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5325 | |microcontroller|power|port| | <p>As I am looking to deploy on a "real" PoE network, the Freetronics stuff is not going to work for me. I've contacted the folks at Akros and arranged to get a protoboard after signing an NDA… But at present Akros does not have a US distributor, so parts availability for homebrew projects is likely to be problematic.</p>
<p>I'm still interested if anyone has suggestions for a similar SoC solution for standards-compliant PoE.</p>
| <p>I am interested in experimenting with PoE for a variety of small embedded controller projects. Is there a hobbiest's source for any of the Akros Silicon PoE evaluation boards? Or is there another bit of kit I should be looking into?</p>
<p>My ideal prototyping board would be something like an Ethernut powered by PoE…</p>
| Is there a hobbiest's source for Akros Silicon PoE evaluation boards? | 2010-10-18T04:34:52.390 |
5330 | |microcontroller|embedded|ethernet|ipv6| | <p>I'm not that sure (like Joby).</p>
<p>If your device is going to live 5-15 years, the problems with IPv4 could have become worse. And at some point there is going to be a switch, IPv4 can't live forever and we can't ignore the problems forever.</p>
<p>But on the other hand NAT will continue to save IPv4,
so your guess is as good as mine.</p>
<p>So my advice is to play it safe and at least see if there is a possibility to upgrade your device to IPv6 if you need it....</p>
| <p>We're nearing the exhaustion of IPv4. What should be my concern about it for embedded devices?</p>
<p>I don't know about others manufacturers but until today, Microchip TCP stack doesn't implement the IPV6.</p>
| Do I have to worry about the depletion of IPv4 addresses in embedded applications? | 2010-10-18T15:27:48.093 |
5333 | |pic|passive-networks| | <p>Is MCLR pulled up? Leaving it floating can cause intermittent operation like that.</p>
| <p>I'm trying to use an RC oscillator on a PIC 16F84A-20 that I have on a breadboard. The code is supposed to (at this point) simply flip an output back and forth every so often.</p>
<p>I don't need it to run very fast, so I figured I'd try using the RC network on CLKIN instead of a crystal. My problem is that my code doesn't seem to be running consistently (I get some LED flashes for a few seconds, then nothing, then perhaps more flashes, etc).</p>
<p>I'm working on a plug-in breadboard. I've got +5 provided by a PIC dev board I had handy.
+5 is reading 4.94 volts via my DMM.
I used a 4.7K resistor from CLKIN to +5, and a 33pf cap to GND. </p>
<p>I put an o-scope on CLKIN, and I see a sawtooth-ish wave of about 2.5Mhz, but I also see some other, longer waveform in the background, if you will (it's far fainter than the sawtooth). it's a much wider, slowly decaying pulse. The sawtooth wave is, unfortunately, only about .2-.3 volt high, and centered between +5 and GND.</p>
<p>I put the scope on CLKOUT, and in the instances where I'm seeing my LEDs blink, I've got a nice squarewave on CLKOUT. Other times it's just flat.</p>
<p>My assumption is that I've made some basic error with the RC circuit that's causing it to not generate a sufficient waveform, and thus not work. I'd like pointers to what I should be checking next.</p>
| PIC 16F84A RC oscillator problems | 2010-10-18T15:43:03.207 |
5336 | |transistors| | <p>Those answers and comments that say, "I know you don't like it but you have to learn the alphabet soup," are wrong.</p>
<p>I was lucky enough to come across EXACTLY the video(s) you want some time ago. It teaches you how to USE transistors without the ubiquitous lesson of how they are made in silicon. </p>
<p>Despite what others say, you will learn BETTER if you leave out the abc soup until you have practical knowledge. I never really understood transistors before; I'd been taught to think of them as little switches (which is very misleading, at best). Now I know enough to comfortably put them into use. Here are the videos:</p>
<p><a href="http://www.youtube.com/watch?v=CkX8SkTgB0g&feature=channel&list=UL" rel="noreferrer" title="What is a transistor? How does a transistor work? Part 1">What is a transistor? How does a transistor work? Part 1</a></p>
<p><a href="http://www.youtube.com/watch?v=4QkRI1Ue208&feature=channel&list=UL" rel="noreferrer" title="What is a transistor? How does a transistor work? Part 2">What is a transistor? How does a transistor work? Part 2</a></p>
| <p>Every reference I can find on transistors immediately launches into theory-heavy alphabet soup. The above seems also to be assumed knowledge for reading a datasheet. I don't care; I just want to get one to work.</p>
<p>I understand there's some relationship between the current/voltage applied to the base to get a particular current to flow from the collector to the emitter. Which numbers on the datasheet relate to that? If I'm only trying to operate the transistor in "switch" mode, do I really need to care what current I apply to the base or will I be fine just whacking a 1k resistor in between my logic level output and the transistor base?</p>
<p>Is the only difference between an NPN and a PNP transistor which way the current flows when a current is applied to the base?</p>
| I don't care how a transistor works, how do I get one to work? | 2010-10-18T16:57:23.867 |
5338 | |esd|microcontroller| | <p>You can certainly use such devices. They are usually a poor choice for anything that has lower power usage requirements as they have high leakage current. </p>
<p>You also have to be careful of the clamping voltage, ESD of ~200V can damage a micro-controller, the device you linked is specced at 500V max. Make sure whatever your trying to protect is actually be protected to the extent it needs.</p>
<p>For digital lines also pay attention to the capacitance of these device/package, they can screw up your signal integrity. </p>
<p>What I usually do if the input is likely to get hit with ESD, like an input that is often connected in the field is use a 2 pronged approach. </p>
<p>First Use a ESD device, or diodes closer to the circuit to protect, which type I would use depends on the signal/circuit in question. This is to protect against lower spikes, say 8kV. More and more you see this type of protection inside devices, especially boundary devices like RS232 drives and line drivers.</p>
<p>Second, when you build the PCB use spark gaps, which is really nothing more than putting 2 pads on the surface of the PCB, 1 being the signal, the other being a good ground and spacing them very close to each other, like 6 thou apart. This will protect against higher voltage hits, like 25kV. Pretty simple concept, the high voltage jumps the gap and goes straight to ground. Just be careful how you place these, as close to the connector as possible with the best possible ground connection. </p>
<p>Also pay attention to the manufacturing process your using, you don't want solder to accidental bridge the gap. </p>
<p>Gaps can be tough to do on digital traces and avoid changing the impedance, usually requires tweaking the signal termination after the prototype run. </p>
<p>There is some argument over the proper shape of the pad, some use half moons, some use pointed triangles with the tips near each other and some use square pads. I've always used square pads, the more area that is close to the other pad the more repeated strikes the gap will survive. The trade off is that the square pads will take the most effort to ensure there is no solder bridging. Best answer is to get your CM to not apply solder to these pads at all, but that can require special effort on their part.</p>
| <p>I'm working with two chips on a board, a dsPIC33F and a PIC24F as well as a serial EEPROM (24FC1025.)</p>
<p>I've seen these little ESD protection devices in 0603 packages:</p>
<p><a href="http://uk.farnell.com/panasonic/ezaeg3a50av/esd-suppressor-0603-15v-0-1pf/dp/1292692RL">http://uk.farnell.com/panasonic/ezaeg3a50av/esd-suppressor-0603-15v-0-1pf/dp/1292692RL</a></p>
<p>For MCUs like I'm using, is this necessary? The boards may be constantly handled and the external interfaces (I2C, UART) may be exposed to ESD. </p>
<p>Would the internal diodes protect the chip anyway and make these pointless?</p>
| ESD protection devices - necessary for MCUs? | 2010-10-18T17:21:56.647 |
5345 | |tl431| | <p>From <a href="http://focus.ti.com/lit/ds/symlink/tl431a.pdf" rel="nofollow">the datasheet</a>:</p>
<blockquote>
<p>The TL432 has exactly the same
functionality and electrical
specifications as the TL431, but has
different pinouts for the DBV, DBZ,
and PK packages.</p>
</blockquote>
| <p>What is the difference between these parts? The datasheet shows completely different pinnings, but both are specified over the same range and both have the A, B and ungraded specifications for tolerance.</p>
<p>Just curious.</p>
| Difference between TL431 and TL432 | 2010-10-18T21:32:27.603 |
5347 | |batteries| | <p>I would not care about age, however if a 12 V battery reads under 10.5 V it usually means a cell is shorted.</p>
<p>If you can, however, get it to like 13 V after it has been charged and the charger disconnected, then it might be possible to resurrect it by desulphating it. Sadly AGM/GEL batteries tend to be harder to desulphate than plan flooded cells but you could still give it a try.</p>
| <p>Got an old 12V UPS battery, a sealed lead acid 17.2Ah battery. Quite a nice YUASA battery. Unfortunately it reads 9.92V so has been discharged badly. Is there any chance of salvaging it?</p>
| Resurrecting a 12V SLA from a UPS | 2010-10-18T22:39:53.747 |
5352 | |pic|compiler| | <p>The most likely aspects to be compiler-dependent are:</p>
<ul>
<li>using single bits (especially in IO ports)</li>
<li>sizes of integers, and char being signed or unsigned </li>
<li>funny pointers: C18 differentiates rom and ram pointers :(</li>
<li>configuration fuses</li>
<li>busy waiting</li>
</ul>
<p>My preferred way to handle this is to write macros for these aspects, and have the compiler select the correct macro based on compiler-specific predefined macros. I made an RFM70 library and example applications this way that run on PIC14 (HiTechC), PIC16 (C18) and ARM (GCC).</p>
<p>(update)
My RFM70 library is now complete. It supports C on PIC 16F (Hitech compiler), C and C++ on LPC11114 (Cortex) and LPC2148 (ARM7TDMI) (GCC compiler) and Arduino (ATMega128, GCC compiler). This is generated (including doxygen documentation) from the same source by doing some preprocessing in a Python script. Jal support is under development, maybe ProtonBasic will follow. <a href="http://www.voti.nl/rfm70" rel="nofollow">http://www.voti.nl/rfm70</a></p>
| <p>As I mentioned, I have just beginned programming pic16f877a. I can now work with 7 segment displays. At present I am using ccs compiler. Nothing wrong with that. But i prefer to be a compiler independent programmer. So i simultaneously want to work in other compilers like IAR or Hitechc. I want to know whether the "program statement declaration in compilers" other than ccs will be different? Please guide me how to approach this thing. I would welcome all forms of suggestions. Thanks in advance.</p>
| PIC 16F beginner.. difference in program-syntax when using different compilers | 2010-10-19T07:41:24.873 |
5355 | |capacitor|simulation| | <p>No, they don't dissipate energy, but they do store it. So energy can flow into a capacitor, and remain there, and then flow back out. Since power is the rate at which energy is used or moved, the power will be non-zero whenever energy is moving. But it's not being dissipated (converted into heat). It's just being moved around and stored.</p>
<p>It's important to remember the difference between instantaneous power and average power. A 1 ohm resistor with 1 V<sub>RMS</sub> AC across it will dissipate an <em>average</em> power of <a href="http://www.wolframalpha.com/input/?i=%281+V%29%5E2%2F1+ohm" rel="nofollow noreferrer">1 W</a>, for instance, but the instantaneous power will vary with the waveform:</p>
<p><a href="http://en.wikipedia.org/wiki/Power_factor" rel="nofollow noreferrer"><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/d/db/Power_factor_1.svg/500px-Power_factor_1.svg.png" alt="average vs instant power for a resistive load"></a></p>
<p>With a reactive element (capacitor or inductor) as the load, the power will fluctuate between positive and negative as energy flows in and out, but the average will be zero:</p>
<p><a href="http://en.wikipedia.org/wiki/Power_factor" rel="nofollow noreferrer"><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/2/23/Power_factor_0.svg/500px-Power_factor_0.svg.png" alt="average vs instant power for an inductive (i think) load"></a></p>
| <p>On several circuit simulators I have seen capacitors with a "Power" figure.</p>
<p>Also, I have wondered how capacitive power supplies work.</p>
<p>Does an ideal, zero resistance, zero leakage, zero inductance capacitor dissipate any power?</p>
<p>See image:</p>
<p><img src="https://i.stack.imgur.com/sLONK.png" alt="cap power"></p>
<p><a href="http://www.falstad.com/circuit/#%24%201%205.0E-6%2010.20027730826997%2050%205.0%2043%0Av%20288%20192%20288%20272%200%201%2040.0%205.0%200.0%200.0%200.5%0Ar%20288%20192%20384%20192%200%20100.0%0Ac%20384%20192%20384%20272%200%201.0E-5%201.6020737594995769%0Aw%20288%20272%20384%20272%200%0Ag%20288%20272%20288%20288%200%0Ao%202%2064%200%2035%205.0%200.0125%200%20-1%0Ao%202%2064%201%2035%200.3125%209.765625E-5%201%20-1%0A" rel="noreferrer">Link to simulation of this schematic</a></p>
| Does an ideal capacitor dissipate power? | 2010-10-19T10:15:31.557 |
5365 | |buck|switch-mode-power-supply|inductor| | <p>I wouldn't worry about it for 2 reasons.</p>
<p>First it is a multiple but, 60Mhz is an even harmonic of 3Mhz. The output of the regulator should be basically a square wave and square waves have content at their fundamental and only odd harmonics. So 3, 9, 15, 21, 27, 33, 39, 45, 51, 57, 63. Of course a non-perfect wave will have some even harmonic content but it should be well below any odd harmonics, if its a good square wave, it'll be in the noise floor. If in question set up your scope to do an FFT on the regulator output and see what its output looks like at 60Mhz.</p>
<p>Second, as the list above shows, you're at a very high harmonic at 60mhz. The switching supply would have to be outputing a square wave with really fast rise/fall times to have much if any content up that high. Usually only the first 3-6 odd harmonics are what you need to worry about with a square wave, depending on rise/fall times. That would work out to a theoretical rule of thumb that as long as the SRF is 5-10 times your switching speed you should be fine.</p>
<p>EDIT: Decided to model this so some degree...</p>
<p>Test Circuit, I used the parameters from the inductor you linked for the inductance, stray capacitance, ESR and shunt resistance. Shunt resistance changes based on frequency and is defined in Eqn. I modeled a generic 10uF ceramic cap for the output filter cap including ESR and ESL and arbitrarily chose 1k for the load. Doing an AC sweep with a 1V source from 0 to 250Mhz then later to 1Ghz to peek at the frequency response. The output resistance of the switcher is a shot in the dark but probably about right.
<img src="https://i.stack.imgur.com/m5V8N.gif" alt="alt text"></p>
<p>Here we are doing a sweep without the output filter cap attached to see the SRF of the inductor model, as expected at 60Mhz.
<img src="https://i.stack.imgur.com/9EWMo.gif" alt="alt text"></p>
<p>Here we sweep with the cap in place:
<img src="https://i.stack.imgur.com/PVcX0.gif" alt="alt text"></p>
<p>This one is actually interesting. Whats happening is that even though the inductor loses its filtering properties at SRF there is still an RC filter formed by Rout,the inductors resistance and the output cap. This filter is capable of blocking the high frequencies somewhat, which is why we don't see as sharp a change is we saw with the inductor only. However at these frequencies the ESL of the cap is really starting to come into play so we see a rising output level as frequency increases.</p>
<p>Finally lets see how it increases:
<img src="https://i.stack.imgur.com/fdGlU.gif" alt="alt text"></p>
<p>At 1 ghz the inductor is completely dominated by the stray capacitance and the filter cap in dominated by the ESL, at 10Ghz (not shown) it levels right off. </p>
<p>Of course there are a bunch of stray inductances,capacitances and variations (especially at the really high frequencies) not included in this simple model but maybe it will aid as a pictorial representation of whats happening. </p>
<p>The most interesting thing that came out of this for me is that SRF isn't a brick wall. The inherent RC filter can mitigate some of the effect of hitting the SRF.</p>
<p>EDIT2: One more edit, mostly because i'm using this as an opportunity to play with Qucs circuit sim for the first time. Cool program.</p>
<p>This shows 2 things. First its displaying the frequency response of the circuit in magnitude (in dB, Blue) and phase (red) this shows more clearly where the component's parasitic capacitance / inductance takes over. It also shows a secondary sweep of the ESL of the output capacitor showing how important it is to minimize this through component selection and PCB layout. Its sweep from 1nH to 101nH in steps of 10nH. You can see if the total inductance on the PCB gets very high you lose almost all of your filtering capability. This will result in EMI issues and/or noise problems.
