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8680 | |rfid|nfc| | <p>You said:
"For example the Nexus S's NFC chip is read only and does not offer any card emulation mode."</p>
<p>Please take a at <a href="http://www.nearfieldcommunicationsworld.com/2011/02/13/35913/uncovered-the-hidden-nfc-potential-of-the-google-nexus-s-and-the-nokia-c7/" rel="nofollow">http://www.nearfieldcommunicationsworld.com/2011/02/13/35913/uncovered-the-hidden-nfc-potential-of-the-google-nexus-s-and-the-nokia-c7/</a></p>
<p>They do say "... So the phone comes with everything we do need for card emulation — SWP and even a secure element within the phone."</p>
| <p>NFC has a mode called "card emulation" in which it can communicate with an RFID reader because it acts as an RFID card. All the literature I have and the web searches I did only got me so far as with card emulation the device should at least "emit a unique ID". But I would like to know if:</p>
<ul>
<li><p>it is possible, according to the NFC definition, for such a card
emulation information to be configured completely free (probably
going as far as emulating a RFID card with a java routine on with its
top limit being the maximum of bytes allowed on a RFID card in the
RFID protocol), and;</p></li>
<li><p>such a unique ID (if not freely configurable) is hardcoded by the
manufacturer or dependent on the SIM card.</p></li>
</ul>
<p>On a side-note, it probably would be interesting to know what manufacturers enable you, as a user, to do and what should be theoretically possible because of protocol definitions. </p>
<p>For example, the Nexus S's NFC chip is read only and does not offer any card emulation mode.</p>
<p>I thank you in advance for all answers.</p>
| Questions about NFC's card emulation mode | 2011-01-06T23:43:07.297 |
8685 | |microprocessor| | <p>The first microprocessors would have been programmed with the help of existing computers which were not based on microprocessors. Before the first CPU was produced on one chip, there already existed advanced computer architectures which were built from discrete components rather than microprocessors. Take a look at, oh, say, IBM 360.</p>
| <p>This has just dawned on me that if you're writing an operating system then what are you writing it on? I ask this as I am reading a microprocessor fundamentals book from 1980 and this question popped in to my head: </p>
<p><strong>How was the first microprocessor chip programmed?</strong></p>
<p>The answer may be obvious but its bugging me. </p>
| How were the first microprocessors programmed? | 2011-01-07T01:15:03.097 |
8690 | |audio|wireless|signal| | <p>I just saw an article about a stylus by Qualcomm used to write on an Android phone. The stylus emits an ultrasonic pulse and then software on the phone is able to locate the pen. Here is a link;</p>
<p><a href="http://seat12f.blogspot.com/2011/02/finger-input-just-cant-keep-good-stylus.html" rel="nofollow">http://seat12f.blogspot.com/2011/02/finger-input-just-cant-keep-good-stylus.html</a></p>
<p>I do also recall reading a few years back about a digitizing pen that used ultrasonics to locate the pen. A small receiver was connected by USB, and it even had a memory so you could clip the device to any notepad to record your writing for later input into the computer. However, I just looked at some of the office supply stores, and it doesn't seem to be around anymore.</p>
| <p>I want to be able to determine the location of an object that will be moving around in a rectangle about 15" X 10"</p>
<p>The location must be accurate to within about 1/4" and be measured at least 100 times per second.</p>
<p>The first idea I had for accomplishing this is to have the object transmit a pulse signal every 10ms and have a receiver in each corner wired to a micro controller and measure the difference in time between when each receiver gets the signal to triangulate it's source. </p>
<p>My first thought was to use IR receivers and transmitters, but I would have no idea how to do the triangulation with signals that move so fast.</p>
<p>So then my second thought was to use sound. I would want to transmit at a frequency above the human hearing range. And it seems to me that higher hertz = greater accuracy. The speed of sound is about 13,400 inches per second. So that means to get 1/4" resolution, I would need 56kHz or higher.</p>
<p>First off, I've never dealt with sounds above the human hearing range. This will probably be on for periods of about an hour, and may be just a few feet away from ears. As long as I use low power, is there any way that this could be a hazard?</p>
<p>Secondly, what kind of speakers are capable of transmitting 56kHz? And similarly, what kind of microphones could pick up 56kHz?</p>
<p>Other methods of triangulation would also be appreciated.</p>
| Signal triangulation | 2011-01-07T02:42:19.123 |
8705 | |capacitor|ceramic| | <p><a href="http://my.execpc.com/~endlr/ceramic.html" rel="noreferrer">This page</a> has the following table:<br>
<img src="https://i.stack.imgur.com/U6PCP.gif" alt="alt text"></p>
<p>So, if the 22uF is a 20% tolerance part such that is may actually be 17.6uF (-20%), and it is really 15uF (-15%) due to heating, it may be reduced to ~10.5uF (-30%) near its tolerance or <strong>~14uF</strong> (-5%) near its operating point. To reduce the effect, use a higher breakdown value capacitor.</p>
<p>Although <a href="http://www.cliftonlaboratories.com/capacitor_voltage_change.htm" rel="noreferrer">this webpage</a> tests much higher breakdown voltage ceramics, the results are illustrative:
<img src="https://i.stack.imgur.com/dpiSY.jpg" alt="alt text"></p>
<p><a href="http://www.avx.com/docs/Catalogs/cx5r.pdf" rel="noreferrer">This part</a>, the <a href="http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=478-3647-2-ND" rel="noreferrer">08056D226MAT2A</a> by AVX, states that it meets its tolerance tested at 0.5 V<sub>RMS</sub>, not close to its breakdown:</p>
<blockquote>
<p>For Cap > 10 μF, 0.5Vrms @ 120Hz</p>
</blockquote>
<p>It also mentions that capacitance may change up to 12.5% over its load life, 7.5% due to soldering thermal shock, and 12% due to <em>flexure fissures</em> (cracks).</p>
<p><sub><strong><em>Info tidbit:</strong> The term <strong>X5R</strong> means it is composed of a <strong>class 2 dielectric</strong> (ie: ceramic) that will maintain its capacitance to within 15% (18.7uF - 25.3uF) over a temperature range -55<sup>o</sup>C to 85<sup>o</sup>C.</em></sub><br>
Something that may interest you, though it has more to do with the final application than the question -- <a href="http://en.wikipedia.org/wiki/X7R" rel="noreferrer">the great 'pedia also mentions:</a></p>
<blockquote>
<p>Due to its piezoelectric properties, they are subject to microphonics.</p>
</blockquote>
<p>... And the previously <a href="http://my.execpc.com/~endlr/ceramic.html" rel="noreferrer">linked page</a>:</p>
<blockquote>
<p>High-K ceramic capacitors can show significant piezoelectric effects; if you tap them they will produce a voltage spike. This is caused by the barium titanate, the main material in high K ceramics. The higher the K, the stronger this affect.</p>
</blockquote>
| <p>I'm using a 22u 6.3V X5R 0805 ceramic capacitor to filter out a 3.3V supply (for a buck converter.) I've heard that applied voltage has an effect on the capacitance of certain ceramic caps; a higher voltage causes a reduction in capacitance. How true is this? Would it decrease too much as to not work as a suitable filter cap? I think 10-15u is probably the minimum for it to remain stable, although the ripple will probably increase at lower capacitance. Any ideas?</p>
| Ceramic caps and applied voltage | 2011-01-07T12:56:04.663 |
8707 | |pic|timing|interrupts|stepper-motor| | <p>As Nick T mentioned, TCP/IP is unfiltered and non-deterministic. You said you want to also interface with SPI and UART devices, and previous versions used USB. These are difficult to do in real time, and probably require significant code space.</p>
<p>On the other hand, you want real-time control of your stepper motors, which requires deterministic execution and rapid interrupts but not a lot of program space. </p>
<p>While you said you wanted to avoid using a separate microcontroller because it would complicate things, this is a <em>perfect</em> example of when you need a co-processor, and I believe that it would make things simpler in the end.</p>
<p>You can develop simple stepper motor controller firmware that run on small, cheap microcontrollers. Design (or discover) a protocol that can use a communication bus available <strong>in hardware</strong> on whatever controller you choose. I'd recommend SPI for this (on a different channel than the device you mentioned in your question; your master should have two SPI peripherals), you don't want to mess with address conflicts given the small number of controllers you'll have. Don't do anything with this controller but run the stepper according to the data it receives over the protocol. You can probably buy something that does this already. The goal is to be able to treat this as a hardware peripheral.</p>
<p>Then, you can develop USB or Ethernet controllers that will plug into these devices. You will have flexibility in the host protocols (Need to use RS485 this time? No problem!), you can use different numbers of motors, and you have greater modularity for designing, testing, debugging, repairing, and replacing. The only reasons I'd try to implement something like this in a single controller would be extreme cost/size restrictions, and/or a lack of hardware modules (like PWM? Did I miss something?) that could do this without interrupting the host processor.</p>
| <p>I have a question regarding stepper motor control while using the TCP/IP stack. </p>
<p>In the past I have used a timer for my stepper motor control. I set the period of a timer to the required time between pulses and then I change the motor phase outputs as needed in the timer tick ISR. In the cases where I have done this my stepper was moving at a maximum rate of around 400 pulses per second which means the interrupt was occurring every 2.5 milliseconds. And I was using USB for communication to the host. </p>
<p>I am now working on a new product which will use the TCP/IP stack to communicate with a PC over Ethernet. It will also be communicating with other devices via SPI and UART modules. This new device must be capable of operating a stepper up to 2000 pulses per second which means the interrupt may be firing every .5 milliseconds if I use the same timer/ISR approach to drive the stepper. The stepper is turned on and off based on commands received from the host, so communication with the host and operation of the motor need to occur harmoniously and simultaneously. If the stepper speed varies slightly that would not be a problem but it is not ideal. Also, if the stepper were to pause for say a 30ms in the middle of it's move that WOULD not be acceptable. </p>
<p>I am considering using a PIC24F with the instruction clock speed of 16MHz (32Mhz/2 using the internal FRC+PLL) for this project. Do you think that the interrupts for the stepper will disrupt the Ethernet communication or vise-versa? Is there a better way of doing this? </p>
<p>I have considered using a separate PIC for the stepper control and then I could send that pic target position commands or halt commands to start and stop the movement but that would add another firmware into the mix and complicate things all around. </p>
| Stepper Motor Control Timing | 2011-01-07T15:46:10.277 |
8712 | |oscilloscope| | <p>Like pretty much all real circuits, oscilloscope inputs have a parasitic capacitance. No matter how small you made it by good design, it would still affect RF signal acquisition, except maybe for a defined 50 Ω connection and attenuation directly at the scope's input, for which case, with the numbers from your question - </p>
<p>$$f_{-3dB} = \frac{1}{2\pi \cdot R_{in,\ scope} \cdot C_{in,\ scope}} = \frac{1}{2\pi \cdot 50 \;\Omega \cdot 12 \;pF} = 256 \;MHz $$</p>
<p>Or even higher, if we would make the scope's input impedance C<sub>in, scope</sub> smaller.</p>
<p>Usually, though, we don't want to load the circuit under test with a defined 50 Ω connection because most circuits under test will have any impedance but 50 Ω (like your signal generator's output would, because it is specifically designed for impedance-matched 50 Ω systems). So what can be done with a capacitance that can't be eliminated? It was chosen to use it in a clever way in the <strong>probe-and-scope combination</strong>. So clever, actually, that any unknown capacitance that may be caused by probe cables and other things in your connection can be compensated just like the scope's input capacitance, and all of them become don't-cares for most cases of practical measurement applications.</p>
<p>The 1:10 probe has an internal resistor of 9 MΩ <strong>and</strong>, in parallel, <strong>an internal capacitor</strong> of [1/9 * C<sub>in, scope</sub>].</p>
<p>It is adjustable because the probe doesn't know the exact capacitance of the particular scope it is connected to.</p>
<p>With the capacitor in the probe properly adjusted, you have not only a resistive divider for the DC part of the signal (9 MΩ at the probe vs. 1 MΩ in the scope), but also a capacitive divider for the higher-frequency AC part of the signal (1.33 pF at the probe vs. 12 pF in the scope, using your numbers), and the combination works beautifully up to or beyond, say, 500 MHz.</p>
<p>Also, you get the advantage of inserting not 1 MΩ and 12 pF into your circuit when probing, but 9 MΩ + 1 MΩ = 10 MΩ and [the series equivalent of 12 pF and (12 pF / 9)] = 1.2 pF</p>
<p><a href="https://i.stack.imgur.com/zsqrI.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zsqrI.gif" alt="enter image description here"></a></p>
<p>Link to the source of the picture: <a href="http://www.hobbyprojects.com/oscilloscope_tutorial/oscilloscope_probes.html" rel="nofollow noreferrer">Here.</a></p>
<p>What the picture in the link doesn't show and what we have neglected so far is the capacitance of the probe's cable, this would just add to the capacitance at the scope's input and can also be compensated for when turning the variable cap in the probe.</p>
<p>Using a 1:10 probe, the probe's small capacitance is in series with the scope's larger input capacitance. The total capacitance (approx. 1.2 pF) is in parallel to the point of your circuit that you are probing. Connecting the scope directly to the circuit, e.g. with just a straight BNC cable, you are indeed putting the entire input capacitance of the scope in parallel to what you are measuring - maybe loading your circuit under test so much that it will not work any more while being measured. At best, it might still work somehow, but the picture on your scope will show results far off the real waveforms in your circuit under test.</p>
<p>It would be possible to build scopes with a much smaller input capacitance - but then, there would be no way compensating the probe's cable capacitance with a small variable capacitor near the probe tip. After all, the 12 pF at the scope's input have been put there <em>on purpose</em>, to make the scope work well <em>together</em> with a good probe.</p>
<p>One last note: Using 1:100 probes, you load your circuit even less. In lack of an active probe with a really small capacitance at the tip, a 1:100 probe can be used in cases where even 1.2 pF would be too much load on your circuit - provided the signal is large enough that you still see something after the probe's 1:100 attenuation.</p>
| <p>My oscilloscope is rated: 1Mohm || 12pF. It's a 100 MHz oscilloscope. However, I don't get the point of the capacitance. If I set my probe on 10X (it's switchable), then it inserts 9Mohm in series. Now we've created an RC filter with -3dB break point of: ~1.473 kHz, and yet, I get higher bandwidth with 10X probes and I certainly don't get a 1.4 kHz bandwidth limiter! What am I missing?</p>
<p>Also, I was simulating the circuit on a circuit simulator. With no probe resistance a 10pF cap conducts 1A at 100 MHz, which would be massive loading compared to the 1 Mohm impedence.</p>
| What does input capacitance mean on an oscilloscope? | 2011-01-07T20:16:37.910 |
8723 | |pic|assembly|firmware| | <p>I haven't used MPASM before, but does this work?</p>
<pre><code>movlw (1 << O_RED) | (1 << O_GREEN) | (1 << O_BLUE)
</code></pre>
<p>Shifting to the left doubles a number.</p>
<p><code>1 << x</code> == 2<sup>x</sup></p>
| <p>I'm writing firmware for a PIC16F877A in assembler, and I want to set some constants at the top of my source code to indicate which port is used for what, so that if needed I can easily change all the i/o pins around by changing the constant values and recompiling.</p>
<p>Like this:</p>
<pre><code>O_LEDS EQU PORTA
CONSTANT O_RED = RA1
CONSTANT O_GREEN = RA2
CONSTANT O_BLUE = RA3
</code></pre>
<p>In my code, I need a bitmask to represent the ports I'm using. My question is, how can I write an expression using assembler directives to calculate the bitmask?</p>
<p>Using my example above:</p>
<pre><code>O_RED = 1
O_GREEN = 2
O_BLUE = 3
</code></pre>
<p>and the bitmask I want is:</p>
<pre><code>movlw b'00001110'
</code></pre>
<p>If there was a <em>to the power of</em> operator, I could do something like this:</p>
<pre><code>movlw (2 ^ O_RED) | (2 ^ O_GREEN) | (2 ^ O_BLUE)
</code></pre>
<p>but <code>^</code> in MPASM is a Bitwise exclusive OR, not <em>to the power of</em>.</p>
<p>Can anyone think of another way to do this?</p>
| Bit position to bitmask conversion using MPASM directives | 2011-01-07T23:34:11.310 |
8725 | |power-supply|switches|mosfet|safety|isolation| | <p>If you want to maintain isolation (I assume you have some legitimate reason for it beyond it being "good", i.e. user-accessible low-voltage electronics) and still drive your floating MOSFETs, you could generate a gate voltage with a full-wave rectifier and a shunt regulator, then switch it using a standard optoisolator. The drive current will be incredibly low if you're only switching at 60 Hz, so your regulator's Iq can also be quite low.</p>
| <p>Context: A digital phase-controlled light dimmer system.</p>
<ul>
<li>120V AC mains</li>
<li>I use an isolating transformer (and rectifying circuit) to generate +12V and +5V DC rails.</li>
</ul>
<p>I want to use reverse phase control (I've read that this produces less EM noise), so I'm looking to switch the AC mains using 2 Power MOSFETS (e.g. FDB14N30) with the source pins connected together.</p>
<p>In order to put the MOSFETs into the "on" state, I need to raise V<sub>gs</sub> to 10V-30V, but in order to do this, I think I need to hook up the MOSFET source pins to my isolated ground rail, and the gate pins to my +12V switching signal.</p>
<p>By doing this, have I defeated the whole purpose of an isolated power supply, in terms of danger of death and damage to components?</p>
| Switching 120V AC with Digital Logic on Isolated Power Supply | 2011-01-08T01:26:56.560 |
8729 | |multimeter|voltage-measurement| | <p>I just wanted to follow up.</p>
<p>I've finally found a device that can do this job. I just wanted to post in case anyone happens upon this thread, searching for the same thing:</p>
<p><a href="http://api-usa.com/pdf/api/apdhvdc.pdf">APD HV-DC High Voltage DC to DC Transmitters, Isolated, Field Rangeable</a></p>
<p>which is made by <a href="http://api-usa.com/">API-USA</a>.</p>
| <p>I am trying to make a high voltage measurement on an industrial sputtering machine. The voltages are in the 50V to 1000V range. Right now, we're using a Fluke DMM because we need a true floating voltage measurement (there's a lot of random common-mode noise that can't be eliminated). It works great, but it is battery powered and doesn't have any computer output capability. </p>
<p>We'd really like to replicate this function with a powered meter that can talk to a computer, so the data can be automatically logged. I've read a lot about this (although I still understand little). I understand that, in order to get a good floating, differential measurement, the meter must be well electrically isolated from our chassis with all the common mode noise and also from its own power signal.</p>
<p>If I could find something that could make this measurement and scale it to, say, a 0-10V output, I would be enthralled. Any suggestions or educations would be appreciated!</p>
| Can anyone suggest a voltmeter that can do the job? | 2011-01-08T02:42:26.847 |
8733 | |filter|interference|emc| | <p>Are you talking about this circuit?</p>
<pre><code> R1 R2
180 1K
+---/\/\/\----------+ +----/\/\/-------------+------------+-----------> 230V
1| |6 | | Hot
+=====+ IC1 | MT1 |
| MOC | TRIAC +-+ |
| 3020| Driver G | | TRIAC |
+=====+ /| | TIC226D |
2| |4 / +-+ |
+-------------------+ | | | MT2 |
+-------------------+ | |
| | |
\ | |
R4 / | | C1
1K \ | --- 100 nF
/ | --- 400V
| | |
| ) |
| ( L1 |
| ) 50..100 |
| ( uH |
| | | Neutral
+--+------------+----o o--> 230V
load
</code></pre>
<p>The values are standard <em>"band-aid"</em> values to improve ripple. They both store energy for the load to use during transitions. The author most likely picked these values from experience instead of calculations, just like one would choose decoupling values for digital IC Vcc pins <em>("Hmm, this one uses about 10mA max, so a single 100nF cap aught'a do'er!")</em> . It's not like a <a href="http://en.wikipedia.org/wiki/Switched-mode_power_supply" rel="nofollow">SMPS</a>, where an inductor's precise value is critical to the device's range of operation. One can make rough estimates by comparing the maximum energy used by the load during <em>"dead time"</em> (time between zero-crossing and SCR switch) and energy stored in the inductor: <em>E<sub>L</sub> = <sup>1</sup>/<sub>2</sub>LI<sup>2</sup></em> (use RMS current). For this application, though, the inductor will likely saturate and empty very quickly, so the stored energy really just smoothes the transitioning voltages.</p>
| <p>Can you point me to a good online resource to learn how to understand and design LC filters?</p>
