variable with load in ways I don't know how to quantify.)</p>
<p>Transformers are often rated by just how much voltage difference there is between full spec'd load and open load. A 5% transformer drops 5%, a 1% transformer drops 1%. So a 5% 20:1 transformer is 20:1 at full load, but more like 21:1 at no load.</p>
<p>To make things worse, the AC input to a transformer from the power grid is not guaranteed to be 230VAC. It's more like 230VAC +-10%, depending on where you are in the world and what time it is. So even if your load was constant, and even if your transformer had zero output impedance, your output voltage will <em>still</em> be unregulated; it will vary with the input voltage.</p>
| <p>A transformer has a fixed output ratio. E.g. 10:1, for a 23Vac supply from 230Vac. But it is found that under light load the voltage rises above the nominal (at rated load) - why?</p>
| Why are transformers unregulated? | 2010-11-20T22:35:46.557 |
7041 | |pcb|analog|noise|pcb-design|decoupling| | <p>I almost always place the decoupling caps immediately under the device for which they are decoupling (though if you can fit the 100 nf on the top side, that's fine).</p>
<p>Generally, you want 1 via per power pin, and you want to place the via as close to the pin as possible, and the 100 nF cap as close to the vias as possible. Also, make the vias as large as will fit. This devices does not have a exposed pad on the bottom, which makes things easier.</p>
<p>The bottom layer is then used for power routing, and the top is for signals.</p>
<p>Putting the decoupling components directly under the part is generally only a problem when you are doing manufacturing, because boards with all components on the top are cheaper than boards with components on both sides.</p>
| <p>I am working on a project that requires the usage of a AD7656 16-bit high speed converter. This chip comes in a 64-LQFP package, which means the package is rather small. Because the prototype boards will be hand soldered, I'm using 100nF 0603 X7R decoupling capacitors in combination with 10uF 1210 ceramic, as a minimum recommended amount in the datasheet. I can't use smaller capacitors, furthermore the footprints are set on Medium density to make it possible to hand solder them.</p>
<p>Unfortunately there isn't a recommended layout specification of this IC available. I have problems routing the decoupling caps. It's impossible to place both the 100nF and 10uF together closely to the IC, whilst maintaining space for the signals (parallel bus, etc.) to get out as well. </p>
<p>Now I have got 2 choices:</p>
<ul>
<li><p>I place the decoupling caps to the back of the PCB, which I don't use around the A/D and MCU for noise purposes. </p></li>
<li><p>I place the caps further away, but that might get to a distance of 5 cm.</p></li>
</ul>
<p>Placing the caps to the back of the PCB seems like the easiest solution, maybe with paralleling 2 via's to the top to reduce the loss of the PCB. My question is, will this 'work' i.e. how will this affect the performance and noise? Or would I be better of keeping all of the capacitors at the top of the PCB?</p>
| Decoupling of A/D converter | 2010-11-21T11:20:48.173 |
7042 | |hdl|manufacturing|asic| | <p>In addition to answers provided here, <em>which remain accurate</em>, the most affordable option yet to surface is provided by <a href="https://tinytapeout.com/" rel="noreferrer">Tiny Tapeout</a>.</p>
<p>You can get a design on a chip for as low as $20*, which brings it within reach of hobbyists. Possibly more importantly, circuits can be designed using free and open-source tools, and allows anyone with a web browser to submit and simulate designs (by leveraging GitHub Actions for synthesis). Contrast this with ~$200k per-user-per-year design tools that are common in the industry.</p>
<p>How can they possibly reach that low price? As the name implies, this targets <strong>tiny</strong> integrated circuits. The basic idea is to order a single MPW (Multi-Project Wafer, as described in other answers) shuttle, and to put tiny designs from multiple people on it, plus a control circuit to address the correct circuit. Currently they order from <a href="https://efabless.com/" rel="noreferrer">efabless</a>.</p>
<p>This has plenty of limitations in terms of surface <a href="https://tinytapeout.com/faq/#how-big-can-my-design-be" rel="noreferrer">(150 x 170 µm)</a> and capabilities (limited pad count and I/O speed), but it also is the most affordable option, which makes it extremely promising for hobbyists and students.</p>
<hr />
<p>*The price there is $20/design for having them fabricated, and $100/board to receive a board that contains a chip with all the designs, <a href="https://tinytapeout.com/runs/" rel="noreferrer">hopefully well documented</a> by their respective authors (though you could just select your own).</p>
| <p>I have browsed several ASIC manufacturer's webs, but I haven't found an actual number.
I assume there would be a fixed cost associated with creating masks and such and then there will be a cost per unit.</p>
<blockquote>
<p><strong><em>Note:</em></strong> that I don't actually want to have an ASIC made, I'm just curious.</p>
</blockquote>
| How much does it cost to have a custom ASIC made? | 2010-11-21T11:23:27.793 |
7049 | |microcontroller|pic|pickit| | <p>Watch for stack overflows. Maybe you have too many nested calls to functions. Try to iron it out by calling them one after another where possible.
Some functions might as well be replaced by macros. That might add a bit more weight to your code, but will keep your stack low.</p>
| <p>I have some buggy code, which is causing my processor to crash. I'm almost certain in what function it's in, but I don't know how to narrow down what the crash is, or where it is, for that matter. I know this isn't a Microchip support forum but I suspect someone there knows how to find out what the problem is. I am <strong>not asking for the solution</strong> but instead how to find the solution. I have a PICkit 2 with software v2.32.0, and I'm debugging a dsPIC33FJ128GP802.</p>
| PICkit 2: find out why my processor is crashing | 2010-11-21T20:17:02.197 |
7062 | |infrared|ir-receiver| | <p>You can build one from the <a href="http://www.lirc.org/receivers.html" rel="nofollow">official LIRC instructions</a>.</p>
<p>You could also very easily hook up an Arduino, Mini, Nano, Pro Mini, or Micro with a simple receiver and library. It will communicate via serial (over USB) to WinLIRC on your computer.</p>
| <p>I need to control my PC with an IR remote control.</p>
<p>The piece of software I think I can use is WinLIRC. Or can someone can suggest something else?</p>
<p>Please can someone give me the simplest hardware design for an IR-Receiver?</p>
| Design for a simple IR-Receiver for PC | 2010-11-22T06:04:16.840 |
7066 | |ac| | <p>Not my field, but if we had say 1-5 hz across long lines and 5-20 for shorter height and distance lines (for safety, so the same effect of not instantly dying from the shock still applies) and then have decently high frequency converted at the entrance to buildings, that way syncing would be quick and easy for grid tie systems, but all the in home transformers would use the high frequency, or something along those lines.</p>
| <p>Someone told me that if we used something like 1 kHz AC instead of 50 or 60 Hz AC, it would end up being much cheaper and efficient, because we could use smaller transformers. Is this true? It seems like it would probably cost more as the generators would have to spin much faster - also, it could lead to more losses due to the skin effect. (Just out of curiosity.)</p>
| High frequency mains transmission | 2010-11-22T09:53:36.263 |
7069 | |analog|integrated-circuit|buffer| | <p>You are looking for AD8244 that has 4 channels in a MSOP-10 package (4 inputs, 4 outputs and 2 for gnd and power supply). There are others like that but are more difficult to find.
The good thing is power supply can go from 3-36Vdc, the bad thing is the only 3MHz bandwith that is good enough for standard microcontrollers ADC but not enough for other uses.
You could use only one opamp but use an analog switch/multiplexer to switch from different sources like the ADG1606 that can switch from 16 inputs
<a href="https://i.stack.imgur.com/gOGq5.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gOGq5.png" alt="AD8244 analog buffer"></a></p>
| <p>I need to buffer an input signal such that I do not load down the source, which is a 100k resistor. However, I need to buffer at least 6 channels, and for more advanced models I'd like to move to 10 channels (for the more advanced one I'd be okay using multiple chips though.) </p>
<p>I'd rather <strong>not use op-amps</strong>, because they will take up considerable space - just wiring the inverting or noninverting to the output, for example, uses a lot of space for traces - also, half the pins would be unneeded. </p>
<p>I'm not sure what chip or type of chip to be looking for - all the buffers I've found so far only work for digital logic, not analog signals. The buffer should have very low input bias current (nanoamps to hundreds of picoamps), like a JFET op-amp.</p>
| Analog buffer without op-amps | 2010-11-22T10:43:36.723 |
7082 | |robotics| | <p>eBay has a bunch of <a href="http://shop.ebay.com/?_nkw=bill+counter" rel="nofollow">bill counters</a> currently listed. If you just need one (rather than needing an OEM part so you can design something for production), this may be a good source.</p>
| <p>At the moment I want to build a machine that counts money (money counter machine). When the user puts in the money bills, it will scan them, count them and send the results to a program running on a PC.</p>
<p>I really don't know the kind of hardware I need to build this machine. I have been googling for a while but can't seem to find any place that will give me a good answer.</p>
<p>I will also create a software that will receive the counting from the machine. Creating the software is not a problem. What I need now is how to build this machine and where to get the hardware.</p>
<p>My main concern now is which hardware do I need to create this machine and probably where to get it.</p>
<p>If I decide to buy an existing machine without building it myself, is it possible to create one software that will work with any machine or do I have to write the software for each particular machine I may choose (in case I change the machine later).</p>
<p>Where can I buy an existing machine?</p>
| Money Counting Machine | 2010-11-22T17:05:48.697 |
7089 | |schematics|dxdesigner|drc| | <p>Here's my working list.</p>
<p>Migration are all on: </p>
<pre><code>drc-001 Property can't be mapped to Common Properties ^(~?[a-zA-Z_0-9+-@.# ]+)$ Error
drc-002 Invalid net name format ^(~?[a-zA-Z_0-9+-.]+)$ Error
drc-003 Invalid property value format Error
drc-004 Invalid symbol name format ^(~?[a-zA-Z_0-9+-]+)$ Error
drc-005 Property name exceeds maximum length 40 Error
drc-006 Property value exceeds maximum length 80 Error
drc-007 Net name exceeds maximum length 120 Error
drc-008 Symbol name exceeds maximum length 120 Error
</code></pre>
<p>Electrical doesn't check voltage and power</p>
<pre><code>drc-201 Open collector pin not pulled up Error
drc-202 Open emitter pin not pulled down Error
drc-206 Tristate buffer not pulled up or down Error
</code></pre>
<p>Integrity</p>
<pre><code>drc-401 Missing symbol property Error
drc-402 Missing symbol pin property Error
</code></pre>
<p>(change the Properties to the column you are using, e.g. ITEM. If it is multiple words, put double quotes around it).
Since I'm not using Links these may not be useful</p>
<pre><code>drc-820 Isolated link Error
drc-821 Un-named link Error
drc-822 Multiple destinations Note
drc-823 Link and net naming consistency Warning
</code></pre>
| <p>I am using DxDesigner for the first time (9.2). When running a Design Rules Check (DRC) there are many rules that can be applied. Many of them make sense to check, e.g. "Property name exceeds maximum length". Others are giving me trouble, e.g. Un-driven Net is an error if I enable it when a net is driven by a transformer with pin type analog. Which ones do you use? Disable? Check, but often ignore the notes or warnings?</p>
<p>Updated 11/23/2010: Under Connectivity here are some I had questions on.</p>
<pre><code>drc-101 Output and bidirectional pins connected together
drc-102 Output and tristate pins connected together
drc-103 Un-loaded net
drc-105 Un-driven Net
drc-106 Multiple Output Drivers
drc-116 Output directly connected to Power or Ground
</code></pre>
<p>Note that I am not doing circuit simulation.</p>
| Suggested schematic check DRC settings for Tools>Verify in DxDesigner | 2010-11-22T18:46:45.160 |
7092 | |high-frequency| | <p>Here you find a physical explanation which is using maxwells law.