<img src="https://i.stack.imgur.com/SBfAf.gif" alt="alt text"></p>
| <p>I'm using the LM2734Z, a 3 MHz buck regulator. It's really fast which means it has a small inductor.</p>
<p>One of the things I'm wondering is how important is the self-resonant frequency of the inductor? I'm using it to step 4.8V to 20V down to 3.3V ±5%.</p>
<p>I found a 3.3µH 2A inductor (as recommended by the datasheet for 3.3V @ 1A, I'm rating the output to 400mA maximum) "SDR0604-3R3ML." Its self-resonant frequency is 60 MHz, which seems to be well clear of 3 MHz, but it is a multiple and I'm wondering if harmonics come into it?</p>
<p>Even if this case is okay, is there a rule of thumb for avoiding certain resonant frequencies (i.e. if they match?)</p>
| How important is self-resonant frequency for an inductor when used in a fast (~3MHz) buck SMPS? | 2010-10-19T17:45:57.607 |
5369 | |resistors| | <p>If you look at a "proper" data sheet (example: <a href="http://www.yageo.com/documents/recent/PYu-RC0603_51_RoHS_L_4.pdf">http://www.yageo.com/documents/recent/PYu-RC0603_51_RoHS_L_4.pdf</a>) you'll usually find that the zero ohm resistor is defined separately using something like < 0.05R.</p>
<p>In this case, you're looking at a more or less automatically generated set of data which is probably more relevant to the other resistors in the range. Multicomp in this case refers to multiple sources so the parts could be coming from anywhere; the data in this case is fairly general and is most likely the lowest common denominator for a variety of alternative devices.</p>
| <p>This <a href="http://uk.farnell.com/multicomp/mc0603wg00000t5e-tr/resistor-0603-0-063w-0r/dp/1692453?Ntt=MC%200.063W%200603%201%25%200R">0Ω resistor</a> has a tolerance of ±1%.</p>
<p>Well it would only be +1% at best because you can't have a negative resistance* but still 1% of zero is still zero?</p>
<p>Shouldn't it be something like 0\$\Omega\$ + 0.001R?</p>
<hr>
<p>*except in very special cases with certain devices but never over the full operating range.</p>
| Zero ohm resistor tolerance? | 2010-10-19T19:48:42.680 |
5370 | |tl431| | <p><strong>Q1</strong><br>
Yes.</p>
<p><strong>Q2</strong><br>
This deserves a longer answer. </p>
<p>\$V_{OUT} = V_{REF} \times (1 + \dfrac{R1}{R2}) + I_{REF} \times R1\$ </p>
<p>To find the upper limit of \$V_{OUT}\$ you have to work with the appropriate limit for each of the factors. Appropriate means that for some it will be the lower limit, for others the higher limit. Here it's the lower limit for R2, the higher for all others. Plugging in the numbers gives us </p>
<p>\$V_{OUT} = (2.495 * 1.005) \times (1 + \dfrac{6340 * 1.001}{31600 * 0.999}) + 0.4 \times 10^{-6} \times (6340 * 1.001) = 3.0141V\$<br>
\$= 3V + 0.47\%\$ </p>
<p>Likewise for the lower limit for \$V_{OUT}\$ : </p>
<p>\$V_{OUT} = (2.495 * 0.995) \times (1 + \dfrac{6340 * 0.999}{31600 * 1.001}) = 2.9796V = 3V - 0.68\%\$ </p>
<p>Why did I drop the term for \$I_{REF}\$ here? For \$I_{REF}\$ only a maximum value is given, no minimum, so thinking worst case it might as well be zero.<br>
If you put on your wiseguy hat you could say "Right, that's the 0.7% I reckoned, I didn't need this complicated calculation for that." No you didn't because the tolerances are real low. For higher tolerances you'll find that simply adding isn't sufficient. </p>
<p>There's another important thing to note. Parameters in a datasheet are always specified under certain conditions. In this case it's a device current of 10mA. We have only a fraction of that, 240\$\mu\$A worst case. So the values may be a bit different. </p>
<p>Which brings us to our next class: philosophy!<br>
Is it worth going through all this trouble and spend money on precision components if you're not quite sure of the outcome? How about the rest of the system? Did you do the same calculations for all other components? Are they all precision parts? Where's the weakest link?<br>
In my freshman year in college I thought DMM showing 6 significant digits were cool. Now I know better. In most cases the last two digits are not reliable, for instance because they will drift as soon as the temperature rises half a degree. That reminds me: temperature controlled voltage references! What happens if the temperature in your product rises by 10°?<br>
I remember an Analog Devices seminar I once attended, where the speaker showed a 5cm trace to an ADC input would introduce several LSBs of error!<br>
I could go on, but the bottom line is: can I really achieve this theoretical precision, and, more importantly: <em>do I really care?</em><br>
Your product will probably perform as well if the reference is 3.01V, right? I guess I would rather focus on <strong>stability</strong> and <strong>noise</strong>. If you still think you need a precise voltage reference I wouldn't make if with a TL431. Google for precision voltage references. You'll come up with devices like Maxim's <a href="http://datasheets.maxim-ic.com/en/ds/MAX6010.pdf" rel="nofollow">MAX6010</a> (one of the first hits for me), which has an initial accuracy of 0.2%. (You'll have to jack up your 3.3V a bit; it has a 200mV dropout.)<br>
The Analog Devices <a href="http://www.analog.com/static/imported-files/data_sheets/AD780.pdf" rel="nofollow">AD780</a> is 1mV precise (or 0.033%), but requires at least 4V (maximum 36V, so you may have this available somewhere).</p>
| <p>I'm using a <a href="http://focus.ti.com/lit/ds/symlink/tl431b.pdf" rel="nofollow noreferrer">TL431B</a> (±0.5%) shunt regulator to get 3V ±1% (max.) from a 3.3V ±5% supply, so from 3.135V to 3.465V. The 3.3V supply is a switcher, so has a decent amount of high frequency (~3 MHz) noise on it. </p>
<p>This is related to my previous question;</p>
<p><a href="https://electronics.stackexchange.com/questions/5213/does-the-tl431-have-a-dropout-voltage-per-se">Does the TL431 have a "dropout voltage" per se?</a></p>
<p>In fact the circuit configuration is very similar but I adjusted the values of the resistors, so I'll use the same diagram drawn in my TomCAD style:</p>
<pre><code> 560R 5%
+3.3V-+-/\/\/\---+----------+-------+-- 3V out
| | | |
--- 100n / | --- 4.7u
--- 16V \ 6.34k | --- 6.3V
| / 0.1% ___|__| |
--- | | / \ ---
- +--------/___\ -
| |
/ |
\ 31.6k |
/ 0.1% |
| |
--- ---
- -
</code></pre>
<p>Two questions:</p>
<ol>
<li><p>Will it work?</p></li>
<li><p>What is the accuracy given the precision ±0.1% resistors and 2.495V ±0.5% reference? Is it the sum, so ±0.7%, or something complicated?</p></li>
</ol>
| TL431, take two | 2010-10-19T19:58:44.420 |
5373 | |soldering|surface-mount| | <p>If you can do it, you might find suitable chips in an old switch or motherboard or some other junk, desolder (hot air/gas/oven) them and use those for practice. Recycle and save the planet. :)</p>
| <p>I'm looking for a cheap source of broken/outdated TQFP-44 and SO-28 ICs or packages which I can test my soldering skills with. The chips I'm using are £3 each and this is money I'd rather not throw away if I damage them. </p>
<p>Any suggestions will be appreciated! Thanks!</p>
| Cheapest TQFP-44's & SO-28's to practice SMD soldering? | 2010-10-19T21:18:19.457 |
5374 | |soldering|surface-mount|reflow| | <p>At my previous work place, the guys would kit all the SMT components into little trays and then do small batches using solder paste and place all the passive resistors and capacitors, then using a handheld hot air soldering iron go over each component briefly until it "wiggled" into place and the solder reflows.</p>
<p>Next phase was for the semiconductors (transistors and mosfets and the like) followed by integrated circuits.</p>
<p>Final stage was handsoldering the larger connectors and through hole components.</p>
<p>Spending the time to kit and prepare good assembly drawings (hand colour coded to match the bins of the parts) it meant placing all the passives went quickly as did the soldering. This method will help speed up small one man batch production, at the expense of setup time.</p>
| <p>I'm considering doing DIY SMT Reflow for production of my Super OSD project.</p>
<p>An overview of the component count:</p>
<ul>
<li>Resistors: ~50 x 0603; precision 0.1% resistors as well as 1% and 5% components</li>
<li>Capacitors: 17 x 0603, 2 x 0805, 1 x 1206 (all ceramics), 2 x EIA-3216 (tantalums.)</li>
<li>Inductors: 1 SDR-0604 package</li>
<li>Chips: SOIC-8 (EEPROM), SOIC-28, TQFP-44, some SOT-23 (temp sensor + TL431.)</li>
<li>Transistors: 3 x SOT-23 (2 x N-ch mosfet, 1 x NPN)</li>
<li>Diodes: 2 x SOT-23, 2 x SOD-323</li>
<li>Misc: polyfuse 0805 x 1, LED 0603 x 1</li>
</ul>
<p>As can be seen this going to be a monster to solder manually so I was thinking of doing DIY toaster oven reflow. Would this be suitable? Are there any pitfalls I need to be aware of?</p>
<p>Otherwise I'm going to have to solder them up myself but I see it being a real problem with almost 80 tiny components per board.</p>
| Reflow at home or solder manually? | 2010-10-19T21:28:17.263 |
5380 | |microcontroller|diodes|microcontroller| | <p>If the pins have clamp diodes, you need only a series resistor to limit the current. You can see in the application note <a href="http://ww1.microchip.com/downloads/en/AppNotes/00521c.pdf" rel="nofollow">AN521</a> from microchip that it connect the pin of the microcontroller directly in the AC.</p>
<p>I have used a voltage divider to connect a PIC to a GPRS module with a speed higher than 19,200 and had no problem.</p>
| <p>As a simple and cheap way of protecting my MCU against higher than 3.3V logic inputs, can I use for low speed data transfers some resistors on the data lines? In theory, these should act in tandem with the pin diodes inside the MCU to clamp the voltage. But will it work in practice? Logic shifter chips aren't an option due to space and cost constraints.</p>
| MCU clamping diodes | 2010-10-19T23:22:22.547 |
5386 | |microcontroller|pic| | <p>The <strong>PIC18F87K22 family of devices is capable of
operating in one of two program memory modes</strong>, using
combinations of on-chip and external program memory.
The functions of the multiplexed port pins depend on
the program memory mode selected, as well as the
setting of the EBDIS bit.
In Microcontroller Mode, the bus is not active and the
pins have their port functions only. Writes to the
MEMCOM register are not permitted. The Reset value
of EBDIS (‘0’) is ignored and the ABW pins behave as
I/O ports.
In Extended Microcontroller Mode, the external
program memory bus shares I/O port functions on the
pins. When the device is fetching or doing table
read/table write operations on the external program
memory space, the pins will have the external bus
function. </p>
| <p>One of my projects would greatly benefit from being able to run a program that isn't stored in the microcontroller (but is instead stored in a SD card).</p>
<p>So, I'm looking for a device that will allow me to load the code from the SD card into RAM and then execute the code from RAM. Currently, I only have the programmer that comes with the PicKit2, so I'd prefer to stay with PICs.</p>
<p>Does anyone know which, if any, PICs can do this? If no PICs are capable of this, then what are some different micro controllers that would work for this? Preferably ones that are available in a breadboard compatible package.</p>
| Execute instructions from RAM in a hobbyist-friendy microcontroller | 2010-10-20T03:07:52.150 |
5399 | |soldering|reflow| | <p>For home DIY one of possible hacks is to use pastes with different liqid points. Reflow one side with 180C paste, then another side with 130C paste.</p>
<p>Also, you can rely on surface tension, if have no heavy components or place those on last reflow side</p>
<blockquote>
<p>I would think that doing the reflow twice (for the other side) might overheat the components already soldered on.</p>
</blockquote>
<p>For DIY that's usually not a problem. Of cause, everything depends on components & situation. Don't apply this answer "for professional use".</p>
| <p>Is it possible to place components on both sides of the board if I'm doing DIY toaster-oven style reflow soldering? I would think that doing the reflow twice (for the other side) might overheat the components already soldered on.</p>
| Components on both sides of the board with reflow | 2010-10-20T14:14:55.043 |
5403 | |pcb|layout| | <p><strong>Charts</strong><br>
<a href="https://en.wikipedia.org/wiki/IPC_%28electronics%29" rel="noreferrer">IPC</a> standard 2221 "Generic Standard on Printed Board Design" (<a href="http://sisko.colorado.edu/CRIA/FILES/REFS/Electronics/IPC_2221A.pdf" rel="noreferrer">pdf</a>, <a href="https://portal.ipc.org/Purchase/ProductDetail.aspx?Product_code=db07d393-2133-e211-bf0f-00155d052876" rel="noreferrer">IPC web-site paid</a>) (page 41) provides the following relationships between current carrying capacity and copper trace width: </p>
<p><a href="https://i.stack.imgur.com/y4p8b.png" rel="noreferrer"><img src="https://i.stack.imgur.com/y4p8b.png" alt="enter image description here"></a>
<em>Figure 1: Cross section area to current. <strong>External layer.</em></strong> </p>
<p>Notes for the figure (also applicable for the Figure 2):<br>
1) Temperature stands for temperature of the trace relative to ambient. That is, if, for instance, ambient temperature is 80C, 20C stands for 100C temperature of the trace.<br>
2) <em>The curves include a nominal 10% derating</em> (on a current basis) to allow for normal variations in etching techniques, copper thickness, conductor width estimates and cross-sectional area.<br>
3) <em>Additional derating of 15% (current-wise) is suggested</em> under the following conditions:<br>
. a) for panel thickness of 0.8 mm or less,<br>
. b) for conductor thickness of 108 um or thicker. </p>
<p><a href="https://i.stack.imgur.com/8YSSv.png" rel="noreferrer"><img src="https://i.stack.imgur.com/8YSSv.png" alt="enter image description here"></a>
<em>Figure 2: Cross section area to current. <strong>Internal layer.</em></strong> </p>
<p><a href="https://i.stack.imgur.com/jk87W.png" rel="noreferrer"><img src="https://i.stack.imgur.com/jk87W.png" alt="enter image description here"></a>
<em>Figure 3: Cross section area to trace width.</em> </p>
<p><strong>What is 1 oz copper?</strong><br>
The <a href="http://www.pcbuniverse.com/pcbu-tech-tips.php?a=4" rel="noreferrer">measure</a> for the copper thickness on a printed circuit board. It's the resulting thickness (height) when 1 oz of copper is pressed flat and spread evenly over a one square foot area. It corresponds to copper thickness of 1.37 mils (34.79 um).</p>
<p><strong>Explaining the relationship between cross section area and trace width (Figure 3)</strong><br>
1) Every curve corresponds to a particular copper thickness (trace height).<br>
2) Area (horizontal axis) is calculated as product of trace width and thickness.</p>
<p>Below is a Matlab script with a calculation example. It shows that for 1 oz copper trace with the area of 9 sq. mils, trace width is 6.6 mils:</p>
<pre><code>thickness=1.37E-3;%inches
area=9*(1E-3)^2;%square inches
width=(area/thickness)*(1/1E-3) %in mils
% result is 6.6 mils
</code></pre>
<p><strong>Example of usage of the charts</strong><br>
1) Internal layer, current 400 mA, copper thickness 1 oz, ambient temperature 80C, trace temperature 100C. What is the appropriate trace width?<br>
2) Look at Figure 2 (internal layer). Find the curve 20C (100C-80C). Find the point (9 sq. mils, 400 mA).<br>
3) Look at Figure 3. Find the curve 1 oz. Find the point (9 sq. mils, 0.07 inches). </p>
<p>The answer is about 7 mils (0.007 inches).</p>
| <p>Is there a standard for the sizes of PCB traces?</p>
<p>That is are some 25 mil and others 10 mil or is can you choose your own?</p>
<p>I plan to run 400mA through some thicker traces, but less than 30mA for all other traces. About what size would I need?</p>
| Standard PCB trace widths? | 2010-10-20T16:54:23.273 |
5404 | |microcontroller|adc|impedance| | <p>In addition to the good points that supercat has raised in his post, there is a further subtlety to note when you are using an unbuffered voltage divider with an external capacitor. </p>
<p>The charge transfer that happens every time you run through a sequence of ADC readings, when multiplied by a sequence repeat rate, becomes a <em>current</em>. The DC average value of this current is Csamp * deltaV * f, where Csamp is the sampling capacitance (not the external capacitance!), deltaV is the voltage between successive input channels, and f is the sequence repeat frequency (how often you cycle through 1 complete sequence of samples).</p>
<p>When you have an external capacitor to reduce the charge transfer effects and keep from having a long sampling time, it has the negative effect of low-pass-filtering this input current required to charge the sampling capacitor, which will appear as an input-voltage-dependent leakage current that causes an offset voltage across your source impedance.</p>
<p>Just for some sample numbers: your voltage divider (100K || 10K) is about 9K, and if deltaV between channels = 3V, Csamp = 10pF, and f = 10kHz, this will cause a voltage error of 2.7mV, or slightly less than 0.1% of deltaV. Not a lot, but enough to be aware of. You should <em>not</em> be using a 1M || 100K voltage divider with 10kHz sequence repeat rate -- of course, this is fairly fast, and for slower repeat rates, you don't need to worry as much.</p>
<p>I've written about this and other ADC driving issues in <a href="http://www.embeddedrelated.com/showarticle/110.php" rel="nofollow">a post on my blog</a>.</p>
| <p>What is the input impedance of a typical MCU ADC? In this case I'm working with a PIC24FJ64GA004. I don't need high speed sampling - a maximum of 100 samples per second.</p>
<p>I wish to connect a resistive divider with a 100k resistor and a 10k resistor, so the impedance should be higher than 1M or else the impedance will start skewing the readings.</p>
| ADC input impedance on MCUs | 2010-10-20T16:56:01.557 |
5411 | |buck|switch-mode-power-supply| | <p><img src="https://i.stack.imgur.com/84Amm.gif" alt="alt text"></p>
<p>Yellow is the critical current flow out, not sure where it goes from the output cap, C3.</p>
<p>Pink is the ground return, kinda sorta, theres a few critical loops in a circuit like this, some follow the path of least resistance, some follow the path of least impedance (follow their supply trace).</p>
<p>Keep in mind your goal is to minimize the size of this loop and minimize the resistance between yellow/pink at high frequency, (minimize impedance to ground).</p>
<p>Lets just quote the datasheet since it covers all of this:</p>
<p>"When planning layout there are a few things to consider when
trying to achieve a clean, regulated output. The most impor-
tant consideration when completing the layout is the close
coupling of the GND connections of the CIN capacitor and the
catch diode D1. These ground ends should be close to one
another and be connected to the GND plane with at <strong>least</strong> two
through-holes. Place these components as close to the IC as
possible. "</p>
<p>C1 and D2 in this case. C1 has a really, really, long path to ground for a power supply decoupling cap. Its also on the other side of the circuit from D2's ground. When your talking about high frequency PCB design when it says "tightly coupled" that doesn't mean just both tied to a ground plane. It means both ground pins are right next to each other, with a surface polygon pour connecting them and multiple via's to a ground plane right next to the pads. </p>
<p>Incidentally aren't your diode silkscreen's backwards?</p>
<p>"Next in importance is the location of the GND con-
nection of the COUT capacitor, which should be near the GND
connections of CIN and D1."</p>
<p>C3 is the output cap and its ground is roughly as far away from the other 2 as you can get.</p>
<p>"The FB pin is a high impedance node and care should be
taken to make the FB trace short to avoid noise pickup and
inaccurate regulation. The feedback resistors should be
placed as close as possible to the IC, with the GND of R2
placed as close as possible to the GND of the IC. The VOUT
trace to R1 should be routed away from the inductor and any
other traces that are switching."</p>
<p>Think your ok with this one, your probably better off running the trace from C3 further away from the inductor but its probably ok.</p>
<p>"High AC currents flow through the VIN, SW and VOUT traces,
so they should be as short and wide as possible. However,
making the traces wide increases radiated noise, so the de-
signer must make this trade-off. Radiated noise can be de-
creased by choosing a shielded inductor."</p>
<p>If were you i'd just use polygon pours for most of these connections, just make sure you have appropriate filtering in place and a shielded inductor.</p>
<p>"The remaining components should also be placed as close
as possible to the IC. Please see Application Note AN-1229
for further considerations and the LM2734 demo board as an
example of a four-layer layout."</p>
<p>If using 4 layer why not reference <a href="http://www.national.com/an/AN/AN-1229.pdf#page=1" rel="noreferrer">that app note?</a> pretty much covers using a big ol' ground pour for the critical ground return and a pour for the SW output.</p>
| <p>After getting some helpful critiques from my original post;</p>
<p><a href="https://electronics.stackexchange.com/questions/5129/critique-my-smps-buck-design">Critique my SMPS buck design</a></p>
<p>I worked on my design and made a few major changes.</p>
<ul>
<li>L1: 3.3uH 2A inductor</li>
<li>C1: 10uF 25V ceramic cap</li>
<li>C2: 0.01uF 16V ceramic cap</li>
<li>C3: 22uF 6.3V ceramic cap</li>
<li>D1: RB160M (input protection)</li>
<li>D2: RB160M (catch diode)</li>
<li>D3: BAV99W (dual diode)</li>
<li>R1: 10k 0.1%</li>
<li>R2: 31.6k 0.1%</li>
<li>R3: 56R</li>
<li>LED1: blue LED, 2.85V, 5mA</li>
<li>U1: LM2734Z (3 MHz variant), SOT-23-6</li>
</ul>
<p>I have added some copper around the pins in an effort to remove heat from the IC. The only thing I'm presently worried about is if the trace for the feedback voltage is too long. </p>
<p><img src="https://i.stack.imgur.com/NKlT8.png" alt="alt text"></p>
| Critique my SMPS buck design, take 2 | 2010-10-20T20:23:50.313 |
5412 | |avr|power-supply|poe| | <p>The <a href="http://www.freetronics.com/products/etherten" rel="nofollow">Freetronics EtherTen</a> web pages claims "Power-over-Ethernet support, both cheapie DIY or full 802.3af standards-compliant."</p>
<p>It appears to be a "open hardware" design, implying you are welcome to download the design files and incorporate as much as you want into your own custom boards.</p>
<p>From the schematic, it appears to use the WIZnet W5100 single-IC Ethernet interface. Circuit Cellar issue 208 (November 2007) has an article by Fred Eady titled "iEthernet Bootcamp - Get Started with the W5100".</p>
| <p>I am looking for a PoE Ethernet chip that I can incorporate in a design I plan on using along with some of the Arduino features. I would prefer to implement a standalone mcu for the Ethernet device capable of providing Ethernet. All possible solutions must support PoE to power the Micro. I do not plan on buying an Arduino nor do I want any shields per se. I am looking for a PoE Ethernet chip that would work well with the Arduino firmware and micro controller. A chip that I can incorporate into my own custom Arduino board. </p>
<p>I would also be interested in any AVR chips which provide the same capabilities (pin wise) as the Arduino ATMega168/etc that has Ethernet built on board.</p>
<p>My devel platform would be AVRStudio or something like it with a Jtag ICE MKII. I do not have the ability to use PIC as I do not have a programmer, the software, nor the cash to invest in another platform.</p>
<p>Thx in advance for your help.</p>
<p><strong>Edit</strong>: Andrew noted that I should post more info. First of all Andrew: I have not looked at the MFGs you mentioned. I will do so now.</p>
<p>I would like to place a few Freeduino type setups around the house to do various home automation tasks. My home is already wired with Cat6 and I plan on plugging certain network drops into a 10/100 8 port Linksys POE switch. I would like to provide network and power to each device without having to hack the network cables. I have verified that the switch conforms to the 802.3af standard.</p>
<p>I would like to create each board to solely pull power off of the PoE lines to provide sensor and relay capability (relays would be SSR - GA8-6D05 from Crouzet which requires 3-32VDC for the relay.</p>
<p>I would expect the PoE chip to deliver either full PoE voltage or be nice enough to drop it down to 7-12VDC. If needed, I can add a 7805 or appropriate chip to ensure voltage regulation. In the end, my micro would need 5V + 3V DC regulated @ 1A.</p>
<p>Hope this answers anything my original post left out.</p>
| Easiest and Best PoE Ethernet Chip/Micro/Design for DIY Interface with Custom Arduino Board (AVR Solution) | 2010-10-20T20:49:41.343 |
5413 | |lcd|hd44780| | <p>I found a workaround for the problem:</p>
<p>I added a 1000milisecond delay at startup, before initializing/configuring the LCD controller.