<p>The goal is digital forward phase control to dim a light bulb. I've read that the EMI produced by the voltage spikes when a TRIAC goes into the "on" state can be bad news for other electrical devices nearby on on the same supply circuit.</p>
<p><a href="http://www.epanorama.net/documents/lights/lightdimmer.html" rel="nofollow">http://www.epanorama.net/documents/lights/lightdimmer.html</a> gives an example circuit with a 50-to-100 microhenry inductor in series with the TRIAC, and a 100 nF capacitor in parallel with it, but I don't know how the author came up with those numbers.</p>
| LC Filter for Phase Control | 2011-01-08T04:42:45.390 |
8734 | |arduino|level-shifting| | <p>It depends what direction the signals are going to.</p>
<ul>
<li>If the 5 V device is going to drive a signal on the 3.3 V device, use a simple resistor division.</li>
<li>If the 3.3 V device is going to drive a signal on the 5 V device, you could use two inverters with the last stage tied to 5 V. However, this requires four resistors and two transistors, which is quite an expense. You could also try out the implementation as shown in <a href="http://www.sparkfun.com/datasheets/BreakoutBoards/Level-Converter-v10.pdf" rel="nofollow noreferrer">Sparkfun's breakbout board</a>.</li>
<li>If the signal is bidirectional (I²C), maybe something in <a href="http://www.kip.uni-heidelberg.de/lhcb/Publications/external/AN97055.pdf" rel="nofollow noreferrer">this appnote on page 10</a> will work (seems similar to what Sparkfun is using).</li>
</ul>
| <p>I want to use an <a href="http://www.hoperf.com/rf_fsk/rfm12b.htm" rel="nofollow noreferrer">RF12B</a> to communicate over radio with an Arduino, but the transceiver is rated at 3.3 V. I hear I need to use a voltage level shifter, but what do these look like and where can I find a schematic to help me hook it up?</p>
| How do I shift voltage levels? | 2011-01-08T05:25:00.530 |
8741 | |fan| | <p>Here's some examples:</p>
<ul>
<li><a href="http://www.globefan.com/new_product.htm" rel="nofollow">M0802512</a> -- <em>"Life Time: On-going testing"</em></li>
<li><a href="http://www.sunon.com.tw/products/pdf/maglev.pdf" rel="nofollow">Sunon Maglev</a> -- N/A (<a href="http://www.sunon.com/uFiles/file/03_products/08-catalog%20download/DR_en.pdf" rel="nofollow">two sources</a>)</li>
</ul>
<p>In comparison to these non-magnetic bearing statistics:</p>
<ul>
<li>Sintec sleeve: <a href="http://img.ebmpapst.com/products/datasheets/412FH-ENG.pdf" rel="nofollow">45'000h @ 20<sup>o</sup>C; 15'000h @ 60<sup>o</sup>C</a></li>
<li>Superflo: <a href="http://media.digikey.com/pdf/Data%20Sheets/Delta%20PDFs/AUB0912VH-CIT.pdf" rel="nofollow">50'000h @ 40<sup>o</sup>C</a></li>
<li>Ball: <a href="http://media.digikey.com/pdf/Data%20Sheets/Delta%20PDFs/EFC0812DB-F00.pdf" rel="nofollow">70'000h @ 40<sup>o</sup>C</a>; <a href="http://www.eminebea.com/content/pdf/TMP00123/I/2410rl.pdf" rel="nofollow">40'000h @ 25<sup>o</sup>C</a></li>
<li>HydroWave: <a href="http://www.eminebea.com/content/pdf/TMP00123/I/fba09a.pdf" rel="nofollow">50'000h @ 40<sup>o</sup>C</a><br><sub><strong><em>Note: 1 year = 8766 hours.</em></strong></sub></li>
</ul>
<p>Looks like traditional bearing MTTF wins! My point is that at the moment this technology is marketing fluff, regardless of its merits. Real MTTF numbers will tell the story... not that <em>these</em> are real numbers: take them with a grain of salt, as they are subject to lawyer jibbajabba and marketing hype. <sup><em>(And no, that doesn't mean manufacturers have to wait 70'000h+ to characterize MTTF -- it is characterized much earlier using techniques to speed up the working hours.)</em></sup></p>
| <p>I asked this on Superuser a while ago, but since fans are often used for cooling electronic devices, I think that the question would be on-topic here too.</p>
<p>So how long is life expectancy of fan with magnetic bearing? I did some looking on catalogs of popular stores and datasheets of some manufacturers, but I couldn't find any information about life expectancy.</p>
| Life expectancy of fan with magnetic bearing? | 2011-01-08T12:47:42.730 |
8742 | |pcb|surface-mount|pcb-assembly| | <p>If higher current handling is needed only in specific traces, I've often seen the use of a tin reinforcement on the copper. It seems to be quite effective, as explained <a href="http://www.eevblog.com/2012/07/21/eevblog-317-pcb-tinning-myth-busting/" rel="nofollow">here</a>.</p>
| <p>I typically use 2 ounce copper as rule for all my PCBs. On a recent board I am using a 0.5mm pitch, relatively large micro, and noticed the pads aren't very flat. Assembly went fine with the protos, but I'm wondering if 1 once copper would provide for a flatter landing service. Does anyone have any experience with using 1 and 2 ounce copper with small pitch devices and/or any advice on assembly reliability related to copper thickness for such devices?</p>
| PCB copper thickness with small pitch SMT components | 2011-01-08T15:35:53.670 |
8744 | |battery-charging| | <p>It's relatively simple. Your battery pack has a maximum wattage. bw.</p>
<p>You source or charger needs to produce at least twice that wattage.</p>
<p>2bw.</p>
<p>The circuit will charge your pack at a rate of efficiency x in time t where t is the time it takes to fully charge the pack @ x.</p>
<p>Now the rest is vague it's been some years since they covered it in school but you can look in a textbook to find out how to set it up properly for your rate of current. </p>
<p>Bw=2Bw times (efficiency) . Usually about 67% with a linear voltage regulator. Or x/t times 100%. Something like that. Your circuit is standard and won't be very efficient since you don't match battery impedence which changes all the time plus constant current chargers bog on modern high capacity batteries you need to add a ocsolator (sp?) at a low frequency rate to produce a sloped high voltage pulse for both charge adsorption and chemistry cooldown along with the constant current. </p>
<p>For example. You charge at a constant current of C/10. Every half a second you pulse a hundred volt positive pulse carrying two hundred millamps into the positive electrode using a separate circuit. Now don't disturb the C/10 constant rate while you do so.</p>
<p>Using the example helps align the dendrites in the cells and produces a much better faster fuller charge that lasts longer.</p>
<p>Lots sa luck.</p>
<p>John.</p>
| <p>I have 12 AAA NiMH batteries(1000mAH and 1.2V per battery) and I want to know what is the optimum voltage for charging them. I am using a simple Constant Current charger(LM317 and 68 Ohm Resistor(R in the circuit diagram). But i'm unsure on what the input voltage needs to be. My circuit doesn't have the diode.<br>
<img src="https://i.stack.imgur.com/lQEBG.gif" alt="LM317 Battery Charger"></p>
| Voltage input for charging NiMH Batteries | 2011-01-08T16:18:06.490 |
8745 | |electromagnetism| | <p>Since you are new to coil guns I would recommend two courses of study to begin with. First understand that coil guns are just solenoids which are just inductors. The difference is you switch the coil off just before the middle of the projectile reaches the middle of the coil. In order to understand this you need a good understanding of Amperes Law and Faraday's law of Induction. Once you get a handle on those two things then it is all a matter of experimentation. I would further say that heeding all the advice about safety precautions above is wise indeed as I have very nearly been injured repeatedly by not observing those very pieces of advice.</p>
| <p>I was wondering how that so-called "coilgun" works, I know what it does but I was wondering how it works under-the-hood and eventually how to make a basic one ? Also, how much energy would be required ?</p>
| How does a "coilgun" work? | 2011-01-08T16:18:29.437 |
8747 | |high-voltage| | <ol>
<li>The problem with MOTs is the voltage is too low to make a sparkgap work reliably. A pair is just-about doable but still not ideal. A neon-sign transformer is an easier and safer transformer for a first-time coil. </li>
<li>Insulation and /or spacing </li>
<li>A ground with a low inductance path, and one that will not damage anything if it sees a HV discharge to it. i.e. not the ground pin on an AC outlet. Stake in the ground is ideal as long as the cable length isn't very long. </li>
<li>You won't need to do any measuraments on the HV side. You will know if there is HV present - corona hiss, ozone smell, arc-overs etc. </li>
</ol>
| <p>I want to have a go at building a Tesla Coil.</p>
<p>Has anybody here tried to build one before? How much do all the parts cost? Is it possible to make a small scale one? When can I get the plans, and what equipment/tools do I need?</p>
<p><strong>UPDATE</strong> To make this question a little more specific... </p>
<p>There are a few parts of the general design of a Telsa coil that I'm unsure about.</p>
<ol>
<li><p>The HV transformer - I've seen that some plans say you can use a microwave oven transformer for this, and other plans say that you need to stack them by wiring the primarys in parallel and secondarys in series, but then you can get insulation breakdown. Is a MOT a good choice? If it's not good to use an MOT, then what?</p></li>
<li><p>The tank cap - the general idea is to get a load of lower voltage caps and solder strings of them in series to get the voltage rating you need, then parallel the strings together to get the capacitance you need... but how do you stop it arcing across the leads?</p></li>
<li><p>Whats an RF ground? Does it mean drive a stake into the ground and attach one side of the secondary to that?</p></li>
<li><p>Finally, nearly every circuit I build fails to work the first time for one reason or another, and I use my meter and scope to work out whats wrong... How can I safely test parts of the circuit without being zapped with 20KV?</p></li>
</ol>
| Building a Tesla Coil | 2011-01-08T17:12:46.650 |
8754 | |thermistor| | <p>NTCs are non-linear and you'll see rather nasty formulas expressing the relationship temperature-resistance.<br>
Adding a pair of ordinary resistors you can linearize their behavior so that this relationship is approximated by a simple linear equation of the form \$y=ax+b\$. The following example is from <a href="https://en.tdk.eu/download/531110/a3be527165c9dd17abca4970f507014f/pdf-applicationnotes.pdf" rel="nofollow noreferrer">this Epcos appnote</a>. </p>
<p><img src="https://i.stack.imgur.com/7TkEf.png" alt="enter image description here"> </p>
<p><img src="https://i.stack.imgur.com/r7lXX.png" alt="enter image description here"> </p>
<p>The curve is virtually straight from 0°C to 60°C, which is sufficient for many applications.</p>
<p>In <a href="https://electronics.stackexchange.com/a/35548/2064">this answer</a> I show how in some cases you can get an almost perfect (15 ppm) linear curve over a limited domain with just a series resistor.</p>
<p><strong>edit</strong><br>
If you don't have the money for a resistor you'll either have to use the Steinhart-Hart equation Nick and Vicatcu refer to, or use a lookup table and interpolation. Both have the disadvantage that they need more memory: Steinhart-Hart contains a logarithm, for which you'll need a floating-point library (I assume your microcontroller doesn't have a floating-point ALU). The lookup table needs some memory as well, and may not give you a better precision than the linearized function if you have to interpolate that.</p>
| <p>I have a <a href="http://extra-parts.com/datasheets/TTC.pdf">TTC103</a> NTC thermistor. It has zero-power resistance of 10 kΩ at 25°C and B25/50 value of 4050. How do I use it to measure temperature?</p>
| How to measure temperature using a NTC thermistor? | 2011-01-08T19:13:43.880 |
8755 | |oscilloscope| | <p>A great place to learn about this would be from some old scope service manuals. The manuals for older models usually have complete schematics and explanation of the operating principle of the circuit.</p>
<p>For example, you can download the tek 2232 <a href="http://www.tek.com/node/830995-manual/2232" rel="nofollow">service manual</a> from the tek website.</p>
| <p>I am trying to design an oscilloscope/BNC input circuit for a side project and to learn more about filters.</p>
<p>The requirements are:</p>
<ul>
<li>150-200 MHz -3dB bandwidth</li>
<li>1 megohm impedance</li>
<li>50 ohm termination option (I can omit this if it causes problems.)</li>
<li>Can be switched between 2x and 20x attenuation</li>
<li>Measures up to 80Vpk (160Vp-p), tolerates up to 400Vpk (800Vp-p) (5Vpk on 50 ohm mode.)</li>
</ul>
<p>I designed a neat circuit that allowed switching between 2x and 20x attenuation while keeping 1 Mohm (or thereabouts) attenuation, as below:</p>
<pre><code> 499k 442k
( Input ) -----/\/\/---+---/\/\/---+----- To JFET input buffer
| |
/ /
499k \ \ 49.9k
/ /
| |
+---+ +---+
| |
\ relay to switch
| attenuation 2x/20x
---
-
</code></pre>
<p>(All resistors 1%.)</p>
<p>However, then I learned oscilloscopes have input capacitance, and I'm not sure how to add it. Also, if I want the input to tolerate 400Vp-p swing but on the wrong input range (2x attenuation leaving 200Vp-p to damage the inputs of the JFETs), I couldn't use diodes as the lowest capacitance I found was 0.13pF for an RF diode, which would limit me to about 612kHz for two diodes (one to each rail, reverse biased.)</p>
| Oscilloscope input circuit | 2011-01-08T19:32:38.783 |
8764 | |level-shifting| | <p>If you have -2.5V available, replace the two resistors with a single resistor to -2.5V.</p>
<p><img src="https://i.stack.imgur.com/en4e4.jpg" alt="alt text"></p>
| <p>What's the simplest way at low speeds (sub 100 Hz) to shift 0-5V to ±2.5V? I was thinking of using a comparator or op-amp, but there must be a simpler / cheaper way. I wanted to avoid a dedicated chip, unless it is cheaper than a discrete solution. Any ideas?</p>
| Shift 0-5V logic to ±2.5V logic | 2011-01-08T22:04:14.437 |
8767 | |project-management| | <p>For Firmware part I use git to manage versioning, and use git information in naming output hex file and as hard-coded variables also inside the code to show for users in startup messages though the debugging console. I wrote a blog post about it "<a href="https://atadiat.com/en/e-how-to-use-git-to-manage-firmware-versions/" rel="nofollow noreferrer">How to Use GIT to Manage Firmware Versions</a>"</p>
| <p>What are some of the good versioning systems for hardware projects? Is there equivalents of Google Code, CVS and SVN? Are such version control systems suitable for hardware projects involving PCB files, schematics..(even firmware code)?</p>
| Version control systems for hardware projects? | 2011-01-08T23:07:22.487 |
8781 | |microcontroller| | <p>"What are some things that novices miss?"</p>
<ul>
<li>First check your hardware. Find a <code>blink-a-led.hex</code> file that is known to work and verify that your hardware works. (I have some on my website, Google is your friend)</li>
<li>You have disabled the watchdog, that is a good start, but there are some more fuses settings that are need, especially the oscillator (XP, HS, internal, etc).</li>
<li>Configure the relevant pins as digital pins (check the A/D and comparator modules)</li>
<li>Set the pin direction (TRIS, you did so)</li>
<li>Avoid the Read-Modify-Write (RMW) curse (write the whole PORT or use shadow or use LATx)</li>
</ul>
| <p>I wrote a program to turn on LEDs on PORTB. The programmer erased, programmed, verified, so far so good. But then nothing happened. No lights. My programmer is a MPLAB Compatible Mini USB PIC Programmer.</p>
<p>What are some things that novices miss?</p>
<p>Below is my code:</p>
<pre><code>#include <p18f4550.h>
#pragma config WDT = OFF
void delay (void)
{
unsigned int i;
for (i = 0; i < 65535 ; i++) ;
}
void main (void)
{
TRISB = 0;
while (1)
{
PORTB = 0;
delay ();
PORTB = 0xFF;
delay ();
}
}
</code></pre>
| PICs for beginners using MPLAB Compatible Mini USB PIC Programmer | 2011-01-09T05:15:18.303 |
8786 | |sensor|atmega|smoke-sensor| | <p>Microchip make the required ICs.</p>
<p><a href="http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=9032&mid=11&lang=en&pageId=79" rel="nofollow">For photo detection</a></p>
<p><a href="http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=9035&mid=11&lang=en&pageId=79" rel="nofollow">For ionisation detection</a></p>
| <p>As the title says, I am looking for a smoke detection sensor. Took a look from SparkFun to Mouser and did not find anything. Is there a part you would recommend? I would prefer something that interfaces with the ATMEGA168/ATMEGA328 via a single wire or two wire interface. Would prefer to avoid a SPI or Serial interface as my circuit already utilizes those pins.</p>
<p>Bumped into a few sensors on Ebay but they were $15+. Is this normal? Is there a cheaper alternative that works great? Should I just buy a cheap smoke alarm and extract the sensor that way?</p>
<p>Thanks in advance for your help.</p>
| Looking for an inexpensive Smoke Detection Sensor | 2011-01-09T07:26:47.737 |
8791 | |capacitor|markings| | <p>The <code>W</code> is for <code>Working</code>; <code>WV</code> = Working Voltage</p>
| <p>I have a capacitor which is marked with "1200uF200wv". What does the "w" mean?</p>
| Need help deciphering markings on an electrolytic capacitor | 2011-01-09T11:02:43.290 |
8793 | |pwm|dc-motor|current-measurement| | <p>Average current may well be half (not always), but instantaneous current could also be (not always) 100%. </p>
<p>I had some 3V motors I was PWMing from a 12V supply a couple of years back. PWM'ing them worked well in staying within the RPM range of those motors, but the instantaneous voltage/current wore out the brushes pretty quickly.</p>
| <p>I have a DC motor that is controlled by a PWM output on an Ardiono and I want to know if I can safely assume that by setting the output to 50% duty cycle, the current in the motor will be 50 % as well
The output is connected to the base on an BC338 transistor through a 1K resistor that I use as a driver.</p>
| Will PWM on 50% duty cycle cut the current in a DC motor in half | 2011-01-09T11:36:09.530 |
8794 | |capacitor|electrolytic-capacitor| | <p>I have got away with electrolytic caps that have been stored for up to 20 years. The storage would have been at room temp . Only reputable brands have been saved and only large power type caps have been saved for cost reasons , by large I mean thousands of microfarads . I never saved small eltec caps because they are cheap and they are supposed to dry out fast and I avoid electros in all designs for reliability reasons . The large saved electros ran fine in prototypes for audio power and energy storage . In my experience its ripple current that kills them not storage . </p>
| <p>Do electrolytic capacitors have a limited shelf life? I would like to know for both aluminium and tantalum.</p>
| Do electrolytic capacitors have a limited shelf life? | 2011-01-09T12:02:08.913 |
8798 | |protection|automotive|tvs| | <p>Here is how you can protect against an automotive load dump</p>
<p><a href="https://www.analog.com/media/en/technical-documentation/data-sheets/LT4356-1-4356-2.pdf" rel="nofollow noreferrer">LT4356 "Surge stopper" data sheet</a></p>
<p>They say</p>
<blockquote>
<p>The LT®4356 surge stopper protects loads from high voltage
transients. It regulates the output during an overvoltage
event, such as load dump in automobiles, by controlling
the gate of an external N-channel MOSFET. The output is
limited to a safe value thereby allowing the loads to continue functioning. The LT4356 also monitors the voltage
drop between the VCC and SNS pins to protect against
overcurrent faults. An internal amplifier limits the current
sense voltage to 50mV. In either fault condition, a timer
is started inversely proportional to MOSFET stress. If the
timer expires, the FLT pin pulls low to warn of an impending power down. If the condition persists, the MOSFET is
turned off. After a cool down period, the GATE pin pulls
up turning on the MOSFET again.</p>
</blockquote>
<p><a href="https://i.stack.imgur.com/GHZbZ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GHZbZ.png" alt="enter image description here" /></a></p>
<p><a href="https://www.analog.com/en/products/lt4356-1.html" rel="nofollow noreferrer">https://www.analog.com/en/products/lt4356-1.html</a></p>
| <p>A <strong>load dump</strong> occurs when the load to which a generator is delivering current is abruptly disconnected. In automotive electronics, this applies to disconnecting a battery while it is being charged by the alternator. It is apparently well-described in <a href="http://standards.sae.org/j1113/11_200706/" rel="nofollow noreferrer">this $65 SAE document</a>; <a href="http://en.wikipedia.org/wiki/Load_dump" rel="nofollow noreferrer">Wikipedia claims</a> it can be <em>"as high as 120 V and may take up to 400 ms to decay"</em>. <a href="http://www.radiocad.com/_downloads/LoadDumpPaper-final.pdf?PHPSESSID=hfh147l" rel="nofollow noreferrer">This document</a> claims a 12V system dump can be as high as 87V and 400ms long:</p>
<blockquote>
<pre><code> 12V system 24V system
Us 65V to 87V 123V to 174V // maximum voltage
Ri 0.5Ω to 4Ω 1Ω to 8Ω // source resistance
td 40ms to 400ms 100ms to 350ms // pulse length
tr 10ms?? 5ms?? // rise time
</code></pre>
</blockquote>
<p>The last linked document also has a table listing TVS (Transient Voltage Suppressor) energy absorption, as follows:</p>
<blockquote>
<p><strong>Table 2 - Energy [J] absorbed (V<sub>clamp</sub>=45V)</strong></p>
<pre><code>td [ms] source resistance [Ω]
0.5 1 1.5 2 2.5 3 3.5 4
50 18.57 9.62 6.26 4.50 3.41 2.68 2.17 1.80
100 37.15 19.23 12.51 8.99 6.83 5.36 4.34 3.59
150 55.72 28.85 18.77 13.49 10.24 8.04 6.51 5.39
200 74.30 38.46 25.02 17.98 13.65 10.72 8.68 7.18
250 92.87 48.08 31.28 22.48 17.07 13.40 10.85 8.98
300 111.44 57.69 37.53 26.98 20.48 16.08 13.02 10.77
350 130.02 67.31 43.79 31.47 23.89 18.76 15.19 12.57
400 148.59 76.92 50.05 35.97 27.31 21.44 17.37 14.3
</code></pre>
</blockquote>
<p>Now, I want to clamp much lower than 45V (say 20V), and would like to recalculate these values. The author writes:</p>
<blockquote>
<ul>
<li>Calculated using the method given in <a href="http://xenona.com/xenonaupl/AHDPO/EMC/ISO/ISO_7637-2_2004.pdf" rel="nofollow noreferrer">Annex E.1.1.(e)</a>