<a href="https://physics.stackexchange.com/questions/5628/skin-effect-and-currents">link to physics.stackoverflow</a></p>
| <p>What is meant by the skin effect?</p>
| What is the skin effect? | 2010-11-22T23:07:24.673 |
7097 | |durability| | <p>Don't use anything mechanical if you can avoid it - use solid state (like SSR's instead of mechanical relays, capacitive sensing/force sensing instead of switches, etc). </p>
<p>Use protection for every possible contingency - if it gets struck by lightning it needs to keep working.</p>
<p>Don't require any active cooling - fans break or get dirty too easily. </p>
<p>If it's in any kind of high-vibration environment, don't use connectors. Solder everything to the board.</p>
<p>If necessary, use redundant modules. I believe one of the Voyager probes has five independent computers any three of which are on at a time. They all work on the same problem and the solution that at least two of them agree on is used. The computer that created the bad solution is turned off and another is turned on in its place.</p>
<p>Have the ability to update any software on the device in the field when you find errors.</p>
| <p>Creating the Electronic circuits is <code>Ok</code> not so much complicated for experts. But needs to think about the persistence of the electronic circuits. Its very difficult to make the circuits to work for life time. But its important to have the long run electronic circuits.</p>
<p>Of course it depends on individual components that we assemble on the PCB. And are there any factors that need to be keep in mind while choosing and assembling the components to have high durability.</p>
| Things that to be considered while choosing electronic components to get high Durability | 2010-11-23T09:07:44.133 |
7103 | |led|button| | <p>I don't usually answer my own questions but I think with a few days of internet research I've found the best one I can get. TL1240 comes in a 6mm x 6mm package and has an LED built in. I'll look for alternatives, but so far this is the best, and even better, is almost the same size as my original non-illuminated switches. <a href="http://gb.mouser.com/ProductDetail/E-Switch/TL1240GQ1JCLR/?qs=sGAEpiMZZMsqIr59i2oRcmmDUi6NoIX9MEv1LMXmH2s%3d" rel="nofollow">Mouser stock them</a> (in the UK) for £1.39 each, which is a pretty good price. Microswitches with LEDs would be good but I think I'd be hoping for too much there!</p>
| <p>I'd like to add some kind of illumination to the buttons on my project. To that end, I was thinking of illuminated pushbuttons, with built in LEDs. However, the ones I found are very big (I'm looking for small microswitches, or at the largest 6mmx6mm tactile switches) and/or they use 120V/240V neon bulbs, not LEDs, and are designed to switch mains.</p>
<p>I was also considering getting transparent switches (made of clear plastic of one form or another) and putting LEDs underneath them. The idea is that the project can be used at night so a green or orange colour would probably work well. Does anyone have experience with this, have you done something similar, what types of buttons did you use?</p>
<p>Something <a href="http://uk.farnell.com/alps/skhhaka010/switch-tactile-pcb-0-98n/dp/1656423" rel="nofollow">like these</a> but with LEDs in them.</p>
<p>Please note I'm not looking for specific part numbers - those would be helpful though - but instead ideas on how to accomplish this and types of switches to be looking out for.</p>
| Illuminating buttons | 2010-11-23T14:01:05.540 |
7109 | |signal|digital-logic| | <p>best to split your bidirectional signal into a send and receive line and then you can level shift each individual and do what you need to on the other side with them. Split them using a open collector transistor or open drain mosfet for the transmit side, and use a driver to pass the signal in the opposite direction for the recieve side.</p>
| <p>I have two digital devices to connect, both use 20 data lines but one works at 3.3V and the other at 1.8V, and most of the lines are bidirectional. The operating frequency should be at least 5 MHz. I stumbled upon this solution:</p>
<p><a href="http://www.rocketnumbernine.com/2009/04/10/5v-33v-bidirectional-level-converter/" rel="nofollow">http://www.rocketnumbernine.com/2009/04/10/5v-33v-bidirectional-level-converter/</a></p>
<p>Which seems adequate (provided I make the corresponding changes for the desired voltage levels) but I don't like the fact that it needs 1 IC and 2 resistors for each data line. Does anyone know about an IC that does a similar job but has many channels (ideally 20 or near that) in a single package, or any equivalent solution to the problem?</p>
| Is there a bidirectional level converter IC for multiple I/O channels? | 2010-11-23T19:39:41.820 |
7113 | |mains| | <p>This doesn't apply to you, but maybe someone searching will find this: Semiconductors are light sensitive. If you have a precision analog circuit, and parts of it are in translucent cases, like glass diodes or metal-can op-amps (the bottom seal is translucent), you can expect significant offset shifts when light shines on the circuit. Modern black epoxy packages are less susceptible. It's easy enough to check if this is causing the problem: If the problem stops when the circuit is covered by a box or something, the problem is the light, not the EMI.</p>
| <p>Whenever I turn on my desk lamp, my board crashes. Sometimes I get garbage out of the serial port, sometimes it resets.</p>
<p>I tried adding some extra bypass capacitors on my breadboard, but that made no difference.</p>
<p>(My desk lamp uses a 20W, 12V halogen bulb. It has a transformer in the base)</p>
<p>Can anyone offer suggestions as to why this might happen and how I can stop it?</p>
<p>Here are two of the boards - they were USB dongles, but are both now powered from a single wall-wart via a 3.3V voltage regulator.</p>
<p>Watching on a scope, when I flick the light switch I see a spike on both 3V3 and wall wart lines.</p>
<p><a href="http://www.flickr.com/photos/54388270@N04/5185260619/lightbox/" rel="nofollow noreferrer"><img src="https://farm5.static.flickr.com/4128/5185260619_6f731b2d43.jpg"></a></p>
<p><b>Edit:</b></p>
<p>Here are traces of the input and output of the 3V3 regulator when turning the light on and off respectively.</p>
<p><a href="http://www.flickr.com/photos/54388270@N04/5203005660/sizes/l/in/photostream/" rel="nofollow noreferrer"><img src="https://farm6.static.flickr.com/5243/5203005660_fe875771ea_m.jpg"></a><a href="http://www.flickr.com/photos/54388270@N04/5203003890/sizes/l/in/photostream/" rel="nofollow noreferrer"><img src="https://farm5.static.flickr.com/4110/5203003890_7a4a748f72_m.jpg"></a></p>
<p>5V is on the top, 3V3 on the bottom</p>
<p>The regulator is a <a href="http://www.datasheetcatalog.org/datasheet/zetexsemiconductors/ZSR.PDF" rel="nofollow noreferrer">ZSR330</a>.</p>
<p>Edit:</p>
<p>Some careful reading of the datasheet threw this up:</p>
<blockquote>
<p>The RESET_N pin is sensitive to noise
and can cause unintended reset of the
chip. For a long reset line add an
external RC filter with values 1 nF
and 2.7 kΩ close to the RESET_N pin.</p>
</blockquote>
<p>My programming cable connects a long wire via a breadboard to the reset pin. I suspect that this was the problem.</p>
| Why does turning on my desk lamp crash my board? | 2010-11-23T22:17:55.003 |
7120 | |surface-mount|mains| | <p>Bear in mind that even though the part is OK for 400V, you may need a slot in the PCB to ensure that there's sufficient clearance between the pads. </p>
<p>In general, axial devices beat SMT for transients simply because they have higher power handling capability. </p>
<p>Power supplies often use tons of surface mount components - cheap, made in Asia commodity power supplies often don't use any SM because they're cheap and commodity products.</p>
<p>(Power supplies that I've help design have hundreds, if not thousands of SM parts - not in the power train, but in control and monitoring.)</p>
| <p>I've found some <a href="http://uk.farnell.com/yageo-phycomp/rv0805jr-07100kl/resistor-0805-high-voltage-5-100k/dp/1376988" rel="nofollow noreferrer">400V 0805 resistors</a>. However, as in my previous question, I noted that <a href="https://electronics.stackexchange.com/questions/6789/why-are-power-supplies-almost-always-made-using-through-hole-components">almost no power supplies used surface mount components</a>.</p>
<p>One of the things I'm working on is a capacitive power supply. This is connected to the mains and has no isolation, but operates inside a completely sealed box so there is no hazard to the user there. However, I'm not entirely sure if it's okay to use 0805's when dealing with such high voltages... it just seems like arc-over or something similar would happen. And, say there was a fault - would through hole be better at handling a line transient than SMT?</p>
| Is it okay to use SMT for 250VAC parts? | 2010-11-24T00:05:49.513 |
7126 | |motor-controller| | <p>I suspect the resistance is the resistance of the internal power MOSFET(s). In which case it's an utterly pointless measurement as the internal resistance of the battery, the resistance of copper tracks, and the virtual "resistance" created by charging and discharging the MOSFET's gate will easily overwhelm this tiny Rds(on). </p>
<p>If you want to know the effective resistance of your ESC you can perform an experiment. Set up a motor on your ESC. Wire it in for maximum speed (this would probably involve wiring the throttle input to a battery line.) Turn on the motor, making sure nothing is attached to the rotor. Put an ammeter in series - preferably a clamp-on one - current will easily exceed the 10A rating of most series meters - and measure the current going to the motor. </p>
<p>Then, measure the voltage across the battery, and across the motor. You could try measuring the drop across the ESC as well but it wouldn't work if it employs some virtual ground or has a current shunt built in, as this will skew your readings. Calculate the voltage drop across the ESC and put this into Ohm's law: R = V/I. Note this is only an average resistance and depends on the state of the battery.</p>
<p>For yuks, measure the current from the battery to the ESC and use that to make input-output power figures. The efficiency is the output divided by the input, in percent. This will probably be more useful than any resistance figure.</p>
| <p>In hobby market (rc planes, cars, robots) one of the parameters manufacturers of the brushless motor ESC specify is resistance. ESC in this case means "electronic speed controller" and is a device used for commutation and speed control of the electric engine. </p>
<p>Is there a standard (written or informal) how this parameter is characterized? If yes how it is done?</p>
| How is resistance in brushless motor ESC calculated by the manufacturers? | 2010-11-24T07:06:22.733 |
7129 | |arm|delay|keil| | <p>A hardware timer reference is preferred because a good optimizer could remove the loop altogether or alter it based on settings. The other problem with timing loops not mentioned here is if an interrupt occurs during your timing loop, it could take much longer. Interrupts should be short anyway but not every system follows that mantra.</p>
| <p>How to implement delay function in Keil ARM MDK that waits given time in microseconds that can be recompiled to any reasonable clock speed defined in Keil project settings ? And all of this without using timers. </p>
| How to implement delay functions in Keil ARM MDK | 2010-11-24T16:56:16.273 |
7133 | |msp430| | <p>Here are some o the projects that i have done,they mainly deals with interfacing 7 segment LED displays,serial and RS485 communication,building robots etc.</p>
<ol>
<li>A DIY tutorial on building a two wheeled robot from scratch using MSP430 launchpad and L293D motor control chip.I have written a detailed account on building the robot base and electronics using commonly available materials.Source codes for controlling the robot are also provided.You can check the link below for details.</li>
</ol>
<p><a href="http://www.xanthium.in/make-your-own-msp430-launchpad-robot" rel="nofollow">http://www.xanthium.in/make-your-own-msp430-launchpad-robot</a> </p>
<ol start="2">
<li>controlling the DC motors connected to Launchpad through RS485 connection.The control software written in Pytho and CSharp runs on PC and controls the motors through RS485 Protocol. Link is given below.</li>
</ol>
<p><a href="http://www.xanthium.in/remotely-controlling-dc-motors-using-rs485-protocol" rel="nofollow">http://www.xanthium.in/remotely-controlling-dc-motors-using-rs485-protocol</a></p>
<ol start="3">
<li>Interfacing MSP430 Launchpad with 7 segment displays.</li>
</ol>
<p><a href="http://xanthium.in/interfacing-7-segment-led-with-msp430-launchpad" rel="nofollow">http://xanthium.in/interfacing-7-segment-led-with-msp430-launchpad</a></p>
<ol start="4">
<li>Creating an RS485 network between a PC and MSP430 Launchpad.</li>
</ol>
<p><a href="http://xanthium.in/RS485-communication-using-MAX485-and-MSP430-Launchpad" rel="nofollow">http://xanthium.in/RS485-communication-using-MAX485-and-MSP430-Launchpad</a> </p>
| <p>I've got 4 launchpads (I'm a hog, I know, I got 'em while I could) and I'm getting used to the programming, e.g. the timers, ADC, PWM, LPM, etc. I don't have a lot of money and would like to do some projects to solidify my knowledge. What are some little projects I could do on a budget to have fun? The blinky apps only go so far.</p>
| What are some good ideas to practice on the MSP430 | 2010-11-24T21:00:16.177 |
7139 | |components|device|identification| | <p>OMG ! That's a Siemens MKT range capacitor,</p>
<p>2.2nF or 2200pF whichever you prefer, 630V.</p>
<p>Polyester film. Used to see lots of them decades ago, Once very popular, especially in European products. The capacitance value is proportional to the length of the body, which is 'cut' to length to suit the value.</p>
<p>Available in 5mm and 7.5mm pitch.</p>
| <p>I'm trying to identify a part I removed from a compact fluorescent lamp manufactured around 9 years ago (date on the PCB is 17.12.01).</p>
<p>It is a gray hexahedron and it's 7 mm wide, 2 mm long and about 4.5 mm high. Contacts are on the 2 mm sides.</p>
<p>The inscription on it says in the first line 2n2 and in the second line 630.</p>
<p>Judging by the inscription, device seems to be manufactured in a long sheet on which numbers were printed and then cut into 5 mm high segments.</p>
<p>At first I thought it could be some sort of capacitor (PCB has capacitor mark on its location), but after some testing, I was unable to charge it and then measure its voltage (on the other hand, it could be that it has very low capacitance so could discharge itself in the time it takes me to switch my multimeter form ohmmeter mode to voltmeter mode). Also, part which is obviously resistor was next to the unknown device and it too had capacitor mark on PCB.</p>
<p>I did some research on the Internet, but as far as I can tell, 2n2630 is a transistor and this definitely does not look like a transistor, so I'm looking here for ideas on what it could be.</p>
<p><strong>EDIT</strong>
I finally managed to get a nice picture of the part on 1 mm grid. Here it is:</p>
<p><img src="https://i.stack.imgur.com/G4JIU.jpg" alt="alt text"></p>
| What is this part: 2n2 630? | 2010-11-24T23:04:16.363 |
7141 | |display| | <p>1000 mAh / 0.8 / 12 hours = about 100 mA, which is plenty. A parametric search on DigiKey landed half a dozen monochrome LCDs (<em>Display Modules - LCD, OLED, Graphic</em>), and they're all expensive ($200). First on the list is DMF-50036ZNBU-FW-BAN, which draws 30-40mA. I wouldn't recommend getting any of these as they are expensive, but you may be able to source similar ones from China.
I meant to put this as a comment to the OP, but I don't have the points yet.</p>
| <p>I am looking for suitable display options for a battery-powered device, kind of like an e-book reader/tablet/mid device. </p>
<ul>
<li><p>size - 10" or so.</p></li>
<li><p>resolution - preferably a high DPI</p></li>
<li><p>colour - mono/gray</p></li>
<li><p>static - low refresh rate/static is
fine</p></li>
<li><p>power - low enough to last 12 hours
on a ~1000 mAH battery assuming 80%
static usage.</p></li>
<li>Brightness - readable in-doors, mainly. </li>
</ul>
<p>I know of the existence of E-ink, Pixel-Qi and even ChLCD displays. I am wondering if there are any other display options available?</p>
| Suitable low-power ~10" graphical display options | 2010-11-25T04:59:39.707 |
7143 | |embedded|programming| | <p>I suggest that once your students have a decent working knowledge of C and can write, compile, debug and run simple "blinky" type code, you introduce them to a simple task scheduler. <a href="https://www.cs.ucr.edu/%7Evahid/rios/" rel="nofollow noreferrer">RIOS</a> is an excellent choice. It is simple but it already bridges from "doing everything in the loop" to an application which is broken into a number of tasks which time share. This is a great intermediate step between bare-metal and OS's of whatever flavour.</p>
| <p>I am looking for some material (books/sites) related to embedded system programming in C language.
Here in the lab we have available three plataforms: one Microchip PIC18f4550, one Freescale HC12 and one ARM (Beagleboard).</p>
<p>We are willing to teach embedded C with the PIC, assembler with Freescale and embedded operational systems with Beagleboard. Each class will be a six month course.</p>
<p>Open to all advices. </p>
<p>Thanks </p>
| Embedded C programming material | 2010-11-25T12:20:54.137 |
7150 | |rf| | <p>Fundamental means that the local oscillator is simply the difference between the IF and the input frequency. The other type is termed a sub-harmonic mixer, which is driven at a lower frequency which is multiplied in the mixer. The latter is used at much higher input frequencies, making it easier to generate the local oscillator signal.</p>
| <p>Fundamental mixers (in the context of RF Electronics). What are they? What do they do?</p>
<p><a href="http://www.hittite.com/products/view.html/view/HMC557LC4" rel="nofollow">http://www.hittite.com/products/view.html/view/HMC557LC4</a></p>
| What are fundamental mixers? | 2010-11-26T04:35:11.810 |
7156 | |accelerometer| | <p>I think that is the <a href="http://www.kionix.com/accelerometers/accelerometer-KXSD9.html" rel="nofollow">KXSD9</a> from Kionix</p>
| <p>Does anyone know which acceleration sensor was used in the HTC Touch Diamond mobile phone?</p>
| Acceleration sensor in HTC phone | 2010-11-26T11:59:00.920 |
7160 | |pic|c|compiler|hi-tech-compiler|tag| | <p>HiTech C for the PIC24 generates code that is not at all size optimized. I called the support team about this and the well optimized code generator is not available for PIC24. They had promised to do this work, but then were acquired by Microchip, and work on the HiTech PIC24 "C" compiler stopped. They suggested C30. I had already paid a lot of money for HiTech PIC24 "C" a while back and got stranded with a half finished compiler and no offer to swap for Microchip C30. Also our large code base was written with HiTech intrinsics and library use, and would have been a pain to port. We're out of ROM space on our PIC24 part which is a shame because a better compiler would free up about 20% of the space based on the wasteful assembly the compiler produces. All-in-all I think Microchip did not think all aspects of their tool support through, and left many of us stranded.</p>
| <p>Specifically, the PIC24 series.</p>
<p>I tried out microchips C30 compiler, but it seems to be a bit too complicated for me, and I couldn't find any libraries with it.</p>
<p>Then I tried CCS, and it seems far too simple, and I cannot view the code for say, I2C_write, which is quite unnerving for me.</p>
<p>What about Hi-tech C? I did not get a chance to check it out yet, is it in your opinion good or bad?</p>
<p>Are there any other C compilers for pic24 out there? Does not matter if they are free or not, as long as they have some examples.</p>
| What PIC24 C compilers are out there, and what is your opinion or review on them? | 2010-11-26T17:07:58.483 |
7163 | |fpga|books|vhdl| | <p>I definitely recommend every <a href="http://academic.csuohio.edu/chu_p/rtl/index.html" rel="nofollow noreferrer">book written by Prof Pong Chu</a>. </p>
<p>They offer a very comprehensive introduction to RTL design using either Verilog or VHDL. They also provide an introduction to traditional soft cores like Nios from Altera or Picoblaze or Microblaze (2017 edition) from Xilinx. The coding style is clean and the methodology to translate algorithm to FSMD (finite state machines that control data paths) is very useful. </p>
<p>I like all the other books cited previously, but Pong Chu books are clearly my favorite. Ashenden books is more advanced concerning VHDL, but the limits of RTL vs simulation is not as clear as Pong Chu's. </p>
| <p><br>
what book titles would you recommend to get started with FPGAs and VHDL? </p>
<p><strong>edit</strong><br>
I noticed that a few of the recommended books date back from 1996. I can imagine that the devices referred to will be seriously outdated, but has VHDL also much evolved since?</p>
| book recommendations on FPGA | 2010-11-26T17:47:19.143 |
7166 | |msp430|rs232|sd|gps| | <p>The MSP430G2231 doesn't have a hardware UART. The best option is to use a timer to clock your bits in and out.</p>
<p>Here's a good example of how to do this:
<a href="http://www.msp430launchpad.com/2010/08/half-duplex-software-uart-on-launchpad.html">http://www.msp430launchpad.com/2010/08/half-duplex-software-uart-on-launchpad.html</a></p>
<p>Wire your GPS to TX, RX and GND on your Launchpad board.</p>
<p>Writing to an SD card is more tricky. SD cards talk a protocol on top of SPI.