It worked pretty good for me. </p>
<p>A lower delay(100, 200ms) not worked so well.
Just a note: It happened only in 4bits databuss.</p>
<p>Good luck!</p>
| <p>I'm using an HD44780 clone LCD module a KS0066U. Everything works ok on the module except when I rapidly power cycle the device (on->off->on). For some reason a very short interruption in the power causes the display module to improperly initialize as a 1-line LCD instead of a 2-line LCD display. What would cause this behavior? Is there any way to prevent it in software?</p>
<p>EDIT: I'm using the display controller in 4-bit mode not 8-bit mode.</p>
| Power-up Initialization of HD44780 LCD Module | 2010-10-20T20:51:02.887 |
5424 | |pcb|open-source| | <p>I have built <a href="https://kitspace.org" rel="nofollow noreferrer">kitspace.org</a> with expressly this purpose. It is an open source site for posting open source hardware electronics projects. The site makes it easy for others to find the Gerber design files and buy the required parts. </p>
| <p>I would like to print a fairly common circuit. But I don't want to design the PCB myself. Where should I look when searching for PCB layouts?</p>
| Is there a directory of open source hardware projects? | 2010-10-20T23:18:59.593 |
5429 | |oscilloscope| | <p>I just saw success with DS1054z BW, additional triggers, memory depth, etc. However, I hear the 5uV option is not a good idea as it's not calibrated properly.</p>
| <p>I'm in the market for an oscilloscope. My previous approach was to get a used Tektronix on eBay. There are plenty of good ones - even 100MHz 4 channel digital scopes for about $1100. However, I started looking at Rigol - specifically the <a href="http://www.rigolna.com/products/digital-oscilloscopes/ds1000d/ds1102d/" rel="nofollow">DS1102D</a>. It's two channel, 100MHz BW and it has a 16 channel logic analyzer as well as USB interface and color screen. I know better than to just compare bullet points because Tektronix is a very well respected brand and Rigol as far as I can tell is of Chinese design and manufacture. Has anyone used it? Are there any gotchas? Anything I should watch out for?</p>
<p>Update</p>
<p>I'm liking the answers so far and I just realized Rigol is the scope that had the bandwidth hack, so I'll extend the question to include the BW hack - who has used it and how did it treat you? And has anyone tried it on anything other than the <a href="http://www.rigolna.com/products/digital-oscilloscopes/ds1000e/ds1052e/" rel="nofollow">DS1052E</a>?</p>
| Has anyone used Rigol and its BW hack? | 2010-10-21T02:26:21.427 |
5435 | |fpga|kits|development| | <p>I would highly recommend going with a CPLD board first (something like <a href="http://www.ecrater.com/p/12583395/altera-max-ii-epm240-cpld?gps=1" rel="nofollow">this</a>), or an Actel flash-based Igloo Nano, or something small like that. Big FPGAs can be kind of overwhelming, and they have <em>so many pins</em> it's quite time-consuming to get things hooked up properly. Plus, as soon as you want to integrate one into your design, you'll realize they come in very large packages, with dozens of power pins. Most of them require several voltages to operate at, not to mention that most FPGAs are SRAM-based, and not flash-based, so as soon as you disconnect power, they lose their design. So, you have to at least have an Active Serial Flash Memory chip wired up, but many people use sidecar CPLDs or microcontrollers to load designs onto the FPGA.</p>
<p>It's all very overwhelming. CPLDs, on the other hand, are great! They're usually single-supply operation, and if you want 5V-compliancy, you can still buy older Altera MAX 7000 chips. Plus they have on-board flash memory, so they don't need other components to bootstrap them. And CPLDs function more or less the same as FPGAs, so you program them by writing VHDL/Verilog, or using a schematic editor. Same jazz about clocking (remember to use crystal OSCILLATORS not crystals!), and same manner of programming over JTAG. CPLDs have far less logic elements than FPGAs, so you can't toss soft processors on them or do anything too crazy. But if you're just getting going, they're definitely the way to go -- and they cost a couple bucks each and come in big-enough packages that can be hand-soldered, which makes them practical to integrate into little projects you may have on your desk.</p>
<p>Another option is the low-end Flash-based FPGAs made by Actel. I've been recently playing around with the Igloo Nano Starter Kit, which is about $100. These devices are just big enough to fit an 8051 core on it along with some custom digital logic, so they're a great option when you're mixing program-flow states with custom logic.</p>
| <p>I intend to purchase an FPGA, development kit and I have looked at both the Xilinx and Digilent website. Both seem to have good development kits.</p>
<p>I have never worked with FPGA's before but have some experience working with microcontrollers. </p>
<p>I see that the entry level Spartan 6 boards are on a par in terms of price with the Spartan 3A/AN boards. I've not compared the features. </p>
<p>From your experience what development kit would you suggest Spartan3A/AN or Spartan6?</p>
| FPGA development kit for beginners , Spartan6 or Spartan3? | 2010-10-21T05:55:31.797 |
5438 | |usb|voltage|multimeter| | <p>The standard pin numbers and colours in a USB cable are shown below.</p>
<pre><code>Pin Number Cable Colour Function
1 Red VBUS (5 volts)
2 White D-
3 Green D+
4 Black Ground
</code></pre>
<p>If there is no device connected to the USB port then the maximum current that the port can support may be quite low. Once a device has enumerated itself on the port then it can negotiate for up to 500mA from the host controller.</p>
<p>To measure the voltage then you either touch the meter probes onto the stripped ends of the wires or, if your cable end is a large connector, then touch the probes (without shorting them together) onto pins 1 and 4 of the connector. The power pins on the USB connector are easy to identify as they are longer than the data pins. This is so that they mate first and ensures that the power is connected before the data.</p>
| <p>If I attach a USB cable to a USB port, and then strip the wire at the end, then how do I connect a multimeter to it to measure the voltage?</p>
| How do I measure the voltage coming out of a USB port? | 2010-10-21T07:42:10.253 |
5443 | |current|current-measurement| | <p>I've used a small high-side <a href="http://www.eetimes.com/design/automotive-design/4010355/Understand-low-side-vs-high-side-current-sensing" rel="nofollow noreferrer">current-sensing resistor</a> and connected an Arduino ADC to each side to measure the voltage on each side (--> voltage difference --> current). </p>
<p>It's not very accurate because of the limited resolution of the converters, and because the important quantity is a small difference between two similar voltages. </p>
<p>You could improve on this by using an op-amp <a href="http://en.wikipedia.org/wiki/Operational_amplifier_applications#Differential_amplifier" rel="nofollow noreferrer">to amplify the difference</a> in voltage, and then output a single DC voltage corresponding to the current. </p>
<p><a href="http://www.eetimes.com/design/automotive-design/4010355/Understand-low-side-vs-high-side-current-sensing" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/NE3Rb.gif" alt="high and low side current sensing resistors"></a></p>
| <p>I would like to know how could I know the current consumed from a battery using this <a href="http://flytron.com/osd-headtrackers/30-50a-current-sensor-for-simpleosd.html" rel="nofollow">sensor</a>, or other similar, using a microcontroller.</p>
<p>What I would like to know is shown in <a href="http://www.youtube.com/watch?v=ZslcHqyIc38" rel="nofollow">this video</a>, where you can see the current consumption.</p>
| Total current consumed from a battery | 2010-10-21T15:56:40.103 |
5446 | |equipment| | <p>I've never used helping hands devices for soldering. Ever. I've always found them to be useless. I've used all kinds of them, including expensive Panavises.</p>
<p>I went a different route. I work on a metal table and have bought some small (1"? 1.5") square rare-earth magnets. I tack the boards down to the table with the magnets and then I'm free to solder away. I primarily work with surface mount devices and find this is perfect for me. When I flip the board over to solder the bottom side, I have some tall rare earth magnets that I use.</p>
| <p>I'm considering buying a "helping hand" and <a href="http://www.velleman.eu/distributor/products/view/?id=18736" rel="noreferrer">this</a> one looks interesting to me. Since I'm pretty new to hobby electronics, my question is what are important things to look for when purchasing such device?</p>
| What to look for when buying a "helping hand" device? | 2010-10-21T17:44:06.023 |
5458 | |audio|operational-amplifier|delay| | <p>There are a lot of ways to get a delay, but I don't know of any that just use "discrete components". The best way to do reverb in the modern world is to use a DSP.</p>
<p>The only way I know of to do this "analog" is to use physical objects like <a href="http://en.wikipedia.org/wiki/Delay_%28audio_effect%29#Analog_delay" rel="nofollow noreferrer">rooms or metal plates, or magnetic tape</a>.</p>
<p>"In the millisecond or second range" is a pretty huge range, you know. If you have a circuit that produces 1 ms of delay, you would need 1,000 of them to get to 1 second. Older reverbs created long tails using feedback, rather than long delay elements. <a href="http://valhalladsp.wordpress.com/2009/05/30/schroeder-reverbs-the-forgotten-algorithm/" rel="nofollow noreferrer">Schroeder reverb</a>, <a href="http://www.bagger288.com/temp/aboutThisReverberationBusiness.pdf" rel="nofollow noreferrer">enhanced version</a></p>
<p>You can use <a href="http://en.wikipedia.org/wiki/All-pass_filter" rel="nofollow noreferrer">all-pass filters</a> to add short delays, but they delay different frequencies by different amounts, resulting in <a href="http://www.audioholics.com/education/acoustics-principles/human-hearing-phase-distortion-audibility-part-2" rel="nofollow noreferrer">phase distortion</a>. <a href="http://www.linkwitzlab.com/filters.htm#4" rel="nofollow noreferrer">4 - Delay correction</a>, <a href="http://www.linkwitzlab.com/page_index.htm#Projects" rel="nofollow noreferrer">Projects</a></p>
<p><img src="https://i.stack.imgur.com/uYudN.gif" alt="alt text">
<img src="https://i.stack.imgur.com/vQMk6.gif" alt="alt text"></p>
<p>Otherwise you need to use <a href="http://en.wikipedia.org/wiki/Bucket-brigade_device" rel="nofollow noreferrer">bucket brigade devices</a>, which emulate a slow transmission line. But they aren't really analog (they used <a href="http://en.wikipedia.org/wiki/Switched_capacitor" rel="nofollow noreferrer">switched capacitors</a> which are analog in voltage but <a href="http://en.wikipedia.org/wiki/Discrete_signal" rel="nofollow noreferrer">discrete in time</a>, so they alias etc just like digital) and aren't feasible to make from discrete components anyway.</p>
<p><img src="https://i.stack.imgur.com/x5QpO.jpg" alt="bucket brigade circuit">
<a href="http://www.soundonsound.com/sos/apr04/articles/synthsecrets.htm" rel="nofollow noreferrer">Figure 1: A simple eight-stage bucket-brigade device (or BBD) delay line.</a></p>
| <p>I would like to make a circuit that causes an audio delay using discrete components.</p>
<p>I know I can do small phase shifts using an opamp, but I am looking for something in the millisecond or second range.</p>
<p>Is there any way, at least easily, to do this with discrete components?</p>
<p>EDIT: I would like to know this for both the purposes of synchronization as well as reverb and such. This may take two completely different paths, but both paths are applicable to work I will be doing.</p>
| Audio delay using discrete components | 2010-10-22T02:12:59.773 |
5459 | |arduino| | <p>TCP/IP on Arduinos isn't exactly the best choice for anything real-time. Ethernet timing isn't deterministic, so regardless of any method that attempts to remove jitter or compensate for latency, it will never be spot on.</p>
<p>You mention "Arduino -> network -> Arduino" as your desired topology, in which case I would throw away the idea of using the (very expensive) Ethernet boards and use something designed for embedded systems, like RS-485. As you have total network control, your master module could send a 'shutter' message for every slave to pick up and act upon after message completion. They would all receive it at the exact same time (+/- 1 ns/foot), so jitter and lag would be negligible for any camera application.</p>
<p>Here's <a href="http://www.robotshop.com/dfrobot-i-o-expansion-board-arduino-v5-1.html" rel="nofollow">a shield that has RS-485 on it</a>, but it's just a single chip (e.g. <a href="http://www.maxim-ic.com/datasheet/index.mvp/id/1111" rel="nofollow">MAX485 & friends</a>) that you could breadboard.</p>
<hr>
<p><strong>Edit:</strong></p>
<p>How far apart are these cameras? If they're only ~10 meters apart and you want a (light?) sensor that goes to each one, just wire up a sensor+shutter+power cable and run them to the same Arduino. It should only be 4-6 wires; buy some good connectors and it should be painless to tear-down and set-up. You might be able to get away with <em>significantly</em> longer cables even, depending on the sensor, etc.</p>
| <p>I am looking to build a 5 DSLR camera triggering system using arduinos over our network. </p>
<p>Currently we have physical trigger cables so that we can trigger each DLSR camera without delay. Even though all the cameras are on the network and running Nikon capture pro, there is a small delay from hitting the "shoot button" in the software, and the camera actually capturing the image. The physical trigger is instantaneous.</p>
<p>Basically I'd like to eliminate the need to run dedicated triggering cable to the cameras, as all I want to run is power, and a couple of ethernet to each camera. I want to have the ability to trigger, and intelligently change camera timings through an arduino or similar ip connectible device, sometimes we may have a single trigger, but slight delays to each shot, like, take one immediately, then two slightly later....</p>
<p>The triggering needs to be done physically, but may be done via sensor, so having an arduino with each camera will give us lots of options.</p>
<p>In the control room we want to be able to trigger any of the cameras with physical buttons, much like you'd see in industrial applications, something that can really take a beating. So from these buttons I would expect to run them all into an arduino, and then that arduino communicates with the others to trigger them.</p>
<p>Signal flow is like this</p>
<p>Button in control room > arduino > internet > arduino > Nikon external trigger cable > Nikon Camera.</p>
<p>Some cameras will trigger at the same time, others with delays.</p>
<p>So my key question is: What is the latency of one ip connected arduino, triggering another?</p>
| Using IP connected arduinos to trigger cameras | 2010-10-22T02:58:25.203 |
5466 | |oscilloscope|logic-analyzer| | <p>Single-channel scopes should be banned! Most of the times you want to see (at least) two signals in relation to each other. Two examples: </p>
<p><strong>Phase</strong><br>
Phase for a single signal is meaningless, you always compare phase with the phase of another signal. You can do this by looking/estimating how much time the signal has shifted, but the better way is to look at the Lissajous figure in XY-mode. Single-channel scopes don't have XY-mode. </p>
<p><strong>Serial protocols</strong><br>
Except for Manchester coding data and clock are separate on most protocols. Want to analyze your data with only the data channel? Like this: </p>
<p><img src="https://i.stack.imgur.com/Ntnqs.png" alt="enter image description here"></p>
<p>Well, good luck! This is the SDA channel of an I2C bus. Any idea of what it represents? Not without the clock: </p>
<p><img src="https://i.stack.imgur.com/uOsi7.png" alt="enter image description here"> </p>
<p>Now you not only can see what SDA is on each clock pulse, you can also see the I2C start condition: SDA going low while the clock is high. Impossible on a single-channel scope.</p>
| <p>So I have spent the past two days going through various budget oscilloscopes and checking their specs VS price. Most of the information I have gathered has been from here and I am almost sold on an MSO-19. The only reason I haven't bought it already is that it's a single channel oscilloscope and before I spend £180 on it, I want to make sure it's going to cover 95% of my electronics needs. I think my major problem is that I don't know what area of electronics I will be going into in the future and so can't predict exactly what I am going to need. </p>
<p>Currently I work as a software engineer and so am already playing around with PICs, AVRs and MSP430s. I think, in the short term, I will be looking into making small intelligent robots (not bump and turn stuff you see on most hobbyist sites but something with 'character'). I have been in AI for a number of years and whilst I'm no Marvin Minsky, I do know a thing or two about what makes something seem intelligent.</p>
<p>The other thing I have been looking at is this 32-channel logic analyser (<a href="http://www.seeedstudio.com/depot/open-workbench-logic-sniffer-p-612.html">Open Workbench Logic Sniffer</a>) which is only £30 and is a more powerful logic analyser than comes with the MSO-19. Would it be a better idea just to buy that?</p>
<p>I'm open to other suggestions too but I don't want to spend over £250 in total if I can help it.</p>
| Is a single channel oscilloscope enough for most purposes? | 2010-10-22T14:08:01.640 |
5476 | |fpga|vhdl|mac| | <h1>Short answer: Yes, but not easily</h1>
<p><a href="http://clifford.at/icestorm" rel="nofollow">icestorm</a> is an open source FPGA compilation toolchain for <strong>verilog</strong> on Lattice ice40 FPGAs only. I have compiled and am able to run it natively under Mac OS X, although setting it up wasn't as trivial as doing the same under Linux.</p>
<p>Icestorm includes some simple examples which are suitable for an introduction to synthesis HDL for FPGA's, but these are in verilog, not VHDL.</p>
<p>So, if you have your heart set on learning VHDL only, <strong>you will need a VHDL to Verilog converter</strong>, as VHDL isn't supported directly. I have not actually ran one of those on Mac OS X, which is why this answer is <strong>Maybe</strong>.</p>
<p>It may well be worthwhile, if you are a beginner to FPGA design, starting with MyHDL (which is a python interface which can both simulate hardware, as well as auto-generate either VHDL or Verilog for FPGA synthesis), until you are familiar with HDL design, then drilling down into detail with VHDL and Verilog later.</p>
<p>If you are serious about learning HDL synthesis for FPGA's, you will probably have to eventually learn be at least passingly familiar with both Verilog and VHDL anyway. The commercial tools support both, even in the same project at once, on a module-by-module basis.</p>
<p>Another very useful simulation tool (which also runs under Mac OS X, via a package in one-or-the-other of homebrew and macports) is <a href="http://www.veripool.org/wiki/verilator" rel="nofollow">Verilator</a>, which allows for compilation of HDL into efficiently-running native binaries for the purposes of running entire SoC's in simulated form. An excellent and useful example of doing so is included in <a href="https://github.com/jamesbowman/swapforth" rel="nofollow">Swapforth</a>, which is used when <code>make -C j1a clean bootstrap</code> is called. Verilator is used to allow the initial Forth image to compile its own initial software installation, which is then re-compiled into the design so the resulting FPGA runs whatever the application is from power up.</p>
<p>Please keep in mind that all of the above is quite non-trivial to get working on MacOS X - you will have to be happy about detecting missing dependencies and installing them via either macports as well as homebrew, as well as hunting around and following notes about </p>
<p>Mac OS X is quite a second-class citizen compared to Linux, for the purpose of FPGA compilation at least. You will find that even FreeBSD has far better support for running the commercial FPGA toolchains (via the linux binary compatibility layer it has that Darwin sadly lacks).</p>
<p>Consequently, it is still far, far easier to either dual-boot or virtualise linux so you can just throw the tools on and get to work. But because <strong>one</strong> useable Open-Source FPGA toolchain now exists, it <em>is possible</em> to run it natively under Mac OS X.</p>
| <p>The title pretty much sums up my question: Are there any native Mac OS X environments for getting started with VHDL / FPGAs?</p>
| Any native Mac OS X environments for getting started with VHDL / FPGAs? | 2010-10-22T18:18:20.130 |
5484 | |robotics|navigation| | <p>Don't forget about simple methods: ultrasound distance measuring. You can build up a map of the room or area and then fine-tune it as you move around. Also consider using angular rate sensors to measure turning as well as accelerometers to measure linear movement. Do look up Kalman filters as mentioned before. You can combine all of these measurements into one reading with kalman filters and improve your consistency (not necessarily accuracy).</p>
| <p>In my spare time I've decided to create something on my own. I've never designed difficult things, but I'm very curious, moreover experience would never be useless ;) I decided to create a robot, but I want to do this from 0: schematic, programming to do this the way I want. And the important one: I want it to be autonomous as more as possible (self charging, path finding - some kind of intellectual robot).</p>
<p>I have experience with MCUs and simple logic devices, so I can imagine, which way should robot move, which way I could control it etc. But to achieve desired autonomy at first I should create a way to interact with it (autonomy dictates - radio transmitter-receiver) and some kind of navigation system. Well, this is my way of thinking and I think so.