where R<sub>i</sub>=R<sub>L</sub> (for maximum power transfer).</li>
</ul>
</blockquote>
<p>This reveals the formula:</p>
<blockquote>
<p>W<sub>e</sub> = (U<sub>s</sub>)<sup>2</sup> <sub><sup>x</sup></sub> t<sub>d</sub> / R<sub>i</sub> / 4.6</p>
</blockquote>
<p>... And updates the table as follows:</p>
<p><strong>Energy [J] absorbed (V<sub>clamp</sub>=20V)</strong></p>
<blockquote>
<pre><code>td [ms] source resistance [Ω]
0.5 1 1.5 2 2.5 3 3.5 4
50 97.59 48.79 32.53 24.40 19.52 16.26 13.94 12.20
100 195.17 97.59 65.06 48.79 39.03 32.53 27.88 24.40
150 292.76 146.38 97.59 73.19 58.55 48.79 41.82 36.60
200 390.35 195.17 130.12 97.59 78.07 65.06 55.76 48.79
250 487.93 243.97 162.64 121.98 97.59 81.32 69.70 60.99
300 585.52 292.76 195.17 146.38 117.10 97.59 83.65 73.19
350 683.11 341.55 227.70 170.78 136.62 113.85 97.59 85.39
400 780.70 390.35 260.23 195.17 156.14 130.12 111.53 97.59
</code></pre>
</blockquote>
<p>This gives a maximum value of 781J. Did I do this correctly? My TVS system must absorb up to ~800J, passing nearly 30A? It seems like a heck of a lot, though it will be for up to 6 parallel semi truck batteries (~100AH each) in addition to its 130A+ alternator. (Could the source resistance be even lower than 0.5Ω?) <strong>What combination of TVS elements can effectively pass 800J without violating its clamping voltage by much, and what makes it more effective than other solutions?</strong></p>
<p><sub>I am protecting low-voltage digital and analog circuitry, which also have their own power filtering.</sub></p>
| How do I protect against an automotive load dump? | 2011-01-09T13:21:24.533 |
8808 | |arduino|rfid| | <p>What about using the difference between the signals from two antennas? </p>
<p>In theory, if two antennas are <em>exactly</em> the same distance from the target, then the two signals should cancel each other out if subtracted. If they are slightly off, then they would be slightly out of phase, and they wouldn't cancel. </p>
<p>You could only use this technique to find the angle to the target. You would have to rotate the antennas to actually read the RFID (because their would be no signal when you were pointing directly at it. </p>
<p>(This technique is used in Ham Radio circles as a poor man's way to find people who interfere with radio repeaters so they can be reported to the FCC.)</p>
| <p>I have been using two <a href="http://www.loc8tor.com/Store/product/Loc8tor-Lite,154,110.aspx" rel="nofollow">Loc8tor</a> devices (an active, highly directional RFID consumer device) on a personal robot to try to locate an RFID tag.</p>
<p>While the Loc8tor has served its purpose of showing an active, directional RFID sensor with high resolution can be used for locating an RFID tag, the Loc8tor itself is not very hacker friendly. I am looking for an alternative reader and tag that can be integrated into my robot.</p>
<p>Ideally, it would meet the following specifications:</p>
<ul>
<li>Each reader would be less than $100, cheaper is definitely better</li>
<li>The reader should be around the size of a credit card to a dollar bill</li>
<li>The tag will be placed in ranges of 0.5 to 3 meters from the reader</li>
<li>The reader should run on some voltage less than 5v, ideally 3.3v or less</li>
<li>The higher the resolution of the reader, the better. Say 3 cm resolution at a 1 meter distance.</li>
<li>The (RSSI?) value from the sensor is easily accessible. Meaning I could wire that into an Arduino input pin and use the value.</li>
<li>Could buy in small (1 to 2) or large quantities (100+)</li>
</ul>
<p>These specifications are ideal, but not all are required (though the price is the most important). I should hopefully be able to list better specifications after I see what alternatives are out there.</p>
| Recommendations for an active, directional RFID sensor | 2011-01-09T19:32:04.407 |
8813 | |batteries|battery-charging| | <p>Not many issues charging big lead acids. Just hook the sucker up, turn it on, wait a while, test the battery for either loaded voltage or charge current (<0.3A), then disconnect or continue. Some issues I've had with standard sealed lead acids:</p>
<ol>
<li>Killing the battery separates the water from solute, which can then freeze. This happens if it dies in the cold. It's basically pooched at this point, but there's nothing stopping you from trying to thaw it out and charge it back up. Sometimes they still work!</li>
<li>Don't use the <em>boost</em> function, if there is one, to attempt to charge the battery more quickly than usual. This is strictly for boosting, and will reduce a battery's MTTF. Note that maximum charge current is 2.16A.</li>
<li>Charge it in a ventilated area. I know it's sealed, but I do this anyway, just in case!</li>
<li>Don't put it on a concrete floor -- stick a piece of cardboard or wood under it. This has been proven a myth a dozen times over, but I still do it to keep Murphy at bay.</li>
<li>Don't use too large a maintenance charge. The battery datasheet states 13.5V-13.8V float voltage.</li>
</ol>
<p>Why did you get a manual charger, anyway? I'd definitely screw that up within a season.</p>
| <p>What are the best practices for recharging a 12V lead acid battery with a manual recharger.</p>
<p>I have a 12V lead acid battery (7.2AH/20HR <a href="http://www.mkbattery.com/images/ES7-12.pdf" rel="nofollow noreferrer">MK ES7-12</a> (PDF)). I've read the advice here on <a href="https://electronics.stackexchange.com/questions/5522/battery-level-how-to-check">how to check the battery level</a> (I have ~12.2 V under no stress, and when powering the system it still currently reads ~12.2 V on the DMM).</p>
<p>When it starts to run low, I'd like to know how best to recharge the battery. I have a manual battery charger (<a href="http://www.batterychargers.com/ProductDetail.aspx?ProductName=94026702" rel="nofollow noreferrer">Schumacher MC-1</a>). I realize the <strong>manual</strong> part means that I cannot just plug the battery in and walk away. How best to monitor the charge? With what frequency? What likely problems should I be aware of?</p>
| How to recharge a battery with a manual battery charger | 2011-01-09T20:26:25.867 |
8822 | |video|hd| | <p>The Spartan 6 FPGA certainly can drive HDMI/DVI signals directly, demonstrated in the <a href="http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,400,836&Prod=ATLYS" rel="nofollow">Atlys</a> board. I've personally driven 1920x1200 VGA from a Spartan 3A starter kit, but the signal wasn't very clean then. You're looking at very high bandwidth signals, however, so the boards must be designed carefully. </p>
<p>If this is for a single hobbyist build, you might be better off using a premade graphics card with its own framebuffer, for instance a USB one. DisplayLink comes to mind. </p>
| <p>What solutions are there, preferably single chip solutions, for getting HD video over DVI/HDMI?</p>
<p>My googling is not giving me much, only about the Blackfin chip from Analog.</p>
<p>I know about the Propellor from Parallax and that it can give SD video out easily, and how FPGA's can do it too, but other than those three I do not know of any other single chip solutions that can give me HD video over DVI/HDMI.</p>
| What solutions are there for getting HD video? | 2011-01-10T05:06:59.440 |
8834 | |arduino|infrared|safety| | <p>I just wonder - if something like this was remotely feasible, wouldn't it have been made by someone and commercialized already? I'm in the opinion that (with the level of technology available today) this is sadly still science fiction stuff, or else requires a disproportionate amount of money.</p>
<p><strong>Added:</strong> From the comments, the idea about am IR thermometer might be worth looking into. If you could get one that can provide realtime measurements (I suppose 4 per second might be needed for a fair operation), you could then attach some optics to get a bigger FoV and get a sort of "measuring gun" that you could point to suspicions places. I think...</p>
<p>Getting such a thermometer might be expensive if at all possible, but maybe you could dismantle some cheap ones and hack them... I don't know. :P</p>
| <p>To avoid public transport and the car, I decided to go to work on foot everyday but I have to pass a small, but dark (in the evening) and scaring wood.</p>
<p>Even if I use flashlights, I'd like to have a kind a "life scanner", like the one used by Predator vs Alien to detect alive (hot/moving) creatures.</p>
<p>Beside the sci fiction side of the question, I was wondering if PIR can be used while moving, so that I can mount on my backpack and control it with an arduino while I'm walking.</p>
<p>If it's not possible, do you have any other ideas?</p>
<p>What I need it's just a way to know if there are alive, enough big to be scaring, creatures in the wilderness around me (for not alive creatures we will discuss later).</p>
<p><strong>Edit</strong></p>
<p>Has pointed out, a good alternative can be an Infrared camera, there are some good tutorial and Howtos in the Net.</p>
<p>I don't need a detailed image, but just to know if and (more or less) where there are alive creatures (hot blood animals?), as an image sometime is better then 1000 words:</p>
<p><img src="https://i.stack.imgur.com/JzqoH.png" alt="Alien Radar"></p>
<p><strong>Edit 2</strong></p>
<p>As it has been pointed out, is this feasible or it's just sci-fiction?</p>
<p>Thermographic cameras exists and are widely used: <a href="http://en.wikipedia.org/wiki/Thermographic_camera" rel="nofollow noreferrer">http://en.wikipedia.org/wiki/Thermographic_camera</a></p>
<p>I found a solution here <a href="http://www.embedds.com/interactive-diy-infrared-and-ultrasonic-scanner/" rel="nofollow noreferrer">http://www.embedds.com/interactive-diy-infrared-and-ultrasonic-scanner/</a> , but the range is really small (21 inches = 0.5 meters)</p>
<p><strong>Edit 3</strong></p>
<p>This is another way to create a "radar" starting from a home made thermographic camera.</p>
<p><a href="http://hackaday.com/2009/07/01/poor-mans-thermographic-camera/" rel="nofollow noreferrer">http://hackaday.com/2009/07/01/poor-mans-thermographic-camera/</a></p>
| Moving PIR sensor (or IR camera), aka Predator like alien scanner | 2011-01-10T13:07:05.590 |
8842 | |power|capacitor|decoupling-capacitor|interference| | <p>The fridge may be dumping noise on your power line, but the real problem is the amplifier driving your speakers. Either the amp itself has bad line filtering, or your setup allows noise to get into its audio inputs.</p>
<p>Disconnect the audio input from the amp and see if the fridge can still cause clicks in the speakers. If so, then the amp has a crappy power supply circuit and needs help in the form of a line filter.</p>
<p>If the noise goes away when the input to the amp has been disconnected, then the noise is already on the audio signal by the time it gets to the amp. There are two likely causes to this, bad shielding and bad grounding. If you are using regular off the shelf shielded audio cable and it is properly connected at each end, then shielding is probably not the cause. The most likely cause is then a ground loop. Is the amp plugged into the same outlet as whatever equipment is producing the line level audio signals going into it? If not, then you have a ground loop. The fridge is probably causing a significant ground bounce when it turns on and off, and this is getting into your audio signal due to the different ground points. Plug all the audio equipment into the same outlet strip plugged into a single outlet in the house. Adding a line filter to that wouldn't be a bad idea.</p>
<p>You can try to reduce the noise the fridge is making, but that's just one noise source of many that the audio system needs to be immune to anyway. Crap on the power line happens, regularly. The audio system should be set up to deal with it properly.</p>
| <p>My fridge is sending bad clacks to my loudspeakers when it turns on/off, I fear for the tweeters. I'd add a snubber/suppressor to the compressor but my notions about RC filters from school are 15 years old and I have no idea how to dimension it.</p>
<p>It's an old european fridge, so mains are 220V 50Hz, and the compressor mentions two other values In=0.8 and Icc=6.3, which I suppose are nominal and startup current. Do I need to compute the motor inductance? What condensator/resistor values to pick? Is an RC snubber even the correct fix?</p>
<p>How to estimate the RC values for snubbing an A/C motor?</p>
<hr>
<p>Trying another approach. I've found a some usual R/C values for suppressors. For instance <a href="http://www.redlion.net/Products/Groups/NoiseSuppression/SNUB/Docs/12027.pdf" rel="nofollow">this one</a> is 47ohm / 0.1µF, giving 33kHz of cutoff frequency... but the datasheet says up to 62Hz? Why is there 3 orders of magnitude difference ?</p>
<hr>
<p>EDIT: in the end I added a capacitor to the fridge and that resolved the problems. That was quite long ago so I don't remember the exact value, but if anyone wants it just bump me…</p>
| Sizing an RC snubber | 2011-01-10T16:45:41.867 |
8846 | |imageprocessing| | <p>There are a few steps here that need to be taken.</p>
<ol>
<li><p>Identify the area you care about. This means either positioning the camera to only include the white board or to do some cropping on your image. If you use black and white images, you can think of them as a 3d array. For cropping you can just say that you will start at column 15 and end at column 506 in order to crop left and right.</p></li>
<li><p>Now that you have identified the area, you will probably need to do some edge detection. In the simplest sense, edge detection is looking for drastic changes in one pixel to the next. There are ways of doing this "pretty", but for someone that wants to keep it simple you could step through each row of each pixel looking for a jump in value. You may even have to compare to several previous versions depending on how sharp your image is. Create a 3d array that is the same size as your original image. Whenever you see a jump, place some value in your new array. This value could be boolean for simplistic sake or it could be some range that represents how big of jump there was.</p></li>
<li><p>Now that you have an array that tells you where there are edges it is time to figure out what shape it is. There is a chance you will need to do some filtering on your data before this, but in a perfect world your previous step should just give you whatever you need to know. This is probably the most difficult part. You will need to find someway to define what each object is in a way that a computer can understand. An example of this would be to scan each row, once you find a row that has an edge on it then look at the next row to see if the spacing of the edges is growing. Keep stepping through until you have no more edge and see if it looks like it started out small, then bigger, then smaller.</p></li>
</ol>
| <p>First of all, I am a total newbie to image processing. I have a project idea, part of which will involve doing the following:</p>
<p>I have a white board and a camera (a normal webcam by z-star). I will draw a shape on the white board. The camera will capture the video and process it to identify the shape I have drawn. To keep it simple, the shapes that can be identified using by the program will be limited.</p>
<p>I want to execute this idea and will learn anything that is required to make it happen. I want to get started in image processing, but just enough so I can execute this for now. Will incrementally study more. Can you give me any pointers on where to get started?</p>
| I want to learn enough image and video processing to execute a project idea, pointers? | 2011-01-10T18:00:28.747 |
8856 | |vlsi| | <p>There isn't really a "worst case" - manufacturing IC's is a statistical process, there will be some (small) percentage of transistors that are a very long way from typical speed (imagine a statistical distribution curve drawn here). The distribution of speeds for the two types of transistors in CMOS (NMOS and PMOS) don't correlate well.</p>
<p>Thus, they pick those 4 corners: Fast/Fast, Slow/Slow, Fast/Slow, Slow/Fast out of their two transistor speed yield curves. </p>
<p>The further out from typical they choose to make the corners, the higher their yield, but the more difficult it is to design. If the corners are too far apart, design for operation at the 4 corners takes too much development time and can increase the die size. Increasing the die size will decrease yield.</p>
<p>The four corners often form more of a parallelogram than a rectangle. If both types of transistors, across one whole die, are all very fast, the part will probably work, maybe well beyond the rated speed, and same for both transistors getting slower - the part will work, but at a very slow speed. The difficult corners are the fast/slow and slow/fast.</p>
<p>The design is indeed fully simulated at typical/typical, and the four corners. Monte Carlo simulation is used to check some of the intermediate combinations. </p>
<p>To increase yield, they can sort the die into bins after manufacture and thus sell the slow/slow parts that would otherwise be thrown away, and sell the fast/fast parts for a premium.</p>
<p>And yes, some manufacturers will use fuses to restrict a part to a certain speed grade. Because manufacturing yield curves and market demand being uncorrelated functions, sometimes they have to down-grade parts.</p>
| <p>During manufacture, integrated circuits are tested at varying frequencies and temperatures to categorise them into speed grades. However, why don't all ICs come out the same and work the same? They all come from the same photolithographic mask, right? Am I missing something?</p>
| Why do chips not always "meet the grade"? | 2011-01-10T23:18:44.550 |
8857 | |current-measurement|high-voltage| | <p>While a wall adapter <em>is</em> usually isolated, it likely isn't rated to 1kV. A simple solution would be to find a DMM with logging capability and CAT III/IV 1kV isolated external power source or long battery life. Here are some candidates:</p>
<ul>
<li><a href="http://www.home.agilent.com/agilent/product.jspx?nid=-34618.956187.00&cc=CA&lc=eng" rel="nofollow">Agilent U1271A</a>: <a href="http://cp.literature.agilent.com/litweb/pdf/5990-6425EN.pdf" rel="nofollow">IR USB connectivity; 300 hour battery life</a></li>
<li><a href="http://www.gossenmetrawatt.com/resources/marcom/prospekte/207_p_gb.pdf" rel="nofollow">Gossen Metrawatt Metrahit X-Tra</a>: <em>"bidirectional IR interface"</em>; <a href="http://www.gossenmetrawatt.com/resources/tt/hit_xtra_pro_base/db_gb.pdf" rel="nofollow">200 hour battery life</a></li>
<li><a href="http://www.fluke.com/Fluke/usen/Digital-Multimeters/Fluke-289.htm?PID=56061" rel="nofollow">Fluke 289</a>/<a href="http://www.fluke.com/Fluke/usen/Digital-Multimeters/Fluke-287.htm?PID=56058" rel="nofollow">287</a>: <em>"Isolated Optical Interface"</em>; 200 hours battery life</li>
</ul>
<p>Another option is to use a simple micro with an ADC, float the whole circuit at chassis voltage, then use proper isolation techniques (more than just optoisolation -- if you're not sure I suggest another question) to communicate with a PC over your preferred serial connection (<code>UART -> opto -> RS232 -> USB -> opto -> PC</code>, with cable shield voltage measurement and warning, would be my choice). Note that this means you can't touch anything on the floating (hot chassis) side of the widget. This way you can eliminate the power supply isolation worries by just using a battery, and still run it easily for 6 months to a year without replacing it, following thought on power consumption and sleep modes (ie: <a href="http://focus.ti.com/mcu/docs/mcuorphan.tsp?contentId=61835&DCMP=MSP430&HQS=Other+OT+ulp" rel="nofollow">MSP430</a>). Also note that a sputtering machine generates electrical noise, so you may need to use RS485 with error detection/correction algorithms.</p>
| <p>I asked this question a few days ago, but I don't think I was clear enough, so I'm going to try again.</p>
<p>Here is a rough diagram of my sputtering system:<br/>
<img src="https://i.stack.imgur.com/RDocL.png" alt="Chamber electrical sketch"></p>
<p>Basically, a DC voltage supply holds the substrate at a large negative voltage (~-1000V) relative to the chamber chassis (Vs) and a DC current supply pushes a large current (~120A) through a plasma into the chassis and substrate (It). Only a small fraction of the total plasma current actually goes through the substrate (~2A out of the total 120A). Most of the current passes directly into the chassis. So, to clarify, there are two power supplies. The voltage supply is providing -1000V to the substrate through which ~2A are passing. The current supply is providing 120A through the target/plasma (at about 20V).</p>
<p>The resistor between the chassis and ground indicates that the chassis is poorly grounded. Furthermore, the resistor should be taken to be variable as the current flow through the stainless steel chassis fluctuates, meaning that the voltage of the chassis relative to earth ground fluctuate significantly over time.</p>
<p>Here is the problem: I want to measure the voltage between the substrate and a particular spot on the chassis without measuring any of the voltage due to the large current flowing through the chassis. The measurement doesn't have to be very precise, it's only used as a check (i.e., +/- 5V is fine).</p>
<p>Right now, this is accomplished using a Fluke battery powered DMM. Since it's battery powered, it makes a real floating differential measurement. What I'd like to do is replace this handheld meter with a non-battery powered solution that could also be hooked to a computer for data-logging purposes. I thought maybe using a 110V AC to 9V DC wall adapter that could hook into the Fluke's battery terminals might be an idea, but I guess there is no electrical isolation and all the current in the chassis would get dumped through the Fluke to the mains ground.</p>
<p>Can anyone suggest an approach? I'm pretty ignorant about this stuff. I've tried reading up on it but can't figure out anything that might work. If I can clarify in any way, I'd be happy to. Any suggestions (including "you're stupid. this can never work") would be appreciated!</p>