I've written a Bus-Pirate-like SPI explorer for the MSP430 which should get you some of the way there:</p>
<p><a href="http://blog.hodgepig.org/2010/09/10/575/">http://blog.hodgepig.org/2010/09/10/575/</a></p>
<p>On top of the SPI code you'll also need an SD card driver and a filesystem driver (likely FAT if you want Windows compatability). You could simplify things by writing raw data to the SD card - though this will make it harder to read at the Windows end. Linux could read it with <code>dd</code>.</p>
| <p>I'd like to make a GPS logger. I've got a GPS from Microsoft Streets and Trips. I read that it communicates at 4800 baud over RS232 at 3.3 or 5v. I've got an MSP430G2231 from the launchpad kit and I'm a bit fuzzy on how to talk RS232 to this thing. I also want to write to an SD card, preferably to a file so I can pull the data off with a computer. The raw NMEA strings are fine, I can parse those on the computer. The more detail the better. Thanks.</p>
| GPS Data logger using MSP430 | 2010-11-26T20:06:35.617 |
7174 | |motor|speed| | <p>The angular speed attained by the motor is limited by <strong><a href="http://en.wikipedia.org/wiki/Counter-electromotive_force" rel="nofollow noreferrer">counter-electromotive force</a></strong>, aka. back EMF.</p>
<hr>
<p>Current flowing through the wire causes a torque at all points where the wire is not parallel to the magnet's field lines (<a href="http://en.wikipedia.org/wiki/Lorentz_force" rel="nofollow noreferrer">Lorentz force</a>).</p>
<p>When the wire starts rotating, the motor will exhibit the property of a generator: a voltage (back EMF) opposing the current flow from the battery is induced, because the magnetic flux through the wire loop <a href="http://en.wikipedia.org/wiki/Faraday%27s_law_of_induction#Example:_Moving_loop_in_uniform_Magnetic_field" rel="nofollow noreferrer">changes due to movement</a>.</p>
<p>The motor will accelerate until the back EMF is roughly equal to the battery's voltage, with only enough current flowing to provide torque to overcome the friction at this speed.
<img src="https://i.stack.imgur.com/KOmEi.png" alt="Homopolar motor: field lines"></p>
<p>The more voltage is applied, the more rotation speed is required to reach this state of equilibrium.</p>
| <p>What determines the speed of rotation of a <a href="http://en.wikipedia.org/wiki/Homopolar_motor" rel="noreferrer">homopolar motor</a>?</p>
<p><a href="http://en.wikipedia.org/wiki/Homopolar_motor" rel="noreferrer"><img src="https://i.stack.imgur.com/FYsbh.jpg" alt="homopolar motor" title="homopolar motor"></a></p>
| What determines the speed of a homopolar motor? | 2010-11-26T23:01:38.200 |
7175 | |capacitor|temperature| | <p>I can't say for certain how it started, but it's right in between the two MIL-PRF temperature ratings (85C and 125C, see <a href="http://www.dscc.dla.mil/Downloads/MilSpec/Docs/MIL-PRF-39018/prf39018.pdf">MIL-PRF-39018</a>, section 6.1 ). As a standard rule, aluminum electrolytics double their lifespan for each 10C drop in operating temperature, so it may be a convenient middle ground used for industrial and high performance consumer products.</p>
<p>I suspect Mike's correct in stating that the electrolyte chemistry has something to do with it and I would guess that improvements over time have made it more economical to produce 105C rated capacitors.</p>
<p>For further reading I'd suggest <a href="http://electrochem.cwru.edu/encycl/misc/c04-appguide.pdf">Cornell Dubilier's excellent application guide for electrolytic capacitors</a>. They mention a connection between maximum rated temperature and total capacitance that implies that lower rated capacitors will likely be smaller than their higher rated counterparts. Extending the low end of the temperature range is possible but with a rapidly rising ESR.</p>
| <p>Electrolytic capacitors are often rated -40°C to +105°C. I've always wondered about the extra 5°C. This also seems to be the temperature range for some types of microcontrollers, and is marketed as an "extended temperature range", although in reality extended usually goes to +125°C. </p>
<p>Is there any particular reason for this temperature - was it chosen to be 5.0161°C above the boiling point of water at 1 atm (99.9839°C or 100°C), or is there another reason?</p>
<p>Curiosity question - not going to be running any components at 105°C any time soon!</p>
| Is there any reasoning behind making capacitors go to 105°C? | 2010-11-26T23:09:01.563 |
7179 | |microcontroller|pins| | <p>Some high-speed CMOS devices may be destroyed if an input is left floating, but the most common problem one will observe is increased current consumption. On PIC series microcontrollers, the extra current is on the order of hundreds of microamps per floating pin. Not enough to cause device damage, but enough to severely impact battery life in an application that would otherwise draw 5uA. Some chips have options to disable a digital input; if an input is disabled, it may freely be left floating.</p>
| <p>I've heard that leaving a pin floating on an MCU when configured as an input (vs. the default output) is bad for the pin, and can eventually cause it to fail prematurely. Is this true? N.B. in my instance the pin is floating somewhere between 0.3V and 1.3V due to an incoming video signal. This sometimes falls in the no man's zone of 0.8V - 2.0V when operating from 3.3V.</p>
| Is it really a bad idea to leave an MCU input pin floating? | 2010-11-26T23:56:46.577 |
7184 | |arm|msp430| | <p>I second a Circuit Cellar subscription. </p>
<p>As for an ARM board, consider the FriendlyARM micro2440, but I am afraid it is a somewhat over $100. For instance here <a href="http://www.aliexpress.com/wholesale/wholesale-micro2440.html" rel="nofollow">http://www.aliexpress.com/wholesale/wholesale-micro2440.html</a> it is $104, but a whopping $43 shipping.</p>
| <p>I'm at a standstill on ideas for what to get him and would really, really appreciate any recommendations you guys can provide! (Also, he frequents this site but promised to not read this.)</p>
<p>So far, I got him an MSP430 (LaunchPad) dev kit. I'm also getting him a box of random components from Mouser or Element14 with things that he could use. What can I get for him to go with the LaunchPad kit?</p>
<p>Are there any ARM development books that you guys could recommend? He constantly links me to ARM dev boards that he wants (one with an LCD, ethernet, USB, good MCU; pref ARM9, Cortex-M3). Any suggestions on what dev board I could get him?</p>
<p>I was also thinking of getting him a subscription to Nuts and Volts magazine. What other electronics hobbyist magazines are there?</p>
<p>For further information, he also was really interested in high voltage stuff (microwave transformers, spark gaps, etc.) and has recently acquired a nonfunctional (ancient) ham radio, bass amp, several broken TVs (that he has repaired/is repairing).. And he has a logic sniffer, oscilloscope, function generator.</p>
<p>Thanks! :)</p>
| Suggestions on what to get my boyfriend for Christmas? (interested in PIC24, MSP430, Propeller, FPGA, ARM, etc..) | 2010-11-27T04:05:32.513 |
7186 | |untagged| | <p>Try: <a href="http://www.adafruit.com/jobs/" rel="nofollow">http://www.adafruit.com/jobs/</a></p>
| <p>For software hackers/developers there are many. </p>
<p>However, I need a hardware guy (or girl?) for a relatively small project. </p>
<p>Is there a site where I can search for people and see ranks, recommendation, etc.?</p>
| Any reliable site where *hardware* engineers can be hired for small (work-from-home/telecommute) projects? | 2010-11-27T05:00:48.643 |
7187 | |atmega|atmel|interrupts| | <p>@ LoneTech: I figured this site was to help people. Not put them down for lack of information, but to provide it for them if the need is there. Also, Interrupts can be used to interrupt other code without hurting the speed of your main loop. If your button is supposed to change a process and your main loop is controlling a wave or something. INT0 could be used. You also don't know what other operations this individual plans on using it for. </p>
<p>@ Michael: This code took me a while to track down and understand as well. I have written code for AVRs for 5+ years now and for PC 13+ years. Its amazing how little documentation is there at your fingertips. I ran across a nice tutorial and finally it clicked.</p>
<pre><code>void InitINT0()
{
// Enable INT0 External Interrupt
EIMSK |= 1<<INT0;
// Falling-Edge Triggered INT0 - This will depend on if you
// are using a pullup resistor or a pulldown resistor on your
// button and port
MCUCR |= 1<<ISC01;
}
int main(void)
{
//Init Timer
InitINT0();
//Which Interrupt pin you need to enable
//can be found in the datasheet, look at the pin
//configuration, usually within the first 5 pages
//track down INT0 - which is PORTD pin 0.
//This needs to be an input.
DDRD &= 0;
// Enable Interrupts
sei();
//Givin that PORTD0 is the INT0, your button should
//be hooked up to it.
while(1)
{
//Do your operation
}
}
// External Interrupt 0 ISR
ISR(INT0_vect)
{
while (/*Button is down*/) //0 is the pin for your button
{
//Pause your operation , this will pause everything though
//because Interrupts take priority over pretty much everything
//This includes other interrupts and your main loop
}
}
</code></pre>
| <p>I am trying to utilize an ATMEGA2560 and it's interrupt. I have some code that must execute until a button is pressed at which time I need the code to stop and wait for another button press to continue. </p>
<p>Is anyone familiar with this type of circuit and the interrupts?</p>
<p>Here is what I am currently referencing for the <a href="http://www.avrfreaks.net/index.php?name=PNphpBB2&file=printview&t=67358&start=0" rel="nofollow">ATMEGA2560 interrupts</a>.</p>
| Does anyone have any examples or suggestions utilizing Atmel's ATMEGA2560 and external interrupt's? | 2010-11-27T05:24:01.183 |
7190 | |arduino|dc-motor| | <p>Not really, but maybe not because it's not powerful enough.