So for now my question is: which ways is it possible to track movements of a robot, current position and what accuracy is achievable?</p>
<p>Broadly used radio-location is useless here because I have no intentions to measure distances about km (really centimetres and meters - in my room). GPS is useless too as signal is lost in-door.</p>
<p>I was thinking about to use servomotors and count ticks(!), but it is not so reliable as wants to be (robot could rotate wheels, but not move).</p>
<p>I was thinking about GPS in miniature: putting several antennae and measure distances (this is just an idea, which may be either nonsense or unrealisable).</p>
<p>Recently I found inertial navigation system (INS) article on wikipedia, but I'm confused with integral error rate. Wiki states error level expected is to be approximately 650m, which is no good at all.</p>
<p>Did anyone deal with similar problems? If someone could tell me practically obtained accuracy values for different navigation systems or some concepts, ideas or even papers concerning that?</p>
<p>I repeat once again - no industrial realisations, I want to do this on my own with available elements, costing reasonable money. </p>
| Primitive navigation system | 2010-10-22T20:01:14.463 |
5493 | |memory| | <p>A quick digikey search with your parameters (>512 MB, serial) reveals these digikey parts:</p>
<ul>
<li><a href="http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=TH58100FT-ND" rel="nofollow">http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=TH58100FT-ND</a></li>
<li>TC58DVG02A1FT-ND</li>
<li>TC58DVM92A1FT-ND</li>
</ul>
<p>(I would have posted 3 hyperlinks but I don't have enough reputation.)</p>
<p>Unfortunately, from brief reading of the data sheet, it looks like their "serial" interface requires you to use a lot more than 2 pins. Also, they're non-stock items and there is no price listed.</p>
| <p>I'm looking for a high density (>512Mbyte) FLASH or other memory device in a small package with a serial interface. I'm hopeful but I can only find sizes up to around 16 MB with serial interfaces.</p>
<p>Does anyone have any suggestions on where to look?</p>
| High density serial interface nonvolatile memory | 2010-10-22T23:26:40.720 |
5494 | |microcontroller|ram| | <p>Feel free to update the information below.</p>
<blockquote>
<p>8-bit AVR: ATmega1284(p), 16kB RAM, 128kB flash, DIP40</p>
<p>32-bit AVR: None</p>
<p>8-bit PIC: PIC18F(2/4)7K42, 8kB RAM, 128kB flash, SDIP28/DIP40</p>
<p>16-bit PIC: dsPIC33EP512xxx02, 48kB RAM, 512kB flash, SDIP28</p>
<p>32-bit PIC: PIC32MXxxxF256B, 64kB RAM, 256kB flash, SDIP28</p>
<p>32-bit ARM: LPC1114FN28, 4kB RAM, 32kB flash, DIP28</p>
</blockquote>
<p>Last updated January 4, 2018</p>
| <p>So far the most RAM laden MCU I have found in a hobbyist friendly DIP package is a dsPIC33FJ128GP802, which has 16KB, and the Parallax Propeller, which has 32KB. But does anyone know of chips with more memory in said packages? This is only for prototyping, I also need surface mount chips for production.</p>
| Most RAM for an MCU in a DIP package | 2010-10-22T23:28:27.793 |
5498 | |usb|current|port|current-source|usb-device| | <p>The above 100 mA current upto 500 mA can be negotiated by the device driver.
However some devices may not get configured properly at boot time if your BIOS has an option titled: "Enable legacy storage" under USB settings. If this setting is off - you may find yourself re-plugging the device after booting up, in case if it does not work properly.
Only with this setting on, if present, the BIOS will provide a current greater than some minimum value, I think 100 mA.</p>
<p>A brute force method may be to get a two male USB to one female USB cable for extra power. CAUTION: may have electrical / power draw safety issues.</p>
| <p>I heard that the current limit for a USB port is 100mA. However, I also heard that some devices can get up to 1.8A from a port. How do you get past the 100mA limit?</p>
| How to get more than 100mA from a USB port | 2010-10-23T09:26:39.547 |
5507 | |multimeter|multimeter|calibration| | <p>Bring them to your university or employer, and see if you can get them to calibrate them for you the next time they do their calibration run. </p>
<p>No, I'm serious. I expect that most schools and employers will be happy to see that their students and employees are developing their skills outside of the school/work environment, and when you've got a production line set up for a hundred meters already, the addition of one (or a few) more meters isn't that big of a deal.</p>
| <p>Without buying an expensive calibration tool, how can I accurately calibrate my multimeters?</p>
| How to calibrate multimeters? | 2010-10-23T13:04:15.680 |
5513 | |stepper-motor| | <p>I looked for the SAA1027 using findchips.com and it looks like no one has it. According to this <a href="http://www.sfu.ca/phys/430/datasheets/saa1027.pdf" rel="nofollow">datasheet from 13 years ago</a>, The SAA 1027 can only provide 0.5 A output current and its inputs require inconvenient voltages: you have to provide it a voltage abpve 7.5 V for it to read as high! This means it would be difficult to interface it with a modern microcontroller running at 3.3 or 5 V.</p>
<p>One modern, popular way of driving stepper motors is to use the A4983 IC. It can provide up to 2 A of current per coil, perform microsteps, and it can easily interface with a microcontroller.</p>
<p>Pololu sells a convenient <a href="http://www.pololu.com/catalog/product/1201" rel="nofollow">carrier board</a> for it so you don't have to do SMT soldering yourself. The reprap community uses this board a lot (<a href="http://reprap.org/wiki/Pololu_Electronics" rel="nofollow">see here</a>).</p>
| <p><br>
My electronics teacher asked me the other day to research the SAA 1027 to drive stepper motors however whats happened to them? In some newer textbooks they talk about using a PIC and then using a ULN2803 to drive it. Is this the new way as SAA 1027 are now obsolete?<br>
Thanks in Advance,<br>
Dean </p>
| What happened to the SAA1027? | 2010-10-23T14:10:33.707 |
5524 | |schematics|eaglecad|stripboard|stripboard| | <p>This is a non circuit, but shows my attempt to use KiCad for strip board design. It's actually quite easy if you stick to a mental plan of using the bottom horizontal copper layers as the strips, and the top layer as vertical jumpers. When ever you see two copper strips end to end (the green ones) you insert a cut /break /drill symbol so that you can break the track at that point. That's the yellow cross (which is actually an alignment symbol). You might create your own, that's actually quite easy too.</p>
<p>In detail, you start laying a track at a component pin on the lower copper layer. Click and then go horizontally for a bit. Then click "V" for via. That automatically switches to the top layer and then go vertically. Click "V" again and another via is introduced and you will be switched back to the bottom layer. Then continue to the next component. If you want to finish at a point along a copper strip instead of a component pin, you add a via and end the track there.</p>
<p>The component placement just needs to allow for the majority of the connections running horizontally, otherwise you end up with more jumpers than copper strips! I guess that's okay too, but then you might as well use one of those prototype boards without any strips at all. Also, make sure that you have the grid set to 0.1" to match the pre drilled holes in the board.</p>
<p>The other beauty of this technique is that you can print off the component silk screen. Print in on to paper and stick it onto the strip board. You then have an ersatz silk screen to aid in component placement if you poke the leads through the paper.</p>
<p>[Can't speak for Eagle though. My recommendation would be to dump the niche tools like VeeCAD and even more esoteric ones. They will have little on line support to help you, slow development /bug resolution and will always be playing catch up with bigger tools. This is not a treatise on EDA tools, but with CERN support for KiCAD, there seems to me to be no reason for newcomers to begin with Eagle.]</p>
<p><a href="https://i.stack.imgur.com/KP0fY.png" rel="noreferrer"><img src="https://i.stack.imgur.com/KP0fY.png" alt="Kicad strip board"></a></p>
| <p>So I have just finished learning the basics of Eagle (Lite) and I really like it. As I don't have the full kit to start home PCB etching yet (something I am looking into now) I would like a tool that could help me design a layout for a veroboard/stripboard. </p>
<p>If I had an Eagle schematic, how would I go about designing an equivilent veroboard/stripboard layout either within Eagle itself or possibly even through an export/import into another tool.</p>
<p>Thanks</p>
| Design a veroboard/stripboard layout from an Eagle schematic | 2010-10-23T20:52:56.590 |
5526 | |i2c|delay|timing| | <p>For anything under 50MHz, difference in trace lengths like that wouldn't be a concern.</p>
| <p>At the moment I'm working on a system which will use a 400KHz I2C bus. The bus wires (SCL, SDA) are different lengths by a few cm, so the delay between them will be in picosecond to nanosecond range - I don't think I need to worry about this but am I misguided?</p>
| Is it worth worrying about propagation delay differences when dealing with relatively slow protocols like I2C @ 400kHz? | 2010-10-23T21:08:55.570 |
5531 | |arduino|telephone| | <p>You <em>can</em> ring a phone with 120 volts at 60 hertz. It sounds somewhat more like a buzz than the musical sound that 20 hertz produces, but you have probably heard 60-hertz ringing in many movies and didn't notice the difference. The bells have to be adjusted closer to the clapper than normal. Usually the attachment holes in the bells are drilled off-center, to allow adjustment by rotating them.</p>
| <p>I just obtained an old rotary phone at a garage sale. I am working on hooking it up to an arduino project, and I was able to get the dial and hook switches figured out pretty easily. I cannot really figure out how the ringer works, or how to wire it up.</p>
<p>It is an old western electric C4A ringer. It has two bells and a striker arm between them. There is a coil, and some magnetic plates that move the ringer, with four wires going into the coil. I have found schematics online for how the thing connects to the other phone components for normal operation, but I really just wanna figure out how to make the thing ring on its own. </p>
<p>I read that most phone lines run in the vicinity of 90 volts ac. Is there any possibility I can make this thing ring with a 12 volt wall wart, or am I gonna need a full 120 line and a relay or something? </p>
| Wiring up old phone ringer to arduino | 2010-10-24T04:21:32.023 |
5537 | |pcb| | <p>No. You get bare, dry boards. Solder paste should be used as soon as possible after application, because the flux contained in the paste will deteriorate when exposed to oxygen. </p>
<p>If you're doing mass manufacture yourself, consider getting a stencil made for your board. I've heard good things about <a href="http://www.stencilsunlimited.com" rel="nofollow">Stencils Unlimited</a> for small-volume work. Then, you just squirt out a little solder paste at one end, run a (sharp steel) squeegee over the stencil, and lift - Perfect solder paste application in seconds! </p>
<p>If you're doing just a few/small boards and the $125 investment in a prototype stencil feels steep, I'd just use standard solder wire. Put a small dome on the PCB pad, position the part, heat the pin until it drops to the PCB, and you're off to the races.</p>
| <p>When it comes down to having PCBs produced is solder paste applied to the pads so I can stick the IC's down or do I have to add paste myself?</p>
| Solder paste, is it standard? | 2010-10-24T10:52:48.277 |
5540 | |pcb|etching| | <p>Actually even 3% peroxide will work at 2 parts peroxide to 1 part muratic (hydrochloric) acid. Stronger peroxide is better if you can get it, particularly for regenerating the solution. I have used three different etchants, and in order of effectiveness they are: Acid + Peroxide, Ferric Chloride, and Ammonium Persulfate. I always got undercutting with Ammonium Persulfate. You can add a little mercuric chloride to the Persulfate, to make it work better, but how is that for a toxic soup, you cannot get rid of? When you are done with the Acid + Peroxide, then add washing soda until it quits foaming and looses most of the blue color. Then filter out the precipitate, and let it dry. Throw the now harmless liquid away. Dig a hole and bury the precipitate, or wrap it in foil, and put it in the trash. The precipitate is powdered up stuff you could buy at the rock and mineral shop, just like azurite, turquoise, lapis, malacite, etc. That stuff comes from the earth, so put it back. They sometimes make a spray out of it for grape vines. just don't eat all of it at once. Most of things we do are not an environmental problem, until there are say... 7 billion other people doing it too.</p>
| <p>Currently purchasing the required kit to start etching my own boards and have gotten to the etching solution stage. Ferric Chloride seems to be the standard for etching but I have also read about <a href="http://www.instructables.com/id/Stop-using-Ferric-Chloride-etchant!--A-better-etc/#step1">Muriatic Acid + Hydrogen Peroxide ecthing</a>, which apparently is better all round (both for the environment and my pocket).</p>
<p>Has anyone had any experience with this method of etching?</p>
| Ferric Chloride or Muriatic Acid + Hydrogen Peroxide for etching? | 2010-10-24T13:28:22.447 |
5544 | |robotics| | <p>I've been in robotics for several years but before then I was in web, information retrieval field. So I can understand how the OP feels when s/he got interested in robotics but the skill set might seem very different. Indeed it is different but I just want to share a bit of my experience.</p>
<p>Basically the other people's responses are more direct and thorough answer.</p>
<p>If you're from web, not necessarily <code>php</code> programmer though, the necessity for web development is about to boom even in robotics. A few areas I can think of that are heavily dependent on web technologies:</p>
<ul>
<li><p>Needs for mobile devices as a human interface is getting bigger & bigger, where web or mobile phone apps do the work. <code>java script</code>, <code>android</code>, <code>iOS</code> are needed. An example of prominent projects might be the one called <a href="http://www.ros.org/wiki/rosbridge" rel="nofollow"><code>rosbridge</code></a>.</p></li>
<li><p>Using web as a source of data is the same in robotics application development. Some people call it as <code>Cloud Robotics</code>.</p></li>
</ul>
| <p>I am a PHP programmer with basic knowledge of c/c++ and electronics. But i have keen interest in robotics and AI. </p>
<ol>
<li>What are the basic things that i
need to learn before switching to
the robotics ?</li>
<li>What languages are
used to write the code and how is
that code transferred to the chips ? </li>
<li>What are the basic components that i
need to know ?</li>
</ol>
<p>I would like to learn about the both hardware components and the programming part. (Are these different streams?)</p>
| How can a PHP programmer go to robotics | 2010-10-24T16:36:23.790 |
5545 | |arduino|wireless|video| | <p>Take a look at the Bug Labs gear - they've got some modules for Wifi, video, 3G and such. <a href="http://www.buglabs.net/products" rel="nofollow">http://www.buglabs.net/products</a></p>
| <p>Is there a Arduino-like hardware platform that allows for wireless connectivity (think remote control) and for connection of a webcam (with streaming that wireless video over the wireless connection)? </p>
<p>I really like the idea of a prebuilt hardware platform and would be interested in getting into robotics. Since I am already a proficient programmer, it would be great to take this into the physical world as well.</p>
| Arduino-like Platform With Wireless and Video? | 2010-10-24T17:08:29.847 |
5549 | |pcb|pcb-fabrication|layout|dfm| | <p>You are setting up DRC at the wrong end of the process.</p>
<p>Whether you set the DRC values to reasonable values (for an open-source project) or specific values for a particular manufacturer, you need to do it at the beginning of a project. Then you run the DRC checker periodically during layout and keep it DRC-clean.</p>
<p>Most pcb layout software, including the one you are using, includes an option to "auto-enforce DRC clearance." This option will help you keep out of trouble.</p>
<p>Now you are at the end of the layout trying to fix up DRC at the end. This is going to be a pain. You may end up re-laying-out most of the board.</p>
<p>Experience is a hard teacher, the lessons come after the tests.</p>
| <p>Are these traces too close for conventional PCB manufacture? DRC check advises against it, but I haven't filled out all the settings for it.</p>
<p><img src="https://i.stack.imgur.com/BljK6.png" alt="alt text"></p>
<p>For scale, the resistors are all 0603.</p>
| How close is too close for traces on a PCB? | 2010-10-24T17:21:02.677 |
5556 | |emc|legal| | <p>To sell in the EU, you will need a CE mark, wheelie bin logo (WEEE) and RoHS statement. You do not need to use an EU test house, but do need to be able to provide evidence to the authorities upon request for all of these. </p>