<p>Thanks a lot in advance,
Brian</p>
| High voltage, high common mode current measurement. Any suggestions? | 2011-01-10T23:40:22.393 |
8858 | |rf|emc|spectrum-analyzer| | <p>If my time was worth nothing, or I was doing this as my own fun project, I would design and build my own rf power meter. There are schematics available for this in AARL back-issues.</p>
<p>If this is for work, I would go and rent the tools.</p>
<p>If this isn't for work, and you don't know very much about RF, and you don't have a lot of money - go make friends with amateur ham radio people in your area and butter them up.</p>
| <p>I need to test that my project will not interfere with radios in the 27 - 72 MHz band.</p>
<p>I can't afford a spectrum analyser. Nor can I afford to buy all tx/rx pairs in between 27 and 72 MHz (27, 35, 47, 72...) My budget is a maximum of £100.</p>
<p>I was thinking of modifying a radio to have a much larger tuning range, but it would need to be sensitive to very low EMI emissions. I've found AM radios are slightly sensitive to noise but probably not enough.</p>
<p>Does anyone have any suggestions?</p>
| What's the cheapest way to do basic EMI testing? | 2011-01-10T23:58:19.133 |
8863 | |simulation|transmission-line| | <p>If I wanted to do it for real use a standard telephone modem and a line voltage generator, if needed. For simulation @krapht is right. Use STP or coax.</p>
| <p>I need to be able to simulate communications with a sensor device over a large length of wire (0-10km). This is for quite low-speed comms (10khz max, usually 1-2khz though). This would be FSK... but at some point I may have to handle a low baud RS232-like signal as well.</p>
<p>Mostly, I'm looking for voltage drop and signal distortions. Delay doesn't matter much.</p>
<p>How would you go about it?</p>
<p>EDIT:</p>
<p>I've been able to determine the cable is indeed a (fairly nonstandard) type of coax. I now know resistance and capacitance per unit length, cross section geometry, and that the insulation resistance is high enough not to matter. It wasn't initially clear if the return line was a separate run or not.</p>
<p>This would be a test setup for multiple target devices. Most are FSK of various frequency choices under 10khz, some are ASK (you could almost use a standard UART after bandpass/filtering). All are riding on a high DC offset (comms over power).</p>
<p>In the past, I've seen people build a simple rotary switch that swaps in resistors, capacitors, and maybe inductors to simulate a given line length. Could that be good enough?</p>
<p>I'm currently trying to build a few simulations in LTspice.</p>
<p>EDIT 2:</p>
<p>Okay, if I go with just adding resistors, caps, and inductors... what does the model look like? The RLGC network below is assuming the grounds are at the same potential I believe (a safe assumption on PCBs w/ground planes). The return in this case is through the outer shell, and it's resistance is probably 3 times higher than the inner conductor. Does that change things significantly? Do I just add another resistor on the bottom rail, and split the capacitance on both sides of it?</p>
| Transmission line simulation (physical) | 2011-01-11T00:38:23.500 |
8874 | |serial|uart| | <p>Use <a href="http://www.termsys.demon.co.uk/vtansi.htm">VT100 escape codes</a> to control the cursor.</p>
<p>Eg.</p>
<pre><code>puts("\033[2J"); // clear screen
puts("\033[0;0H"); // set cursor to 0,0
puts("\033[10B"); // move cursor down 10 lines
puts("\033[5A"); // move cursor up 5 lines
</code></pre>
| <p>I think it is possible due to how I can run vi straight from my serial port looking via TeraTerm. There, I can edit some text, go to the next line, then come back and edit the first line! How do they do this?</p>
<p>What character over UART could I send through to go "up a line"?</p>
<p>EDIT: Apparently line feed works. "\f" to clear the screen. However, this only works for Hyperterminal on my machine and not Teraterm. Anyone know why?</p>
| Is it possible to send characters through serial to go up a line on the console window? | 2011-01-11T04:47:31.167 |
8885 | |arduino|range-detector| | <p>Check your input voltage supply to the sensor. I was powering the sensor from my Mega 2560 (5V) and could not get a clean signal. I am still using the 5V from the Mega 2560 but instead ran it through a simple ($1.99) voltage regulator from radio shack (quick run to a local store). This greatly cleaned the signal up. To clean it up further I ran the return signal through a low pass filter. I chose the frequency at 1/10 and sized the resistor and cap accordingly.</p>
| <p>I'm in the very early stages of trying to build a robot that wanders around and builds up a map of its environment. I'm using an Arduino and I currently have a Sharp <a href="http://www.sharpsma.com/webfm_send/1208" rel="nofollow">2Y0A21</a> IR range detector sat on top of a servo so it can take a 180 degree sweep in 10 degree increments.</p>
<p>The trouble is that the voltage readings back from the Sharp IR sensor aren't consistent. If I write an app that simple sends the value it reads from the sensor through the serial port and display it on my laptop, sitting the sensor pointing at an object, the values bounce around.</p>
<p>Watching the values, I can see that it tends to report one value more than the rest, so I wrote a SharpReader class that takes 20 samples and then returns the Mode of these values. This now means I get more consistent values, but not as good as I would like.</p>
<p>I have some code that performs the 180 degree scan and sends the angle and distance down the serial. I then have a python script that receives these values and draws what it sees on screen, ignoring any values at either end of the sensors range. So putting it in front of a box, it should draw a straight line on screen, but it doesn't - the line is crooked and not consistently crooked, which confirms to me that it's the readings that are off, not my code.</p>
<p>I have read in the datasheet that it is advisable to put a capacitor (can't remember the value offhand) in between the GND and PWR lines on the Sharp IR - I tried forcing the legs of the capacitor into the JST connector of the Sharp IR, but it made no difference. I'll try soldering it to the sensor and see if that makes any difference.</p>
<p>Can anyone recommend anything else to try, or am I just expecting too much from the Sharp IR?</p>
<p>I'm also considering buying a second servo and Sharp IR and running two at the same time like a pair of eyes, then trying to take an average of the two values to see if that increases the accuracy.</p>
<p>BTW, I'm a newbie to electronics, my background is in programming.</p>
| Can't get consistent readings from Sharp IR range detector | 2011-01-11T10:43:20.983 |
8889 | |soldering| | <p>That looks like a tip from a Radio Shack butane soldering iron. I have one just like that and it does tend to run VERY hot! Even with the adjustment at the lowest setting. The tip seems to have a fluffy fiberglass like substance in it which acts like a catalyst. But because the soldering iron runs so hot it tends to burn out the catalyst until there's nothing left. I've found that you can replace the burned out catalyst material with a very (very) small amount of fluffed up fiberglass insulation material. After replacing the catalyst you will need to let the tip flame for a few minutes before it starts to glow. But keep the heat turned down or you will burn out the fiberglass again.</p>
| <p>I've <a href="https://electronics.stackexchange.com/questions/5144/how-to-clean-my-soldering-iron-tip-or-how-to-determine-that-its-beyond-repair">read</a> the <a href="https://electronics.stackexchange.com/questions/4470/going-through-soldering-tips-quickly">other</a> posts on <a href="https://electronics.stackexchange.com/questions/216/soldering-iron-maintenance">iron cleaning</a> technique and I'm pretty sure I left it dirty often enough that <a href="https://electronics.stackexchange.com/questions/7718/why-does-solder-turn-dull-grey-on-my-iron-and-exhibit-poor-wetting">it's toast</a>, it seems the iron coating on the tip has flaked off completely; since I've got nothing to lose I'll attack it with a file in a second and see if I can get another small job out of it. $15 lesson learned.</p>
<p>The real question is why the plating up near the catalyst is flaking off and the whole tip is bending. Does this indicate I'm using too much heat? </p>
<p><img src="https://i.stack.imgur.com/obogg.jpg" width="400"></p>
| Is my butane soldering iron's tip dead? (pic) | 2011-01-11T14:09:04.387 |
8899 | |rf|fsk| | <p>The number '2' refers to the number of tones used to encode the signal. For example, 2-FSK is essentially sending binary data using two frequencies. One symbol (time slice) has the potential for two values only. <strong>2-FSK is usually what is meant by an unqualified mention of FSK</strong>.</p>
<p>It's possible to use more than two tones. These modulation schemes usually are called <a href="http://en.wikipedia.org/wiki/Multiple_frequency-shift_keying">MFSK</a> for Multiple Frequency Shift Keying. A common MFSK scheme in amateur radio is MFSK16, which uses 16 different frequencies to represent 4 binary bits in each symbol. By your notation, this would be 16-FSK.</p>
<p>The more frequencies that you use in a symbol, the more complicated your modulation/demodulation circuit. Typical MFSK applications in amateur radio require a computer sound card and CPU for signal processing. Analog circuitry can be developed somewhat easily for FSK using two band-pass filters.</p>
| <p>In the documentation for <a href="http://focus.ti.com/docs/prod/folders/print/cc1110f32.html" rel="noreferrer">a radio chip</a>, I keep seeing the term 2-FSK, which seems to be a modulation scheme.</p>
<p>My understanding is that in FSK, data is encoded by emitting a carrier wave on a number of different frequencies. Is this right? How does this differ to 2-FSK?</p>
| What is 2-FSK modulation? | 2011-01-11T17:46:40.470 |
8908 | |current-measurement| | <p>The working principle is simple, and it takes just three parts to do what the ZXCT1009 does:</p>
<p><img src="https://i.stack.imgur.com/KtGBR.png" alt="enter image description here"></p>
<p>The opamp will try to keep the voltage drops across \$R_{SENSE}\$ and the 100\$\Omega\$ equal by controlling the current through the 100\$\Omega\$ resistor. So if your \$R_{SENSE}\$ is 1\$\Omega\$ the collector current will be 1/100th of that, or 100\$\mu\$A if your microcontroller draws 10mA. If you place a 10k\$\Omega\$ resistor between emitter and ground you get 1V/10mA out.</p>
<p>Yes, a resistor + a transistor + an opamp is cheaper than the Zetex device. But you have to pay attention to the details. \$V_{SENSE+}\$ will be your battery voltage, also your opamp's power supply. At 5mA the input voltages will be 5mV below the power supply. Obviously that calls for a Rail-to-Rail opamp. But 5mV is <em>very</em> close, so you start digging in datasheets if the opamp can handle it. (Don't bother, the datasheet doesn't say.)<br>
Anyway, is it worth it? Not to me. The ZXCT1009 costs 1 dollar in 1's and is 1% accurate. It might be different if I would need 100k/year of them, but for just one? If you can't afford the dollar perhaps you've chosen the wrong hobby.</p>
| <p>I'm looking to measure current consumption of my microcontroller as an in-built feature of the final design. Should I buy and use high-side current monitors that are available on the market (e.g. <a href="http://www.diodes.com/datasheets/ZXCT1009.pdf" rel="nofollow">Zetex ZXCT1009</a>)? Or is it possible to build one out of discrete parts that's cheaper and better?</p>
<p>Device operating out of a lithium polymer battery, so 3.7V typical only. Drawing around 0 to 30mA.</p>
| Use a current monitor IC or roll my own? | 2011-01-11T22:29:41.777 |
8909 | |avr| | <p><a href="http://www.nongnu.org/avrdude/user-manual/avrdude_1.html" rel="nofollow">AVRDude</a> supports programming AVR microcontrollers via the STK500.</p>
<p>The STK500 appears to have many peripherals. You might want to look at projects like <a href="http://www.procyonengineering.com/embedded/avr/avrlib/docs/html/index.html/" rel="nofollow">avrlib</a>. Alternatively, you might choose to ignore the peripherals and focus on the basics.</p>
| <p>I have a Atmel STK500. And I can't get my head around what half of the board does. Does any one know of any good resources for learning about it. I have the following books: </p>
<p><img src="https://i.stack.imgur.com/RCbFD.jpg">
<img src="https://i.stack.imgur.com/UFoTi.jpg" width="250"></p>
<p>The primer book is good with the STK500 but only talks about the mega16(I think I maybe wrong on that don't have it to hand). But then stops after the first couple of pages and tells you how to only program the one microcontroller with it. Is there anything else I can look at to use my STK500 to its full potential? And configuring the jumpers as they confuse me being a novice. I would like to program other microcontrollers from atmel with it. </p>
| Good resources for learning about my STK500 | 2011-01-11T22:50:28.343 |
8915 | |capacitor|range-detector| | <p>See my answer to your previous question <a href="https://electronics.stackexchange.com/questions/8885">here</a>, specifically this image:<br>
<img src="https://i.stack.imgur.com/6y27R.jpg" alt="this image">. </p>
<p>You want the caps to be as close as possible to the components which are drawing current. The voltage varies due to to trace/wire inductance, so it doesn't help to locate the cap before this inductance. The caps absolutely must be on the sensor. You should already have output caps on your power board and decoupling caps near every IC on your 'processing board'. </p>
| <p>Following on from this <a href="https://electronics.stackexchange.com/questions/8885/cant-get-consistent-readings-from-sharp-ir">question</a>. Can I place the capacitor anywhere in the circuit before the IR Distance Sensor? In my project I have 2 PCBs: A power circuit and a Processing Circuit. In the Diagram below you see the two PCBs Power Board and Processing as well as the Sharp distance sensor. Following the diagram, can I place the capacitor on the power board or will it be ineffective by the time it reaches the sensor? I don't want to damage my expensive sensors. </p>
<pre><code>--------------- 12V ------------------
| |-------------------------| |
| Power board | 5V | Processing |
| |-------------------------| Board |
| | GND | |
|_____________|-------------------------|________________|
| | |
| | |
GND | Out | 5V |
| | |
------------------
| Sensor |
------------------
</code></pre>
| Where to put stabilising capacitor? | 2011-01-11T23:14:31.293 |
8924 | |attiny|shift-register| | <p>The following code works great. The latch signal is connected to <code>PB5</code>. The <code>SIG_PIN_CHANGE</code> handler does its work on both edges of the latch signal but it doesn't matter, and the last time I tried adding the check it did not work.</p>
<pre><code>#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/sleep.h>
ISR(SIG_PIN_CHANGE)
{
USIDR = PINA | (PIND & 0b01111100) | (PINB << 7);
USISR = (1 << USIOIF); // clear overflow bit, set counter to 0
USICR |= (1 << USIOIE); // enable overflow interrupt
}
ISR(SIG_USI_OVERFLOW)
{
USIDR = (PINB << 3) | 0x0f;
USISR |= (1 << USIOIF); // clear overflow bit
USICR &= (0xff ^ (1 << USIOIE)); // disable overflow interrupt
}
int main() {
USIDR = 0xff;
USICR = (1 << USIWM0) | (1 << USICS1); // 3-wire mode; external, positive edge.
DDRA = 0;
DDRD = 0;
DDRB = 1 << 6; // MISO
// Enable pullups
PORTA = 0x3;
PORTB = 0b11111;
PORTD = 0xfc;
// USIDR is shifted out MSB first.
// pin change interrupt for latch pin
PCMSK = (1 << 5);
GIMSK |= (1 << PCIE);
sei();
while (1) {
sleep_mode();
}
}
</code></pre>
| <p>I would like to use an ATtiny2313 to emulate a Super Nintendo controller because I have an ATtiny2313 but I do not have an input shift register and I don't feel like soldering wires onto an existing SNES controller board.</p>
<p>This application requires 12 inputs (bits 13-16 are always 1) and a latch, clock, and data out pin.</p>
<p>Do you have this code lying around? It can't be more than 20 instructions.</p>
| Does anyone have code to emulate a 16-bit input shift register with an ATtiny2313? | 2011-01-12T03:32:47.520 |
8929 | |arduino| | <p>I just used an arduino to drive a servo to 90degrees then back again, and mounted the servo so it would actuate the kettles switch, I also used one of those solar cell battery's for charging your phone so that power is always there
handy with an xbee to remotely control it</p>
| <p>First of I have no experience with electronics so I am not sure what I should be searching for to get this done. </p>
<p>All I have with me at the moment is a arduino and a few connectors and LED's. Is it possible to switch the kettle on/off using just these basics (i.e. I dont want to buy more stuff for now).</p>
<p>The kettle is the most basic kind , i.e. the ones that plug into a wall outlet and have a single switch to turn it on or off. Let me know if you need more info.</p>
| Switching a Kettle On/Off using a arduino | 2011-01-12T07:42:07.763 |
8940 | |microcontroller|capacitor|resistors|sound|inductor| | <p>it is not analog, but </p>
<ul>
<li><p>you can use R-2R Resistor ladder (acting as a simple DAC) on the outputs of a controller </p></li>
<li><p>or you can create a chain of counters addressing an E/EPROM in a loop, on Memory outputs again R-2R ladder. You can usee 2, 3 or more of the MSB address lines with switch to choose different sound</p></li>
</ul>
<p><img src="https://i.stack.imgur.com/uPznS.gif" alt="like this"></p>
| <p>I've been wanting to make a laser gun sound effect attachment for my son's bike. Currently, I'm using the electronics salvaged from his old laser gun toys. All of them seem to use electronics hidden under a black blob of resin or epoxy, which I assume is an ASIC?</p>
<p>I'd love to be able to make this more cheaply, and was wondering if there's any resource out there to show how to make something like this with analog components. I have an old fart machine that seems to use a combination of resistors, capacitors, and inductors to generate multiple sounds (i.e. no microcontroller), so I figure that it must be possible.</p>
<p>I only need one sound, but it would be great to be able to select from multiple, or somehow use a <a href="https://electronics.stackexchange.com/questions/2057/polyphonic-sounds-from-a-microcontroller">microcontroller + DAC</a> to do it, although the latter would increase the price.</p>
<p>EDIT -- <a href="http://www.web-tronics.com/gunbombsounds.html" rel="nofollow noreferrer">something like this</a>, but cheaper than $10 would be nice
EDIT -- also found <a href="http://circuitzoo.com/2010/05/24/electronics/simple-sound-effect-generator-circuit-diagram-using-ht2884" rel="nofollow noreferrer">this schematic</a> but it needs an IC called the HT2884</p>
| Plans / tutorial for sound effect generator using only analog components? | 2011-01-12T14:20:56.500 |
8946 | |audio|display| | <p>An ARM might be able to do a good job of estimating the energy in each frequency component, at least if one uses a little assembly language and is using a nice ARM variant (e.g. Cortex-M3 or ARM7-TDMI, rather than a Cortex-M0).</p>
<p>Assuming the original data and reference wave are 16 bits, and one has separate copies of the reference waveform for each frequency of interest (probably not too hard if there are only twelve of them) the inner loop might look something like:</p>
<pre>
; R0 - Data source pointer
; R1 - Reference wave pointer
; R2 - Data source end, plus one
; R3 - Reference wave end
; R4 - Reference wave length
; R5 - Reference wave cosine delta
; R8 - Sine total L
; R9 - Sine total H
; R10 - Cosine total L
; R11 - Cosine total H
lp:
ldrsh r6,[r0],#2 ; I forget the syntax for post-increment
ldrsh r7,[r2,r5] ; Fetch cosine reference
smlal r10,r11,r6,r7
ldrsh r7,[r2],#2
smlal r8,r9,r6,r7
; Repeat the above a few times if desired, if wave length will always be
; a multiple of the number of repetitions. Note that the reference wave
; may need to be extended a bit to accommodate this (it must be extended
; be a quarter-wavelength to accommodate the cosine term).
cmp r1,r3 ; Carry set if r1 has gotten as bit as r3
subcs r1,r4 ; If passed end of wave, wrap
cmp r0,r2 ; See if at end of wave
bcc lp
</pre>
<p>I think that inner loop would take about 20 cycles to process the sine and cosine terms for one same of one frequency. So for twelve frequencies, you'd have to spend 240 cycles of front-line processing. Even a 16MHz ARM should have no trouble handling that.</p>
| <p>I want to build a circuit that shows the real-time frequency components of an audio signal on a number of bar graphs of some sort. Currently, my plan is to build 12 band-pass op-amp filters, and then use a rectifier and RC circuit to create a DC envelope for each output, and then use that signal to drive a LED bargraph or something similar.</p>
<p>The circuit will use a single +3.3V supply, and using 12 band-pass filters is not really negotiable. If I want a 12-channel bar graph, am I stuck using <a href="http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=160-1066-ND">12 bar-graph LEDs</a> and <a href="http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LM3914N-1-ND">bar-graph LED Driver</a> pairs? That comes out to $45! Is there a better/less expensive/simpler method of getting a similar result? Ideally, I would not need a microcontroller.</p>
| Multi-channel bar graph LED drivers | 2011-01-12T18:57:14.990 |
8953 | |comparator|negative| | <p>If you can tolerate a slight current into the circuit (adjustable by modifying the pullup resistors), you can use a diode to offset the voltage:</p>
<pre>
/-- o ----------o-------------------\
| | ___ - ___ |
| `-|___|-\ `-|___|-\ |\|
| .--o-----------)---------|-\ Output
| | .---| | >---
| | | \---------|+/
--- 5V V V |/|
- - - |
| | | |
/-----o--------)-------o--)---------------/
| | | | | |
=== | | ___ | | .-.