A DC motor, in general, is built such as when the commutator changes the polarity of the two halves of the coil, a short but very heavy current/voltage impulse is inducated (self-induction) that will basically burn the CMOS chips in the AVR.</p>
<p>If this is really a very small motor, you can avoid this current by adding an antiparallel diode between the AVR output and the ground (a so called runback diode) to short-circuit those inducated pulses, protecting the output of the chip.</p>
| <p>Can I connect a DC motor directly to an Arduino?</p>
| Arduino motor control | 2010-11-27T10:07:46.273 |
7198 | |wifi| | <p>As an alternative to putting an access point onboard, there are some cellphones and PDA's that might have this functionality. They might be smaller and carry their own batteries but might add weight.</p>
| <p>I just read on the description of a <a href="http://www.youtube.com/watch?v=pgqmJyFpWDM" rel="nofollow">YouTube vid</a> that Parrot AR Drone creates its own wifi hotspot. How does it do that? Is it possible to do a similar thing for a UAV project I've been thinking about?</p>
| How do I add a wireless hotspot to my project? | 2010-11-27T13:58:08.527 |
7214 | |microcontroller|programmer| | <p>What we do for production, is to first load a program into the PIC that tests out the board (using a small test board that independently verifies the 3.3v rail is within spec using a couple of comparators, and then we use the ADC on the PIC to check everything else out. We had enough pins left over to allow this (it required some extra resistors to act as voltage dividers for the voltages over 3v). </p>
<p>After the tests pass, the real production code is flashed into the micro. Some additional tests are run, and the PCB is ready for assembly into a case.</p>
<p>This is all done via a program on the PC that only requires an operator to connect the board, click one button, and wait for the result PASS/FAIL. All test results (including ADC readings) are logged. The entire process (including the programming of the PICs via an ICD 3) is controlled via the PC program, which runs batch scripts to do the actual programming. Communication to the PIC to control the tests is done via one of the UARTs, whose pins are brought out to the test board (so in addition to the pins required for programming, we also have TX/RX as a minimum).</p>
<p>We set up several stations like this at our contract manufacturer.</p>
<p>BTW the ICD 3 is <em>much</em> faster than the ICD 2 (USB 2.0 vs 1.1).</p>
| <p>For my Super OSD project I'm going to need to program large batches of MCU's, probably about 10-15 boards an hour. I could just use my trusty PICkit 2 to program them (there are two - maybe three - on each board) but it would be very laborious to load each file (up to 128KB and 256KB in size), hit program, and repeat for each MCU, and probably wouldn't allow me to meet my target speed. Also, the MCU's are surface mount, so I have to have headers on the board to allow this. Ideally, I'd like to remove these headers, but it may not be an option.</p>
<p>So what options are there for mass programming of MCU's - are there faster ways to do it? I'm kind of on a budget of less than $100 USD, so things like Microchip's MPLAB PM3 at $895 USD, while nice, wouldn't be an option.</p>
<p>I'm dealing with PIC microcontrollers of various types. There's a PIC16F887, PIC24FJ64GA002 and dsPIC33FJ128GP802. However, I am also interested in options for AT32 and STM32 processors, as I may also be using them.</p>
<p>Please note, I'm not currently considering ordering chips from the manufacturers pre-programmed because the software may change by the time the chips arrive, and because of the additional cost involved. </p>
| What options are there for programming MCU's in production? | 2010-11-27T21:31:05.530 |
7231 | |microcontroller|arm| | <p>Here is my options:</p>
<ul>
<li>Lots of IO but slow speed acceptable? Gang up AVRs. I have tried talking SMBus over I2C lines and it is at least acceptable.</li>
<li>Need speed? ATSAM series seems good with TQFP100 and TQFP144 packages. We have Arduino SAM3X8E in Arduino Duo. ATSAM also have MII/RMII but interface chip can be challenging. If you want ATSAMA5 line read on and think again, Allwinner A20 probably beats it there.</li>
<li>More speed, multimedia, probably Linux support? Since I am from China a particular native manufacturer is really interesting: Allwinner. Their Cortex-A7 SoCs, $5 dual-core A20 and $10 quad-core A31s, as well as a octa-core big.LITTLE Cortex-A15/7 SoC A80 at $20, all with respectable OpenGL and OpenCL-capable GPU built in, despite in BGA packages, are good enough for middle-to-high-level Android tablets, more than good enough for full-blown Ubuntu Server a few daemons burning GPUs crunching numbers, routing packets at 1Gbps line speed, or driving two 1080P or a 4K display.</li>
</ul>
| <p>I've been using 8-bit AVRS for a few years now. Lately, I've been feeling limited by the peripheral data transfer speeds and higher level libraries. </p>
<p>I'm having trouble finding/picking a new line of microcontrollers to explore. I've looked at </p>
<ul>
<li>NXP - Can't find a programmer</li>
<li>Freescale - Have to register for IDE</li>
<li>AVR32 - Limited chip selection on digikey</li>
</ul>
<p>The NXP chips look really nice, but as with anything that isn't PIC/AVR/Ardiuno the learning curve is pretty steep. </p>
<p>I was wondering if anybody could suggest a line of micro controllers that satisfy (in order of importance) the following requirements</p>
<ol>
<li>Hand solder-able chips. (I can do LQFP 100)</li>
<li>32 bit</li>
<li>Linux host</li>
<li>Free toolchain</li>
<li>Good/free IDE</li>
<li><500$ startup cost for unlimited programming/debugging/compiling</li>
<li>CAN support</li>
<li>Ethernet/USB support</li>
</ol>
<p>I'm willing to look at Freescale and NXP again, if somebody can show me that I've missed some information on their toolchain and programmers. I guess you could say AVR32s are exactly what I'm looking for, but I'm just not happy with their chip selection. They all have higher pin counts and low stock on digikey. </p>
<p>Thanks.</p>
| out growing 8-bit AVRs, not sure where to move on to | 2010-11-28T07:22:51.267 |
7235 | |motor|transistors|driver| | <p>Yes, it can be done very simply, but you don't get much power or position control.</p>
<p><img src="https://i.stack.imgur.com/74lXI.png" alt="schematic" /></p>
<p><sup><a href="/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f74lXI.png">simulate this circuit</a> – Schematic created using <a href="https://www.circuitlab.com/" rel="nofollow">CircuitLab</a></sup></p>
<p>The circuit uses the back-EMF from a single motor coil to drive the transistor, so that one transistor is all that is needed to turn the motor. Because of the back-EMF drive, it can work on different kinds of motors such as pendulums as shown in <a href="https://www.softspotsoftware.com/bedinimotors/Novelty%20Electric%20Motor.pdf" rel="nofollow noreferrer">this patent</a>, <a href="https://bedinimotors.blogspot.com/2010/06/bedini-ssg-circuit.html" rel="nofollow noreferrer">here</a> is a also a good link.</p>
| <p>Is it possible to build a motor driver using only a 2N2222 transistor?</p>
<p>If yes, then how?</p>
| Motor driver using only a 2N2222 transistor? | 2010-11-28T08:31:32.067 |
7244 | |diodes|h-bridge| | <p>Yes. The 1N4007 can withstand a higher reverse voltage(\$V_r\$), 1000V vs. 50V. The 1N4007 may even be a better choice, esp. if your motor is powered by a voltage near 35V. (The 1N4001 is rated for a \$V_{r(RMS)}\$ of 35V.) </p>
<p>While diodes like 1N400x may be well suited as freewheeling diodes in terms of voltage and current (rated at 1A), they're not exactly fast. To protect your transistors Schottky diodes would be a better choice, but they usually have limited \$V_r\$. </p>
<p>Here's the \$V_r\$ for the 1N400x series: </p>
<blockquote>
<p>1N4001: 50V<br>
1N4002: 100V<br>
1N4003: 200V<br>
1N4004: 400V<br>
1N4005: 600V<br>
1N4006: 800V<br>
1N4007: 1000V</p>
</blockquote>
| <p>I'm trying to make a <a href="http://www.robotroom.com/BipolarHBridge.html" rel="noreferrer">bipolar H-Bridge motor driver</a>. But instead of the mentioned diode(1N4001), I've got a 1N4007 diode. Can I use that instead?</p>
| 1N4007 comparable with 1N4001 diode? | 2010-11-28T13:03:39.410 |
7256 | |power|usb| | <p>It really depends on the implementation. A common set up is to power the interface device off the VBUS. If that is used the device will of course fail without it. But even if the interface is self-powered, VBUS is sometimes used to hold an active low RESET pin high, so the interface chip is held reset if VBUS is not present. (Cable unplugged is what they are intending to check for). </p>
| <p>I want to remove the Vcc pin from a USB cable and connect my computer to a device. My goal is to allow the device to communicate with the computer while not charging the device.</p>
<p>Does some section of the USB spec permit this?
Is my plan flawed in some way?</p>
<ol>
<li>Will communication fail to happen?</li>
<li>Is the device likely to charge the battery anyway from the D+ pin?</li>
<li>Is there an error in this plan that I'm not anticipating?</li>
</ol>
| USB without Vcc | 2010-11-28T21:46:43.380 |
7264 | |555| | <p>Within limits, it is possible to get quite good accuracy, better than possible with a DAC with 10 bits of precision if you don't need speed. While it is true that extreme resistances (open circuit and short circuit) are hard to measure, that is true in general. The main trick with using the 555 is to not rely on frequency, but use the duty cycle instead to compute the ratio of R1 and R2. That way, the exact value of the capacitor doesn't matter at all. To me, the main strength is that a really large range of values can be measured. For example, when using a 100K NTC, resistance might vary between 100K and 250 ohm. Using an ADC with a straight voltage divider makes it hard to get accuracy at both the low and the high end of the scale.</p>
<p>-Geert</p>
| <p>Since we know that a 555 timer configured as an astable multivibrator depends on the resistance the timing capacitor sees, what stops people from using a 555 as an ohmmeter? How does the accuracy compare to using a traditional ADC to sense resistance via a resistive divider and looking at the voltage drop?</p>
| What are the disadvantages of using a 555 timer as a resistance to frequency converter? | 2010-11-29T03:26:24.673 |
7267 | |microcontroller|arm| | <p>You can use Yagarto to compile for any ARM micro controller (NXP included of course), and I have done this for NXP's lpc4330. HOWEVER, Yagarto only has support for soft floating point (At least, I've tried to use it for hard FP and it complains because of lack of support, so I have to presume it wasn't compiled with hard FP built in). If you ever want to use hard floating point (my NXP lpc4330 supports this), you'll need to build your own compiler, or use the IAR, Keil, or some other prebuilt one that has hard floating point support. Just something to be aware of. Also, lpc_dfu comes in handy if you don't develop in a Windows environ and would like to flash something to SPIFI. Works extremely well.</p>
<p>Basically, I use:</p>
<p>dfu-util --> You need this to talk to send anything to NXP's boot loader. Plus, you need to use -L to add the LPC header (at least for the lpc4330... Maybe the other's are different, but I wouldn't think NXP would change their boot loader that much).</p>
<p>lpc_dfu --> I use this to talk to NXP's spi flashing tool. You send over the tool first with dfu-util, then you use this to flash your code.</p>
<p>gcc --> I built my own here, but as I said above, Yagarto works (I've used it), and there are a few others you can get. Basically, just about anything that will turn out an ARM binary will work here. HOWEVER, familiarize yourself with linker scripts. If you fail to do this, you will be wondering why your processor doesn't work. If you've used AVR though, I suspect you probably already ARE familiar with these, although there are a number of tools for AVR products, so maybe not. It really is pretty easy to write linker scripts for the NXP products though. And I like knowing precisely where my code goes.</p>
<p>If you decide to use something like OpenOCD with the lpc4330 (I have an lpc4330-xplorer that is pretty nice. Has a few issues, but its got me really liking their lpc4330 chip. I LOVE the SCT. That is a really nice peripheral.), be aware there might be an issue. My lpc4330-xplorer has to typically have 2 resets when booting from SPI flash. This causes OpenOCD difficulty. Other NXP demo boards, or chips likely don't have this issue, but it is something to be aware of with the lpc4330. Anyway, hope you find the right setup for you.</p>
| <p>I asked this question ago. (Don't need to read it to answer this one)</p>
<p><a href="https://electronics.stackexchange.com/questions/7231/out-growing-8-bit-avrs-not-sure-where-to-move-on-to">out growing 8-bit AVRs, not sure where to move on to</a></p>
<p>I really liked the answers about the NXP line of microcontrollers. I'm about to invest in some hardware to get started playing with them, and I wanted to run it by this forum to make sure that I'm not paying too much or buying the wrong part. </p>
<p>I'm not interested in the mbed chip. I prefer to have the option to build something from scratch using the full line of micro-controllers. That means I have to buy a programmer. </p>
<p>I'm interested in the ULINK2 from Keil. It is 411 CND on digikey.ca.
<a href="http://www.keil.com/ulink2/" rel="nofollow noreferrer">http://www.keil.com/ulink2/</a></p>
<p>It integrates with the Keil Development environment. If it turns out I can't or don't want to use the Keil IDE can I use the ULINK2 with FOSS on Linux? What about on windows without Keil? If I decide now that I don't want to go with Keil, is it worth getting another generic JTAG programmer? </p>
<p>Ultimately the goal is to be able to compile and program</p>
<ul>
<li>LPC2921/2923/2925 (ARM9) (this is the least important category for me)</li>
<li>All LPC21/22/23 (ARM7)</li>
<li>All Cortex M0 and M3</li>
</ul>
<p>I wasn't able to find any instructions on setting up a toolchain and flash/debugger program for NXP microcontrollers, and that is the only reason I'm talking about Keil related products. I would rather just use GCC and some other uploader. I'm used to avrdude for AVRs. </p>
<p>What kind of setup do you guys use for ARM or NXP uCs? What JTAG programmers do you recommend? Any other FOSS toolchain instructions or other software I should know about?</p>
| getting started with NXP microcontrollers - Programmers/IDEs/Compilers/Eval Boards | 2010-11-29T04:11:18.447 |
7270 | |sensor| | <p>This is why grad students were invented. I'm sure you could do this electronically eventually, but there would have to be a lot of lectures before it is worth doing that compared to having someone with a brain handle the camera.</p>
| <p>I want to record some lectures I am giving next semester. I have a video camera, and can change its direction using a servo of some sort. However I have no idea how to detect where I am. Me carrying some broadcasting device would be fine. Mostly the sensitivity should be able to determine if I am in the left or right side of the room, but I do not need much more than that.</p>
| Making a camera follow me | 2010-11-29T06:47:23.817 |
7280 | |identification| | <p>I had the same problem with a similar component, but finally I found it. You were right; it is an optocoupler: HCPL0501. Check the <a href="http://www.fairchildsemi.com/ds/HC/HCPL0531.pdf" rel="nofollow">Fairchild HCPL0XXX datasheet</a>. </p>
<p>If you want to look for similar components just type HCPL-0xxx and the mark code on your IC. Good luck!</p>
| <p>I have a rail of unidentified SOIC-8 ICs with marking </p>
<pre><code>501
115
</code></pre>
<p>Nothing else. No manufaturers logo, no nothing. Does anybody know what this could be? </p>
<p><strong>edit</strong><br>
(picture added)<br>
At 3mm they're quite high for SOIC-8, so they could be optocouplers or so?</p>
<p><img src="https://i.stack.imgur.com/50qyE.jpg" alt="alt text"> </p>
<p>Grid is 5mm. (Yes, I know the devices aren't properly aligned, but I did this on my scanner with a sheet of paper over the devices...:-)) </p>
<p><strong>update/conclusion</strong><br>
It's almost certainly an Agilent HCPL-0501. The marking matches completely: the <code>501</code> refers to the type number, the <code>115</code> means week 15 of the year 2001. And the date code appears below the type number (which was a problem with the TR115).<br>
Also diode tests all pass. The 5-6 test which passed was an error; I probably held the testprobe on pin 6 and 7 simultaneously, and 5-7 is the transistor's base-emitter diode.<br>
Thanks for all the replies.</p>
| Identifying IC w/ marking "501 115" | 2010-11-29T11:59:50.467 |
7286 | |8051|ideas| | <p>Do you really want to use them in a single project? Two things that come to mind are: Sell them or make a batch of 500 (kits?) of some '51 project. Educational SBC with Paulmon or some other monitor, some external memory and peripherals comes to mind.</p>
| <p>I happen to have some 500 old AT89C52 controllers and am looking for ideas how to use them in a project. That's an 8051-based controller with 8K Flash, so you get an idea. And no, trashing them is not a project! :-)<br>
I remember that in the 80s Steve Ciarcia (of Circuit Cellar fame) wrote in Byte Magazine about a "supercomputer" he built with sixty-four 8048s. Nowadays a quad core Pentium will easily beat five hundred 89C52s, so maybe that's not the way to go. Instead I'm thinking of a series of separate devices, each with its own controller (where a single Pentium would be of little use).<br>
Suggestions?</p>
| Project ideas for five hundred AT89C52s? | 2010-11-29T14:35:42.470 |
7306 | |jtag|intel-fpga| | <p>Use the Altera USB blaster. Then read it out as @Leon Heller suggsted.</p>
| <p>Well, I have a little problem in my hands, I need to clone an Altera Max EPM7128ELC84, luckily the PLD comes in a socketable PLCC84 package and has a JTAG interface.</p>
<p>Now my question: what approach should I take? this can be done?</p>
<p>I have:</p>
<ul>
<li>A generic JTAG-USB adapter</li>
<li>The means to make a socket with the cables attacehd to the JTAG</li>
<li>The <a href="http://www.altera.com/literature/ds/m7000.pdf" rel="nofollow">datasheet</a></li>
<li>A little experience programming FPGAs </li>
</ul>
<p>Thanks in advance</p>
| Reading the configuration array of a MAX7000 PLD | 2010-11-29T22:25:04.317 |
7311 | |audio|automotive| | <p>This is an issue with what is called a ground loop. When you have a device that powered by its own internal battery ground loops aren't an issue, but is an issue otherwise.</p>
<p>The simplest way I know how to explain a ground loop is that when you have 2 devices that have grounds at slightly different potentials they will start to fight with each other causing an audible hum to enter into your sound system.</p>
<p><img src="https://i.stack.imgur.com/FpsKO.png" alt="ground loop"></p>
<p>This is a simple diagram of how your grounds will be connected. In an ideal world your wires has no inductance, resistance, or capacitance. Also in an ideal world ground is ground is ground. However, we don't live in an ideal world. In our world our wires have a resistance and you can generate a slight voltage difference between the ground of each device. When each of these devices creates its slight voltage offset on its ground lines, I am sure you could start to imagine a nasty problem to solve in order to determine whats actually going to happen in the loop. In general a resonance will be found in the fluctuations of voltages on the ground resulting in the hum I mentioned before. In addition to this, a loop like this can pick up lots of noise from the environment around it.</p>
<p>Now, if you leave the connection between the car battery and interface disconnected you leave a single ground path for current to follow. As you add more devices you will want to follow a star or tree style topology. These topologies will remove all loops preventing all of the issues I described above. You will still have cases were there will be slightly different ground potentials, but this isn't a huge issue as they won't be having to battle with each other.</p>
| <p>This is a specific question about a specific circuit, but I'm trying to use it as a learning experience as I'm still new to electronics and need to take practical knowledge where I can get it.</p>
<p>I recently purchased a box online that plugs into the cd-changer port on my stock Honda car stereo and will allow me to use any RCA stereo source as an input. It's got one plug on it and an exposed wire coming off of the box-side of the plug. The included diagram has this single hanging wire labeled as "Chassis ground when using portable device" and the step-by-step instructions say "NOTE: Chassis ground BLACK/WHITE wire ONLY when installing a battery operated audio device. (i.e. MP3 Player)"</p>
<p>I'm reading this as "if the AUX device you're using is not connected to the car battery, you need to ground the box," but my question is: why? Why would I have to ground the circuit box only when the AUX device is not using the same power source? Would it hurt to ground the box when the AUX is connected to the car battery? I'm not really interested in this specific device, but the principles involved in the decision.</p>
<p>P.S. <a href="http://www.logjamelectronics.com/piehon98aux.html" rel="nofollow">This</a> is the box.</p>
| Question About the Ground Wire on Aux Attachment Circuit for my Car | 2010-11-30T01:34:09.940 |
7314 | |conductive| | <p>What you want is foil tape with conductive <em>adhesive</em> - used for EMI shielding. Most foil tapes that I've found are not made this way, however 3M does have a range specifically for this purpose.</p>
<p><a href="http://solutions.3m.com/wps/portal/3M/en_US/electronics/home/productsandservices/products/ProductNavigator/TapeReel/?PC_7_RJH9U5230GE3E02LECIE20KAB4_nid=4LT3S54QPSbeRQ89J1RQDXgl" rel="nofollow">3M™ EMI Aluminum Foil Shielding Tape 1170, Conductive Acrylic Adhesive</a></p>
<p>You can find it through various suppliers:</p>
<ul>
<li><a href="http://au.element14.com/3m/1170/tape-adhesive-aluminium-19mm/dp/1208990?Ntt=1208990" rel="nofollow">Farnell</a> (now Element 14 in
AU/NZ)</li>
<li><a href="http://rads.stackoverflow.com/amzn/click/B0000WRJIE" rel="nofollow">Amazon</a></li>
</ul>
<p><strong>Edit:</strong> You mention a sliding contact, so I thought it was worth mentioning that this product is just like aluminium foil - so may not be durable enough for that application. YMMV.</p>
| <p>I have an application where I need to place something conductive, like aluminum foil, to a contact where an object will be sliding onto. So it needs to be adhesive on one side, yet conduct from the top side to the bottom side.</p>
<p>What product will do this or can be modified to do this? Both thinness and durability are helpful variables but the requirements do not appear high.</p>
| Is there a conductive tape product that conducts from top to bottom? | 2010-11-30T02:58:18.357 |
7319 | |arduino|motor|driver| | <p>Connect the control pin for your motor driver to a digital output pin of the Arduino, 13 is a good choice.