<p>If you are manufacturing in China, they will generally provide you with a RoHS statement. If buying from China they will also provide the CE Mark (remember to ask for documentation). </p>
<p>Not sure about what is required to get an FCC mark.</p>
| <p>I am going to be selling my project, Super OSD. It has a 3 MHz SMPS PSU and an 8 MHz crystal oscillator, but is not intended to emit radio signals. Will it be necessary to get testing to sell in Europe? I am selling from Europe, the UK to be specific.</p>
| What certification is needed for electronic devices in Europe? | 2010-10-24T18:27:18.980 |
5557 | |polyfuse| | <p>Because they have to absorb a (relatively) large amount of energy in a short time. <a href="http://www.littelfuse.com/data/en/Data_Sheets/Littelfuse_PTC_0805L.pdf" rel="nofollow">This 0805, 500mA Poly-Fuse</a> has a minimum resistance of 150m\$\Omega\$, and at 8A trips in 0.1s. That's 10W in 0.1s, the same energy as 1W during a second. Note that 0805 resistors are only rated at 125mW. </p>
<p>And yes, they also exist in <a href="http://www.littelfuse.com/data/en/Data_Sheets/Littelfuse_PTC_0603L.pdf" rel="nofollow">0603</a>.</p>
| <p>Why are polyfuses so big? I was looking at a 500mA polyfuse, it is in an 0805 package, but there was only one of them - the rest were 1206. I have two questions.</p>
<ol>
<li>Why so big?</li>
<li>Does anyone make 0603 polyfuses?</li>
</ol>
| Why are polyfuses so big? | 2010-10-24T18:30:13.140 |
5565 | |arm|embedded| | <p>Getting the power light to work is step 0. Once you know it might be in working condition (You might also want to see if you can poke around with an oscilloscope and see if anything appears to be working). After that, step 1 is finding the datasheets/manuals. You want the quick start manual and/or one-page advertisement for the basic specs, then the datasheet for the board, the manufacturer's datasheet for the processor, and the ARM datasheet(s) for the processor. Here's what I found with some brief Googling: </p>
<ul>
<li><a href="http://www.cirrus.com/en/pubs/manual/EP7209QS-1.pdf" rel="nofollow">Quick Start User's Guide</a></li>
<li><a href="http://ecos.sourceware.org/ecos/boards/edb7209.html" rel="nofollow">eCos page</a></li>
<li><a href="http://infocenter.arm.com/help/topic/com.arm.doc.ddi0192a/DDI0192A.pdf" rel="nofollow">ARM 720T Technical Reference Manual</a></li>
</ul>
<p>Step 2 is to blink an LED, and Step 3 is to start up some kind of communication between the device and a development PC. Step 4 is completely up to you.</p>
<p>Alternatively, you can load the device with whatever OS you want to play with (this platform appears to have good OS support in spite of its age), and work from there. I'd advise more knowledge about the inner workings of the processor before going too far here, but it's your choice. </p>
<p>Be aware that the board has been <a href="http://www.cirrus.com/en/products/eol/detail/EOL60.html" rel="nofollow">discontinued since around 2003</a>. You might have some luck bugging Cirrus for support, and seeing if you can convince them to send you a newer version :) </p>
<p>Note that <a href="http://www.cirrus.com/en/products/eol/index.html" rel="nofollow">they do say</a> that they can't provide applications engineering support for discontinued products.</p>
<p>Finally, I'd recommend against using this board if your real goal is to learn to develop software for the ARM processors. This is using a v4 architecture from the early 2000s, they're on v7 now. From the "Classic Processors" section of arm.com: </p>
<blockquote>
<p>While the ARM7 processor family
continues to be used today for simple
32-bit devices, newer embedded designs
are increasingly making use of latest
ARM processors such as the Cortex™-M0
and Cortex-M3 processors, both of
which offer significant technical
enhancements over the ARM7* family.</p>
</blockquote>
<p>This is more for the continuingly and overwhelmingly popular ARTM7TDMI than any other processor in this lineup. I'd strongly suggest, if you want to learn software development for ARM processors as a marketable skill, that you learn on a newer processor like a Cortex-M0 or -M3 (or a Cortex-A9 if the better embedded OS support and MMU on the 720T is important to you). If you just want to have fun with some donated hardware, then you're going to need some serious Google-fu in your fingertips.</p>
<p>*The ARM7 family and ARMv7 architecture version are very different things. ARM7 is [mostly] related to ARMv4, but also ARMv3 and v5, and ARMv4 is related to ARM7, 8, and 9. The Cortex family and v7 architecture are mostly equivalent. See the <a href="http://en.wikipedia.org/wiki/ARM_architecture" rel="nofollow">Wikipedia article</a> for more information.</p>
| <p><br>
I got given a Cirrus Logic EDB7209-2B.0 with LCD Display. It powers up(the power LED lights up and there is power on the board accessing the ARM CPU) but i'm unsure on what to do with it has anyone got any experience with one of these development boards? I know when it left the factory it was running some basic MP3 player. It has some NAND Flash, Flash and DRAM memory. But i have no programming cable for it. Is there a jtag cable i can make? The main processsor is a Cirrus Logic EP7209-CV-C. I would quite like the board to be able to program to play with software development for the ARM processors.<br>
Thanks in Advance,<br>
Dean </p>
| Any ideas on what to do with a board that condition is unknown? | 2010-10-24T20:47:37.237 |
5566 | |batteries|resistance| | <p>You wouldn't know it by purchasing from a department store, but battery manufacturers (like <a href="http://data.energizer.com/">Energizer</a>, <a href="http://www1.duracell.com/procell/productdata/">Duracell</a>, etc.) publish datasheets. Look for their industrial/OEM sections. </p>
<p>A standard alkaline Energizer AA battery has an internal series resistance of 150 to 300 milliohms, from the datasheet <a href="http://data.energizer.com/PDFs/E91.pdf">here</a>. The asterisk by that number will refer you to Energizer's <a href="http://data.energizer.com/PDFs/BatteryIR.pdf">whitepaper on battery internal resistance</a>. </p>
<p>Take some time to look around <a href="http://data.energizer.com/">data.energizer.com</a>, it's really a very good resource.</p>
| <p>In one of the answers on this site, I found link to <a href="http://www.evilmadscientist.com/article.php/nightlight">this</a> project. That article mentions internal resistance of batteries and cells. Where can I find data about common ranges of internal resistances for batteries? I've always heard that it's low, but I couldn't find anywhere how low is low and common resistances for common battery types.</p>
| Internal resistance of batteries? | 2010-10-24T20:49:05.547 |
5577 | |power-supply|atx|repair| | <p>I'm going to go with Tim's answer. The caps are my first suspect. I once checked out a DVD player whose 5V line would pulse, much like your 12V line. Turned out to be a bad cap in the rectifier. I almost missed it, until I started touching the tops of all the caps with my finger (this is a good time to remind you to avoid getting yourself a Darwin award!). It was then immediately apparent which cap was bulging.</p>
| <p>I have an 800W ATX power supply given to me by a friend because it doesn't work any more. It's quite a beast and would set me back a considerable amount new, so I'd like to see if I can fix it.</p>
<p>Well, here's the story. It has standby power at 5.15V. The power indicator on the back lights up (on the mains switch - it's an LED not a neon apparently, because when you turn off the unit it fades slowly, making me think it's not directly connected to the mains.) Anyway, when you turn it on (by grounding the PS_ON pin) it makes a faint clicking sound but does nothing else. With my scope I have found three short pulses of ~11.8V on the 12V rail for about 500 ms to 1.5 seconds before the supply goes dead, which makes me think some kind of protection system is being activated, as the power supply does work - it is producing the required output. </p>
<p>If it doesn't work it is going in the trash, so no loss there.</p>
| Fixing an ATX PSU | 2010-10-24T23:10:39.433 |
5585 | |pcb| | <p>By default gEDA PCB Designer will just cover all the vias with the solder mask, to change this you can hover over the via with your cursor and press <<em>key</em>> k to uncover the vias, use <<em>key</em>> <em>shift</em> k to go back to tented.</p>
<p>Check out PCB's manual entry on vias for more info-</p>
<p><a href="http://pcb.gpleda.org/pcb-cvs/pcb.html#Via-Objects" rel="nofollow">http://pcb.gpleda.org/pcb-cvs/pcb.html#Via-Objects</a> </p>
<p>Plus- <a href="http://www.delorie.com/pcb/docs/gs/gs.html" rel="nofollow">This page</a> by DJ Delorie describes how Geda PCB handles solder masking, it also has some great illustrations of the different masked vias. </p>
| <p>See image below;</p>
<p><img src="https://i.stack.imgur.com/MI84B.png" alt="alt text"></p>
<p>My suspicions would say that part of the silkscreen would disappear over a via, does this happen in production?</p>
| What happens when you get silkscreen over a via? | 2010-10-25T00:30:14.780 |
5592 | |microprocessor|cpu|architecture| | <p>First instructions are not necessarily "executed sequentially" even on a non-VLIW ISA, execution only needs to appear sequential. An in-order superscalar implementation can execute more than one instruction in parallel with another. To do this effectively the hardware for decoding instructions must be increased (widened), hardware must be added to ensure data independence of instructions to be executed in parallel, the execution resources must be increased, and the number of register file ports is generally increased. All of these add transistors.</p>
<p>An out-of-order implementation, which allows later instructions to be executed before earlier ones as long as there are no data dependencies, uses additional hardware to handle scheduling of instructions as soon as data becomes available and adds rename registers and hardware for mapping, allocating, and freeing them (more transistors) to avoid write-after-read and write-after-write hazards. Out-of-order execution allows the processor to avoid stalling.</p>
<p>The reordering of loads and stores in an out-of-order processor requires ensuring that stores earlier in program order will forward results to later loads of the same address. This implies address comparison logic as well as storage for the addresses (and size) of stores (and storage for the data) until the store has been committed to memory (the cache). (For an ISA with a less weak memory consistency model, it is also necessary to check that loads are ordered properly with respect to stores from other processors--more transistors.)</p>
<p>Pipelining adds some additional control and buffering overhead and prevents the reuse of logic for different parts of instruction handling, but allows the different parts of handling an instruction to overlap in time for different instructions.</p>
<p>Pipelining and superscalar execution increase the impact of control hazards (i.e., conditional branches and jumps). Pipelining (and also out-of-order execution) can delay the availability of the target of even unconditional jumps, so adding hardware to predict targets (and direction for conditional branches) allows fetching of instructions to continue without waiting for the execution portion of the processor to make the necessary data available. More accurate predictors tend to require more transistors.</p>
<p>For an out-of-order processor, it can be desirable to allow a load from memory to execute before the addresses of all preceding stores have been computed, so some hardware to handle such speculation is required, potentially including a predictor.</p>
<p>Caches can reduce the latency and increase the bandwidth of memory accesses, but add transistors to store the data and to store tags (and compare tags with the requested address). Additional hardware is also needed to implement the replacement policy. Hardware prefetching will add more transistors.</p>
<p>Implementing functionality in hardware rather than software can increase performance (while requiring more transistors). E.g., TLB management, complex operations like multiplication or floating point operations, specialized operations like count leading zeros. (Adding instructions also increase the complexity of instruction decode and typically the complexity of execution as well--e.g., to control which parts of the execution hardware will be used.)</p>
<p>SIMD/vector operations increase the amount of work performed per instruction but require more data storage (wider registers) and typically use more execution resources.</p>
<p>(Speculative multithreading could also allow multiple processors to execute a single threaded program faster. Obviously adding processors to a chip will increase the transistor count.)</p>
<p>Having more transistors available can also allow computer architects to provide an ISA with more registers visible to software, potentially reducing the frequency of memory accesses which tend to be slower than register accesses and involve some degree of indirection (e.g., adding an offset to the stack pointer) which increases latency.</p>
<p>Integration--which increases the number of transistors on a chip but not in the system--reduces communication latency and increases bandwidth, obviously allowing an increase in performance. (There is also a reduction in power consumption which may be translated into increased performance.)</p>
<p>Even at the level of instruction execution, adding transistors can increase performance. E.g., a carry select adder adds upper bits twice in parallel with different assumptions of the carry-in from the lower bits, selecting the correct sum of upper bits when the carry out from the lower bits is available, obviously requiring more transistors than a simple ripple carry adder but reducing the delay in producing the full sum. Similarly a multiplier with a single row of carry-save adders uses fewer transistors (but is slower) than a Dadda (or Wallace) tree multiplier and cannot be pipelined (so would have to be replicated to allow another multiply to begin execution while an earlier multiply was in progress).</p>
<p>The above may be exhausting but is not exhaustive!</p>
| <p>According to Wikipedia, processing power is strongly linked with Moore's law:</p>
<p><a href="http://en.wikipedia.org/wiki/Moore%27s_law">http://en.wikipedia.org/wiki/Moore's_law</a> </p>
<blockquote>
<p>The number of transistors that can be
placed inexpensively on an integrated
circuit has doubled approximately
every two years. The trend has
continued for more than half a century
and is not expected to stop until 2015
or later. The capabilities of many
digital electronic devices are
strongly linked to Moore's law:
processing speed, memory capacity,
sensors and even the number and size
of pixels in digital cameras. All
of these are improving at (roughly)
exponential rates as well.</p>
</blockquote>
<p>As someone who has some background in computer architecture, I don't understand why throwing in more transistors in a CPU would boost a its power since ultimately, instructions are roughly read/executed sequentially. Could anyone explain which part I'm missing?</p>
| Why does more transistors = more processing power? | 2010-10-25T10:04:19.670 |
5597 | |pcb-design|crystal| | <p>I would move C13 and C14 to the right of the crystal.</p>
<p>I would also put more space between the oscillator signals and the RTC signals.</p>
<p>On C14, you have the trace going right through it. I've seen recommendations against this for thermal reasons. That pad will leak more heat and cause the solder to solidify differently. The recommended way is to put a small stub from the main trace to the pad.</p>
| <p>The HC-49 xtal is an 8 MHz crystal, and the radial crystal is an RTC 32.768 kHz crystal. C11, C12 are 22pF, and C13, C14 are 18pF.</p>
<p><img src="https://i.stack.imgur.com/nxOuK.png" alt="alt text"></p>
<p>The traces go directly into a micro (a PIC24F.)</p>
<p>I tried to follow Microchip's guidelines on this, but they advised using surface mount xtals and talked about "guard rings" which are alien to me.</p>
| How's my crystal oscillator layout? | 2010-10-25T11:58:15.270 |
5598 | |microcontroller|adc|voltage-measurement|protection| | <p>if your multimeter supports differential inputs, i.e. +-10V or -+10V, you also need two zeners back to back, study the schematics of old multimeters like the 8842A and 34401 to learn more</p>
| <p>I'm designing an auto-ranging voltmeter using the on-board ADC of my micro for A to D and a digital potentiometer as a programmable resistive divider to control the range. </p>
<p>My concern is the possibility of the ADC input being momentarily shorted to the measured input voltage before the micro-controller has adjusted the pot for the appropriate range. </p>
<p>How is over-voltage protection usually implemented in this type of scenario?</p>
<p>Also if there are resources for digital multimeter design, e.g schematics etc, that would also be very useful for ideas (as I'm sure there are probably better ways to approach this than mine), Ive have searched but haven't found much.</p>
<hr>
<p><strong>Update</strong></p>
<p>Thanks to everyone for the informative answers.
Here is the over-voltage protection circuit that Iv decided on.