GND --- V- |-|___|-/ \->| |POT
- | SHUNT | |
| // | Res '-'
o-----<|-/ |
| LED ___ |
\--------------|___|----/
</pre>
<p>You'll need to give the pot the same polarity and ground reference as the shunt resistor, and you'll want to make sure that your diodes have identical forward voltages (use the same diode, and try to find one that characterizes Vf very precisely). </p>
<p>The pullup resistors to 5V should be very large, and the currents through them very small in comparison with the resistances of the pot and shunt resistor and their current values.</p>
<p>(Mega ASCII circuit created with <a href="http://www.tech-chat.de/aacircuit.html" rel="nofollow">AACircuit</a>)</p>
| <p>I need to compare a negative voltage with a positive one, each on the order of a few hundred millivolts each; I want to compare the magnitudes, ignoring the signs, although only for this particular quadrant (I don't need all other signs.) How can I do it? I thought of using resistors to pull the negative voltage positive, but it only gives me a small signal on top of a DC offset, and that is difficult to compare with.</p>
| Compare negative with positive, ignoring sign | 2011-01-12T23:11:42.710 |
8966 | |enclosure|7segmentdisplay|optoelectronics| | <p>Darkening will attenuate the indicator as well. Try a plastic foil appearing nearly same color with the indicator, to filter out other colors.</p>
| <p>I'm building a basic thermometer that displays the temperature on 4 seven segment LEDs. I want to put the circuit in a <a href="http://cpc.farnell.com/boss-enclosures/33102005/box-clear-lid-190x115x75mm/dp/EN82380" rel="nofollow">box with a clear plastic lid</a>.</p>
<p>I'll mount the LEDs on the PCB around the other components, and fix this flat against the base of the box so the LEDs shine up through the clear plastic lid.</p>
<p>My question is how can I hide the electronics (i.e. the MCU, temp sensor, resistors, etc) but still be able to see the LED display, by some how darkening the clear plastic lid, and make it look more professional?</p>
<p>Alternatively, can you get enclosures with a translucent lid? I've searched but can't find any.</p>
| 7 Segment Display - Hiding the electronics | 2011-01-13T09:35:13.447 |
8969 | |usb|uart|attiny| | <p>Because software USB on AVR can only be 1.0 which is 1mbit max. If we subtract overheads on USB protocol and processing, even 384kbit looks awesome. If you need more - take specialized chip from FTDI for example.</p>
<p>SOIC soldering is not hard, and possible without fancy equipment.
If you want to prototype with SOIC you can solder tiny wires to leads.</p>
| <p>I know there are several solutions for V-USB using only DIP Parts (especially the ATtiny) like</p>
<p>IgorPlug</p>
<ul>
<li><a href="http://obdev.at/products/vusb/easylogger.html" rel="nofollow">http://obdev.at/products/vusb/easylogger.html</a></li>
<li><a href="http://cesko.host.sk/IgorPlugUSB/IgorPlug-USB%20%28AVR%29_eng.htm" rel="nofollow">http://cesko.host.sk/IgorPlugUSB/IgorPlug-USB%20%28AVR%29_eng.htm</a></li>
<li><a href="http://www.recursion.jp/avrcdc/cdc-232.html" rel="nofollow">http://www.recursion.jp/avrcdc/cdc-232.html</a></li>
</ul>
<p>But they are limited to 38400bps!</p>
<ul>
<li>Why?</li>
<li>Are there other solutions only using DIP packaged parts for easy soldering?</li>
</ul>
| ATtiny V-USB with 115200bps? DIP only | 2011-01-13T11:01:59.103 |
8981 | |interface|touchscreen|touch-panel| | <p>I'm assuming you want help with connections to the touchscreen, not with making your FEZ look like a keyboard to the computer (or with configuring a keyboard as input for the FEZ, depending on your project). </p>
<p>There are essentially two options: Use ADC (analog-to-digital converter) lines on your FEZ to directly connect to the touchscreen, or use a touchscreen controller IC to do the low-level stuff and then connect with SPI or I2C to the controller to get the digital data.</p>
<p>The first option is cheaper (you don't have to buy anything special), but will take more processing time on your FEZ, and will require you to do a little bit of analog design work. Atmel's appnote <a href="http://www.atmel.com/dyn/resources/prod_documents/doc8091.pdf" rel="nofollow">AVR341</a> is a good reference, and easily translates to other microcontrollers. Page 7 gives some good requirements: You need a fairly accurate A/D source, 15-25mA source/sink currents, and a processor capable of taking new measurements 70-200 times per second. I'm not sure how well the FEZ works with frequent interrupts like that, so the second option might be more attractive.</p>
<p>The second option eases the processing you'll have to do. Chips like TI's <a href="http://focus.ti.com/lit/ds/symlink/tsc2200.pdf" rel="nofollow">TSC2200</a> even go as far as to give you a keypad interface so that you can simply wait for the chip to tell you that someone's pressed a key (it's 4x4 keys, not a keyboard!). However, the more features you ask of it, the more complexity will be present in the interface. For a .NET application, you probably want to see an interface rather than connecting right to the hardware,</p>
<p>Regarding the suitability of a touchscreen interface, consider that it can be uncomfortable to type on a rigid surface for a long time, and resistive touchscreens are even worse because you need to apply significant pressure. Don't expect to sustain high typing speeds for very long without causing pain in your fingertips. Also, you'll want some kind of feedback mechanism. The Apple iPod/iPhone/iPad screens are as nice as they are because they (1) indicate the letter you're touching and (2) increase the sensing radius of letters that are likely to come up with predictive algorithms and dictionaries. It's very hard to get a touchscreen keyboard to feel natural.</p>
| <p>I am evaluating whether it can use "resistive touch film" in project-based cards using <a href="http://www.tinyclr.com/hardware/2/fez-mini/" rel="nofollow">USBizi Chipset-100</a> in place of a conventional keyboard.<br>
I would like to see some similar design to see howto make interface.<br>
Any suggestions?</p>
| touch film replacing keyboard | 2011-01-13T17:44:19.573 |
8994 | |enclosure| | <p>While you're probably looking at "full size" structural extruded aluminum T-slot,
for completeness I'm going to mention miniature versions:</p>
<p>MakerBeam is developing the Mini-T standard for open source hardware. <a href="http://www.makerbeam.com/" rel="noreferrer">http://www.makerbeam.com/</a></p>
<p>MicroRAX a light weight mini T-Slot building kit.
<a href="http://www.microrax.com/" rel="noreferrer">http://www.microrax.com/</a></p>
<p><img src="https://i.stack.imgur.com/Cjp6o.jpg" alt="alt text"></p>
<p><img src="https://i.stack.imgur.com/uenXI.jpg" alt="alt text"></p>
| <p>I see tubing used all over the place in machines, but I do not know what it is called. The cross section looks somewhat like this drawn picture. Can someone clue me in on it?</p>
<p><img src="https://i.stack.imgur.com/GDDlb.png" alt="Tubing"></p>
| What is the name of this common metal tubing? | 2011-01-13T21:56:03.313 |
9005 | |pcb|integrated-circuit| | <p>X-ray won't tell you much. Dimensions of the chip and where the bonds are attached. Decap is probably necessary. You should be able to get the manufacturer from text on the die, which will be a big clue. If you are really lucky, the manufacturer will put something on the die to help you ID the part number.</p>
<p>If you have a subscription to a tear-down company, you could scan their die photos and if you are luck find a match.</p>
<p>For a fee, a tear-down company will do this work for you and send you a full report on the part. Here's a list of a few such companies:</p>
<ul>
<li><a href="http://www.teardown.com/">TechInsights</a></li>
<li><a href="http://www.isuppli.com/Pages/Home.aspx">iSuppli Market Intelligence</a></li>
<li><a href="http://www.chipworks.com/">Chipworks</a></li>
<li><a href="http://www.anloy.com/tierworksheet.pdf">Anloy Chip Extraction</a></li>
</ul>
| <p>What tools and techniques can I use to identify an unknown IC with no markings?</p>
<p>Today I encountered a microcontroller under an epoxy blob. The blob had 11 pads on each of four sides, perhaps 44tqfp. From the board, I know which pin is the reset line and I probably know which pins make up an SPI interface. </p>
<p>Is there such a thing as an expert system for answering these puzzles with the information I have?</p>
<p>Are there any searchable databases of pinouts online?</p>
<p>Would X-raying/Decapping the package be worthwhile?</p>
| Tips for identifying an unknown chip? | 2011-01-14T00:38:43.190 |
9006 | |avr|power-supply|light|inverter|el-wire| | <p>Depends on how many feet your are planning to light at the same time. If not sure go with the total. Some inverters also have a min. number of feet, check that, you can always hang on some that is always on, or put in a dummy cap.</p>
| <p>I'm trying to use an 8 channel EL sequencer (<a href="http://www.sparkfun.com/products/9203" rel="nofollow">found here</a>) to control eight 10-foot segments of EL wire. I'm having trouble figuring out what the appropriate length rating is that I need on an inverter. I've read conflicting opinions. One states I need my inverter to handle the "total" length (in my case 80 feet), while another says it just needs to handle the longest strand (10 feet then). Which is correct? </p>
<p>I'm looking at <a href="http://www.coolight.com/product-p/ifw-3294.htm" rel="nofollow">this one</a> currently (rated 5 to 15 feet). Is that enough? Or do I need to find one rated for at least 80 feet? Thanks.</p>
<p><strong>edit</strong></p>
<p>If I need an inverter that can handle 80 feet of EL wire then I'm worried that this will conflict with a sequencer. If the sequencer turns off say 3 channels (30 feet of the wire), then my load would only be 50 feet I would think. I've read that this is an issue because the inverter might break if I have less than the minimum load. Is this the case?</p>
| Correct EL Driver Rating for 8 Channel Sequencer | 2011-01-14T01:19:41.500 |
9008 | |relay|switches| | <p>You actually can do this with two resistors. Connect a 7kohm resistor from the signal line to your pin. Then connect a 5k resistor from your pin to your ground.(This is for 5V input, if you have 3.3 us a ~4k and a ~8k)</p>
<p>When 12V is input, it will show up as the logic level the chip knows, when 0V is there you will get 0V on the pin.</p>
| <p>I have a project where I need to detect whether a 12V circuit is live or not. If it is I want to close a switch (actually close a digital IO input on an Adicon SECU16 Digital IO controller).</p>
<p>I am not an EE and would prefer to find a component off the shelf that I can tie into the 12V circuit and provide the relay. </p>
<p>I <em>could</em> choose to not use digital (Supervised) input and instead do analog, but I really don't care how much voltage I'm seeing just whether it's on or off. </p>
<p>I'm capable of soldering a few components on a prototype board, but my lack of EE knowledge means I need some serious help selcting the right components. The simpler the better.</p>
<p>Thanks in advance.</p>
| Need circuit to close switch on detecting current (12V) | 2011-01-14T02:39:17.693 |
9015 | |microcontroller|power-supply|design| | <p><img src="https://i.stack.imgur.com/valXi.jpg" alt="alt text"></p>
<p>This example uses a <a href="http://www.maxim-ic.com/datasheet/index.mvp/id/2455" rel="noreferrer">Maxim MAX1835</a> step-up regulator, but could be applied to others as well that have a shutdown pin.</p>
<p>The circuit is normally powered down. When the user presses the pushbutton, the battery is fed into the -SHDN pin, enabling the regulator and turning on the 3.3V to the microcontroller. The microcontroller then puts a logic 1 on the POWER ON lead, holding the power on after the user releases the pushbutton. When the microcontroller wants to shut itself off, it sets the POWER ON lead to 0.</p>
| <p>I want to design a circuit such that the microcontroller can toggle a GPIO pin and shut the whole system (including microcontroller itself) down. And when the user presses a momentary button, the power is brought back up again.</p>
<p>Is this possible?</p>
| How to implement a soft power switch controllable by microcontroller? | 2011-01-14T08:06:30.257 |
9026 | |power-supply|current| | <p>It will only draw what it needs. The .75A supply probably didn't work because the board will draw more at startup and the supply couldn't source it.</p>
| <p>I have to do some work on a PC/104 <a href="http://www.eurotech.com/en/products/embedded+boards/pc104+cpu+modules/cpu+pc104/isis+xl" rel="nofollow noreferrer">CPU board</a>. Until now I have been powering this from a separate power module (acs-5151 at the same link) that took in 8-40V and gave +12, +5, and +3.3 out. Until now, I was able to power the CPU module with the 5V line but don't have access to that anymore. The CPU module is an 8W system and in the past we were able to see that it was only drawing about 0.5A. I tried using a small lab power supply but it didn't boot up the CPU (although some of the LEDs did light up). As this supply says it is only capable of 0.75A continuous I thought that perhaps this wasn't enough to boot the it up. Then I was thinking that I could use the 5V line from a normal PC power supply. When I check the supply though it says 5V /22A. A friend suggested that the CPU might only draw what it needs but wasn't sure. I'm afriad to try it as it's a very expensive piece of hardware and can't afford to damage it.</p>
<p>I was wondering if anyone could tell me whether a PC power supply will only give the current needed or if there a danger of it damaging the PC/104 module?</p>
| PC Power supply for a PC/104. Current output | 2011-01-14T15:35:56.237 |
9027 | |microprocessor| | <p>The CMOS 6502 (65c02) and 65816 are still in production today, with no end in sight, made by Western Design Center (<a href="http://www.westerndesigncenter.com/" rel="nofollow">http://www.westerndesigncenter.com/</a>). They are conservatively rated for 14MHz and have many hardware and software enhancements over the original MOS 6502. There is a huge amount of support for them at 6502.org and forum.6502.org. I have a 6502 primer at <a href="http://wilsonminesco.com/6502primer/index.html" rel="nofollow">http://wilsonminesco.com/6502primer/index.html</a> in 22 chapters covering address decoding, memory-map requirements, interrupt connections, 74xx logic families and timing margins (plus "Do I need bus transceivers?", and static-handling precautions), clock generation, reset circuits, what to do with the "mystery" pins, construction for good AC performance, expansion buses and interfaces, getting more on a board, answering wire-wrap questions and doubts, "What about custom PC boards?", I/O ICs (plus extra info on 6551 ACIA clocking options), displays, where to buy 65-family parts, general steps for a successful project, program-wiriting: "Where do I start?" (and what to put in your .asm file), debugging, programming tips (some affecting hardware design too), basic workbench equipment, and a potpourri of circuits to interface real-world stuff. Happy building! </p>
| <p>I'm reading about a microprocessors at the moment and wondering if I could get started with an 8-bit microprocessor. What would I need to get started. I understand that they need external RAM and ROM. I don't know whether it is still possible to get an Intel 8-bit one as my book is from 1980. So are there any other recommendations?. I am looking for the circuit diagrams for creating my own PCBs, is this advisable? Something like a single board computer is what I'm looking for. </p>
| Getting started with a microprocessor | 2011-01-14T15:47:34.500 |
9041 | |rf|pcb-design|filter| | <p>Very late answer, but, I would think that 3 - 30 GHz is a wide enough passpand that you can implement the bandpass filter by cascading a low-pass filter (at 30 GHz) and a high-pass filter (at 3 GHz). Which simplifies your problem somewhat. But it doesn't mean that designing either of the two component filters for operation out to 30 GHz will be easy.</p>
<p>With this wide a band, you will probably not be able to use any simple transmission line structures to implement your filter, because that generally only works over a fraction of an octave. Some kind of distributed structure (multiple stubs of different lengths connected periodically to your main line) may be possible. </p>
| <p><em><strong>How would one approach designing bandpass filters in the 3GHz - 30GHz range</strong>, each with ~2.4GHz bandwidth, for a 50Ω spectrum analyzer or sampling oscilloscope? I've learned how to implement some simple RF designs in the 1GHz-5GHz range, and some of what to look out for.</em></p>
<ul>
<li><p>What circuit topologies are used? (Eg. coupled line vs capacitive-gap resonator vs capacitive coupled shunt resonator.)</p></li>
<li><p>Any active components?</p></li>
<li><p>What bandwidths and falloffs can be expected?</p></li>
</ul>
| How to approach designing a 30GHz bandpass filter? | 2011-01-14T20:13:50.493 |
9048 | |rf|design|device|inductance| | <p>Microwaves are actually rather ineffective in ice. Water molecules in ice are in a crystalline structure and will not polarize at microwave frequencies like liquid water will. They more easily resonate in the kHz region, which I suppose you would make the design frequency of any induction based system.</p>
<p>See <a href="http://www1.lsbu.ac.uk/water/microwave_water.html" rel="nofollow noreferrer">http://www1.lsbu.ac.uk/water/microwave_water.html</a> for much more info on water's response to RF radiation, especially the graph right after Figure 1.</p>
| <p>Last week we had very cold weather; and as a result there were lots of frosted pipes (iron and plastic). I spent a lot of time defrosting metal pipes with a torch, but could not do the same with plastic ones.</p>
<p>Could a practical gadget be made to thaw the ice trapped inside metal/plastic pipes based on induction? What would a blueprint of such look like?</p>
| Could induction thaw ice? | 2011-01-15T01:04:01.560 |
9058 | |rf| | <p>On Farnell they found by searching for 'Screening Cans'. Most of them are from the brand PERANCEA. I got some of them as well, they seem to work fine. Make sure you order them and fit them on your PCB design before you sent out an order to make dozens.. </p>
<p>It might require some fitting before you want to be sure to get them designed in. What I mean is that the ones that have a removable lid might be a bit larger from the drawings. The case itself folds over itself within the case, making it twice as thick as shown. On wrong measurements, it might also mean you end up with a screening case that is slightly rotated to make it fit.</p>
<p>If you search for 'screening' (at farnell) you might also find metal strips that you can place on PCB's as 'dividers'. I don't know what Digikey or Mouser has to offer, but I suspect they might have more. Screening, shielding, all EMC terms should give good results.</p>
<p>However, I do know distrelec has got many items under the search result 'screening'. They also got SMD mounted screening cans etc.</p>
| <p>Where can I find those metal shield cans that you can solder directly on a pcb for EMI shielding? Just like the ones on the back of XBee modules? I'm not having any luck searching on farnell, perhaps with the wrong keywords, or maybe it's not a commonly bought item?</p>
| Buying RF metal shields | 2011-01-15T10:27:30.897 |
9071 | |soldering| | <p>I've got a similar Metcal system. If the handpiece and cartridge are working properly just the green LED on the STSS power unit should be on, otherwise the amber one will be lit as well.</p>
<p>They use RF heating at about 14 MHz, via a coaxial cable. It's very unlikely that you will get that handpiece working properly, I'd just buy a new one. You could try testing the power unit with a suitable 100W 50R resistor, it'll need to be non-inductive. Just the green LED should come on. I can't be sure that test will work as I don't think the impedance has been published, but it won't do any damage.</p>
<p>I got mine second-hand from a supplier here in the UK, with a new MX-500 handpiece and selection of cartridges. I subsequently picked up a second STSS unit on Ebay, as a spare. The power units are very reliable, so yours is probably OK.</p>
| <p>I bought a Metcal STSS-PS2V-02 soldering iron from eBay, it was cheap and in need of repair. The previous owner had some problems with the handpiece and tried to fix it himself.</p>
<p>I can't get it to heat up at all.</p>
<p>If I turn the base station on without the handpiece connected, it draws virtually no power. With it connected, about 10W.</p>
<p>It appears that he has sawn the handpiece in two, then attempted to resolder the cable. With no soldering tip attached, I am seeing 0Ω between the inner and wire and sheath of the cable, does this mean that his resoldering has shorted it, or should I expect this?</p>
<p><img src="https://farm6.static.flickr.com/5241/5357993910_5b5acde271_m.jpg"></p>
<p><img src="https://farm6.static.flickr.com/5126/5357377339_aece186fee.jpg"></p>
<p>Next week, I'll be able to test the base station against a known working handpiece and determine if the base is working properly, but is there any other way I can tell?</p>
| Fixing a broken Metcal handpiece | 2011-01-15T19:51:46.107 |
9077 | |simulation|spice| | <p>There are several ways to get corner simulations, but without seeing your models we can only guess as to how it is implemented. Also, keep in mind that not every model supports corner simulations! The best advice I can give you is to read the documentation that came with your models - if corner or Monte Carlo simulation is available they will tell you how to access it.</p>
<p>Here are a few ways that I've seen process corners implemented (some of these I've seen using Spectre):</p>
<ul>
<li>Separate model files for each corner</li>
<li>The models have different sections for each corner case that must be selected</li>
<li>You edit the sigma values for the models in one of the include files.</li>
<li>FF/SS corners are not defined but models still have statistical data for Monte Carlo</li>
</ul>
| <p>How can I apply process corners (TT, SS, FF) to my simulation in HSPICE? </p>
| How to apply process corners in HSPICE? | 2011-01-15T22:43:44.193 |
9085 | |pic|uart|microchip| | <p>See page 110 of the data sheet.</p>
<p>Also, you need to disable the analogue inputs on the pins you are using.</p>
| <p>The problem I am having is with my PIC24FJ64GA002 and the UART module(s). The 24F I have is in a SPDIP28 package and it is a new B5 chip (just one under the latest B8 revision) from Microchip Direct. I have checked for errata issues which afflicted me last time with the I2C module.</p>
<p>Anyway, I am setting the UART1 module up as a simple transmitter. I am using PPS pin RP8 as the RX, RP9 as the TX and RP11 as the CTS pin. For now I have grounded RX and CTS as I do not need them. I have set the BRG at 115,200 (actual rate ~114,285.7, but it's close enough.) I am using the code below. I expect to see a series of bytes streaming out on RP9, but I do not. RB15 is a debug output: it pulses on each byte being sent. On RB15 I get a really slow clock, about 700 Hz, which is very low for a 115,200 baud link; I'd expect about 14 kHz.</p>
<pre><code>#include <p24fj64ga002.h>
#include <uart.h>
#include <pps.h>
void init_osc()
{
// Must be programmed for FRCPLL mode.