Connect the Arduino's ground pin to the ground of your driver.</p>
<p>Here's an Arduino sketch to loop, turning it on and off.</p>
<pre><code>int CTLPin = 13; // CTL connected to digital pin 13
void setup()
{
pinMode(CTLPin, OUTPUT); // sets the digital pin as output
}
void loop()
{
digitalWrite(CTLPin, HIGH); // sets the motor on
delay(1000); // waits for a second
digitalWrite(CTLPin, LOW); // sets the motor off
delay(1000); // waits for a second
}
</code></pre>
| <p>I made a simple motor driver as suggested <a href="https://electronics.stackexchange.com/questions/7235/motor-driver-using-only-2n2222-transistor">here</a></p>
<pre><code>+12V ---------+---------+
| |
/ \ |
|M| motor --- 1N4001
\ / / \
| |
+---------+
|
|/
CTL -/\/\/--| 2N2222 NPN
1k |\>
|
---
-
</code></pre>
<p>How do I connect and control this with and Arduino?</p>
<p>Could you please post instructions or direct me to some links I may find useful.</p>
| DC Motor driver with Arduino | 2010-11-30T14:56:01.683 |
7322 | |driver| | <p>Most of my recent experience in writing actual OS drivers has been with Linux, and the best reference IMO is Linux Device Drivers, 3rd Edition by Jonathan Corbet, Alessandro Rubini, and Greg Kroah-Hartman (2005), which has already been mentioned. It is available on <a href="http://rads.stackoverflow.com/amzn/click/0596005903">Amazon</a>, <a href="http://my.safaribooksonline.com/operating-systems-and-server-administration/linux/0596005903">Safari Books On-Line</a>, and also as a <a href="http://lwn.net/Kernel/LDD3/">free download</a>.</p>
<p>A couple more books on the same subject are <a href="http://rads.stackoverflow.com/amzn/click/0132396556">Essential Linux Device Drivers</a>, by Sreekrishnan Venkateswaran (2008) (also available on <a href="http://my.safaribooksonline.com/operating-systems-and-server-administration/linux/9780132396554">Safari Books Online</a>) and <a href="http://rads.stackoverflow.com/amzn/click/1448672384">Writing Linux Device Drivers: a guide with exercises (Volume 3)</a> by Dr Jerry Cooperstein (2009).</p>
<p>For Windows device drivers, the latest book on the subject (published two weeks ago) appears to be <a href="http://rads.stackoverflow.com/amzn/click/0321670213">Windows 7 Device Driver</a>, by Ronald D. Reeves, Ph.D. (2010). It is also available on <a href="http://my.safaribooksonline.com/programming/microsoft-windows/9780321670540">Safari Books Online</a>.</p>
<p>An older book, which would cover Windows XP, is: <a href="http://rads.stackoverflow.com/amzn/click/0735618038">Programming the Microsoft Windows Driver Model, Second Edition</a>, by Walter Oney (2002). It is also available on <a href="http://my.safaribooksonline.com/programming/9780735642140">Safari Books Online</a>.</p>
<p>Another book, which appears to be out of print but available on Safari Books Online, is <a href="http://my.safaribooksonline.com/programming/9780735623743">Developing Drivers with the Windows Driver Foundation</a>, by Penny Orwick and Guy Smith (2007). I assume it would cover Windows Vista.</p>
<p>Finally, Microsoft has pointers to a lot of <a href="http://www.microsoft.com/whdc/resources/blogs.mspx">blogs etc.</a> discussing driver development.</p>
| <p>I have a decent amount of experience designing hardware and embedded systems in general, but I have never written a driver for an operating system.</p>
<p>I would like to know if there are any good guides, preferably online, although good books would interest me, that will give me a good start on what I need to know to design and implement drivers for an operating system.</p>
<p>This will probably have people shooting at me, and although I would love to see a good guide no matter what OS it is based on, I would like to see a guide that is windows based, mostly due to the fact that most of the people I would sell a product would have windows.</p>
<p>Please let me know if there is any extra information I can add to make this more clear.</p>
| Are there resources for learning to write drivers? | 2010-11-30T15:29:52.490 |
7323 | |microcontroller|1-wire| | <p>As you've noticed, RC on the reset pin is not going to work when you have very slow voltage rise times.</p>
<p>Built-in brownout detection may work, but read the microprocessor's datasheet carefully to see if there is a minimum rise time on the supply voltage.</p>
<p>If you are not sure built-in brownout detection will work, you can use a "voltage supervisor" chip. The basic supervisor is a three-terminal device that connects to power and ground, and pulls the output low when the power voltage is below the setpoint. Connect it to reset and you're good to go. You can buy these in a variety of voltages and turn-on delays.</p>
| <p>To <a href="https://electronics.stackexchange.com/questions/3139/1-wire-parasitically-powered-microcontroller">follow up and enhance the question</a> on powering MCU with parasitc 1-Wire interface. </p>
<p>How to ensure proper power on reset of MCU in such situation?</p>
<p>For example this two standard method of generating power on reset may fail: </p>
<p>a) resistor/capacitor delay generated reset -> during power rump up, for extensive period of time data line can be low (for example due to data transmission) or pulled up only by significant resistance. This may slow MCU local supply rise time to the level that will render RC delay useless. </p>
<p>b) global, board level reset may not work as most probably will be removed before local MCU supply will stabilize as the "master" side of 1-wire will provide power only after reset is removed (not to mention that routing reset line defy point of using 1-Wire interface)?</p>
<p>What kind of precautions needs to be taken in such situations? Should MCU be equipped with brownout detection? Is that enough?</p>
| How to ensure proper power on reset in 1-Wire parasiticly supplied MCU? | 2010-11-30T15:40:44.653 |
7325 | |frequency|filter|signal| | <p>For that many passbands, you can take your signal, chunk it into windows, then FFT the window. (You will need a huge window for a million bins.) Then scale the magnitude of each frequency bin as desired, then do the inverse FFT, then reassemble the chunks into a continuous stream.</p>
<p>This will scramble phase a little bit, but it works well enough in many applications.</p>
| <p>I have a signal that consists of N frequencies all with unknown phase and frequency(N) = frequency(N-1) + 2Hz. I would like to selectively scale the amplitudes of some of those signals in such a way that I can change which frequencies to scale and how much to scale them on the fly.</p>
<p>Is this possible?
How complex of a circuit would this be?</p>
<p>Analog? Digital? or Both?</p>
<p>Where should I start?</p>
<p>Thanks</p>
| Frequency Filtration | 2010-11-30T16:04:46.937 |
7330 | |atmega|rs232|gps| | <p>If the GPS has a TTL async serial port and the AVR has as a TTL async serial port, I don't think you need a (MAX232) level shifter, since neither does the full voltage RS232 (like a PC, modem or a terminal). Are you sure this whole thing is necessary? </p>
| <p>I'm working on getting an ATMega168 to talk to my GPS that I ripped out of the casing from Microsoft Streets and Trips. I know it talks RS232 @ 5v (according to <a href="http://www.flickr.com/photos/imager/4383334403/" rel="nofollow">this post</a>) and I just need to listen on pin 3 and apply 5v to pin 5 and ground to pin 2. I'm having a hard time finding good info on how to use the MAX232 and I just followed a diagram from somewhere but I omitted all capacitors as I need to get some. I'm using the FTDI from an Arduino to forward any TTL to my computer and I get a special "y" symbol coming in when I unplug the data out from the GPS and I get the initial "Hello World" serial message I have in there, so I think the MCU side is all good. Do I really need these caps that I ommitted on the MAX232 chip? Why? Is there some other issue? How do I troubleshoot? I've got no scope.</p>
<p>Here's my pinout for the MAX232:</p>
<pre><code>2 -> +5v
6 -> GND
8 -> GPS RX (pin 3)
9 -> MCU Digital in (software UART)
15 -> GND
16 -> +5v
</code></pre>
| Arduino + MAX232 + Pharos GPS360 | 2010-11-30T16:38:31.197 |
7334 | |uart| | <p>Typically an asynchronous communication pin is sampled at 16 times the bit rate. This implies a baudrate generator of:</p>
<p>\$\frac{24000000}{16}\frac{1}{38400} = 39.0625 \$</p>
<p>Since the resulting integer value is 39, the resulting error is:</p>
<p>\$\frac{0.0625}{39.0625} = 0.0016 \$</p>
<p>or 0.16%</p>
| <p>For a 24MHz system, the local clock error associated with transmitting 10-bit character frames at 38.4 Kbaud using the SCI of a Freescale Micro is 0.16%. </p>
<p>How? I can't figure out the math that actually makes sense to get that number. Any ideas? I'm sure it's easy.</p>
| Serial Communication and Local Clock error calculation | 2010-11-30T16:47:14.433 |
7340 | |sensor| | <p>Calling them degrees of freedom is market speech, but it makes some sense.</p>
<p>When you speak of degrees of freedom of an rigid body, you mean the <em>independent</em> parameters that define its position and orientation in space.</p>
<p>When you speak about sensors, you have accelerometers, which give you the second derivative of position in space, so not really degrees of freedom, but still <em>independent</em>. Gyroscopes, first derivative of orientation, again not degrees of freedom but <em>independent</em>. Together, under given assumptions they allow you to compute the six degrees of freedom.</p>
<p>Then came the market speech: boxes sold which included the six sensors, then boxes came along including magnetometers, so six became nine. Maybe tomorrow we will add barometer to get to 10?</p>
| <p><br>
I found on SparkFun a <a href="http://www.sparkfun.com/products/9623">module</a> which detects movement in 9 degrees of freedom (DOF). I'm only aware of 6 DOF: translation in X, Y, Z direction, and rotation about X, Y and Z axis. What are the other three? </p>
<p><strong>edit</strong><br>
I'm aware that there are robots with more than 6 DOF, but in these each segment has only 6 DOF maximum. The human hand (including wrist) has 23 DOF.</p>
| What are 9 degrees of freedom in robotics? | 2010-11-30T17:10:58.457 |
7344 | |led|transistors|555| | <h3>Short Answer</h3>
<p>Transistor part numbers are totally arbitrary and seldom have anything to do with a particular parameter. The best way to find one you need is 1) look through what you have, and if that fails 2) use parametric searches on distributors (e.g. Digi-Key <a href="http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=1376376" rel="nofollow noreferrer">BJTs</a> or <a href="http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=1376381" rel="nofollow noreferrer">MOSFETs</a>)</p>
<p>A 2N2222 (very common NPN) should be able to power 10x LEDs well.</p>
<h3>Long Answer</h3>
<p>You're using a moderate amount of current, so I might use an N-channel MOSFET instead of a BJT, it's the easiest to control and doesn't have a fixed voltage drop. A <a href="http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=ZVN4206A-ND" rel="nofollow noreferrer">ZVN4206A</a> would be a TO-92 that might work. Regardless between that and a BJT, you need a transistor with:</p>
<ul>
<li>A voltage rating, <em>Vds</em> (or <em>Vce</em> for a BJT), greater than your supply (1.5x or more recommended)</li>
<li>A current rating, <em>Id</em> (or <em>Ic</em>), greater than the current that your LEDs will take (this depends on temperature; if you will be running it outside of room temperature you will have to derate this)</li>
<li>A threshold voltage, <em>Vgs(th)</em>, that will allow it to be fully turned on with your input voltage ("logic-level" is something to look for)
<ul>
<li>For a BJT you need to make sure you can drive enough current into the base to saturate the transistor against the base-emitter saturation voltage, <em>Vbe(sat)</em>.</li>
</ul>
</li>
</ul>
<p>Connect it like so (image from <a href="http://www.electronics-tutorials.ws/transistor/tran_7.html" rel="nofollow noreferrer">Electronics Tutorials</a>)</p>
<p><img src="https://i.stack.imgur.com/6AsA9.gif" alt="alt text" /></p>
<p>(For a BJT, it would be similar, but Collector instead of D(rain), Base for G(ate), and Emitter--S(ource))</p>
<p>The "lamp" would be your string of LEDs, however you want to configure them. The diode isn't required for non-inductive loads (generally "things that aren't motors").</p>
<p>One of the advantages of this low-side switch configuration is your logic can be at a fairly low voltage (3.3-5 V), while your load supply voltage can be whatever your transistor can withstand (500-1000 V, whatever).</p>
<hr />
<h2>Edit</h2>
<p>You mention this is for a specific LED flashlight project. If your main focus is powering LEDs, you could look at something more advanced: an LED driver. The Linear Technology <a href="http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1042,C1035,P2079" rel="nofollow noreferrer">LT1618</a> can step up voltage from 1.8 V allowing you to supply it with 2 or 3 alkaline cells, and provides current regulation, so you can eliminate all (or at least most of) the LED ballast resistors.</p>
<p>Example from the datasheet:</p>
<p><img src="https://i.stack.imgur.com/1TG3M.png" alt="alt text" /></p>
<p>The LT1618 or a similar step-up regulator would provide you with the most efficient driving method, both from an electrical point of view and mechanical, as you can use more space-efficient cells (D > C > AA >> AAA >>> 9V)</p>
| <p>This question is continuation of <a href="https://electronics.stackexchange.com/q/6629/1240">this</a> question.</p>
<p>I did some research on previous question and made a circuit as a starting point. Here's a picture:
<img src="https://i.stack.imgur.com/CoK9t.png" alt="image of the circuit as displayed in a simulator"></p>
<p>Now my problem is that TS555 device I plan to use can't drive those LEDs, so I'll most likely have to use a transistor for switching. My problem is that I have no idea where to start looking for a suitable transistor and that I'm generally confused about transistor naming schemes.</p>
<p>Also, general comments are welcome.</p>
| LED flashlight project: Need transistor ideas | 2010-11-30T18:30:06.193 |
7346 | |batteries| | <p>There are two types of battery resistance:</p>
<p>Electrical resistance which is virtually instantaneous and usually constant.</p>
<p>Ionic resistance which is what causes the terminal voltage of the battery to rise after the load is disconnected and the battery has been left alone for a while; and vice versa, causing the voltage to decay after a few hundred milliseconds when a load is added.</p>