I plan to use schottky diodes for greater precision.</p>
<blockquote>
<p>During a negative voltage transient,
the bottom diode will conduct, thereby
clamping the voltage to one diode drop
below ground. During a positive
voltage transient, the top diode will
be forward biased, thus conducting the
surge to the power rail.</p>
</blockquote>
<p>From: <a href="http://www.conformity.com/artman/publish/printer_116.shtml" rel="nofollow noreferrer">http://www.conformity.com/artman/publish/printer_116.shtml</a></p>
<p><img src="https://i.stack.imgur.com/PkEV8.jpg" alt="alt text"></p>
| Auto-Ranging Meter Design | 2010-10-25T12:16:41.047 |
5620 | |connector| | <p>i'd probably solder some 18-20awg stranded wire to the ends of the flex, after you solder, coat the joint with some decent strength insulating epoxy such that there is a firm physical attachment between the wire and the flex material to remove any stress from the solder joint. The stranded wire should be strong but flexible enough to not break and run back to your controlling box which i assume will be on your belt or something. </p>
<p>The wire shouldn't be too bad on the weight of the clothing if you use some light stuff with thin insulation and loosly stitch it into the cloth so it can slide back and forth a bit. The wire attachment into the control box could be screw terminals, although i'd recommend some sort of quick disconnect with a tension relieving mechanism for the wire, 3m makes a lot of connectors that would work. </p>
<p>Ideally leave enough slack in the wire that the slack doesn't get into the way but there isn't a tension issue on the connection to the box. You can probably stitch a sliding loop of wire into the back of the top of the 'clothing' such that tension on the wire that results from crazy dancing around fires just contracts the loop rather than putting much strain on the wire connectors. </p>
<p>I don't know if that picture you posted is of the actual strips you plan to use but if so i'd go over all the exposed solder joints with epoxy or some other sealing insulator. Between the heat and the shenanigans at Burning Man i wouldn't count on those strips staying dry. </p>
<p>As for field repair, bring a tube of epoxy (an environmentally friendly type highly recommended for Burning Man) and a <a href="http://rads.stackoverflow.com/amzn/click/B000S63P9E" rel="nofollow">battery powered solder iron</a>. I imagine you'll have a solar battery charger of some sort with you anyway so that should cover it, maybe a bit of solder. Worst case you can be the town soldering helper, i'm sure you'll find someone in need.</p>
| <p>Does anyone have a good solution for a mechanical connector for flexible printed PCB, like those used for strips of common-cathode RGB LEDs?</p>
<p><img src="https://i.stack.imgur.com/FzpQc.jpg" alt="alt text"></p>
<p>(You can cut the strip across any of the solder pads and scrape back the silicon insulation)</p>
<p>"Just solder" isn't the answer I want to hear (neither is "get better at soldering") as a) I need to do <em>lots</em> of these joins which need to be b) mechanically sound and ideally c) field-repairable, in quite a tough field (on the playa at Burning Man.) The joints need to be mechanically sound as I plan to sew about 30 x 50cm strips into a garment.</p>
<p>Ideally I'd like some kind of screw-terminal. But I don't know what to ask for and can't find one on my own.</p>
<p>Another idea I've come up with is taking 90° header pins and pushing/piercing/drilling little holes for them through the printed track and soldering those in (a much easier task—I've found component-through-hole soldering orders of magnitude easier than wire-to-pad soldering; tracks lift and it's hard to get everything to bloody stay still.) Anyone think this might work and/or tried it? </p>
| Mechanical connectors for flexible PCBs? | 2010-10-25T17:41:56.907 |
5621 | |frequency|oscillator|low-power| | <p>Power = switching factor * Capacitance * (VDD^2) * frequency.</p>
<p>As the fast clock has higher switching factor, and also higher frequency, thus higher dynamic power consumption.</p>
| <p>If you overclock a microcontroller, it gets hot.</p>
<p>If you overclock a microcontroller, it needs more voltage.</p>
<p>In some abstract way it makes sense: it is doing more computation, so it needs more energy (and being less than perfect, some of that energy dissipates as heat).</p>
<p>However, from a just plain old Ohm's law level electricity and magnetism, what is going on?</p>
<blockquote>
<p>Why does the clock frequency have anything to do with power dissipation or voltage?</p>
</blockquote>
<p>As far as I know, the frequency of AC has nothing to do with its voltage or power, and a clock is just a super-position of a DC and a (square) AC. Frequency doesn't affect the DC.</p>
<blockquote>
<p>Is there some equation relating clock frequency and voltage or clock frequency and power?</p>
</blockquote>
<p>I mean does a high speed oscillator need more voltage or power than a low speed one?</p>
| Why does a faster clock require more power? | 2010-10-25T17:58:15.170 |
5628 | |sd| | <p>Howzzabout just signing on so you do not have to put a disclaimer on what would predictably be an SD card socket? Clearly your strict answer on interoperability (which you tested adequately, we imagine) is No; and if you look at MSDN you can cite their nice definition of free (if you really do not want to block out a single file occupied completely with XFS) on the matter of recently used filesystems. However, you surely want the fastest card access available and can access an organization with a common desire for this sensibility? Before we even start groaning years hence that it's not teracomm holodiamond-readable?</p>
| <p>I'm designing something which will use an SD card. The device will be able to read and write the cards, using publicly available specifications. Do I need to pay the SD card people?</p>
| Do I need to pay royalties to the SD card people if my device "just happens" to be compatible with SD cards? | 2010-10-25T19:49:39.047 |
5629 | |pic|spi|eeprom| | <p>In the past I have noticed that some of the PIC datasheets do not correctly show the SPI CPOL and CPHA registers, there was some issues that when looking at the output on a scope, two of the four combinations were back to front from what was expected. So double check you are actually getting the expected waveform out of your PIC and that the waveform matches what is needed on the EEPROM.</p>
<p>I have also come across some A/D converters that worked intermittently when I had incorrect SPI settings on a HC12, drove me banana's trying to work it out, was one of my first projects as a professional engineer, eventually I worked it out. But I digress. So it is possible to get intermittent problems using SPI bus due to incorrectly set CPOL/CPHA. As it is a shift register after all, and the last bit on one character may be being read of the first of the next character. This type of problem may not be noticed straight away either. </p>
<p>So ensure you have the correct settings on a scope, and do not relay on just setting the registers of the PIC. </p>
| <p>I'm attempting to interface a PIC18F4520 to a 25LC640 via SPI protocol. I'm using the built in MSSP hardware of the PIC. The PIC18F4520 is the only master on the bus. I'm reading 16 bytes of data from the EEPROM 32 times per second. I've double-checked the following items:</p>
<ol>
<li>TRIS Registers for SDI, SDO, SCK, and CS</li>
<li>Baud Rate ~ 1 Mhz</li>
<li>SPI Mode 0,0</li>
</ol>
<p>I've checked the signals on an oscilloscope and everything looks fine. I've tried using a BusBee to log the data coming from the EEPROM and 99% of the time it's correct. Every once in a while there are a string of requests where the MOSI (SDO) line does not seem to contain the correct EEPROM read instruction causing the data being clocked into the micro to be invalid. This happens even though I'm writing the same read instruction in the SSPBUF each time. What else can go wrong with a SPI bus?</p>
| Intermittent SPI bus | 2010-10-25T19:54:45.190 |
5630 | |video|oscilloscope| | <p>I'm guessing that the source is AC coupled ( and shouldn't be)</p>
<p>you've got dc offset shifting with picture brightness. Video should be DC coupled and terminated into 75ohms. If that sounds like something that your wouldn't string across a room, congratulations; it was never designed to. I remember reading that in-studio distribution was never raw analog video. So check the source path for a cap.</p>
<p>Unless it's just a really bad ground connection (high resistance) ;and the ground is elevating with brightness, which is consistent with that. So check the return path resistance too.</p>
<p>Analog video; it's frustrating because it was never intended to go very far as a baseband signal.</p>
| <p>See this image, it's a composite video signal on my scope.</p>
<p><img src="https://i.stack.imgur.com/rGfCW.jpg" alt="Scope shot"></p>
<p>As can be seen the dc offset of the signal is varying with time; it also varies with brightness in the scene. </p>
<p>I am plugging the signal from a composite video signal directly into my scope, however the cable is also spliced and goes to my computer's TV card. Without the TV card attached I do not see this. Now I would like to be able to debug my signal using the TV card, but it seems to be interfering (maybe it's loading the signal too much) - what could be causing this? I have another card I'm going to try but I'm not hopeful. Apart from buffering the signal using expensive video buffer amps, what can I try?</p>
| What's causing this ramp on a video signal? | 2010-10-25T19:57:19.957 |
5634 | |batteries|supercapacitor| | <p>Some ballpark figures I remember from a year or two ago:</p>
<ul>
<li><p>Batteries have 10 times the energy density of supercaps.</p></li>
<li><p>Supercaps have 10 times the power density of batteries.</p></li>
</ul>
<p>So for the same size you can store a lot more energy in batteries, but draw much more power from supercaps.</p>
<p>That's why some <a href="https://web.archive.org/web/20130309013712/https://www.bombardier.com/en/transportation/sustainability/technology/mitrac-energy-saver?docID=0901260d80048697" rel="nofollow noreferrer">trams</a> use supercaps and not lithium batteries.</p>
| <p>What is the current state of things when it comes to super capacitors and batteries? Are super caps anywhere near rivalling LiPo's in capacity?</p>
<p>I've often heard people talking about super caps as being a viable replacement for batteries, in that you can charge virtually instantly and recharge millions of times, but is this just a pipe dream?</p>
| Supercap compared to a battery | 2010-10-25T20:57:36.120 |
5635 | |dsp| | <p>There's also:</p>
<p><a href="http://www.gnu.org/software/octave/" rel="nofollow">Octave</a></p>
<p>and </p>
<p><a href="http://rlab.sourceforge.net/" rel="nofollow">Rlab</a></p>
<p>which may have some of the functionality you're looking for.</p>
<p>The site <a href="http://www.dspguru.com/" rel="nofollow">dspGuru</a> may have other useful suggestions for you too.</p>
| <p>I'm looking for some freeware that will do (as much as possible) of what Matlab does DSP-wise...</p>
<ul>
<li>Filtering tools</li>
<li>Modulation</li>
<li>File I/O (as I need these to compare vhdl simulation results to software computed results)</li>
</ul>
<p>I've used both Scilab and Octave. I'm wondering which one (or another unmentioned option) would be the best freeware DSP design replacement.</p>
| Which freeware analysis software most closely resembles the functionality of Matlab DSP toolbox | 2010-10-25T21:04:09.077 |
5647 | |microcontroller|pic|sensor| | <p>If you don't mind disassembling the drive you could look into the interlock or drive open switch, which should be fairly easy to wire in to. It may even have a pull-up, providing a logic signal directly to your device of choice.</p>
| <p>What would be a sensor that I could use to detect if my desktop's CD tray has opened? </p>
<p>There are so many sensors to choose from in the Digikey catalog. </p>
<p>Should I use a mechanical component?</p>
<p>A light beam interference component?</p>
<p>Which one would allow me to detect if my CD tray is open such that the information can be fed into a PIC MCU?</p>
<p>I know I can do a system call for this sort of question, but I would prefer some sort of external sensor.</p>
| What external sensor could detect if a cd-tray had opened? | 2010-10-26T02:23:38.010 |
5649 | |pic|timer|interrupts| | <h2> Why is it hard?</h2>
<p>This is not the easiest thing to do. you have picked a crystal oscillator that is specifically chosen to give easy division to common baud rates.</p>
<p>For example:</p>
<p>11.0592MHz/9600 is 1152</p>
<p>11.0592MHz/115200 is 96</p>
<p>That means you can hit some standard baud rates perfectly with a certain divider. Gives very consistent UART. Now you want to count time.</p>
<h2>Counting 1 Second</h2>
<p>If you take a 11.0592MHZ then divide by 256 and 64 you get a value of 675. This means if you want an accurate count of seconds you need to have that interrupt every 256 * 64 clock cycles and count with a variable in your interrupt you can hit it.</p>
<h2>How to make it easier</h2>
<p>You have two options, accepting error. First, your equation you divided by 255 since you are counting from 0 to 255, but since the interrupt is on overflow it is actually as you count to 256, so you should be dividing by 256.</p>
<h3>My clock has error?</h3>
<p>Decide how much precision you need. Often you do not need spot on precision, if this is the case, accept that it is almost a second and use what Thomas said in comment. Count to as close as you can get and cope. Timer 1 will allow you to divide by 65536 and spend more time doing things other than handling interrupts.</p>
<h3>I need precision in my clock!</h3>
<p>You need to pick an <a href="http://en.wikipedia.org/wiki/Crystal_oscillator_frequencies" rel="nofollow">oscillator value that is a multiple of 32768 Hz</a>. What you want is something that can be reduced to 1Hz from division by a power of 2.</p>
<p>If you need the nice baud rate and a nice counter, the wiki page has a mark for RTC(good for real time clock). 4.608 MHz is a great thing, it divides to 1Hz pretty easy and is good for 115200 baud also.</p>
| <p>I have learned that the maximum 'delay' possible in pic16f877a running with a source of 11.0592MHz (11059200 / 4 actually) is 23 ms.. without using software delays (delay_ms( ))..</p>
<p>the calculation was max_delay = ((FF-00)xPrescalarxTimeperiod) = (255x256x3.62xe-7) = ~23ms..</p>
<p>My question is how to 'increase this delay to 1 second' without using software delay?</p>
| Increasing the delay using 'option' register in Pic16f877a | 2010-10-26T05:50:15.637 |
5654 | |temperature| | <p>Temperature extremes will damage the physical package itself and interconnecting wires. It is the different expansion rates or silicon, metal wires (gold??), and plastic housing that will effectively destroy the part. The silicon itself will normally survive to a limit. That is why earlier on in electronic development there was a difference between plastic dip and ceramic dip packages which had different temperature ranges. The silicon was the same, just the packaging was different. It was this difference in packaging that allowed the 'military' ceramic packages to have a greater usable temperature range than commercial plastic package.</p>
<p>With SMD packages, this has changed slightly and they all tend to have greater temperature range, but you can still get commercial, industrial and military temperature ranges of 0 to 85, -40 to 125, and -55 to 125 as a general rule. </p>
<p>That is why devices have lower limits and medium range upper limits, due to packages constraints. </p>
<p>There are also phsyics limits for the upper end where the silicon itself may become damaged and the dopants might defuse? I am not sure of the exact function here or temperature limit. </p>
| <p>Many integrated circuits I have seen have the specification of maximum junction temperature (150°C) but storage temperature is invariably higher (165°C) and often lower, e.g. -55°C. Why the discrepancy? Surely the junction will be damaged whether or not it has current flowing through it...?</p>
| Why the difference between maximum junction temp (150°C) and storage temp (165°C)? | 2010-10-26T09:47:09.690 |
5659 | |avr|current|ethernet|debugging|enc28j60| | <p>The Center Tap of the receive magnetics should not be connected to R5 and R6.</p>
| <p>I have a problem with a relatively simple board which consists of an ENC28J60 Ethernet controller and an ATmega168.</p>
<p>The circuit around the ENC28J60 is straight out of the datasheet and I have the same circuit built up in a prototype with DIP parts where it works, but in my SMD version the ENC sucks down 40 mA @ 3.3V and it gets pretty hot.</p>
<p>The datasheet mentions that a relatively high current is sunk by the two TPOUT pins and that the total current is around 180 mA, but there is no mention of how much current the ENC itself will pull out of VDD.</p>
<p>The oscillator runs perfectly and CLKOUT is 6.25 MHz, so the chip is not completely dead.</p>
<p>I've measured the voltage at every pin and:</p>
<ul>
<li>Every VSS pin is 0V</li>
<li>Every VDD pin is 3.3V</li>
<li>The oscillator and CLKOUT out are good.</li>
<li>VCAP is 2.65V</li>
<li>RBIAS is at 1.2V.</li>
<li>!RESET is 3.3V.</li>
<li>SPI looks ok.</li>
</ul>
<p>Yet, I can't seem to raise the chip over SPI from the AVR and it gets pretty damn hot.</p>
<p>I've tried yanking !RESET low and that doesn't affect the power usage. Any clues?</p>
<p>Notice that the pin numbers for OSC1, OSC2, VDDOSC and VSSOSC are wrong in the schematic, I fixed that bug after exporting that version of the PDF however it is no longer available online.</p>
<p>OK, here's the real list of problems with my design that led to my problem:</p>
<ol>
<li>My 3.3V regulator is dumping waaay too much power, so it gets too hot.</li>
<li>The ENC28J60 eats lots of power, even when working normally, so that gets hot too.</li>
<li>I messed up and forgot to double check the Eagle library pinout, so I had to do some board hacking to fix that.</li>
<li>The RX center tap should not be connected.</li>
<li>I forgot to update my Makefile to build for the Mega168 part.</li>
</ol>
<p>Problem number 5 was the real source of my problem, #1 & #2 kept me looking at the hardware for far too long, which is doubly embarrassing because I make my living writing software.</p>
| Hot ENC28J60 @ 132 mW | 2010-10-26T11:42:07.663 |
5666 | |batteries| | <p>This isn't a direct answer to your question, but it's related. I assume you're using multiple AA batteries in series (in order to achieve a higher voltage for your circuit to operate). In that case, you might consider using a buck/boost circuit to boost the voltage from one AA battery. You'll pay a penalty in terms of how much current you can supply, but compared to a coin cell, it will be better.
<a href="http://www.sparkfun.com/products/10255" rel="nofollow">Sparkfun sells a kit that will take in down to 0.3v and output 5v at 500 mA</a>, for example.</p>
| <p>I am currently using AA batteries in my projects but would like to look at cell batteries for my next project, due to their compactness.</p>
<p>Apart from the physical appearance, how do cell batteries differ from the more chunky AA batteries? (I am guessing the mAH would suffer for example?)</p>
| Are coin cells a suitable replacement for AA batteries? | 2010-10-26T13:07:59.830 |
5670 | |diodes|maximum-ratings| | <p>From looking at a diode curve you can see that its reverse current sharply rises at Vr much like the forward current does. From this I would imagine that repetitively hitting the diode with reverse voltage in excess of Vrrm would cause the diode to conduct significant current and the resultant power dissipation to either melt the silicon and fail open, or, if the supply is limited, fail shorted.</p>
<p>A diode will certainly not "conduct almost unlimited current" -- the device has a designed power dissipation and will not conduct more than this amount for very much time. When reverse-biased you are essentially damaging the thin junction and it is for this reason that it's not the same as simply forward-biasing the diode. Avalanche and Zener diodes are designed to operate reverse-biased and have differently-formed junctions which are designed to withstand this mode of operation. Zener diodes especially have a much more heavily doped junction than normal diodes.</p>
| <p>How is a diode damaged by exceeding its Vrrm (maximum peak repetitive reverse voltage)? At this point it conducts more current than usual, so is it the current flow that damages it? Why would that be any different from being forward biased when it conducts almost unlimited current? Or is there some other factor?</p>
| Damage to diodes by exceeding Vrrm | 2010-10-26T15:04:46.500 |
5671 | |equipment| | <p>As a relative newbie into electronics at a later point in life, I concur with the myDAQ suggestion. You also get LabView with it that is very robust plus a ton of other benefits and features including MultiSim. This doesn't even scratch the surface.</p>
<p>TechShop (www.techshop.com) opened a location near me late last year (Austin/Round Rock location), and they have them available at the educational price and also have training classes. In addition to all of their other tools and machinery, there's also an electronics lab there with scopes, function generators, most of the usual bench equipment, a small re-flow oven and a little ShopBot for making PCB's, just to name a few.</p>
| <p>Is a function generator necessary for every day lab use, or is it special purpose equipment? That is, does it have similar utility to an oscilloscope, or multimeter - would you use it regularly enough to justify it's cost?</p>
| Is it worth getting a function generator? | 2010-10-26T15:34:07.820 |
5680 | |power-line-communication| | <p>I think it would be helpful to consider power line modems as radio devices since they use traditional radio techniques (modulation) to achieve data transfer. If you take two radio modems and plug a cable between them instead of an antenna they will still be able to communicate (impedance matching aside).</p>
<p>The basic idea is not to encode the data as high-low voltage levels (which can be prone to interference) but as frequency/phase of (a set of) sinusoids. The second thing to do is to eliminate low-frequency components by clever encoding and/or frequency conversion. This makes it possible to separate different users by frequency filtering (in addition to being critical in radio since electromagnetic waves won't happen from a DC signal).</p>
| <p>I have some powerline networking adapters which can transfer at a peak rate of 200 Mbps (I get around 60 Mbps typical, but I am sharing the network with many other devices and many pieces of equipment are running on the line.) How do they do it? I always thought that it was during the zero crossing, but packing so many bits into such a space must be very difficult, nigh impossible. HowStuffWorks has an article on it, but it's only relevant to adapters which go at 14 Mbps.</p>
| How do these powerline networking adapters work? | 2010-10-26T17:30:27.127 |
5681 | |power-supply| | <p>This isn't exactly a hobbyist project by any stretch of the imagination, but:</p>
<p>If you're into transformers (or need isolation) you could design a flyback converter. The -120V rail would be your regulated output, and the -108V and +60V rails would be slave windings (loosely regulated simply based on the turns ratio). There are many integrated devices on the market which contain a HV MOSFET and simple controller for flybacks. </p>
<p>If you don't care about isolation, you could design a boost for the +60 and something exotic like a Cuk for the -108/-120V rails. </p>
| <p>I'm designing a regulator/converter that can generate -120/-108/+60Vdc for a current of 180mA each from a supply of 12Vdc or 24Vdc (5A like it's nothing, 15A tops) and I was choosing a MC34063 but the absolute maximum rating for Vout is 40Vdc:</p>
<ul>
<li><strong>Is it sane to overspec for 300%?</strong> In the datasheet there is a circuit for use with external transistors, but I really know little of supply design.</li>
<li><strong>Is there another ubiquitous IC for doing this?</strong> (I googled it and all that I can find are car inverters)</li>
</ul>
<p><strong>EDIT: the three separate rails can be independently regulated</strong></p>
<p><strong>EDIT</strong>: for the record there is a circuit called the <a href="http://en.wikipedia.org/wiki/Voltage_multiplier" rel="nofollow">Villard cascade</a> that works for very low currents (like the CRT screens), but it was too dangerous to prototype (by me).</p>
<hr>
<p><strong>Final Update</strong>
I found a full LED replacement for the screen I was planning to supply and for the old ones we salvaged supplies from older equipment.</p>
| High voltage/Mid current boost converter | 2010-10-26T17:32:01.603 |
5697 | |adc|microcontroller|sampling| | <p>I think that you've confused two different things:</p>
<p><strong>Supersampling</strong> (a.k.a oversampling) is the process of increasing signal time-resolution (you might say: horizontal). It multiplies the sampling rate of a sampled signal by adding extra samples between existing ones with interpolated values. This allows for higher-precision processing further the road and helps minimize some processing artifacts. This process applies only to digital signals, because analogue signal isn't sampled, it's continuous. One could say that an analogue (voltage) signal has infinitely high sampling rate, but that's not technically true, it's just a figure.</p>
<p><strong>Dithering</strong> is adding noise to increase the dynamic (vertical) resolution of the digital signal that is about to be quantized. Quantization is necessary to store samples in finite precision numbers (digital files). Adding noise before quantization replaces the quantization distortion that produces audible artifacts called quantization distortion, with much less audible noise floor.</p>
<p>You can't increase sampling rate (and therefor frequency range) by adding noise to the signal, but you can increase the dynamic range by replacing quantization distortion with it.</p>
| <p>Is it possible to increase the resolution of an ADC by supersampling on a PIC24F ADC, which has 10 bits of resolution and is implemented using a successive approximation engine? Speed is not critical - greater than 1 kHz or so.</p>
<p>My initial thought was no, as it is not a Delta-Sigma ADC and results are not cumulative, so I thought I could add noise to the voltage reference (3V nominal) using a pin of the MCU and a high valued resistor. Would this work? The additional noise should improve the resolution, but I'm unsure if this applies for all types of ADC's.</p>
| Increasing ADC resolution by supersampling on a successive approximation ADC | 2010-10-27T01:24:17.367 |
5700 | |resistors|voltage| | <p>If you have a bunch of components, all with different tolerances, you do a <a href="http://en.wikipedia.org/wiki/Monte_Carlo_method" rel="nofollow">Monte Carlo analysis</a> to see what kind of risk the worst case is, but also what a probable case is, since it's not likely that every component is at it's worst. This gets as detailed as you want to make it.</p>
| <p>If I have two 1k resistors rated at 1% fed by a perfect 10V source then what is the otuput guaranteed to be? 5V ±1% or 5V ±2% or some other value?</p>
<p>I can work out this case easily, assume that R1 is at the minimum, R2 is at the maximum, then the output is 4.95V; for the reverse case it is 5.05V, which is ±1%.</p>
<p>But is there a general rule for differing values? What about differing tolerances - what if one resistor were ±0.1% and one ±1%. While you can work it out by plugging values into the voltage divider formula, I'm looking for some general rule of thumb.</p>
| Tolerance of voltage dividers with different values for R1 and R2 | 2010-10-27T01:33:22.847 |
5713 | |microcontroller|led|multiplexer| | <p>If you really have only 1 pin available the Dallas 1-wire bus looks like the most obvious thing. However, since this is output-only, there are cheaper solutions. A serial PWM bus which carries both data and clock is easy to set up; see for instance <a href="http://www.romanblack.com/shift1.htm" rel="nofollow">Roman Black's page</a> as also mentioned by davidcary. You only need serial-in parallel-out shift registers like the <a href="http://www.fairchildsemi.com/ds/74/74VHC164.pdf" rel="nofollow">74VHC164</a>, which you can cascade for as many outputs as you want (one '164 has 8 outputs).<br>
In this solution LEDs are driven statically. </p>
<p>If you do have other I/O you can share, like SPI of I2C, you may go for more luxurious solutions, like Maxim's <a href="http://www.maxim-ic.com/datasheet/index.mvp/id/3195" rel="nofollow">MAX6950</a>. The MAX6950 has blinking and brightness control, and slew-rate limiting, to name a few features. LEDs are multiplexed, which means you only need one 16-pin driver.</p>
| <p>I have a microcontroller with one available digital pin.</p>
<p>How can I control 25 LEDs?</p>
| Serial control of 25 LEDs from a single pin | 2010-10-27T05:44:54.833 |
5721 | |microcontroller|motor|stepper-motor| | <p>Here's a suggestion:</p>
<p>Check out <a href="http://www.cs.uiowa.edu/~jones/step/index.html">Jones on Stepper Motors</a>, with links to manufacturers, controllers, distributors, etc. and a ton of information on how to control them. The control signals will come from your microcontroller. The control power will likely come from a Driver. If you use AVR or PIC, the manufacturer will have tutorials and white papers, with code, on motor control. Read about the different types of stepper motors, and how they're driven with a pulse train.</p>
<p>Then, pick your motor. Shop around on google to see what's available. Have an idea of what kind of stepper motor you want (bipolar and unipolar are popular). You are looking at what the holding torque is, and what the rated voltage and current are. I'm assuming your positioning can be quite coarse.</p>
<p>To decide what kind of holding torque you need:</p>
<p>Measure the amount of torque the motor has to have, either with a torque wrench or by estimation. To estimate: you probably the know the length of the arm that needs to move (say, 6" or 15cm), and the amount of weight that needs to be moved (say, 0.1lb or 45 grams). </p>
<ol>
<li>Multiply those numbers together to get 6" * 0.1lb = 0.6 ft*lb or 15 * 45 = 675 cm*g = 0.675 kg*cm) </li>
<li>Multiply by some safety factor to give you some margin (anywhere from 1.3 to 3, 1.3 is probably fine for you, so 0.675 * 1.3 = 0.8775 kg*cm) </li>
<li>Then you look for a stepper motor rated with a hold torque of at least that 0.88 kg*cm. That's its maximum torque if you feed its rated voltage and current. Now look at that motor's rated voltage and current, can you supply that? (As in, if it asks for 120VDC at 1mA, you probably don't want that motor.) If you don't like it, look for a different motor, or look more carefully at what you're trying to move.</li>
</ol>
| <p>I am planning to create a robot arm using the MicroController.