//UNLOCK_OSC();
CLKDIVbits.RCDIV = 0;
//LOCK_OSC();
}
void main()
{
int i = 0x55;
PPSUnLock;
// Initialize oscillator (set FRC to 8 MHz.)
init_osc();
// Initialize UART1 PPS.
iPPSInput(IN_FN_PPS_U1RX, IN_PIN_PPS_RP8);
iPPSInput(IN_FN_PPS_U1CTS, IN_PIN_PPS_RP11);
iPPSOutput(OUT_PIN_PPS_RP9, OUT_FN_PPS_U1TX);
PPSLock;
// Interrupts disabled for now.
//ConfigIntUART1(UART_RX_INT_EN | UART_RX_INT_PR6 | UART_TX_INT_EN | UART_TX_INT_PR6);
OpenUART1(UART_EN & UART_BRGH_SIXTEEN & UART_NO_PAR_8BIT & UART_1STOPBIT, UART_TX_ENABLE, 34);
TRISBbits.TRISB15 = 0;
while(1)
{
LATBbits.RB15 = 1;
LATBbits.RB15 = 0;
while(BusyUART1());
WriteUART1(i);
i++;
}
CloseUART1();
}
</code></pre>
<p>I feel like I have missed something obvious, but cannot figure out what it is. If anyone has had previous experience with the UART module on 24F series devices, please let me know! I've had little luck with the Microchip forums.</p>
| Problem with PIC24F UART | 2011-01-16T01:08:04.490 |
9099 | |resistance| | <p>No, it cannot be ignored.</p>
<p>The internal resistance of Lithium ion/NiMh batteries is comparable to one of the wires. Also you should keep in mind that a significant part of the resistance is in the connections to the battery.</p>
<p>So, for precise measurement, you can go for 4-wire measurement, or accurately measure the resistance of the wires and <strong>connections</strong>, and subtract it.</p>
| <p><br>
I'm trying to calculate the internal resistance of my rechargeable batteries and haven't got a single battery holder so using I am having to using Banana plugs and Crocodile clips for holding my resistor. Then holding the banana clip on the negative end of my battery and reading the current. But could this be affecting my readings as I've tried different resistors and I'm still out in my calculation first time i got ~1000(with a 10k load) ohm now down to 10 ohm(with 68 ohm load). I have even smaller loads to test with now 1 ohm and 0.1 ohm. But this just popped in to my head as it might be problem. The leads I'm using are what we normally use for connecting our PCBs to the PSU, this is why I thought it could be ignored but maybe not when trying to calculate some thing very accurately.</p>
| Can Resistance of wires be ignored? | 2011-01-16T16:11:22.000 |
9100 | |arduino|power-supply| | <p>You usually need a common ground but don't want to connect power rails, even if they are the same potential (don't tie two separate 5V rails together, for example). There are some exceptions. You can communicate across isolated grounds using opto isolators and there are some regulators designed to be safely used in parallel, such as Linear Technology's LT3080. Otherwise, there is not much math. You just need to make sure you can provide enough current for each of you rails' load requirements. The only other thing I would mention is that if you do use separate rails of the same potential, and communicate between them, make sure you can't violate any I/O specs of your devices. If you are using two separate 5V rails, for example, each +/-10% , one rail could be 4.5V and the other 5.5V. Outputting a 5.5V signal to an input pin with a 4.5V supply could potentially damage the IC. This is why, when using the same potential across multiple devices that communicate with each other, it's usually preferred to use a single supply rail for all devices. This isn't always easy to do when connecting kits, however, such as the Arduino to some external device.</p>
<p>Edit, if you use one supply, tie all loads to it in parallel. If you were to tie two loads in series to a 5V supply, for example, each load wouldn't be getting 5V. If the two loads were exactly equal, they'd be seeing 2.5V each. You design the supply for the rated load, taking into account heat considerations. 1.5A is a large load which will generate a lot of heat with a linear regulator. You'd need to make sure that A) your regulator can provide at least your maximum load (with some room to spare) and B) can radiate the heat generated by the voltage drop. This means you may require a heat sink. Almost all regulator's data sheets will tell you how much heat is generated for a given amount of power. The National Semi LM317, for example, says it's TO-3 package increases 39 degrees C for each Watt of dissipation. If you are regulating 5V off a 9V rail at 1 Amp, the package would be dissipating (9V-5V) x 1A which equals 4W, or 146 degrees C over ambient temp! Well beyond the maximum spec'd temp. This is where heat sinks come into play, or the use of a switching regulator which are much more efficient, but probably too advanced for your first project. The other thing to be concerned about for regulators is dropout voltage. The supply rail needs to be some amount of voltage greater than your regulated voltage. This is all assuming you have a AC to DC power supply to give you your main power rail. But if this is the case, why not just buy a regulated AC to DC supply at the voltage or voltages you require with the current capability you require. You can buy cheap wall warts with regulated output voltages in most common voltages and with various current capacities.</p>
| <p>I have a project I am looking to power where the secondary load is more than my Arduino can provide amp-wise. I need to know the simplest way to power the whole system. I will be powering the Arduino and a 5v 1.2amp load. Diagrams I have seen show a common ground with two power supplies but I don't know the math for anything beyond a simple circuit. Links to other resources are welcome with all answers. I am looking to learn more about power and circuits in general so more info is better.</p>
<p><strong>EDIT</strong></p>
<p>If I use one supply, how should I design the circuit? e.g. Series or Paralell. Also, how would I go about determining the requirements for that power supply?</p>
| Beyond board power, understanding multiple power supplies and loads in a circuit | 2011-01-16T16:28:06.887 |
9106 | |antenna|gps| | <p>As far as commercial-off-the-shelf, SparkFun sells a helical antenna based receiver, also using the u-Blox chipset, the <a href="http://www.sparkfun.com/products/9436" rel="noreferrer">GS407 Helical GPS Receiver</a>. It's using a Sarantel SL1206 Antenna. You may be able to find more antennas to your liking directly available from <a href="http://www.sarantel.com/products/index.php" rel="noreferrer">Sarantel</a>. Also, if you are eventually looking to embed this into a product, purchasing from SparkFun may prove to be more costly, so going directly from the manufacturer may save money. One drawback to the SparkFun product is that it's limited to 4Hz update, according to the datasheet, and 2Hz according some of the comments on the product page.</p>
<p>If you are feeling more DIY, then you can check out <a href="http://www.helenav.nl/antlinks.htm" rel="noreferrer">this page of DIY GPS antennas</a>.</p>
<p>If you are looking for more ideas, it might be worthwhile to purchase a few of the "runners watches" that are currently available on the market and see what they do. I know that Garmin and the like manufacture these in pretty tightly-integrated packages, so they have approached the problem before.</p>
<p>Also, as an additional data point, I believe that the iPhone uses a patch antenna (I wouldn't imagine that there is much room for much else in there), and it seems to successfully track me when mounted on my arm during runs, so patch may be a viable option with some clever design.</p>
| <p>I'm looking around for a decent GPS module for a project of mine. The <a href="http://www.sparkfun.com/tutorials/127" rel="nofollow">Sparkfun GPS Buying Guide</a> is nice, but focuses mostly on modules with patch antennae.</p>
<p>My project is a wrist- or upper-arm-mounted GPS logger. It will be displayless and log continually, and thus there can be no assumptions about the orientation of the device (as there probably could be if the user were to read a display). As far as I've understood, this means I should go for a helical antenna instead of a patch one for better omnidirectionality. Is this correct?</p>
<p>If so, does anyone have any recommendations for a decent (and decently priced) GPS module with a helical antenna? An antenna-less module with a third-party antenna is also possible, but I'd prefer a complete module. The last time I looked into this a few months ago, the most interesting device I found was the <a href="http://www.falcom.de/products/gps-modules/fsa03/" rel="nofollow">Falcom FSA03</a> based on the u-blox UBX-G5010. I also see there's a UBX-G6010 based FSA03-LP out now. Does anybody have any experience with these?</p>
<p><strong>Edit:</strong> I've also been hearing about PCB loop antennae. Any experiences with those? From what I've understood, these are often used in cellphones...</p>
<p>I don't have very specific requirements, but the size should be small. I'm not looking for the tiniest of the tiny, but it shouldn't be bulky either - this is vague, I know, but I'm looking for something suited to a small wrist-mounted device. Low power consumption is important. And of course, the more reasonably priced, the better.</p>
<p>Thanks in advance for any recommendations!</p>
<p><strong>Conclusion</strong> (in case anybody comes across this at a later point): I went for a <a href="http://www.u-blox.com/en/gps-modules/pvt-modules/lea-6-family.html" rel="nofollow">u-blox LEA-6H</a> module ($50 on eBay) and a <a href="http://sarantel.com/products/index.php" rel="nofollow">Sarantel SL1300</a> antenna (€10 at <a href="http://www.mirifica.it/" rel="nofollow">Mirifica</a>). I haven't had the time to try things out yet, but it seems to be exactly what I need.</p>
| Suggestion for a GPS module with helical/omnidirectional antenna | 2011-01-16T21:30:04.350 |
9108 | |uart|parity| | <p>You don't want parity. You want a more reliable communication. </p>
<p>The reason parity is little used is that it's expensive in terms of data throughput. It starts by making a frame almost 10% longer: start bit + 8 data bits + parity + stop bit = 11 bits instead of 10. But it's far worse than that. If you have a way to tell if you received the data correctly you have the duty to do something with that. Simply ignoring the erroneous communication won't do; the transmitter has to send it again. So it needs to know whether it was received well. You'll have to send an acknowledge (<code>ACK</code>/<code>NAK</code>) after each byte, and the transmitter can't send the next byte before it has received the <code>ACK</code>.
If you use ASCII codes that's 11 return bits. So this <strong>halves</strong> the thoughput, and we already lost 10%, so we're now at a <strong>36% payload efficiency</strong>, from 80%. And <em>that</em>'s the reason why nobody is really fond of parity. </p>
<blockquote>
<p>Notes:<br>
1. You don't need to acknowledge the receipt of an acknowledge; the <strong>Hamming distance</strong> between the ASCII codes for <code>ACK</code> and <code>NAK</code> is 3 (with parity even 4), so an error in the reception of <code>ACK/NAK</code> can be not only detected, but also <strong>corrected</strong>.<br>
2. Many UARTs can work with data lengths down to 5 bits, and it's possible to switch to 5 bits for sending the <code>ACK</code>, but this is mere window-dressing, and it only complicates communication.</p>
</blockquote>
<p>A better solution can be to use a <strong>CRC</strong> at the end of each block. CRCs are better than parity bits at capturing multiple errors (yet they still can't correct them). Improved efficiency can only be obtained for long blocks; if a block consists of only 2 bytes it's no use to add an 8-bit CRC.<br>
Another disadvantage would be that you still have to acknowledge correct reception. So that's probably not it either. </p>
<p>How about <strong>self-correcting</strong> codes? <strong>Hamming codes</strong> add little overhead, and allow you to correct 1 erroneous bit yourself; no longer need for acknowledging. Like CRCs Hamming codes are more efficient on longer blocks; the number of additional bits is defined as </p>
<blockquote>
<p>\$N + H < 2^H\$</p>
</blockquote>
<p>where N = number of data bits, and H = number of Hamming bits. So to correct 1 bit in an 8-bit communication you need to add 4 Hamming bits; a fifth Hamming bit is only required from 12 data bits. This is the most efficient way of error detection/correction on short messages (a few bytes), though it requires some juggling with your data: the Hamming bits have to be inserted at specific positions between your data bits. </p>
<p>Now before you add Hamming error correction codes it's worth looking into your setup. You can expect errors on a 100m line running between heavy machinery, but you shouldn't have errors on a 2cm line. If it picks up noise it may be too high impedance. Are the drivers push/pull? If so they should be able to give you fast edges, except if you "cable" is capacitive, which it won't be at this short distance. Are there high current traces running parallel to the data lines? They could induce noise. Do you really need this high speed, and do clocks on both sides match closely enough? Slowing down to 57600 bits per second may solve the problem.</p>
| <p>I am considering whether to use parity or not with my UART. It is a board level high speed (upwards of 115,200 baud) signal. The traces are very short (less than 2 cm), MCU to DSP, but they could pick up noise. During a logic analysing session using my logic sniffer I noticed one byte was captured incorrectly, it was just a single error. I couldn't replicate it. Now I'm wondering whether I should include parity. </p>
<p>My application is somewhat safety critical in that a failure would lead to a graphical error on a HUD/OSD which could provide incorrect information to someone piloting a model aircraft. However, the HUD is updated at 30 frames per second, so any glitch would be temporary. One problem that could happen is it could send a command which put the OSD into an incorrect state where it did not display anything, leaving the pilot blind about 25 km away from home... which is not good. </p>
<p>Will including parity protect me against common glitches or will it just make the protocol slower? Why is it that most UART protocols do not have parity? And is there a reason to select odd or even parity over each other?</p>
| For UART, should I use parity on a board level? | 2011-01-16T21:50:18.573 |
9112 | |psoc|system-on-chip| | <p>My own research, now four years later, turned up <a href="http://www.ieiworld.com/product_groups/industrial/detail_list.aspx?keyword=PICOe-b&gid=00001000010000000001&cid=08141333914287007902&id=0C090521963186388827" rel="nofollow noreferrer">iEi's line of PCIe cpu cards</a>. No word on pricing yet, but some might fall into that range.</p>
<p>Edit: Three years later that link is dead - however if you search for IEI PCIe CPU card, you end up finding their <a href="https://www.ieiworld.com/en/product/items_by_cat.php?CA=1&cat23=1_2" rel="nofollow noreferrer">half-size SBC</a> cards, which are more or less the thing.</p>
| <p>Does anyone know a <a href="http://en.wikipedia.org/wiki/Computer-on-module" rel="nofollow">COM</a> which is put on a PCIe card, which has some flash memory, some RAM, JTAG support (or some kind of debugging support), some input ports like USB, perhaps support some output like via VGA or LVDS, just like this board: <a href="http://www.knjn.com/FPGA-PCIe.html" rel="nofollow">http://www.knjn.com/FPGA-PCIe.html</a> but not for FPGA development, but for microprocessors, preferably x86.</p>
<p>Something similar <a href="http://hardware.slashdot.org/hardware/08/10/02/2244229.shtml" rel="nofollow">has been done</a> in the past, but the link is dead, and it should have enough documentation and be hacker-friendly (and cheap, not more than 100-150 USD).</p>
<p>I will be writing the driver for the host system (linux), for inter-system communication, but the PCIe board itself should be pretty stand-alone (beside the operating system for the "guest OS" on the PCIe card which I will also have to write).</p>
<p><strong>Addendum</strong></p>
<p>(upon more research)</p>
<p>Sun used to have <a href="http://en.wikipedia.org/wiki/SunPCi" rel="nofollow">SunPCI</a>, but those cards are hard to get. Besides, I want something more modern.</p>
<p>Thanks</p>
| Programmable system on chip (SOC) pluggable on a host via PCIe | 2011-01-17T00:26:40.960 |
9120 | |capacitor|ldo|ceramic|tantalum| | <p>4 V tantalum capacitors will be just fine, but personally I love the ceramic ones so much. Also, each µF of a ceramic capacitor is "better" than a tantalum one due to lower <a href="https://en.wikipedia.org/wiki/Equivalent_series_resistance" rel="nofollow">ESR</a>.</p>
<p>So before going for tantalum, I would check the price of ceramic capacitors with a better dielectric which still gives you 4.7 µF at 85 °C (185 °F).</p>
<p>You should check your LDO specification on ESR limits. Some might oscillate with too-low ESR. And if it's stable with a 1 µF ceramic one at 85 °C - I would personally stay with ceramic. Just more reliability.</p>
| <p>I was originally considering using a 10 µF 6.3 V 0603 ceramic capacitor for stabilising the onboard voltage regulator on my microcontrollers. However, it may not be capable because of temperature coefficients, tolerances and applied voltage (losing up to 60% of the rating). Therefore, I am considering moving to using tantalum capacitors.</p>
<p>The microcontroller <a href="https://en.wikipedia.org/wiki/Low-dropout_regulator" rel="nofollow">LDOs</a> output 2.25 V - 2.75 V for powering the internal core. I am using a <a href="http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en026375" rel="nofollow">PIC24FJ64GA004</a> and <a href="http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en532299" rel="nofollow">dsPIC33FJ128GP804</a>. Would it be fine to use a 4 V capacitor here? I have always used 2-3x rating for electrolytic capacitors, but maybe the same problems with aluminum electrolytic capacitors as for tantalum capacitors do not apply (with lifetime decreasing over applied voltage considerably.)</p>
<p>Ideally I'd like to reach a 50,000-100,000 hr MTTF. If tantalum capacitors aren't an option I'm considering using a 22 µF 6.3 V 0805 ceramic capacitor in place (I might have to resize the footprint), because even with a loss of 60% it stays within the minimum requirement of 4.7 µF. Any tips? Has anyone used tantalum capacitors before? What about ceramic capacitors for microcontroller LDOs? </p>
| Voltage rating and tantalum capacitors | 2011-01-17T10:29:51.383 |
9121 | |temperature| | <p>I once made a small oven to dry my photosensitive lacquer PCBs. It was basically a matrix of 1W resistors directly 230V AC powered. I mounted the resistors 1cm above a PCB so that the air could flow freely around them and the heat was distributed well without hot spots. This heater was temperature controlled by a (unfortunately long obsolete) <a href="http://www.datasheetcatalog.org/datasheet/philips/TDA1024.pdf" rel="nofollow noreferrer">TDA1024</a> + NTC temperature sensor. </p>
<p><img src="https://i.stack.imgur.com/LVBXB.png" alt="TDA1024 application"></p>
<p>The TDA1024 can be replaced by a transformerless power supply to feed a comparator.