<p>If you're driving a stepper motor, both will be important. The first is important for any load really; but pulse loads such as stepper motors will be affected by ionic resistance more. If you step your motor on a battery with high ionic resistance you will find it runs fast for a few seconds but then slows down. The effect is more prominent on batteries near their end of life.</p>
| <p>In my project I am planning on using 10 AAA Batteries(to give me 12v as each battery is 1.2v) to power my project. I am wondering if there will be any voltage drop when I connect a load. If so how can it be calculated? This is so that I can account for it.</p>
| Will there be any voltage drop when connecting load to batteries? | 2010-11-30T21:36:07.427 |
7348 | |microcontroller|avr|msp430|low-power| | <p>AVR watchdog timers aren't as bad as you seem to think. According to the ATTiny13A datasheet, current draw in power-down mode @3V is 2μA without the WDT enabled, and 4μA with. Sure, it's 2x more, but the current itself is small enough for around 6.2 years of operation, which is around the same amount of time it takes the battery to degrade by itself anyway (source: the best-before date). </p>
<p>Additionally, practically anything else you hook up around the μC would draw lots more. In fact, the trickiest part of designing such a low-power circuit is shutting off all current in the rest of the schematic during the sleep period.</p>
<p>The wakeup delay is also nicely configurable, from ~12ms to 8s, if memory serves. The actual frequency doesn't make any noticeable difference if short interrupt routines are used: I got away with turning on the ADC, sampling a 1K pot, calculating some stuff from the results and going back to sleep with no noticeable change in overall consumption (smoothed with a large capacitor to compensate for the sluggishness of my multimeter).</p>
<p>Do note that the WDT is not an accurate timekeeping tool, so you might want to hook up an external RTC. Those can consume mere nanoamps, so it should be a good pairing. In fact, if the RTC in question can generate regular pulses, you could use that as your wakeup source instead of the WDT at the cost of using up a pin.</p>
| <p>Most microcontrollers (e.g. AVRs,MSP430s, PICs, etc) support a number of different sleep modes. The "deepest" sleep mode is the one that purports the lowest power draw (e.g. "Power Down", "Shut Down"), but all the clock systems are typically halted in these modes and it seems to me that the only way to "wake up" from them is via external stimulus (e.g. pin change interrupts, chip reset). Am I missing something? Are there awesomely low power methods of generating a periodic wakeup signal for an MCU?</p>
<p>Assuming my goal is to minimize power consumption (i.e. sleep deeply for as long as possible, stay awake as briefly as possible), while periodically waking up to execute a function, what's the common way to achieve this type of behavior? To further simplify matters, lets assume that my function is stateless (I don't have to remember anything from the past to perform it). </p>
<p>I've had some success using the WDT on the MSP430 to get this effect. I just made my main routine be my function, with the last line enabling the watchdog timer to expire after a certain period and going into LPM4.5 or whatever the "deep sleep" mode is called. The net result is the function is performed, the MCU sleeps, the WDT expires, and the chip resets, ad nauseum. Seems to work, just wondering if there is a "better" or "more elegant" or "more power efficient" way of getting this type of behavior?</p>
<p>I haven't tried this approach with an AVR yet, but I think the WDT is more "power hungry" in the AVRs than on the MSP430 so it may be less attractive for low power work. Perhaps there is not a "universal" approach to low power, and you have to use the tools afforded by a given product line? I know the new picoPower line has lots of whiz-bang features like the Event System and Sleep Walking that in some cases hardly require the CPU to be awake at all if you can make your application fit into that structure...</p>
<p>OK enough of my wandering, lets here what ya'll have to say :)</p>
<p><em>Edit</em>
Concrete examples illustrating techniques would also be cool!</p>
| Waking Up From Deep Sleep Modes | 2010-11-30T21:49:57.287 |
7354 | |arduino|arm|open-source| | <p>I would say being another <em>*</em>*duino project will make it less interesting, but there probably is a group of people who only care about or have access to that platform. I expect that applies to a lot of other platforms.</p>
<p>My personal take on platform choice is that you shouldn't care or think about popularity. If you're after a project, you pick the tools that make sense to you and use those.</p>
| <p>I am debating which micro-controller to use for a new open source hardware project. Spec wise, I would rather use an ARM Cortex M3, which is at a similar price-point to an Arduino(avr) based solution but with more processing power/peripherals. The only concern I have going with ARM based hardware is I don't want to lose potential contributors/developers who might be put off by working with ARM. Or competition wise--someone reproducing the project but with an arduino instead(e.g. Ardupilot overtaking Paparazzi)</p>
<p>I realize there is no straightforward answer to this question but I would like to hear your thoughts on the topic, and what other factors you think might weigh more on the success of the project.</p>
| Does my open source project need be Arduino based to be successful? | 2010-11-30T22:10:54.883 |
7366 | |motor|datasheet| | <p><a href="http://www.cnczone.com/forums/servo_motors_drives/9435-techical_specification_electrocraft_0643-08-013_a.html" rel="nofollow">http://www.cnczone.com/forums/servo_motors_drives/9435-techical_specification_electrocraft_0643-08-013_a.html</a></p>
<blockquote>
<p>I have the catalogue specs on
0643-31-011 & 0643-32-011 models,
these were the 0643 off-the-shelf
models and I believe the other numbers
are special order and may have been
just different mounts or shaft size
etc.<br>
Al </p>
<p>I will post them here in case someone
has the same question in the future.
Of the two models, one show the specs
in oz-in and the other in lb-in, but
converted they appear to be close to
the same.
0643-33-004<br>
continuous stall 155 oz-in<br>
pk torque 720 oz-in<br>
max terminal voltage 60<br>
max speed 4800 rpm<br>
inertia .0304 oz-in-sec^<br>
Kt 16.8 oz-in/amp<br>
Ke 12.4 v/krpm<br>
max pulse current 43 amp<br>
Inductance .5mH </p>
<p>0643-32-004<br>
continuous stall 9.7 lb-in<br>
pk torque 45 lb-in<br>
max terminal voltage 60<br>
max speed 3700 rpm<br>
inertia .0019 lb-in-sec^<br>
Kt 1.34 lb-in/amp<br>
Ke 15.9 v/krpm<br>
max pulse current 33 amp<br>
Inductance .8mH<br>
Good luck<br>
Al </p>
</blockquote>
| <p>More details from the motor casing:</p>
<ul>
<li>Electrocraft</li>
<li>Model: E19-2</li>
<li>Serial: A01314</li>
<li>Part #: 0643-08-013</li>
</ul>
<p>It looks like it was made by Robbins Myers Motor & Control Systems Division.</p>
<p>In case anyone is wondering, this motor comes from inside of a PUMA 560 robotic arm.</p>
<p>It also has an encoder/potentiometer attached to it which I am interested in getting datasheets for as well:</p>
<ul>
<li>esoline (? it's actually kind of hard to read the first character on the label) encoder.</li>
<li>Type: P.4201717</li>
<li>S. No.: 70754086</li>
<li>7223C30903</li>
</ul>
<p>Any help in finding datasheets, or at the very least pinouts for either of these would be much appreciated.</p>
| Does anyone know where to find the datasheet for an Electrocraft Model E19-2 motor? | 2010-12-01T01:22:01.250 |
7369 | |usb|mosfet|pnp| | <p>if the line is high when it is non-active(instead of floating) you should be able to remove the pullup and leave the 3k and have it work without modification.</p>
<p>When the P Channel has it's gate high it should be in cutoff, as you would want. When the gate goes low you can expect it to saturate, allowing full conduction through the mosfet like a short. MOSFETs are slower, you want to make sure you have one that has a switching frequency that is relatively close to the rate they suggest, but you should have no issues with this, the USB control will not be toggled at an extremely high rate(>10MHz).</p>
<p>The 3k resistor you have in series you can leave to avoid you pulling too much current when changing states, but it will probably work better if you reduce that a significant amount. </p>
<p>You want to make sure that the change in Voltage your output pin must drive divided by your resistance is less than the maximum current you pin can drive. This will protect your circuit without slowing the drive time of the MOSFET. The MOSFET is effectively a capacitance, so you can think of the capacitance with the resistance causing a delay to your signal (4 tau or 5 tau, depending on philosophy).</p>
| <p>With the LPC1343 microcontroller (Cortex M3), there is a USB_CONNECT line which goes low when the micro is ready to connect to the computer via USB. This "soft connect" feature is implemented on the LPC Baseboard with a PNP transistor circuit. Would I be able to use a p-channel mosfet instead? I have already built the p-channel mosfet equivalent, and it works, but wondering about its reliability and whether it is "good practice".</p>
<p>Possible issues that (I think) may arise could be due to the fact that mosfets are voltage controlled devices, and on power up of the device, the gate voltage may not rise as fast as the voltage supply (3V3) (although they are tied via a 33k resistor in my implementation), and the mosfet would erroneously "conduct".</p>
<p>Note: My p-channel mosfet circuit just consists of replacing Q1 with a p-channel, R69 remaining the same, eliminating R68, and changing R66 to a 33K (no particular choice, had one on hand)<img src="https://i.stack.imgur.com/Oj5LW.png" alt="alt text"></p>
| Using a P-channel mosfet instead of a PNP | 2010-12-01T03:22:32.700 |
7373 | |embedded|software|bootloader|debugging| | <p>How did you configure it to build for the AT91?</p>
<p>The code tree appears to be designed such that any architecture specific stuff is located in the 'arch/(cpu class)/(cpu type)/...' tree. I found AT91 code under arch/arm/cpu/arm926ejs/at91... is the variant specific stuff you're looking to alter not located there? There's not that awfully much to look through in that directory, especially since almost half the files are individual AT91 variant-specific.</p>
<p>Sorry if this is obvious... but you didn't mention checking this.</p>
<p>I hadn't looked at the uBoot code tree yet, but your post scared me into doing so. A back burner project of mine involves eventually using uBoot and Linux on a custom iMX233 PCB. I'm very interested in getting this sort of feedback on how well the uBoot architecture and variant-specific stuff is isolated and how big of a pain that's going to be.</p>
| <p>I recently figured out the cause of a nasty bug I've been working on with an Atmel AT91SAM9G20 SBC running <a href="http://www.denx.de/wiki/U-Boot">U-boot</a>, an open source bootloader. The core of the problem was that U-boot expected the hardware to be configured differently than I had built it, so some of the device registers were misconfigured.</p>
<p>Now that I've figured out the problem, I need to tweak U-boot to configure the registers correctly. I can do this blindly by adding a few lines of code at the end of the program, but that's messy.</p>
<p>This brings me to my question: how can I figure out how U-boot works more efficiently than starting at main() and reading all possible code paths across all files? I've tried grepping around in the files and looking at the code near relevant identifiers. This has proved ineffective; it seems that most of the code is drivers for subsystems I don't care about. I actually understand how the bootloader works pretty well by now, but I'm hoping there exists a better method than my naive approach.</p>
| Good tools or methods for understanding structure of bootloader? | 2010-12-01T07:26:06.100 |
7375 | |sensor|electromagnetism| | <p>You mentioned:</p>
<blockquote>
<p>some form of optical sensor probably based on intensity with fiber wires for the sending and receiving light using some form of modulation and filtering</p>
</blockquote>
<p>This is a good idea. You can do very precise measurements with lasers, measuring phase differences to get distance. This is sometimes done with the laser wavelength itself to get micron resolution; for larger resolution and range, you modulate the beam to a specific wavelength.<br>
I'm not sure I understand the application entirely, but it seems like you will be measuring two different points at the same time, each with a different range. For a certain range, I would choose a wavelength at least 4x that -- this sets a maximum modulation frequency. For example, <em>c/(4x6cm)=1.25GHz</em> for the end of the beam. (You can use a much lower frequency, too). Resolution has a theoretical minimum set by the wavelength as well, but will be practically set by your detection setup. The idea is to compare the reflected phase with a reference.</p>
<p>Here's how <a href="http://www.avrfreaks.net/index.php?name=PNphpBB2&file=profile&mode=viewprofile&u=135348" rel="nofollow">Brad</a> did it to pick up minute sound vibrations on surfaces far away -- a laser spy device: <a href="http://www.lucidscience.com/pro-laser%20spy%20device-1.aspx" rel="nofollow">http://www.lucidscience.com/pro-laser%20spy%20device-1.aspx</a></p>
| <p>I relies the displacement is very small and with up to a decent frequency. </p>
<p><img src="https://i.stack.imgur.com/r2cfA.jpg" alt="alt text"></p>
<p>Here is details of the Magnet data
Magnet poles North/South over the height(h) = 1.5 mm
Coating: Nickel
Length(a) = 8.5 mm
Width(b) = 2 mm
Height(h) = 1.5 mm </p>
<p>Material/grade: 48H
max.operation temperature = 120 °C
Flux density inside the magnet = 1.37 Tesla = 13700 Gauss
Flux density on the surface = 2600 Gauss</p>
<p>Dead weight: 0.19 g
Holding force on a steel plate: 4.64 Newton
Weight, which the magnet can lift: 0.47 kg</p>
<p>Small displacement needs to be measured of around +-.3mm
Sensor can be up to 3cm away (min 1mm) from the stationary point of the displacement. But there is a second margent not moving 1.5mm away from the first.
Frequency of change between the max and min could be as high as 400Hz and displacement could be as low as +-0.05mm at times.</p>
<p>The sensor has to be of little effect on the system as possible although a small effect can be compensated for. System should be non contact to the moving base.</p>
<p>One idea that was suggested was a hall effect sensor. However such a large gauss with a small displacement and the other magnet nearby with such a large offset makes me think this idea is possibly not going to work although I could be wrong.