The robot arm should move from the angle of 0 degrees to 60 degrees.</p>
<p>I am going to use this robot arm in my application to stop and allow the small small toy vehicles on a dummy road. This is for demonstration of my project.</p>
<p>What are the specifications that I need to keep in mind while choosing the Stepper Motor and MicroController.</p>
| Create a robot arm using microcontroller | 2010-10-27T07:32:59.980 |
5722 | |pcb|design|bga|pcb-design| | <p>Here's a <a href="http://www.altera.com/literature/an/an114.pdf" rel="nofollow">PDF</a> from Altera. I've usually seen the diagonal via location because this gives the most space between the via and ball. You can also Google "BGA fan out" to get more help.</p>
| <p>Are there any good resources for learning the intricacies of PCB layout when dealing with BGA packages?</p>
<p>I'm very familiar with layout for almost every SMT part that has leads on the edge (QFP, TSSOP, QFN, etc...) However, I have not ever had a chance to work with BGA parts because of the difficulties involved in their assembly, as the shop where I work does not have the facilities to do so.</p>
<p>Anyways, I've been looking into farming assembly out, and am hoping for some reference material for dealing with BGA devices. </p>
<p>I'm interested in both general and specifics. Escape routing, blind vias, vias in pad, SMD pads vs NSMD pads, filled and open vias, etc... </p>
<p>I've done a lot of sporadic reading (blogs, mainly), but am missing the bigger picture, namely how different techniques interact and a lot of basic common sense knowledge that likely comes through actual experience, even if only by proxy.</p>
<p>So far, I have spent some time studying any open-source project that uses BGA I can find (the BeagleBoard, Mainly) but most open source projects are not at the level of complexity that requires a BGA device, and the ones that do are rather rare.</p>
| Getting started with PCB Layout for BGA Packages | 2010-10-27T08:29:42.593 |
5735 | |microcontroller|ratings| | <p>So that is 3V (with a 1% tolerance) to 3.6V (again with approx 1% tolerance)</p>
<p>OR</p>
<p>as Thomas O commented 3.3V +/- 10%</p>
| <p>I've seen several microcontrollers rated to operate from 2.97V to 3.63V. Others I've seen rated from 3V to 3.6V.</p>
<p>What's with the extra 30mV on either end of the scale? It doesn't seem like it would make any difference, but maybe I'm missing something.</p>
| What a weird operating range, 2.97V to 3.63V | 2010-10-27T13:17:50.200 |
5743 | |embedded|ethernet|linux| | <p>I second the switch suggestion.</p>
<p>If you need to separate different networks then configure the switch chip to split the ports into different VLANs and trunk all VLANs to the port that the Linux box is on.</p>
<p>Linux will be able to access all VLANs as though the system had individual network interfaces to the different networks.</p>
<p>Most, if not all, switch chips can be configured via a serial EEPROM, so modifying an off-the-shelf switch for a POC or a one-off hack ought to be easy enough.</p>
| <p>I have an embedded Linux system with a single Ethernet port, but I need to go to many ports. It is obvious I need to add magnetics and ports. The trickier parts follow.</p>
<p>My processor has an on-board MAC and I'm using a single-driver PHY. Do I only need a new PHY with more drivers? Is it possible to use multiple PHYs on the same MAC? Do I need a MAC for each port?</p>
| What is needed to go from single Ethernet to many? | 2010-10-27T16:09:00.443 |
5747 | |light| | <p>seems the new bulbs are made in bulk with cost saving strategy. Not a novelty any more. We will have to figure out what brands are lasting and what brands are blowing early. I have had 9 of these bulbs blow in 4 months. However, I have larger ones that have lasted over 6 years now. Seems the compact ones are the problem. I have them enclosed and open. </p>
| <p>I know that this question may be off-topic here, but I'll ask it anyway since they do have electronics inside.</p>
<p>I've noticed that my fluorescent lamps keep dying after only couple of months of use. When they die, they die in groups of 2-3 and as far as I can see, both new and old lamps may die during such events. As far as I can see, electronics inside dead lamps look normal to me, but then again, I don't have much experience in electronics, so I could be wrong. </p>
<p>So I'm asking you people what could be the cause and how can I prevent it? I'm thinking about bad electricity supply, because I have frequent brown-outs, but as far as I can see, deaths of lamps aren't more frequent during times when I have brown-outs. I'm thinking about connecting lamps over a UPS or "power conditioner".</p>
<p><strong>UPDATE:</strong><br>
I did some investigating and I think that I've found source for my problem. As I mentioned, I had brownouts. I noticed that nobody in my area had brownouts, so I the problem was probably with my installation. Then I noticed that voltage for two phases was between 220 V and 230 V, as expected, but one was between 190 V and 200 V. The main cause for that seems to be a 35 A DIAZED DIII fuse which is connected to the phase which powers my lamps. It turned out that the tip of the cartridge and fitting element of the fuse case were corroded and were sparking and overheating (the cartridge was so hot that I had difficulties removing it). It also turned out that when power company replaced my electromechanical meter with solid state meter, they installed new circuit breakers in such way that fuses are serially connected to breakers and are "downstream" from them. I talked to few electrical engineers and electricians and they all believe that since circuit breakers are installed, fuses should be removed. I'll get an electrician to remove them will report back how that effected lifetime of my lamps.</p>
| Why do my compact fluorescent lamps keep dying? | 2010-10-27T17:45:19.330 |
5752 | |voltage-regulator|noise|lm317| | <p>The LM1117 instead of the LM317, with some protection diode and improved ripple rejection should do this job. Oh, and don't use an <a href="http://en.wikipedia.org/wiki/Switched-mode_power_supply" rel="nofollow">SMPS</a> direcly with the LM317. You can use the SMPS itself to give many more voltages than it has.</p>
<p>Examples:</p>
<ul>
<li>+5 v to GND = 5 V</li>
<li>+12 V to 5 V = 7 V</li>
</ul>
<p>AND most "GOOD" computer <a href="http://en.wikipedia.org/wiki/Power_supply_unit_%28computer%29" rel="nofollow">PSUs</a> have a "GOOD, stable" 3.3 V supply for the processor. Afraid of its current? Limit it with a 33 ohm resistor (100 mA maximum) and be happy.</p>
| <p>I'm using an LM317T to regulate 5 V to 3.38 V for a microcontroller. R1 is 330 ohms and R2 is 560 ohms. There isn't any input capacitor and the output capacitor is 470 µF 25V, because I had that value in a pack of 50. The microcontroller is drawing at least 50 mA, so I'm fairly sure I'm meeting the minimum load specifications. The regulator is being powered from a computer <a href="http://en.wikipedia.org/wiki/Switched-mode_power_supply" rel="nofollow noreferrer">SMPS</a>, but I had a very similar configuration set up last time running off an SMPS without any problems.</p>
<p>Here's a scope trace of an I/O pin to show you what I mean:</p>
<p><img src="https://i.stack.imgur.com/xdRpD.jpg" alt="Alt text"></p>
<p>The ripple is about 60 mV<sub>p-p</sub>, but as you can see it also happens when the pin is low. I'm worried it might affect the microcontroller itself (for example, make it unstable.)</p>
<p>What I'm more worried about are these large bursts of noise which occur seemingly randomly about 100 times per second:</p>
<p><img src="https://i.stack.imgur.com/pZA1A.jpg" alt="Alt text"></p>
<p><strong>It turns out this noise is coming from my power line network adapters</strong>; it's leaking through from the power line into the computer SMPS and to the 5 V output.</p>
| What's causing this high frequency ripple on the output of my LM317? | 2010-10-27T20:10:01.870 |
5757 | |arduino|atmega|xbee|zigbee| | <p>I think what I am missing is that the XBee's modules must be programmed both to send and to receive data. In the following thread there is someone claiming that acomplished that and posting some code which will run in a ATMega processor:</p>
<p><a href="http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1223492621/all" rel="nofollow">http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1223492621/all</a></p>
<p>I also found a tutorial of how to configure the XBee module using a graphical environment:</p>
<p><a href="http://forums.trossenrobotics.com/tutorials/how-to-diy-128/xbee-basics-3259/" rel="nofollow">http://forums.trossenrobotics.com/tutorials/how-to-diy-128/xbee-basics-3259/</a></p>
<p>From what I read above, I tested it, and I finally established a connection, then I wrote a tutorial showing how I did it.</p>
<p><a href="http://arduinolessons.blogspot.com/2010/10/how-to-use-xbee-module.html" rel="nofollow">http://arduinolessons.blogspot.com/2010/10/how-to-use-xbee-module.html</a></p>
<p>Unfortunately not all data gets through though...</p>
<p>Since I'm using a XB24-B the following blog gave me some light:</p>
<p><a href="http://lizard43.blogspot.com/2009/04/xbee-series-2-jv-channel-verification.html" rel="nofollow">http://lizard43.blogspot.com/2009/04/xbee-series-2-jv-channel-verification.html</a></p>
| <p>I bought</p>
<ol>
<li><a href="http://www.seeedstudio.com/depot/uartsbee-v31-p-688.html?cPath=104_109&zenid=0c4f29549324dc90d977325a5ca19eea" rel="nofollow">Seeeduino Stalker</a></li>
<li><a href="http://www.seeedstudio.com/depot/uartsbee-v31-p-688.html?cPath=104_109&zenid=0c4f29549324dc90d977325a5ca19eea" rel="nofollow">UartsBee</a></li>
<li>Two <a href="http://www.seeedstudio.com/depot/xbee%C3%82%C2%AE-rf-modules-znet-25-1-mw-chip-antenna-p-226.html?cPath=2" rel="nofollow">XBees</a></li>
</ol>
<p>When I physically connect (1), (2) and the computer USB, I can receive on my computer data sent by (1) at 115200 Kbps. But when I physically disconnect (1) and to (2), and link them again using the XBees the computer receives no data.</p>
<p>I noticed that in (1) the UART Tx and Rx are directly connected to XBee's Dout and Dint. But in (2) there are 1k resistors in each of those connections. Can such resistance be the cause of the problem?</p>
<p>The UartsBee is configured to use 3V, and I tested both connecting and disconnecting the DTR interrupt from the XBee to the ATMega328 (there is a jumper slot for it on (1)). The board is supplied with a 9V 200mA wall adapter. Both XBees were installed pointing the closest edges of the respective boards.</p>
| How to send data through XBee using ATMega328? | 2010-10-27T22:40:07.030 |
5759 | |power-supply|voltage|voltage-regulator|voltage-measurement|adapter| | <p>One thing to note when using unregulated wall-bricks to drive linear regulators (a common pattern) is that the amount of heat produced by the regulator will be the product of the current drawn and the amount by which the input voltage of the regulator exceeds the output. If one is trying to get +5V from a wall-brick which outputs 12 volts at 1mA but only 7 volts at 500mA, then when only 1mA is being drawn from the regulator, the regulator will have to dissipate 7 volts (the difference between 12 and 5) times 1mA, i.e. 7mW. If the wall-brick voltage didn't drop as current increased, heat dissipation would increase proportional to current; at 500mA, the regulator would have to dissipate 7V times 500mA, which is 3.5 watts. If the wall-brick voltage drops as current increases, however, this will reduce the power the regulator has to dissipate (e.g. if a 500mA load drops the voltage to 7V, then it would only have to drop (7V-5V)*500mA, which is to say one watt, not 3.5.</p>
| <p>When I measure a 9V DC wall adapter power supply with a multimeter it shows 11.8V. When connected to my board this voltage lowers to 10V. Is this normal? Should I be afraid of toasting my <a href="http://www.alldatasheet.com/datasheet-pdf/pdf/205686/ADMOS/AMS1117CD-5.0.html">1117CD-5.0</a> supplied board when using this adapter?</p>
<p><strong>Edit</strong>: This regulator accepts up to 12V inputs. So that will be no problem. A second "9V" adapter yields 15V to the multimeter. Will this one burn my circuit?</p>
| Is it normal for DC wall adapter power supplies to provide voltages above the nominal ones? | 2010-10-27T23:14:06.160 |
5764 | |arduino|communication|telephone| | <p>About 10 years ago, I bought a device called "Party Line" from a company whose name escapes me. This device has six telephone jacks on it, and simulates the telephone main office. You could plug in up to six regular phones, and they could call one another. Think of it as a very simple PBX (with no connection to the real phone network).</p>
<p>Any phone can dial any of the other five by dialing a 7-digit number where one of the digits indicates the line to connect to. It only supports one connection at a time, though. But for two phones, that's all you need.</p>
<p>I bought it as a kit, and assembled it myself. Inside it has a PIC and some discrete circuitry. I used it while developing some software that would transfer data over a modem connection. I had two computers with 56K modems, each connected to the Party Line. It worked very well, and I made thousands of calls from one system to the other without tying up my real line or incurring any charges.</p>
| <p>I am hacking some old phones into my arduino project. I am currently controlling all of the ringers, dials, and hooks through my board.</p>
<p>At a certain point, I would like to connect the two handsets and let them function kind of like a basic intercom. There are four wires into each handset, two for the microphone, and two for the speaker. As I understand it they function much like any cheap microphone or headphones you could plug into your computer. </p>
<p>My initial thought is that I could just connect the mic of one to the speaker of the other, but I don't know audio circuits very well and am not sure if additional circuitry or op-amps would be required. What is the simplest way to do this?</p>
<p>Also, what would be the best way to toggle this connection, so I can control if the lines are open or closed?</p>
| Connecting two phone handsets to talk | 2010-10-28T02:59:18.063 |
5774 | |rf|antenna| | <p>First, a caveat - I'm primarily a CE, so this is just my understanding of the matter:</p>
<p>1. Generally, the worst reception is when the antenna is upside-down, or nearly so, and the best is when it is vertical. However, horizontal orientations are nearly as good as vertical; the radiation pattern is usually something like this, with "up" in the picture corresponding to the positive Z axis (defects overemphasized): </p>
<p><img src="https://i.stack.imgur.com/D43K4.png" alt="alt text"></p>
<p>2. Again, your antenna manufacturer will likely have a reference design for this. Sarantel publishes sample gerbers for many of its antennas. If the antenna is not directly coupled with a ground plane, near-field radiation will still be helpful.</p>
<p>3. No idea. I doubt that it would matter as long as both antennas had decent signal strength. Back-to-back might not be ideal, but everywhere else should work fine.</p>
<p>4. No, it's hardly directional at all.The reason you use a helical antenna is because you want near-omnidirectional performance. If orientation is controllable, use a different antenna.</p>
| <p>A batch of questions here really (if it helps I'm operating at 433.92MHz):</p>
<ol>
<li><p>How should I orient a helical antenna with respect to my board (i.e. my "ground plane") to get the best range performance?</p>
</li>
<li><p>What should the dimensions of my ground plane have to be in order to get good performance / how much does this matter compared to orientation?</p>
</li>
<li><p>I'm also wondering what effect (if any) the relative orientation of these types of antennas between the transmitter and receiver has on link quality (due to polarization?).</p>
</li>
<li><p>Is the antenna pattern directional for these types of antennas (related to 3), and if so how narrowly?</p>
<p>Sorry if this question is a little bit all over the place - I've got an EE background, but RF can be kind of mysterious (if you know what I mean)...</p>
</li>
</ol>
<p>Regards,
Vic</p>
<p><strong>[Edit]</strong> 3-d visuals would be really helpful in helping me get my head around this as well <strong>[/Edit]</strong></p>
<p><strong>[Edit2]</strong>
5. Going to attempt some ASCII art here - what's the best way to mount my antennas? slashes (/) are the helix orientation, underbars (_) are the ground plane, and vertical bar (is the feed point):</p>
<pre><code> Transmitter Receiver
**A**
/ /
/ /
/ /
/ /
____|____ ____|____
**B**
//////// ////////
_|_________ _|_________
**C**
//////// ////////
_|_________ ________|__
**D**
/
/
/
/ ////////
____|____ _|_________
**E**
/
/
/
/ ////////
____|____ ________|__
</code></pre>
<p><strong>[/Edit2]</strong></p>
| Helical antennas and orientation | 2010-10-28T14:58:58.593 |
5778 | |rf| | <p>As a quick rule of thumb for 50 ohms, you want the ratio of the trace width to the height above the ground plane (probably your board thickness) to be around 1.8 with 2-oz copper. With a standard 0.063" thick PCB, that means a trace width around 120 mil. (Fat!)</p>
<p>Formulas for calculating this can be found in various places. If you access to an engineering library, try chapter 4 of High Speed Digital Design by Johnson and Graham. (Equation 4.90 on p. 187 is the key one.)</p>
<p>Here's an online calculator: <a href="http://referencedesigner.com/tutorials/si/si_06.php">http://referencedesigner.com/tutorials/si/si_06.php</a></p>
| <p>I'm trying design a video transmitter around an 5.8GHz Airwave module. The documentation says the trace to the antenna must have a characteristic impedance of 50 ohms. How do I calculate the characteristic impedance of my trace?</p>
| Characteristic impedance of a trace | 2010-10-28T16:43:47.903 |
5780 | |serial|cellphone| | <p>The USB port will provide wired serial (or did you mean UART/SPI/I2C?) communication cheaply. I doubt (but I don't know positively) that the Torch can act as a USB host, so you'll have to find a device capable of doing that to interface with the Torch.</p>
<p>Another alternative is to remove the microSD card (assuming that you don't need it), and use those connections for this purpose. There's probably an SPI port (or at least a few GPIO with which to bit-bang a serial connection) in that slot. A PCB with a right-angle connector should make this connection possible, if not pretty.</p>
| <p>I have a Blackberry Torch that needs to send 10 bytes per second to a serial device. The serial device will probably be a basic stamp 2 or other microcontroller. The Blackberry does not need to receive any data.</p>
<p>Is there an interface that will let me do this for less than $50?</p>
<p>Using the Wifi or Bluetooth connections are the obvious choices but those options look more expensive.</p>
<p>I also thought about using the headphone jack to send out different frequencies and an intermediate circuit could convert the sound into bytes, but I'm not sure where to start with that cicuit.</p>
<p>Thanks.</p>
| How to interface a Blackberry Torch with a serial device? | 2010-10-28T17:12:10.307 |
5788 | |decoupling-capacitor| | <p>You overlooked \$V_{CAP}/V_{DDCORE}\$. If you take that in account you'll see that there's a \$V_{SS}\$ for every power pin. </p>
<p><img src="https://i.stack.imgur.com/WZyWW.png" alt="enter image description here"> </p>
<p>I only wish Microchip would have placed the \$V_{SS}\$ of pin 8 and the \$V_{DD}\$ of pin 13 on adjacent pins, like it did for pins 19/20 and 27/28. </p>
<p>As explained in section 2.3 of the datasheet there's an internal voltage regulator for the core, which needs an output capacitor for stability. That's \$V_{CAP}/V_{DDCORE}\$. You connect a 4.7\$\mu\$F to 10\$\mu\$F between this pin and ground. That's all you need the pin for, the rest is internal. </p>
<p>Section 2.2 in the datasheet covers decoupling and shows this schematic: </p>
<p><img src="https://i.stack.imgur.com/TyEjW.png" alt="enter image description here"></p>
<p>Some designers will draw power rails in a corner of the schematic and place all decoupling capacitors there. Their excuse is that the decoupling in the schematic itself will clutter it and make it less clear. IMO that's a bad idea. Especially if someone else will create the PCB layout it's not clear where the capacitors belong physically. If you draw them like in the above schematic it's at least suggested which pins a capacitor belongs to and the PCB layout engineer will know that it has to be placed close to the pins.</p>
| <p>Many IC's I've seen suggest decoupling capacitors across Vdd to Vss - this is sensible.</p>
<p>However some IC's for example the dsPIC33FJ128GP802 has THREE Vss pins and only two Vdd pins (AVdd and Vdd.) So would I put a decoupling capacitor on each Vdd pin, or from each Vdd pin to each Vss pin? </p>
| Decoupling capacitors | 2010-10-28T22:58:36.767 |
5790 | |microcontroller| | <p>Check the PIC24 range - there are some 44 pin parts, some with USB host, which may have more than normal RAM to support the USB functions.