My thermostat was set at a fixed 50°C, but with a potmeter you can vary the temperature. </p>
| <p>I want to make sure my product will work over a large temperature range of -40C to +75C. I can verify on the low end down to about -18C using a household freezer (which is probably good enough) but I'm not sure how to test it on the high end. Any tips?</p>
| Cheap way of temperature testing my boards | 2011-01-17T10:34:01.547 |
9122 | |surface-mount| | <p>In respect to some comments to never trust the marking, there are TSOT23 packages that solely rely on the top marking of that package. An example is the MP2457 from MPS</p>
<p><a href="https://i.stack.imgur.com/S4Fry.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/S4Fry.png" alt="enter image description here" /></a></p>
<p>Note 7 of <a href="https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MP2457/document_id/5011/" rel="nofollow noreferrer">this PDF</a> says: "Pin 1 is lower left pin when reading top mark from left to right, (see example top mark)".</p>
| <p>Well, I have a 6-pin SOT23 and it is absolutely tiny. When I say tiny I mean it. Anyway, it is unclear which way it goes around as it has no indicator, so I don't know how I can install them on my boards. It has some writing on it but that is the only clue on how they are aligned. For those who need to know it is an <a href="http://cds.linear.com/docs/Datasheet/1933fe.pdf" rel="nofollow">LT1933</a> or <a href="http://www.national.com/ds/LM/LM2734.pdf" rel="nofollow">LM2734Y</a> (depending on the version.) I'm actually starting to wonder how feasible it will be to assemble these boards of mine with such tiny components, even using a reflow method.</p>
| How do you know which way round a 6-pin SOT23 goes? | 2011-01-17T10:37:59.223 |
9129 | |capacitor|identification| | <p>I found <a href="http://www.elecraft.com/Apps/caps.htm" rel="nofollow">this</a> page interesting, when I had similar problems.</p>
| <p>I bought a mixed bag of ceramic capacitors from Maplin and I'm struggling to identify most of them. I'm a bit of an electronics newb, but I understood that a capacitor usually has 3 numbers on and sometimes a letter at the end of the numbers. The third number indicates the amount of zeros you add to the first two to get the value in pF. Am I correct?</p>
<p>Well with that in mind, I introduce you to:</p>
<p><img src="https://i.stack.imgur.com/YWfrO.jpg" alt="alt text"></p>
<p><img src="https://i.stack.imgur.com/rRvEm.jpg" alt="alt text"></p>
<p>The first one is a bit blurry, but it seems to have 8P2 printed on it. Next has n51 with Sy below it. The 3rd and 5th ones have a horizontal line under the number, and what might be a number one, or a corresponding vertical line, can't decide which it is. The 4th one seems a bit more clear now that I can see the writing more clearly in the picture - I assume this is 180pF? Finally the last one has 82 on it, is this simply 82pF?</p>
<p>Is there a way to test the capacitance at all? I have countless smaller ones with either blurry text, or nothing written on.</p>
| Identifying Capacitors | 2011-01-17T12:02:58.893 |
9137 | |components|integrated-circuit| | <p>It is a "Chip on board". It is an ic wire bonded directly to the board, and then protected with some epoxi (the "black thing").</p>
<p><img src="https://i.stack.imgur.com/K4QUM.jpg" alt="enter image description here"></p>
<p><img src="https://i.stack.imgur.com/IXcXD.gif" alt="enter image description here"></p>
| <p>In low-cost mass-produced items I often run into black blobs of what looks like resin applied directly on top of something on the PCB. What are these things exactly? I suspect this is some kind of custom IC that is layed out directly on the PCB to save on the plastic housing/connector pins. Is this correct? If so, what is this technique called?</p>
<p><img src="https://i.stack.imgur.com/eeENZ.jpg" alt="The Blob"></p>
<p>This is a photograph of the inside of a cheap digital multimeter. The black blob is the only non-basic piece of circuitry present, along with an op-amp (top) and a single bipolar junction transistor.</p>
| What kind of components are black blobs on a PCB? | 2011-01-17T16:13:17.863 |
9147 | |soldering|ffc| | <p>You need to tin the wires and pins (I usually tin both, especially if using stranded wire) before bringing them together. Put one in a third hand/vice/under a heavy object, making sure that the grip is far enough away to avoid melting the insulation. Flux both ends, because the flux which was in the solder before tinning the wires has been activated and is no longer useful. Then, hold the one wire in one hand and your soldering iron in another, and bring the two together. </p>
<p>Always include some heat shrink or other strain relief (I like hot glue) for any of these joints.</p>
| <p>After a simple flashy-LED kit's worth of practice, through-hole soldering is fairly straightforward. What I'm still having trouble with is wire-to-pad and wire-to-wire soldering.</p>
<p>The first problem is keeing stuff still. Blu-tac helps but gets melty, and I've never used a "third hand" that was worth a damn. Is it worth paying more for a better one? Any other tips?</p>
<p>My particular application is soldering <a href="http://www.google.com.au/images?q=sil+sockets&oe=UTF-8&hl=en&client=safari&um=1&ie=UTF-8&source=univ&ei=pb80TZr8Co7NrQfcy-HvCA&sa=X&oi=image_result_group&ct=title&resnum=1&ved=0CCQQsAQwAA" rel="nofollow noreferrer">0.1" SIL sockets</a> to flat flex cable (<a href="https://electronics.stackexchange.com/questions/5620/mechanical-connectors-for-flexible-pcbs">me again!</a>). Would solder paste and the heat gun attachment on my butane iron work well?</p>
| Tips for wire-to-pad and wire-to-wire soldering? | 2011-01-17T22:22:41.697 |
9160 | |bias| | <p><strong>quick explanation:</strong> The biased voltage can be regarded as a superposition of the contribution from V<sup>+</sup> (calculated above, called <em>biasing term</em>) and the contribution from V<sub>i</sub> (the other term, with V<sub>i</sub>sC in the numerator):<br> V<sub>o</sub> = V<sub>o,V<sup>+</sup></sub> + V<sub>o,V<sub>i</sub></sub> = V<sup>+</sup>/[R<sub>1</sub>(<sup>1</sup>/<sub>R<sub>1</sub></sub> + <sup>1</sup>/<sub>R<sub>2</sub></sub> + sC)] + (V<sub>i</sub>sC)/(<sup>1</sup>/<sub>R<sub>1</sub></sub> + <sup>1</sup>/<sub>R<sub>2</sub></sub> + sC), where</p>
<ul>
<li>V<sub>o,V<sup>+</sup></sub> = V<sup>+</sup>/[R<sub>1</sub>(<sup>1</sup>/<sub>R<sub>1</sub></sub> + <sup>1</sup>/<sub>R<sub>2</sub></sub> + sC)] and</li>
<li>V<sub>o,V<sub>i</sub></sub> = (V<sub>i</sub>sC)/(<sup>1</sup>/<sub>R<sub>1</sub></sub> + <sup>1</sup>/<sub>R<sub>2</sub></sub> + sC)</li>
</ul>
<p>When one uses superposition, they redraw the circuit with all other voltage sources shorted and other current sources opened (other than the one being considered). This means that when considering the contribution from V<sup>+</sup>, V<sub>i</sub> is grounded, so the frequency[-ies] in the V<sub>o,V<sup>+</sup></sub> term is that present in V<sup>+</sup>, which should be near zero for a DC source. Using the same arguments, the frequency in the V<sub>o,V<sub>i</sub></sub> term is that present in V<sub>i</sub>.</p>
<p>Superposition makes sense for many reasons; one of the arguments I've made to justify it to myself is to look at Fourier analysis, which shows that any signal can be decomposed into the superposition of sinusoids, and those sinusoids can be extracted by filtering out the others; the <a href="http://en.wikipedia.org/wiki/Gibbs_phenomenon" rel="nofollow noreferrer">Gibbs phenomenon</a> is often seen in practice as <a href="http://en.wikipedia.org/wiki/Ringing_(signal)" rel="nofollow noreferrer">ringing</a>.</p>
<p>To be more precise though, we should take into account the load resistance that would be connected between V<sub>o</sub> and ground.</p>
<hr>
<p><strong>simplified analysis:</strong> The capacitor in this circuit is called a <strong><em>DC blocking capacitor</em></strong>, because it doesn't pass any DC signals. A common and useful technique to analyzing circuits that separate <em>high frequency</em> AC and DC signals like this is to approximate the blocking capacitor as an <strong>open circuit to DC signals</strong> and <strong>short circuit to AC signals</strong>. This greatly simplifies analysis of more complicated systems. For <em>mid-band</em> frequencies -- those for which the capacitor presents an impedance comparable, over 5%-10%, to that of R<sub>1</sub>||R<sub>2</sub> -- the complicated impedance formula needs to be used. For low frequency signals, where the capacitor impedance is more than ~100·R<sub>1</sub>||R<sub>2</sub>, the cap can be regarded as an open circuit. Of course, this depends on the sensitivities of your circuitry, but that will be apparent if these considerations are of value.</p>
| <p>I'd like to formally understand this simple biasing circuit:</p>
<p><img src="https://i.stack.imgur.com/ZpcOS.png" alt="circuit diagram"></p>
<p>Let V<sup>+</sup> be the supply voltage, V<sub>i</sub> be the input voltage at the seemingly unconnected terminal of the capacitor, and let V<sub>o</sub> be the output voltage at the junction between the resistors and capacitor. Let S be the impedance unit (i*omega)</p>
<p>using VI relations and Kirchoffs laws:
(V<sup>+</sup> - V<sub>o</sub>) / R<sub>1</sub> - V<sub>o</sub>/R<sub>2</sub> + (V<sub>i</sub>-V<sub>o</sub>) * C*S = 0</p>
<p>which after rearranging gives:</p>
<p>V<sub>o</sub> = (V<sup>+</sup>/R<sub>1</sub> + V<sub>i</sub><em>C</em>S) / (1/R<sub>1</sub> + 1/R<sub>2</sub> + C*S)</p>
<p>decomposing the numerator it becomes clear that the biasing term is:</p>
<p>= (V<sup>+</sup>/R<sub>1</sub>) / (1/R<sub>1</sub> + 1/R<sub>2</sub> + C*S) = V<sup>+</sup> / (1+R<sub>1</sub>/R<sub>2</sub> + R<sub>1</sub><em>C</em>S)</p>
<p>Does the amount of bias really depend on the driving frequency? At DC, S=0 and everything reduces to a voltage divider regardless of the voltage at V<sub>i</sub>.</p>
<p>(Sorry for the eye-sore math. Is it possible to do math input on this website like it is on math.stackexchange ?)</p>
| Simple Biasing Circuit | 2011-01-18T04:28:34.387 |
9165 | |sensor|uav|distance| | <p>In reality, a single sensor will probably not be accurate enough to do what you want. Most of what I know is related to AGVs (Ground Vehicles), but I think that some of the same principles apply.</p>
<p>You probably want to use a combination of sensors to get the accuracy that you need. Some of these can be quite expensive.</p>
<ul>
<li><p>GPS: A standard GPS module should be able to get you down to about 1m +/- accuracy. If you step up to a differential setup (one station on the ground, one on the plane), then you should be able to get significantly more accuracy, but at a much higher cost. Something like 10cm or even 1cm should be possible (with velocity data), but with a significantly higher cost.</p></li>
<li><p>INS: You can supplement your GPS system with intertial measurements. The boom in MEMS devices has made relatively decent solid-state sensors available at consumer prices. Adding accelerometer, gyrometer, and magnetometer data to the GPS data should make the signal more accurate, and account for possible "glitches" in you GPS readings.</p></li>
<li><p>Radio-assisted navigation: I'm not entirely up on this, but many airports use a radio-assist to help land the planes. You may be able to research how these systems actually work and implement your own (legally, of course).</p></li>
</ul>
<p>For a more detailed look at some of these considerations, I would check out DIYDrones. They have put together some pretty tightly-integrated systems using GPS, INS, Barometers, and a large array of other sensors. They have also tackled some of the difficult filtering challenges that come with multiple sources of data in an airborne system.</p>
| <p>How do I implement drone-to-ground distance-measuring for autopilot landings for heights over 10m? I found ultrasonic to be too inacurate, let alone GPS. Maximum height is 1000m, Vmax is 100 km/h, Vaverage is 72 km/h. The drone is plane-like, no *copter or so. </p>
<p>Thank you for any input!</p>
| How do I implement accurate distance measuring (to ground) on a plane-like UAV for heights over 10m? | 2011-01-18T10:42:09.483 |
9172 | |avr|atmega|atmel|architecture| | <p>Check out the white papers in the <em>Other Docs</em> section of Atmel's website: <a href="http://www.atmel.com/dyn/products/other_docs.asp?family_id=607#White_Paper" rel="nofollow">http://www.atmel.com/dyn/products/other_docs.asp?family_id=607#White_Paper</a> .</p>
<p>A long time ago I read the one called <em>The AVR Microcontroller and C Compiler Co-Design</em> which explains why they think the AVR instruction set is well-suited for the C language. Some of the other documents there explain the AVR architecture or a series of chips in general.</p>
| <p>I think I have used enough of the AVR series by atmel to say that I understand how to use it. I know somethings about how it actually works, but I would like to know more. Are there any good resources which describe the architecture of Atmega or RISC architecture in general? I know the datasheet has all this (and I really looooovvee the datasheet, its kinda my bible) but I need something little more simple than that. Any help?</p>
| Resources to learn about the AVR/RISC architecture | 2011-01-18T15:21:51.913 |
9183 | |batteries| | <p>Batteries have an internal resistance, this is generally measured in milli-ohms. As more current is drawn from the battery there will be a progressively larger voltage drop due to this internal resistance. V = I*R. This is obviously a high level answer, the details can vary based on battery chemistry.</p>
<p>A battery's voltage will also generally drop as the battery ages (runs out of juice). The exact chemical process varies based on battery chemistry but simply put the battery is running out of charge.</p>
| <p><br>
Why is it when you connect a battery to a heavy load does the voltage coming out of the supply drop?</p>
| Why do battery/power supply supply voltages drop under a load? | 2011-01-18T22:57:54.630 |
9185 | |microcontroller|power-supply| | <p>This looks like a good project which does everything I need.</p>
<p><a href="http://www.tuxgraphics.org/electronics/201005/bench-power-supply-v3.shtml" rel="nofollow">http://www.tuxgraphics.org/electronics/201005/bench-power-supply-v3.shtml</a></p>
<p><a href="http://shop.tuxgraphics.org/electronic/detail_microcontroller_powersupply.html" rel="nofollow">http://shop.tuxgraphics.org/electronic/detail_microcontroller_powersupply.html</a></p>
| <p>I'd like to build a power supply for my desk. I've found a few projects based on the <a href="http://www.st.com/stonline/books/pdf/docs/1678.pdf" rel="nofollow noreferrer">L200</a> adjustable voltage regulator.</p>
<p>In the example below, how could I replace R3 with a microcontroller, so that varying the current limit can be automated?</p>
<p><img src="https://i.stack.imgur.com/2tM4W.png"></p>
<p>Likewise, how can R2/R1 be controlled?</p>
<p>Is there a better device for a task like this?</p>
| Voltage regulation and current limiting with a microcontroller | 2011-01-19T00:08:57.943 |
9187 | |power-supply|oscilloscope|transformer|emc| | <p>Fake Name pretty much took care of the "Why", I'll try to help with the "What now". </p>
<p>Of course, since the field strength is inversely proportional to the distance squared, moving the scope and PSU away from each other could also do the trick. Similarly, changing the orientation of the two devices so the CRT screen is perpendicular to the magnetic field lines could reduce the distortion and flicker to something more readable. Finally, I'm guessing that this is a linear power supply with only low frequencies on the transformer, so if having the scope and the controls for the PSU in the same location or on top of each other is important, you could probably put the transformer in its own box, and run a cable back to the PSU.</p>
<p>Another easy (but expensive) fix is to get a scope with an LCD. Most new scopes are like this. Now your oscilloscope won't be affected by the magnetic field. However, remember that you still have a significant magnetic field at your workstation. You can forget about working with magnetometers. </p>
<p>The third option is to encase the transformer in a material with a high magnetic permeability, like mu-metal. This will form the equivalent of a Faraday cage (which should, analogously, have high conductivity) to block stray magnetic forces. <a href="http://en.wikipedia.org/wiki/Mu-metal" rel="nofollow">Mu-metal</a> is a nickle/iron alloy with traces of copper and molybdenum that is often used for this purpose. Other nickle/iron alloys will also work. Layers of encasement will increase the attenuation exponentially if a single layer is insufficient to do the job. </p>
<p>You can get shielding from <a href="http://www.aircraftspruce.com/catalog/elpages/edmomumetal.php" rel="nofollow">aircraft supply companies</a> in tape form, used to wrap the magnetos and prevent radio interference. <a href="http://www.lessemf.com/mag-shld.html" rel="nofollow">LessEMF.com</a> sells various other forms such as sheet metal, 1" tape, and a more flexible mesh; shields were more popular when CRT monitors and TVs were in wide use so there are probably lots of other sources. You are probably dealing with relatively week magnetic fields, though, so it might be worthwhile to try out cheap steel sheet metal before buying something more exotic and expensive.</p>
| <p>I recently bought a 0-35V 0-3A (105W) CC/CV linear power supply, made by Takasago in Japan, second hand. It's a nice unit, and inside of it is a massive power transformer along with three pass transistors on a very large heatsink (it is interesting why there are three transistors but I can only suspect that they are to reduce the load on an individual transistor), and it weighs a ton. I've fully tested it to 105W, although only for about 5 seconds as even my 2x25W resistors were getting too hot.</p>
<p>I originally had plans to put it on top of my HP 54501A, a digitising oscilloscope with a CRT raster monitor (unlike a normal CRT scope which draws a trace by moving the electron beam - this sets pixels on and off representing the trace.) However, I found that when turned on, whether above the scope or on the bench below, the CRT would have a weird ripple effect or would shift position randomly. It didn't matter if the supply was loaded down or not. The trace was not affected, just the display (even text and graphics). Why would the supply cause this? I suspect it has something to do with the transformer because that makes a humming sound in operation if you listen carefully.</p>
| Why would a power supply mess with my scope? | 2011-01-19T00:52:41.317 |
9190 | |electromagnetism|actuator| | <p>You need to rethink your requirements. Opening and closing a mechanical shutter in 500 microseconds is an extreme demand. Most mechanical shutters take several times as long to open completely. The shutters in SLRs achieve sub-millisecond exposures by opening partially and moving the opening across the frame so each portion "sees" light for a brief interval, but the overall exposure takes longer. <a href="http://en.wikipedia.org/wiki/Rapatronic_camera" rel="nofollow noreferrer">Extremely fast opening and closing times</a> are the domain of <a href="https://electronics.stackexchange.com/questions/7697/where-can-i-find-a-fast-1khz-lcd-plate">electro-optical shutters</a>.</p>
| <p>I'd like to drive a pair of mechanical shutter / apertures with an electromagnet. For those curious, we're using a <a href="http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=1461" rel="nofollow">shutter from Edmond optical</a>. For the particular application, I'd like to design a compact actuator to drive it. (I had considered just hacking a camera lens with a shutter, but couldn't find one that was large enough for my needs).</p>
<p>So at present I am thinking about attaching a neodymium magnet to the lever of the shutter and then using a series of electromagnets to push it between open and closed. Which all leads to my first question: how can build compact electromagnet?</p>
<p>It seems like the steps involved are to find a solenoid and then to drive it with a decent voltage difference. I wonder if anyone could recommend a good small solenoid for such purposes. Does it make more sense to roll my own with an iron core and insulated wire?</p>
<p>My second question is more open-ended: can you think of a better way to drive such a shutter? How would you design the shutter motor?</p>
<p>UPDATE: in response to comments:</p>
<p>@tyblu the shutter needs to be open or closed in about 500 microseconds (but exactness is not important). </p>
<p>@bt2 a solenoid is interesting, are you thinking of hitting the lever and letting momentum carry it across to the close position?</p>
| Controlling a mechanical shutter with an electromagnet | 2011-01-19T05:10:03.423 |
9194 | |arduino|soldering| | <p>As far as your question about soldering the gyro sensor to the aeroquad shield goes, if you look a the tiny picture on their website, in the center of the board there is a region marked "gyro". You'll take the single inline pin strips (also pictured) and break off 7 pins as a group. Then you'll solder the short end into the gyro board. Then (unfortunately) it looks like you'll have to solder the gyro board into aeroquad.</p>
<p>As far as shields go, in my experience (Arduino Duemilanove) the spirit behind the shield concept is to allow them to stack up. The aeroquad "shield" doesn't appear to allow this, so I imagine you'll want to get single inline headers and solder them into the aeroquad so you can plug in the Arduino.</p>
<p>So if you want to add more breakout boards, the general procedure would be to get the headers with the extra long pins, and put those through your protoboards so that other shields can stack on top of them. This allows everyone access to the pins in the Arduino that they need.</p>
| <p>I need to solder some breakout boards onto an Arduino shield. What's the general procedure to do this? Do I solder it onto a header? Do I need any other mechanical connection or hold-down?</p>
<p>For example, I would like solder this gyro sensor onto this aeroquad shield:</p>
<p>gyro sensor: <a href="http://www.aeroquadstore.com/ProductDetails.asp?ProductCode=SEN-09801" rel="nofollow">http://www.aeroquadstore.com/ProductDetails.asp?ProductCode=SEN-09801</a></p>
<p>aeroquad shield: <a href="http://www.aeroquadstore.com/ProductDetails.asp?ProductCode=AQ2-000" rel="nofollow">http://www.aeroquadstore.com/ProductDetails.asp?ProductCode=AQ2-000</a></p>
| How do I solder a Sparkfun breakout board to a shield? | 2011-01-19T06:24:05.620 |
9195 | |sensor| | <p>A magnetometer will 'work' anywhere there is a magnetic field that is large enough to be detected by that particular sensor. This is determined by the noise floor of the sensor, i.e. the magnitude at which the S/N ratio is large enough that the signal information can be recognized over the system noise level.</p>
<p>And direction matters. Even for vector sensors.</p>
<p>I don't think that there is anywhere on Earth, or in the Solar System inside of the orbit of Venus, where, say, a squid (or a SERF) couldn't detect a magnetic field. I think there are many fluxgates that could detect a magnetic field anywhere on Earth (which, off the top of my head, is around 0.5 Gauss - a very large value).</p>
<p>The important thing to recall is that there are around a dozen major classes of magnetic sensors and they all have different specs, the main one being the resolution (i.e. the smallest signal they can detect, - the noise floor).</p>
<p>Why do you want to find a place they don't work? </p>
| <p>Are there any places on the globe where magnetometers won't work?</p>
<p>For example, if you took a <a href="http://www.sparkfun.com/products/9441" rel="nofollow">Honeywell HMC5843</a> to the North or South magnetic pole, would they fail to function properly?</p>
| magnetometers: do they work all over the globe? | 2011-01-19T06:40:20.647 |
9208 | |can| | <p>It seems that you have a situation where one node can RX/TX, but the other cannot TX, but still RXs. This is relatively common failure mode.</p>
<p>RX can work without TX working, but TX must have RX feedback, so if only RX is working, you have isolated it to your TX line.</p>
<p>I start with easy, which involves checking for cold joints and for disconnected pins. Do connectivity checks towards from the device sending the signal. </p>
<p>If this is your issue, it seems you may have a problem. Also, if you have a slope control pin, make sure that it has the required signal.</p>
| <p>I am using the <a href="http://cache.freescale.com/files/32bit/doc/ref_manual/MCF5253RM.pdf" rel="nofollow">MFC5253 controller</a>. It has two CAN channels, CAN 1 and CAN 2. In my project, I am using both of them. Their registers are the same, except for the name (1 and 2).</p>
<p>I can transmit and receive data correctly from CAN1 but not from CAN 2.... How do I fix this problem? </p>
| MCF5253 CAN controller transmission problem | 2011-01-19T14:26:03.247 |
9216 | |led|diodes|resistance|parallel| | <p>Ordinary resistors are linear devices; if 10V over a resistor results in a 1mA current, then 20V will give you 2mA. That's easy enough, but few components are that simple.<br>
A LED (or any diode for that matter) for instance doesn't behave like that. </p>
<p><img src="https://i.stack.imgur.com/PZGB5.png" alt="enter image description here"></p>
<p>If you put a low voltage like 100mV over a diode there will hardly be any current. If you slowly increase the voltage you'll see that around 0.7V the current begins to flow, to reach a high value very soon, see graph. We can see that the voltage over the diode is more or less constant. The 0.7V is for a common silicon diode, for LEDs this voltage will be higher, mainly depending on the color, but the graph is basically the same. Because the current will increase so suddenly to a value that will destroy the LED you have to use a current-limiting resistor. The increase in current will be sudden, but not immediate; the line in the graph is not quite vertical. That's because the LED has also a small resistance, but this is too small to limit the current to a safe value.