The surface for sensing is the size of the magnet if using hall effect or inductance or a maximum of around 8.5mm x 15mm </p>
<p>Another two options suggested where a capacitive sensor as the moving part is grounded and conducting however there is also ground all around so good shielding would have to be implemented or some form of optical sensor probably based on intensity with fiber wires for the sending and receiving light using some form of modulation and filtering to keep costs down.</p>
<p>I am open to any other suggestions or where someone might know a good sensor suitable, circuit diagram or informational website. I know this system is a lot to ask.</p>
<p>If the displacement oscillates at a sinusoidal waveform the output should reflect this and be analog if possible. if there is a phase shift that shift would have to be known and frequency would need to remain the same but the amplitude does not have to accurately represent the total displacement.</p>
<p>Thanks for any ideas or suggestions</p>
| Small displacement measurement of a conducting beam with Neodymium magnets | 2010-12-01T10:38:04.297 |
7382 | |project-management| | <p>When you say "hardware" designs, I know you're probably talking about PCB and discrete component solutions, but I have some experience with designing ASICs that may be useful in a conceptual level.</p>
<p>When we design an ASIC that is fairly complicated, we use hierarchy from the beginning. One major reason for that is that as the designs get bigger, your ability to thoroughly evaluate and simulate them decreases. Also, ASIC designs can get quite large, and without a well organized hierarchy it can be difficult to manage the whole design.</p>
<p>We have a strong culture of reuse for our building blocks. For example, if we have an op-amp design that someone spent a lot of time designing and validating, that design would be packaged so that another designer could easily import that design into their own workspace. We have a centralized server for storing these packages, so all the parts you need are easy to find.</p>
<p>While an individual block may have been designed for a specific circuit (e.g. a voltage reference for an op-amp), it usually can be re-used without modifying the original design. The design cycle lasts for a month or longer, and includes validation of a layout. Designing one of these blocks takes time to familiarize oneself with the problem set, so even if the block isn't ideal, you would probably try to use it anyways. </p>
| <p>At my company we do a lot of original hardware designs each of which are designed by only a small sub-section of our engineers. We are looking at ways to better document and distribute what has been done on each project so that information can be distributed and potentially reused. How does your company handle this?</p>
| How does your company manage hardware reuse? | 2010-12-01T15:06:41.630 |
7388 | |soldering| | <p>You don't need to make any process changes, as most RoHS components are plated with 100% matte tin, which is compatible with PbSn.</p>
<p>I've only heard of problems when mixing RoHS and non-RoHS for very fine-pitch, leadless packages as the stresses they can generate (leaded components have a little give) are much less tolerant of any undesirable intermetallics, and especially BGAs as they bring their own solder (balls) to the party (though hand soldering BGAs is extremely dubious at best.)</p>
<p>Assuming you've been using leaded solder with non-RoHS components before, keep the temperature the same, the matte tin coating needs negligible additional heat relative to everything else to dissolve into the tin-lead solder.</p>
| <p>How is soldering RoHS components with good old Pb-Sn solder different from soldering non-RoHS components? I'm talking about hand-soldering, not wave or reflow.</p>
| Soldering RoHS components with Pb-Sn solder | 2010-12-01T17:16:59.610 |
7391 | |karnaugh-map| | <p>The essential thing about Karnaugh maps is that when you compare the binary numbers assigned to adjacent cells, they will differ in exactly one bit. This is what enables you graphically simplify an expression by collecting adjacent cells. You could write in the decimal equivalents of the binary patterns if you like, but doing so doesn't really provide any useful advantages.</p>
| <p>Do Karnaugh maps use a base ten numbering system??</p>
| Do Karnaugh maps use a base ten numbering system? | 2010-12-01T19:16:26.803 |
7400 | |capacitor| | <p>I'd say for electrical insulation. It could easily arc since it's rated for 400v.</p>
| <p>Large, through-hole capacitors (typically electrolytic) sometimes have a foam pad on the bottom like the one in this picture:</p>
<p><img src="https://i.stack.imgur.com/tZYPs.jpg" alt="Capacitor with foam pad"></p>
<p>What is the pad for?</p>
| What is the foam pad on the bottom of a large, through-hole capacitor for? | 2010-12-01T22:26:13.697 |
7423 | |resistors|terminology| | <p>So when we don’t use pull down resistor we get the floating values that’s why we use this resistor to ensure that the reverse digit is delivered when we pressed the button but why we get the floating values, I’m not sure but may be the micro controller unpredictably take the input from the pin as logic high or low so I think may due to this we get the floating values.</p>
<p>And if we don’t use pull up resistor then make a ckt and we can see that this always gives high value at output.
(Here i consider using a switch and read the value throung a pin connected to arduino)
But this concept apply everywhere
<a href="https://i.stack.imgur.com/q9TwX.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/q9TwX.png" alt="enter image description here" /></a></p>
| <p><br>
Can some one explain this terminology please I think I understand it but not completely sure. </p>
<p>I think pull down is where you place a resistor between +V and the other component and pull up is where you place the resistor between 0v and the component. </p>
<p>If I am completely wrong then let me know!</p>
| What is a pull up and pull down? | 2010-12-02T12:05:33.697 |
7427 | |automotive| | <p>My experience with cars is that modifying the security system is often the easiest way to disable (or enable/hot wire) a car. For example, my old car, a Passat, had the security system in a box mounted on the left of the driver's foot well, so it was very easily accessible. You could just open this box, connect two terminals and the car would start. Below is a diagram showing the security module in a Volvo 850:</p>
<p><img src="https://i.stack.imgur.com/JmfiC.png" alt="Volvo 850 security module"></p>
<p>As you can see it is very easily accessible right under the dash on the driver's side. You can easily hot wire the car through this module OR you can prevent it from starting, your choice.</p>
<p>The security module has the ignition routed through it and is designed to connect or cut off the ignition as needed, so it is already configured to do exactly what you want: control the starting of the car. By modifying the module you can add whatever functionality you need.</p>
| <p>Assume that I do <strong>not</strong> want to replace a factory Engine Control Unit (ECU) with a custom ECU.</p>
<p>What are the other possible intercept points that I can use to allow/prevent a car from starting up? I only want to allow/prevent starting up.</p>
<p>I can think of possibly connecting the car battery through a relay and turning the relay on/off. Any other good ways to do it?</p>
| What are the ways to allow/prevent a car engine from starting up? | 2010-12-02T12:30:02.807 |
7435 | |diodes| | <p>Jfets can be used as diodes. TI has an app note on this where a diode connected JFET is used to protect an op amp input from overvoltage. Leakage current was in the sub 100 femtoampere range (<a href="http://www.ti.com/lit/an/sboa058/sboa058.pdf" rel="noreferrer">http://www.ti.com/lit/an/sboa058/sboa058.pdf</a>). See also: <a href="https://books.google.com/books?id=03JmxpE39N4C&lpg=PA181&ots=5xftO62lA4&dq=2n4117%20low%20leakage%20diode&pg=PA180#v=onepage&q=2n4117%20low%20leakage%20diode&f=false" rel="noreferrer">Current Sources and Voltage References: A Design Reference for Electronics Engineer p180-183</a></p>
<p>The 2N4117A referred to is no longer available, but the <a href="http://www.digikey.com/product-detail/en/MMBF4117/MMBF4117CT-ND/3042811" rel="noreferrer">MMBF4117</a> is a good replacement, and has the same guaranteed maximum leakage of 10pA at room temperature and a reverse bias of 20V. Note that the leakage current is less at lower voltages, so since Vdd is at most 5.5V for the PCF8563, the leakage current is even less.</p>
<p>For best results connect the source and drain together as one terminal of your diode and the gate as the other.</p>
<p>A note regarding temperature and this applies to all PN junctions, diodes (including low-leakage diodes), JFETs, BJTs MOSFETs (etc):</p>
<blockquote>
<p>The reverse-biased leakage of a P-N junction has a strong positive
temperature coefficient, approximately doubling for each 10°C
increment in temperature. This exponential increase racks up quickly
as shown in the normalized graph of figure 1. At 125°C leakage climbs
to approximately 1000-times the room temperature value.</p>
</blockquote>
<p>source:<a href="https://e2e.ti.com/blogs_/archives/b/thesignal/archive/2012/11/14/temperature-effects-on-input-bias-current-plus-a-random-quiz" rel="noreferrer">https://e2e.ti.com/blogs_/archives/b/thesignal/archive/2012/11/14/temperature-effects-on-input-bias-current-plus-a-random-quiz</a></p>
| <p>The idea struck my mind while I was looking at this typical application for the PCF8563. </p>
<p><img src="https://i.stack.imgur.com/UsMBX.png" alt="alt text"></p>
<p>This RTC requires typically 250nA (interface inactive, like in circuit in power-down), but a general-purpose diode like the 1N4148 already leaks 10% of that. The gate reverse current of a JFET is only a fraction of that; max 1nA for the MMBF4391.<br>
The whole circuit is very low voltage and dito power. Are there reasons not to use a JFET as a blocking diode here?</p>
| JFET as blocking diode? | 2010-12-02T14:34:48.437 |
7443 | |voltage-regulator| | <p>There are plenty of dual regs, but it is often cheaper to use two seperate ones unless you have severe space constraints, as there are many more parts to choose from in single-output versions.</p>
| <p>I am working on a circuit design that has multiple IC's on it. My MCU requires 2.5-3.3 VDC for it's power. Another IC that I am using requires 5V for it's logic power. So what is the cheapest and simplest solution for powering both of these devices. I figure my options are:</p>
<p>A) Use two voltage regulators a 3.3 and a 5V.
B) Use just a 5V regulator and used diodes or something to drop the voltage down the an acceptable level for the PIC.
C) Maybe there is a dual voltage regulator out there?
D) Something else?</p>
| Is there a Dual Voltage Regulator? | 2010-12-02T17:24:16.057 |
7448 | |power|sound|high-voltage| | <p>Good stuff in the answers so far, but I work with power lines and want to put in my two cents.</p>
<p>This isn't technically a partial discharge; occasionally you may be hearing the crackle of what is usually called a corona discharge. I admit the phenomenon is related, but it is not the same.</p>
<p>See, all uninsulated lines show corona. Its just not a big deal until you're dealing with a pretty high voltage. As the voltage goes from a very big positive to a very big negative, the air around it gets ionized, so about 50 or 60 times a second, it switches direction. This is the normal mains hum discussed in another answer. </p>
<p>Water is much, much heavier than air, and it ionizes just as easily. So on a rainy or humid day, the corona is pulsing with water in it. This gives it momentum, so the heavier water particles travel out farther. But they themselves are ionized, which means they can ionize more air than the line could normally reach on its own, and ionized air is conductive.</p>
<p>And there's almost always 3 of these lines pretty close together. The sound you're hearing is a million teeny tiny electrostatic discharges from all the charged up water particles interacting with each other with nearby lines or grounded objects. This is actually the worst time to be anywhere near them; the air is supposed to be their insulator, and at that moment it isn't working as well.</p>
<p>Occasionally you might see a full corona discharging with the naked eye; it looks like a tiny bit of lighting crawling up the line. If it gets really bad, you'll see a momentary line to line or line to ground short, which looks exactly like a real lighting bolt, just not from the sky.</p>
| <p>I noticed when walking home the other day that the high voltage (200kv I believe) lines running through here were hissing in the rain. What is causing them to hiss?</p>
| Why do high voltage power lines hiss when it's raining? | 2010-12-02T18:44:22.013 |
7455 | |usb|rs232|ftdi| | <p>Assuming your product already has a micro, the cheapest way is usually to use one with onboard USB. </p>
| <p>I'm looking for USB to serial FTDI cables. However, the cheapest I can find is $20 US each, which is <em>way</em> too expensive, given my price target for the entire product is $70. I'm hoping they can be found for $5 each somewhere, but even FTDI themselves has them for £16 (about $25) each. Anyone know of any other options?</p>
| Low cost FTDI cables? | 2010-12-02T21:43:47.277 |
7463 | |voltage-regulator| | <p>Voltage regulators basically can be divided in two big groups: <strong>linear regulators</strong> and <strong>SMPSs</strong>, short for Switch-Mode Power Supplies, aka "switchers". Switchers are the most versatile, they allow you to go from a lower voltage to a higher one or vice versa, and they often do so with high efficiency, often > 90%. That means that when your load consumes 10W the switcher will only dissipate 1W.<br>
Linear regulators are different. They are like a variable series resistor between input and output, causing a voltage drop across the regulator. </p>
<p><img src="https://i.stack.imgur.com/6Dg7x.png" alt="Linear regulator principle"></p>
<p>A control element will vary the resistance (in practice a transistor) so that the output voltage will remain constant regardless of input voltage and load. But since there's this <strong>voltage drop</strong> the input voltage has to be higher than the output voltage. How much higher depends on the type of regulator. There are <strong>LDOs</strong> (Low Drop-Out) which still can regulate the output if the input is only a few hundreds of mV higher and there are even ultra low drop-out types which only need <a href="http://www.micrel.com/_PDF/mic5301.pdf" rel="noreferrer">a few tens of mV</a>.</p>
<p>The 7812 is a non-LDO linear regulator, which means it needs a higher input voltage. The <a href="http://www.fairchildsemi.com/ds/LM/LM7812.pdf" rel="noreferrer">datasheet</a> <em>does</em> say how much it needs, but you may have to look for it. This is a snapshot of page 8: </p>
<p><img src="https://i.stack.imgur.com/wHeDV.png" alt="LM7812 specs"></p>
<p>All parameters are specified under certain conditions, and for the output voltage we can see that the condition is that the input voltage is minimum 14.5V. The 2.5V dropout is typical for a three-legged linear regulator. If we look further we can see two values for line regulation; it appears that this is best if the input voltage is at least 16V. </p>
<p>So you won't find a parameter "minimum input voltage", but it is mentioned as a condition for proper operation within certain limits. </p>
<p>A note on dissipation:<br>
From the above it may look like you best make your input voltage a lot higher than the 12V output, but that's not true. The current to your load flows through the regulator and is the same current as will be drawn from the input voltage. So if you have a 12W load it will draw 1A from the regulator. If you have an input voltage of 20V the same 1A will be drawn from that 20V. So the 20V delivers 20W, while the load only consumes 12W. The difference of 8W will be dissipated in the regulator. That's a lot. Therefore it's best to keep the input voltage just above the minimum to prevent the regulator to become overheated.</p>
| <p>On <a href="http://www.fairchildsemi.com/ds/LM/LM7812.pdf" rel="noreferrer">the datasheet</a> it doesn't mention an input voltage. Must the input voltage be higher than the output voltage or does it increase to 12 V if I input 8 V for example?</p>
<p>If so, what is the current like that it outputs? </p>
| 7812 minimum input voltage? | 2010-12-02T23:56:25.487 |