You don't often see large RAM or flash in low pin counts due to the size of the die - the large pin count isn't a major factor in cost, it's the die size for the RAM etc.
Similarly you don't see large pin counts on low-end devices as the size of the pad ring dictates the die size, so it would be a waste of silicon to not use it for functionality.</p>
| <p>I'm looking for a microcontroller in a TQFP-44 package with 30 KB or more of RAM and, if possible 40 MIPS instruction cycle speed or faster. I can find dsPIC33F's with 30 KB of RAM, but they come in TQFP-100 packages, and I'm only going to be using maybe 15-20 pins of those so it seems like a massive waste of space and money. </p>
<p>So I'm looking for some reasonably sized package with lots of RAM. I've given up on the SO28's but if anyone finds one it would be excellent as well.</p>
<p>Current candidates are the Parallax Propeller, but that only has 20 MIPS instruction cycle, and the dsPIC's in TQFP-100's. One parameter but not both!!</p>
<p>This is for my Super OSD project.</p>
| Microcontroller with >30KB RAM and high performance in a TQFP-44 or similar package | 2010-10-28T23:08:47.353 |
5796 | |switches| | <p>The response of a hand clapper is basically the impulse response of your transfer function. Since the response is the transfer function itself, you can design your transfer function to suit your needs accordingly. The best way is, to sample your sound analyzer input and interface it with a digital signal processor and then go crazy with discrete laplaces and FFTs.</p>
| <p>I'd like to know how a 'hand clap' switch works. You know, the kind where you *clap-clap* and the light turns on, *clap-clap* again and the light turns off.</p>
<p>How is the clapping sound detected? How can it be differentiated from whistling, people talking, a barking dog, ... ? Can it be another kind of sound?</p>
<p>What kind of components would I need to build such a sensor/switch, assuming everything works on DC?</p>
<p><em>Note: I am <strong>not</strong> interested in just buying a Velleman kit :-)</em></p>
| How do 'hand clap' switches work? | 2010-10-29T00:00:38.110 |
5800 | |analog|i2c|comparator| | <p>If your micro has I2C and that many free IO's, does it have a built in DAC? If so then what reemrevnivek suggested would work. You don't need a separate DAC chip if you have one onboard...</p>
| <p>I'm looking for a programmable comparator which has a digital or open-drain output and a voltage reference which can be programmed over I2C. My searches at my favourite sites of Microchip and Farnell haven't brought up anything interesting.</p>
<p>If this isn't possible I'd be looking at making an external R-2R (or R = 2^n) divider (precision not critical) from 4-5 IO pins to get 16 or 32 levels granularity. The setpoint needs to be adjusted to compensate for varying video levels. </p>
<p>Edit: such comparator should also have <1µs response time. Most comparators satisfy this, but there are a few cheap ones that don't.</p>
| Comparator over I2C with programmable reference | 2010-10-29T00:41:12.873 |
5801 | |microcontroller|rs232| | <p>Most serial devices implement some sort of 'flow control' == this is either via extra wires (RTS 'Request to Send', CTS 'Clear to Send') a 'handshake' that lets the recieving device set CTS hi or lo to suspend transmission ..</p>
<p>.. OR (for those devices that use only a RxD/TxD lines) 'software flow control' ( == you send them some specific ascii code to say 'stop sending' and onother to say 'ok, start again now') </p>
<p>Look up 'Flow control' in your GPS data sheet ..</p>
| <p>I have a GPS device which I need to pull data from (the NMEA strings.) However, many times per second my MCU will be busy processing something else. Is there any way to "pause" an UART/RS232 TTL signal or buffer it while my MCU does stuff? I'm looking at either a dsPIC33FJ128GP802 or an AT32UC38x.</p>
<p>The processing of my OSD cannot be interrupted, so interrupts are out.</p>
| How to poll UART while processing lots of other stuff | 2010-10-29T00:43:53.977 |
5819 | |buck| | <p>Check <a href="https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&ved=0ahUKEwiI3fK8y53OAhXLnRoKHRnxC-EQFggtMAU&url=http%3A%2F%2Fwww.seeedstudio.com%2Fwiki%2Fimages%2F4%2F4e%2FMP1584_r1.0.pdf&usg=AFQjCNHlXp_FSJvJCVdZj0Y6DuRg1_lgbQ&sig2=aaK04mojVlOWZdaUTddPsQ" rel="nofollow">MP1584</a> out. This chip has a maximum frequency of 1.5MHZ and can deliver up to 3mA current. A friend of mine uses a module sold from china containing this chip to charge his tablet. The datasheet contains the inductor specifications and I can see all of them are less than 30uH.</p>
| <p>I'm looking for a buck converter in a SOIC-8 package which requires a small inductor (preferably ≤10µH) which can convert 6V-16V to 5V @ 1A. Unfortunately the package <em>must</em> be a SOIC package, because the person I'm designing for requires the SOIC package to be easy to place and solder. At the moment I've drawn a blank: all the high speed buck converters I have found only have a 6V or so maximum input voltage or they come in strange packages which are difficult to hand solder.</p>
| Looking for a small inductor buck converter in a SOIC-8 package | 2010-10-29T09:51:00.770 |
5821 | |adc|pwm| | <p>As a side note, I see you already accepted an answer.</p>
<p>You can use an RC circuit with a cutoff frequency below the frequency of your PWM to average the PWM. You need it to have a cut-off of a low enough frequency to stop you having a varying output based on the phase of the PWM going by, but you must also pick a PWM that will react to a change in duty cycle fast enough for you to see it.</p>
<p>I hope that makes sense. This is a very easy way to do it, and with some external comparators you could use it to easily tell if a certain threshold value is violated.</p>
| <p>I want to read 8 PWM inputs (standard servo PWM, 1ms to 2ms) without an input capture module (my module only has 7 channels.) Could I use a capacitor and the ADC on my MCU? Does anyone know of any successful implementation of this, or have any references for this?</p>
| Reading up to 8 PWM's | 2010-10-29T11:28:39.277 |
5825 | |digital-logic|programmable-logic|rom| | <p>We can think of a simple programmable logic device as an array of AND gates followed by an array of OR gates (in reality it may actually be implemented as two arrays of NAND gates).</p>
<p>In a PROM the "AND array" is fixed and the "OR array" is programmable. Every combination of inputs generates exactly one output from the AND array. The "OR array" is then programmed to define the logic function. This allows every output to implement any logic function of the inputs.</p>
<p>Being able to implement arbitrary logic functions sounds attractive but there are two practical problems to using PROMs for logic. Firstly, it doesn't scale well, each extra input you add doubles the required size of the and array. Secondly, it is very prone to output glitches because the product terms used each cover exactly one input combination.</p>
<p>In a PAL the "OR array" is fixed and the "AND array" is programmable. Each output must be formed from a restricted number of product terms but those product terms can each cover multiple input combinations. </p>
<p>In a PLA both arrays are programmable. This gives you more flexibility if some outputs need more product terms than others or if several outputs have product terms in common.</p>
| <p>I'm finding it hard to understand. What is the difference between PLA and ROM? Can somebody please provide a link or explanation?</p>
| What is the difference between PLA and ROM? | 2010-10-29T13:55:17.513 |
5826 | |cmos| | <p>Quoting Wikipedia: "The original 4000 series was available in two versions: The A series was unbuffered, while the B series featured buffered inputs and outputs (in the form of additional, simple logic gates). The buffered outputs are able to source or sink more current than the unbuffered outputs, thus eliminating the need for discrete switching transistors in some designs."</p>
<p>I think it's pretty safe to say that the CD4000 number is the generic number, not caring about specific properties like buffered outputs, just the basic logic function. The suffix letter, according to wikipedia, will tell you about the output buffer. Further suffix letters (2nd, 3rd, ... letter) will tell you about packaging options and the like; this may differ from one manufacturer to another and is noted in the data sheet.</p>
<p>Today, only the B versions of the 4000 logic ICs seem to be available. At least that's what the manufacturers' websites tell me. Do you have a link for the 4000 (without B) series data sheet? Is there a manufacturer's logo on the chip?</p>
<p>It might be the case that some manufacturers produce the buffered version (-B), but mark the actual devices without the B. To be sure, you would need a data sheet that tells you the specifics about device marking code.</p>
| <p>I have a choice between a CD4017 and a CD4017B.</p>
<p>I've also seen CD4026 and CD4026B. </p>
<p>What is the difference between these - is it a silicon revision or do they have different functionality?</p>
| Difference between CD4017 and CD4017B | 2010-10-29T14:08:03.493 |
5830 | |batteries|decoupling-capacitor| | <p>Every time a transistor changes state in a digital system, it takes a tiny bit of current to switch. Tons of the transistors in a logic chip or microcontroller are changing at nearly the same instant. When that happens, the power consumed by the chip spikes briefly. Bypass (or decoupling) capacitors help supply that power so that those brief load spikes don't cause the supply voltage on other chips to drop. (Especially since the other chips might be briefly needing their own surge of current at the same time.)</p>
<p>That's why you want very fast (small, low ESR) caps located near each IC, as close to the power pins as practical.</p>
<p>The big caps near the power supply provide the current to carry the load while the AC supply goes through 0V, and the small/medium caps near the supply help refill the bypass caps scattered all over the board.</p>
| <p>Currently I run all my gadgets from batteries and don't use decoupling capacitors. Are they generally needed/useful when drawing energy from a battery?</p>
| Are decoupling capacitors needed with battery power? | 2010-10-29T15:27:09.537 |
5835 | |pcb|pcb-fabrication| | <p>You'd normally put power/gnd planes on inner layers, mostly as these are the least likely to need track-hacking to fix errors or aid debugging. Almost all 4L PCBs you'll see do it like this. You will often have space available on the power plane to route a few signals.
There can sometimes be some marginal benefits in EMC and track density (due to via size) by putting them on outer layers but you'd only do this if you'really struggling to avoid going to 6 layers, or need a little extra EMC performance due to the shielding effect of outer planes.</p>
| <p>For my Super OSD Pro project (Super OSD is divided into two versions: Lite and Pro) I'm going to be using a 4-layer board. Are there any gotchas to be aware of when using 4 layer boards? </p>
<p>I was thinking of having the most widely used nets (+3.3V and GND) on layers 1 and 2, and having layers 3 and 4 for carrying signals. I could also occasionally use layers 1 and 2 for carrying signals where 3 and 4 are full up.</p>
<p>One other thing I'm also concerned about is how to connect pins to the right layers? Say I want to connect a pin on the top to layer 2. I've always routed a trace from the pin to a via, then dropped the via to that layer, but is there a better way? I've heard of via on pad but I've also heard that can produce bad results and is only really for BGA's, not the TQFP's I'll be working with.</p>
| General tips for 4 layer boards | 2010-10-29T17:45:50.903 |
5845 | |ceramic| | <p>For decoupling purposes the variation in value is practically irrelevant. The standard practice is to specify .1uF, but there's nothing inherent in that number that makes it right for this purpose, and it could just as well be .22uF or .047uF. In other words a change of a factor of 2 won't really make any difference. So yes the Y5V is perfectly fine for decoupling. In the majority of digital electronics applications, the value isn't so important, as long as it's "big enough", so just use whatever you can find. If you're worried about the possible loss of capacitance at high temp (-80% for Y5V) then just select a larger value like .15uF or .22uF. </p>
| <p>Y5V capacitors are much more temperature dependent, but is that really critical for decoupling capacitors and a product operating over a -40°C to +85°C range maximum (typical -20°C to +55°C)?</p>
<p>The reason I ask this is the cost is much lower, compare 0.8p with 8p per capacitor.</p>
| Is Y5V okay for decoupling capacitors? | 2010-10-29T20:10:19.433 |
5850 | |microcontroller|uart|frequency| | <p>One point not yet mentioned is that some devices expect to transmit a byte of data for every byte of data they receive. If such a device is fed data continuously, its baud rate is even 0.1% slower than that of the transmitting device, and it has no facility to send out slightly-shrunken stop bits, its output will will fall a byte behind for every 1000 consecutive bytes that come in. If the device is limited to 16 bytes of buffering, it will drop a byte of data after passing roughly 16,000 and will drop roughly one byte per thousand thereafter. It's worthwhile to note that so-called "1200 baud" modems actually operate at a rate slightly higher than 1200 bits/second (I think it's about 1202) for precisely this reason (so that even if the transmitter is 0.15% faster than it should be, the modem will still pass through all the data).</p>
| <p>I'm going to be using an 8 MHz crystal to run my microcontroller at 16 MIPS (PLL 4x, 2 cycle instructions.) However, 8 MHz doesn't divide into any UART frequencies AFAIK... so how critical are these frequencies? I plan to use 115,200 baud.</p>
<p>Can UART run within ±1%? If this doesn't work, what frequency should I use? (I would like to get as near to 16 MIPS as possible, for maximum processing speed.) If it matters, I'm using a PIC24FJ64GA004.</p>
| How critical are UART frequencies? | 2010-10-29T22:27:23.043 |
5853 | |connector| | <p><strong>4P/F to 1P/F Jumper Wire</strong></p>
<p><a href="http://www.mdfly.com/index.php?main_page=product_info&cPath=65_69&products_id=74&zenid=035ga7ae4fmop7s4bmpi424h65" rel="nofollow noreferrer">MDFLY</a></p>
<p>Jumper wire with one 4-pin female connector on one end and four 1-pin female connectors on the other end.</p>
<p><img src="https://i.stack.imgur.com/T4IQ9.jpg" alt="4P/F to 1P/F Jumper Wire"></p>
<p><strong>'x'P/F to 'x'P/F Jumper Wire Combination</strong></p>
<p><a href="http://www.mdfly.com/index.php?main_page=product_info&cPath=65_69&products_id=79&zenid=035ga7ae4fmop7s4bmpi424h65" rel="nofollow noreferrer">MDFLY</a></p>
<p>Select a jumper wire with 1-pin to 8-pin female connector on each end.</p>
<p><img src="https://i.stack.imgur.com/WUpLn.jpg" alt="alt text"></p>
| <p>Headers like these:</p>
<p><a href="http://uk.farnell.com/harwin/m20-8760342/header-smt-vertical-2x3way/dp/1517388">http://uk.farnell.com/harwin/m20-8760342/header-smt-vertical-2x3way/dp/1517388</a></p>
<p>I'm looking for cables that connect to these, with female headers on either end. Any length more than ~5cm is ideal. But I can't seem to find any results on my favourite websites. I'd rather not spend time crimping them myself as I have to produce a lot of them.</p>
<p>For this application I need 4 way connections, but it would be nice if many different way counts were available, so I know what to buy in future.</p>
| Where to find pre-made wires for plugging into headers? | 2010-10-30T00:03:16.970 |