7464 | |power-supply|accelerometer|gyro|ldo| | <p>You're right to look within linear regulators if you want to get the best performance from analog chips ("digital" accelerometers/gyros are still analog at their core), SMPS almost always have much more ripple unless you're looking at really old linear regulators with tons of input ripple</p>
<p>Accuracy shouldn't matter (within part tolerances) as the sensors are generally ratiometric, though as always, check the datasheet.</p>
<p>You want low noise, but how you minimize that depends on the broader context. If this is battery powered there shouldn't be much input noise, so a general low-noise regulator would be best. However, if you also have other parts on the same voltage rail (e.g. a radio) that might switch on occasionally and eat tons of current, choosing one with good transient response might be better. If it's line driven, you may want better input rejection (if you have a terrible AC/DC supply).</p>
<p>The best performance you could squeeze out of them would be to put them (and other analog parts) on their own voltage supply where you would know that nothing would be switching in and out very fast, putting noise on the supply.</p>
<p>From my limited experience with some MEMS accelerometers five years ago, it's pretty easy to hit the noise limits of the device (though they've come way down in price and performance has probably gone up as well), so don't go overboard unless you know your supply is what ails you.</p>
| <p>Should I choose a linear regulator that has good transient response? or ultra low Vrms noise? or high accuracy?</p>
<p>I am using digital accelerometers and gyros (BMA180 and ITG3200).</p>
| Choosing regulator for gyro's and accelerometer | 2010-12-03T00:15:40.787 |
7478 | |usb|adapter| | <p>This probably won't help you accomplish your overall goal of simultaneous use of a USB peripheral from two computers, but a <a href="http://www.usbgear.com/USB-Sharing.html" rel="nofollow">USB switch</a> can allow non-simultaneous use of a USB peripheral from two or more computers. They seem to work similarly to a KVM switch, and the cheap switches need to be switched manually, but some also support switching via software.</p>
| <p>Ultimately, my goal is to have a "keypad" with between 5 and 10 buttons, where pressing one of those buttons effectively presses some key on two computers simultaneously.</p>
<p>In the ideal scenario, the "keypad" would just plug into both computers, sending whatever signal I generated out over 2 USB lines. As far as I can tell, this flat doesn't work (a single USB device cannot connect to two hosts).</p>
<p>I saw online some <a href="http://www.instructables.com/id/DOUBLE-KEYBOARD/" rel="nofollow">instructions</a> for connecting a USB keyboard to a hacked-together pair of PS2-USB adapters (connecting the PS2 side, which apparently is happy to have multiple "hosts" with a single device). Even without doing the hacking part, my current <a href="http://xkeys.com/xkeys/xkstick.php" rel="nofollow">keypad</a> won't work when plugged in via keypad->USB to PS2->PS2 to USB->computer. Cutting apart connectors to allow it to be keypad->USB to PS2->2 x PS2 to USB->computer isn't likely to improve that any. I'm not clear if Windows no longer supports PS2 (saw that somewhere online), if the hardware keypad doesn't send the necessary signal to be "converted" to PS2, or what.</p>
<p>Are there any other approaches I'm missing? Any intelligent ways to do it with software (so the keypad plugs into one computer and that computer sends the signal to the other computer)? Immediacy is pretty important, but that route seems to have some legs.</p>
| How can I plug an arbitrary USB device into two computers? | 2010-12-03T04:59:03.487 |
7479 | |avr|cortex-m3|lpc| | <p>May as well copy the best responses from a relevant AVRFreaks thread: <a href="http://goo.gl/Yv2aa" rel="nofollow">http://goo.gl/Yv2aa</a></p>
<p>Q: (toalan)</p>
<blockquote>
<p>I just got my ARM cortex M3 dev board. I was able to compile and debug a simple example program. I read through the datasheet a bit. Everything looks really good, almost too good. Are there any landmines that I should be aware of? </p>
</blockquote>
<p>A: (toalan)</p>
<blockquote>
<p>I tried using ARM GCC, but there are so many things to configure and the IDE for it was like a flashback from the early 90's. </p>
<p>Currently I use an evalutation copy of Keil, and I bought a Ulink debugger clone from ebay for $50. Ulink is the official Keil debugger. Ulink2 is out now, you can pickup a clone on ebay for $100. I read that Ulink1 can not debug cortex, but mine seems to work for cortex. </p>
<p>Also I find that the datasheet for Cortex is much better than the ARM7 datasheet. This is because typically for ARM there is 1 super huge datasheet that covers a large number of ARM7 devices and you have to figure out what sections apply to what ARM7 uC. There are not many Cortex devices on the market yet, so it is easier to figure which section applies to which Cortex uC. </p>
<p>I spent in total about 4 hours to install the software and debug my first program. It was a night a day difference from my frustration with ARM7. </p>
<p>I got this board from futurlec, <a href="http://www.futurlec.com/STM32_Development_Board.shtml" rel="nofollow">http://www.futurlec.com/STM32_Development_Board.shtml</a></p>
</blockquote>
<p>A: (leon_heller)</p>
<blockquote>
<p>I built my own LPC2106 board when the chip first came out. I downloaded gcc for the ARM, got it working in a few minutes, and wrote a simple test program for my hardware. </p>
<p>I now use Rowley CrossWorks for LPC2000 ARM7 development. The compiler is gcc, with their own libraries, with their excellent IDE.</p>
</blockquote>
<p>A: (Thomas Strand)</p>
<blockquote>
<p>GCC always works right away. But I think OpenOCD (for flash writing and debugging) is a mess. Configuration files and scripts all over the place. </p>
<p>When it coms to IDE's, I think it's hard to beat Eclipse. Granted, it is a bit daunting at first, but I went through a setup tutorial and got comfortable with it. </p>
<p>Eclipse has some nice features I like:<br>
- Macro expansion on mouseover<br>
- Function implementation popup on mouseover<br>
- Refactoring</p>
</blockquote>
<p>A: (jesper)</p>
<blockquote>
<p>clawson wrote:</p>
<blockquote>
<p>but on ARM7 TDMI parallel I/O is slower </p>
</blockquote>
<p>You mean on an Atmel SAM7 using an ARM7TDMI the I/O is slower? I/O is slower on all ARM7's because of the internal bus structure, pipeline breaks e.t.c.
For instance, the code </p>
<p>while (1) {<br>
PORTX = 1;<br>
PORTX = 0;<br>
}<br>
on a 90 MHz ARM7 (Philips LPC series), creates a frequency of about 3.5 MHz on the I/O port. An AVR would create about fCLK/4.</p>
<p>It IS possible to get OCD to (sorta) work, however you'll have about as much hair as me when you get it work reasonably. Getting it to work reliably, is probably impossible.</p>
</blockquote>
<p>A: (jesper)</p>
<blockquote>
<p>clawson wrote:</p>
<blockquote>
<p>Are you aware that the LPC also has "fast IO"? The following diagram (8-17) from the LPC 2101/2102/2103 User manual shows the difference between traditional slow IO and the fast IO. This is on a chip with the PLL running at 60MHz. It's true the 4.26MHz from a 60MHz clock is a bit sad. But the 15.4mHz ain't too shabby.</p>
</blockquote>
<p>Aha, this is new since I used the LPC's. But it seems it's only the 2101/2102/2103 that has this special feature. I didn't read the DS about it, but if there's no special limitations in using it, it sure is very useful. However, the 15.4 MHz above is probably from four consecutive instructions, set/clear/set/clear or something like that. But it a loop the effect of a broken pipeline may make it may be slower. Can't remember exactly how much the penalty is.</p>
</blockquote>
<p><a href="http://goo.gl/NTWtI" rel="nofollow">The second link</a> leads to a 26-page long dialogue concerning ARM. I'll read it later!</p>
| <p>I've just recently gotten my Cortex M3 (LPC1343) up and running, following Microbuilder's instructions to get a GNU C compiler working for it. I've run some example code and in general, the code seems to be a lot more complex than what I've been used to with AVR's.</p>
<p>What are the major differences in programming AVR's (8-bit ATMEGAs) and Cortex M3's? Anything I should watch out for?</p>
| What are the things to watch out for when switching from AVRs to Cortex M3? | 2010-12-03T05:07:03.910 |
7484 | |datasheet| | <p>The word <em>typical</em> is "content free". Real statistical estimates require at least a range, and a confidence. Better yet, a density function.</p>
<p>For instance, <em>quantity X falls between 3.7 and 4.3, with 95% confidence</em> means something, whereas <em>quantity X is typically 4.0</em> is absurd. What does that mean? What is the probability that X lies between, say, 3.999 and 4.001?</p>
<p>If there is any earnestness in such a "typical" claim, the interpretation <em>should</em> be like this. Since the 4.0 is given as two significant figures, it means that there is some high confidence (like 95%: two standard deviations, or 99.7%: three standard deviations) that it will not fall bellow 3.95, which would cause it to be rounded down to 3.9, nor rise to or above 4.05, which will cause it to be rounded off to 4.1.</p>
<p>That is to say, if, say, 95% or more of the time a parameter measurement, when rounded to two significant figures, does not show 3.9 or less, nor 4.1 or greater, then we have justification in claiming that it is "typically 4.0" (but not necessarily that it is "typically 4.00").</p>
<p>I don't know of any source of assurance that datasheets apply this sort of standard to "typically".</p>
| <p>When working on a design I always work with minimum/maximum values from the datasheet (whichever is worst case), never typical values. I was reminded when in another discussion the leakage current for a BAS416 diode came up: 3pA typical, 5nA maximum. That's a factor 1000! In this case I surely would dismiss the 3pA.<br>
What's the relevance of "typical values" in general? Do you use them in a design?</p>
| What is the relevance of "typical values" in datasheets? | 2010-12-03T08:36:43.690 |
7489 | |soldering|wire| | <p>Use a lighter to get it off. It works really well!</p>
| <p>How do you remove insulation from headphone wires (these tiny) to prepare it for soldering?</p>
| How do you remove insulation from headphone wires? | 2010-12-03T13:54:28.203 |
7493 | |tools|potentiometer| | <p>While at first sight they may look that way, trimmer potmeters are not meant to be trimmed with a cruciform screwdriver like a Phillips or Pozidriv. What appears to be a cross is actually a slot with an arrow in it, which points to the position of the wiper.<br>
So simply use a small flat-head screwdriver, like one from a jeweler's set.</p>
| <p>Is there any special tool used to adjust trimmer potentiometers?<br>
I have some similar to the one on the picture:</p>
<p><img src="https://i.stack.imgur.com/d0h2U.jpg" alt="PIHER PT10LV trimmer potentiometer"></p>
<p>I've tried using small slot, Phillips and Pozidriv screwdrivers, but they all don't seem to fit nicely giving me impression that there is some special tool used to adjust trimmer potentiometers.</p>
<p>If there isn't any special tool, what has proven to work well for you?</p>
| Are there any special tools used to adjust trimmer potentiometers? | 2010-12-03T15:16:56.760 |
7505 | |mechanical| | <p>Some printers have a clear striped ( across the axis ) material that is scanned by photo cells to make a long linear encoder. This does not move. You could use your current drive ( or almost any other ) and use the encoder for feedback to make the motion as precise as the stripes.</p>
| <p>I would like to mount a slow-moving robotic "car" to a linear track of any incline from horizontal to vertical. The track should be rigid (attached to a boom if necessary) so that it can be propped up on one end or leaned against a wall to provide the incline.</p>
<p>The car should be able to:</p>
<ul>
<li>carry an 800 g load when the track is exactly vertical,</li>
<li>move approximately 5 cm/min,</li>
<li>hold position without power, and</li>
<li>travel several meters or more.</li>
</ul>
<p>I suspect I need hardware such as the following, but I don't know where to begin. Can anyone help narrow my search?</p>
<ul>
<li>Track hardware</li>
<li>Drive system for a small platform weighing upwards of a kilogram</li>
<li>Brake (to allow the car to remain at rest with zero work)</li>
</ul>
| Track-mounted drive system | 2010-12-03T20:32:34.860 |
7510 | |mac|filter|spice| | <p>The 3db cut-off frequency is \$\dfrac{1}{2 \cdot \pi \cdot RC}\$ = 159 Hz, which is quite close to your 156 Hz.</p>
| <p>I have a very simple low-pass filter with an AC source a capacitor and a resistance in series. Now I set C and R so that R*C=100 but when I plot the diagram whit db(out), it looses 3dB at 156Hz instead of 100Hz.</p>
<pre><code>Vin in 0 DC 0.0 AC 1.0 0.0
C1 out 0 1uF
R1 in out 1kOhm
ac dec 50 0.1Hz 100kHz
</code></pre>
<p>I'm just starting with this things, can someone help me?</p>
| Very simple circuit on spice | 2010-12-04T01:42:36.593 |
7516 | |components|solid-state-relay|pricing| | <p>Principally, you're paying for the testing. UL and CE testing is <em>Very</em> expensive. Also, lifetime and reliability testing (the crydom relays are specced to 100,000 cycles), which means that crydom has actually run a number of the devices through 100,000 cycles at load.</p>
<p>Furthermore, you're also paying for liability insurance. If an appliance fails and kills someone, and the only AC-facing component was a crydom relay, it's crydom's problem. If the AC components are your own, it's your problem.</p>
<p>Lastly, while it's true that a discrete relay solution is preferable in large volumes, you often see SSRs in small-volume or specialty products, where assembly and testing costs dominate the expenses, rather than raw component costs.</p>
| <blockquote>
<p>Solid State Relay (SSR) Crydom CN240A24: Eur 10.72 </p>
</blockquote>
<p><img src="https://i.stack.imgur.com/R3JYL.jpg" alt="alt text"></p>
<p>Same function with basic components </p>
<blockquote>
<p>Optocoupler MOC3043 (zero-crossing detect, triac out): Eur 0.726<br>
Triac BTA06-600CWRG (snubberless): Eur 1.16<br>
2 resistors: Eur 0.212</p>
</blockquote>
<p>Total for the second solution: Eur 2.10, or 80% less than the SSR solution.
Prices from the Mouser catalogue. Similar devices from other manufacturers have similar prices (quick check).</p>
<p><img src="https://i.stack.imgur.com/GlPBp.png" alt="alt text"> </p>
<p>So, the question is: what's so special about Solid State Relays that they cost so much? </p>
<p><strong>edit</strong><br>
I guess at Crydom the LED and photo-triac are bonded directly to the thin PCB. Packaged components may be used for small production runs, though.</p>
| Why do Solid State Relays cost so much? | 2010-12-04T16:52:59.553 |
7517 | |arduino| | <p>Sparkfun has a handy package: <a href="http://www.sparkfun.com/products/10007" rel="nofollow">Arduino Stackable Header Kit</a>.</p>
<p>For the actual Arduino itself, you would use these <a href="http://www.sparkfun.com/products/115" rel="nofollow">0.100" breakaway female headers</a></p>
| <p>Picked up my first Arduino shield today and I was surprised to see that it doesn't have any pins on it - just empty mount holes. What's the cusomary thing to solder to the shield to get it to mount to my arduino? From what I understand these shields should be stackable so I need to solder something to both the top and bottom sides of the shield.</p>
| Arduino shield - what should I solder to the pin mounts? | 2010-12-04T17:00:36.117 |
7522 | |fpga|jtag|ftdi|xilinx| | <p>You'll want a look at <a href="http://forums.xilinx.com/t5/Spartan-Family-FPGAs/Spartan3-JTAG-interface-3-3V/m-p/51026" rel="nofollow">Xilinx app note 453</a>, title "The 3.3V Configuration of Spartan-3 FPGAs". Basically the advice is putting resistors in series to limit the current through the protection diodes, and one over the 2.5V to sink the remaining current. Using level shifting circuitry instead would also work.</p>
| <p>I have some boards with Xilinx Spartan 3 FPGAs, I would like to upload new bitstreams over JTAG. I was planning on using <A href="http://urjtag.sourceforge.net/book/index.html" rel="nofollow">UrJTAG</a>.</p>
<p>I already have a couple of <a href="http://www.olimex.com/dev/arm-usb-ocd.html" rel="nofollow">FTDI based JTAG adapters</a> for ARM targets - can these be used?</p>
<p>They run at 3V3, I read that the Xilinx JTAG is at 2V5 will this be a problem?</p>
<p>Alternatively, I have a few FTDI FT232s, is there a simple cable I could build?</p>
| FTDI based Xilinx JTAG | 2010-12-04T20:37:30.957 |
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