So what does this mean in a circuit? </p>
<p><img src="https://i.stack.imgur.com/JfWio.gif" alt="enter image description here"> </p>
<p>Two of the basic things in circuits (apart from Ohm's Law) are Kirchhoff's Laws, there's a Kirchhoff's Voltage Law, aka KVL, and a Kirchhoff's Current Law (KCL). We forget KCL for a moment and have a look at KVL, the voltage law. This says that the sum of the voltages in any closed loop is zero. You choose a direction in which you go through the loop. We choose clockwise. The power supply's voltage is usually chosen as positive, going clockwise we go from negative to positive. Then the voltages over the resistor and LED are negative, because we encounter positive first. Then Kirchhoff says: \$V_{BAT} - V_{R} - V_{LED} = 0\$, or \$V_{BAT} = V_{R} + V_{LED}\$. Let's assume the LED has a voltage of 2V. Then we can calculate \$V_{R} = V_{BAT} - V_{LED} = 6V - 2V = 4V\$, and the current through the circuit \$I = \frac{V_{R}}{R} = \frac{4V}{330 \Omega} = 12mA\$. </p>
<p>What happens if we place a switch parallel to the LED? If the switch is closed it has zero resistance, and according to Ohm's Law it will have zero voltage over it. And still according to Ohm zero voltage over any resistance means zero current, so given the LED's resistance there will flow no current through it.</p>
| <p>I've been playing around with an Arduino for a while now, and while I know just enough about simple circuits to get little projects up and running, I still don't know enough to figure out what's going on in all but the simplest of circuits. </p>
<p>I've read a few books on electronics and a handful of online articles, and while I think I understand how voltage, current, resistors, capacitors and other components work; when I see a schematic with lots of them in, I don't know what's going on where. </p>
<p>In a bit to finally get to grips with it, I bought a 300-in-1 Electronics Project Set, however it seems to jump from "Here is a circuit with two resistors in parallel" to things more complex, without explaining how it works. </p>
<p>For example, it shows a simple battery->resistor->LED circuit, but shows that if you wire a button up in parallel with the LED, pressing the button turns the LED off. </p>
<p>I get that the current must be travelling through the path of least resistance, but I don't understand <strong>why it doesn't travel through both</strong>. </p>
<p>I'm taught that wiring two resistors up in parallel causes the current to flow through both, and so more current flows in the circuit. I've also tried replacing the button in the circuit above with resistors of varying values, and as I suspected, a high value resistor doesn't affect the bulb at all, but lower values start to dim the bulb. </p>
<p>I'm not sure <strong>how to apply the E = IR equation</strong> to all of this. </p>
<p>Also, <strong>how much resistance does an LED have?</strong> I tried measuring it with my multimeter, but it wouldn't give a reading. </p>
<p>Sorry if I've waffled on loads here, but I'm trying to paint a picture of what I think I understand and what I want to understand. Not sure I've achieved that!</p>
<p>Oh yeah, and expect lots more of this as I delve deeper into my 300-in-1 project kit!</p>
| How do I calculate the current in parallel branches? | 2011-01-19T19:29:12.040 |
9219 | |high-voltage|piezoelectricity| | <p>This is actually quite a simple circuit which works by stepping up the collapse of a magnetic field in a small audio transformer.</p>
<p>The schematic looks like this:</p>
<p><img src="https://i.stack.imgur.com/K1uzd.jpg" alt="schematic"></p>
<p>I think something <a href="http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MT4135-ND" rel="noreferrer">like this part</a> should work for the transformer.</p>
<p>If you touch the two output wires, you'll get a very small electric shock as you release the push button.</p>
| <p>Can anyone tell me how to make a simple electric shocking device (like a electric pen or hand buzzer style). I've seen people use piezoelectric elements from lighters (is that correct?) but I would like to know how to create one from scratch, and also what current and voltage is needed to give a small shock. Thanks, ell.</p>
| Simple Electric Shock Device | 2011-01-19T20:04:03.660 |
9222 | |safety| | <p>The HAM Radio Technician Class examination question provides this answer:</p>
<pre><code>2010 Pool - Question T0A01
Category: T0A - AC power circuits; hazardous voltages, fuses and
circuit breakers, grounding, lightning protection,
battery safety, electrical code compliance
Which is a commonly accepted value for the lowest
voltage that can cause a dangerous electric shock?
A 30 volts
</code></pre>
| <p>What's the point below which electrical current is generally considered safe for "casual" human contact?</p>
<p>Is either voltage or amperage more "dangerous" (e.g. high voltage / low amperage vs. low voltage / high amperage), or is the only consideration the total current?</p>
| Safe current limit for human contact? | 2011-01-19T22:45:13.070 |
9224 | |pcb|soldering|surface-mount|library|tqfp| | <p>Funnily enough, I recently followed a manufacturer's recommended land pattern for a TQFP, and got bitten.</p>
<p>Microchip have an excellent repository of IC drawings and associated land patterns here: <a href="https://www.microchip.com/en-us/support/package-drawings" rel="nofollow noreferrer">https://www.microchip.com/en-us/support/package-drawings</a></p>
<p>Amongst them is the "32-Lead Plastic Thin Quad Flatpack (3BB)" a 7x7x1.0mm TQFP with 0.8mm pitch. The land pattern recommends 8.50mm between pad centres, with each pad 0.55x1.60mm. This makes them 6.90mm apart, and 10.10mm from edge to edge.</p>
<p><a href="https://i.stack.imgur.com/ipGMU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ipGMU.png" alt="enter image description here" /></a></p>
<p>This happens to be exactly the pattern in the KiCad standard library:</p>
<p><a href="https://i.stack.imgur.com/05Nkb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/05Nkb.png" alt="enter image description here" /></a></p>
<p>The edge to edge distance of the pins themselves is 9.00mm, and the length of the pin contact area is about 0.60mm. So regarding your questions about centring, this works out to be pretty much exactly centred.</p>
<p>Which is it came unstuck for me. After reflow I had a few bridges to tidy up but even after removing what I could see I still had a short. Removing the part revealed this:</p>
<p><a href="https://i.stack.imgur.com/Zt5Ev.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Zt5Ev.jpg" alt="enter image description here" /></a></p>
<p>Notice how the 3 or 4 pins at the top left have ridges towards the <em>inside</em> of the pad? There was so much solder building up <em>behind</em> the pin that I was getting an invisible short.</p>
<p>I fixed this instance by removing a substantial portion of the solder and reflowing. But in future I will be shortening the pads so they mostly extend to the <em>outside</em> of the pin, not the inside. This still provides plenty of solder contact area, but exposes it where I can see and touch it.</p>
<p>I think you still want a bit of pad on the inside to allow the part to self-centre, but I'd much prefer having to be more accurate with my placement than have to remove excess solder from under the part.</p>
<p>Here's what it looks like successfully soldered (note it's the same part, different location). Notice how much pad is visible on the outside of the pins, and therefore how much pad is hiding underneath the part.</p>
<p><a href="https://i.stack.imgur.com/m0ier.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/m0ier.jpg" alt="enter image description here" /></a></p>
| <p>I'm putting together a footprint for a 100-pin, 14x14mm TQFP, and I'm finding conflicting designs. The pitch and width of the pads are all basically the same, but the length and centering of the pads horizontally varies a good deal.</p>
<p>The following images are from the Microchip <a href="http://www.microchip.com/stellent/groups/techpub_sg/documents/packagingspec/en012702.pdf" rel="noreferrer">packaging specifications document</a> (see page 282-283), so that we can have names to use for the dimensions.<br>
<b>Physical Package:</b> </p>
<p><img src="https://i.stack.imgur.com/cqlXs.png" alt="overall pins"> <img src="https://i.stack.imgur.com/VgWee.png" alt="pin lengths"> </p>
<p><b>Recommended Footprint:</b> </p>
<p><img src="https://i.stack.imgur.com/LOHoX.png" alt="center to center overall"> <img src="https://i.stack.imgur.com/zDu1b.png" alt="pad length"> </p>
<p><sub>There's a table with numbers for each dimension, but the exact details aren't really important here.</sub></p>
<p>Where should the pin go on the pad lengthwise? </p>
<ol>
<li> Should the pin be centered on the pad? </li>
(C1 = D - L) If so, what should Y1 be? L, L+tolerance, 2L?
<li> Should the inner edge of the pad line up with the inner edge of the pin?</li>
(C1 - Y1 = D - 2L) If so, how far should the pad stick out in front of the pin?
<li> Should the pad and pin have some other dimension?
</ol>
<p>Note that the question is basically moot if Y1=L. I'm assuming that I'll want a little extra pad to hit with the soldering iron.</p>
<p>It might be relevant that L1 is allowed to vary by ±25%, which feels like a bigger variation if you read 'between 0.45 and 0.75mm'. It might not be relevant.</p>
<p>I'm interested in solderability, avoiding invisible solder bridges under the chip, routing traces underneath (and outside of) the chip. Of course, I don't want to use absurdly long pads for heat dissipation and board space reasons.</p>
| Pad dimensions and land patterns for QFPs | 2011-01-19T23:50:15.300 |
9226 | |usb|avr|software|teensy|lufa| | <p>You need to edit the HID report descriptor, but also the main code. Change this portion of the HID descriptor:</p>
<pre><code> 0x05, 0x09, /* Usage Page (Button) */
0x09, 0x02, /* Usage (Button 2) */
0x09, 0x01, /* Usage (Button 1) */
0x15, 0x00, /* Logical Minimum (0) */
0x25, 0x01, /* Logical Maximum (1) */
0x75, 0x01, /* Report Size (1) */
0x95, 0x02, /* Report Count (2) */
0x81, 0x02, /* Input (Data, Variable, Absolute) */
0x75, 0x06, /* Report Size (6) */
0x95, 0x01, /* Report Count (1) */
0x81, 0x01, /* Input (Constant) */
0xc0 /* End Collection */
</code></pre>
<p>To this:</p>
<pre><code> 0x05, 0x09, /* Usage Page (Button) */
0x09, 0x03, /* Usage (Button 3) */
0x09, 0x02, /* Usage (Button 2) */
0x09, 0x01, /* Usage (Button 1) */
0x15, 0x00, /* Logical Minimum (0) */
0x25, 0x01, /* Logical Maximum (1) */
0x75, 0x01, /* Report Size (1) */
0x95, 0x03, /* Report Count (3) */
0x81, 0x02, /* Input (Data, Variable, Absolute) */
0x75, 0x06, /* Report Size (5) */
0x95, 0x01, /* Report Count (1) */
0x81, 0x01, /* Input (Constant) */
0xc0 /* End Collection */
</code></pre>
<p>And set the third bit of the Buttons element in the element in the <code>CALLBACK_HID_Device_CreateHIDReport()</code> function of the main source file, i.e. to "push" the new third button, use:</p>
<pre><code> if (ButtonStatus_LCL & BUTTONS_BUTTON1)
JoystickReport->Button |= (1 << 2);
</code></pre>
| <p>I'm trying to jump in the USB world with <a href="http://www.fourwalledcubicle.com/LUFA.php" rel="nofollow"><strong>LUFA</strong></a> on a <a href="http://www.pjrc.com/teensy/" rel="nofollow">Teensy dev board</a>, but I'm stuck in the understanding of the descriptors.</p>
<p>Currently I'm trying to add one button to the joystick demo without sucess. <strong><em>Does anyone know some resource that explains step by step how to set up a USB descriptor?</em></strong></p>
<p>edti :
After reading USB in a nutshel, I think I may not modified the Descriptor at all but the HIDReport instead...</p>
| USB descriptor (LUFA) | 2011-01-20T00:11:33.243 |
9227 | |switch-mode-power-supply|protection|boost| | <p>In boost PFC applications, there is peak current limiting usually through a combination of two current transformers (one sensing the switch current, the other sensing the diode current) which works by collapsing the duty cycle of the converter, reducing the output voltage and (if the load is not CC) the current.</p>
<p>There is no way to protect against a hard short except for opening some sort of limiting device (i.e. fuse)</p>
| <p>Is it possible to add short circuit protection to a boost converter?</p>
<p>My initial instinct was <em>no</em>, as the switch does not directly control the input to the inductor and this means the minimum output is Vin or so.</p>
<p>But are there ways to protect such a converter?</p>
| Short circuit protection for a boost converter | 2011-01-20T01:19:57.857 |
9237 | |resistors|current|switches|dip| | <p>If you connect all your switches to the single resistor all your switches will be parallel, and you'll have only 1 output instead of 8. In fact this is a NOR gate: if at least one switch is closed the output will go low, if all switches are open the output will be high. This may have its application, but it's not the functionality you want. </p>
<p>You need a pullup resistor per switch.</p>
<p>Like <em>BarsMonster</em> says resistors are cheap (not only the SMDs). Don't buy a single part, a single 1/4W carbon film resistor costs 8 cent at Digikey, at set of 100 costs 2.2 cent per resistor. Have a few standard values at hand, like 1k\$\Omega\$ (typical for a transistor's base resistor) and 10k\$\Omega\$ (typical for pullup).</p>
| <p>I was thinking of giving each switch it's own pull-up resistor, but this seems like it would be expensive and a little bit of overkill. But using just one pull-up for the entire block seems like it might overload the resistor (unless I just use a big one).</p>
<p>Are there any guidelines in this situation?</p>
| How many resistors do I need for an 8 switch DIP switch block? | 2011-01-20T14:42:47.720 |
9246 | |sensor| | <p>The one you picture here is a polymer film that has conducting particles held within it (think of something like novolac resist or SU8 with metal micro-particles evenly distributed within it). The film has a non-zero conductivity.</p>
<p>When you press on it some of the micro-particles touch, increasing the conductivity. Pretty simple.</p>
<p>It's not the same as the piezo-resistive effect, which depends on the shape of a crystal lattice in the atomic structure. when you bend it, the crystal lattice either expands or contracts, causing the resistance to increase or decrease because of a slight change in the energy bands of the crystal.</p>
| <p>How does a Force-Sensitive Resistor work?</p>
<p>Does it work by sensing the number of tracks the user covers meaning that the more force the user pushes on the sensor the less resistance it causes?</p>
<p>Here is a picture of one:</p>
<p><img src="https://i.stack.imgur.com/G8FlZ.jpg" width="500"></p>
| How do Force-Sensitive Resistors work? | 2011-01-20T21:39:24.203 |
9251 | |control|pid-controller| | <p>There are several points why the Z-transform form has higher utility.</p>
<p>Ask anyone promoting the time-based/simple/sans-PHD approach what the set their Kd term to.
They are likely to answer 'zero' and they are likely to say D is unstable (without a low-pass filter).
Before I learned how all this comes together, I would have and did say such things.</p>
<p>Tuning Kd is difficult in the time-domain.
When you can see the transfer function (the Z-transform of the PID sub-system) you can readily see how stable it is.
You an also readily see how the D term is affecting the controller relative to the other parameters. If your Kd parameter contributes 0.00001 to the z-polynomial coefficients but your Ki term is putting in 10.5 then your D term is too small to have a real effect on the system. You can also see the balance between the Kp & Ki terms.</p>
<p>DSP's are designed to calculate finite-difference-equations (FDE).
They have op-codes that will multiply a coefficient, sum to an accumulator, and shift a value in a buffer in one instruction cycle. This exploits the parallel nature of FDE's.
If the machine lacks this op-code... it's not a DSP.
Embedded PowerPC's (MPC) have a peripheral dedicated to calculation of FDE's (they call it the decimation unit).
DSP's are designed to calculate FDE's because it's trivial to transform a transfer-function into a FDE.
16-bits is not quite enough dynamic range to easily quantize coefficients.
Many early DSP's actually had 24-bit words for this reason (I believe 32-bit words is common today.)</p>
<p>IIRC, the so-called bilinear transform takes a transfer function (a z-transform of a time-domain-controller) and turns it into a FDE. Proving it is 'hard', using it to obtain a result is trivial - you just need the expanded form (multiply everything out) and the polynomial coefficients are the FDE coefficients.</p>
<p>A PI controller is not a great approach - a better approach is to build a model of how your system behaves and use PID for error correction.
The model should be simple and based on the basic physics of what you are doing.
This is the feed-forward into the control block.
A PID block then corrects for error using feedback from the system under control.</p>
<p>If you use normalized values, [-1 .. 1] or [0 ... 1], for the set-point (reference), feedback, & feed-forward then you can implement one 2-pole 2-zero algorithm in optimized DSP assembly and you can use it to implement any 2nd order filter which includes PID and the most basic low-pass (or high-pass) filter.
This is why DSP's have op-codes that presume normalized values, e.g. one that will output an estimate of the inverse-squareroot for the range (0..1]
You can put two 2p2z filters in series and create a 4p4z filter, this allows you to leverage your 2p2z DSP code to, say, implement a 4-tap low-pass Butterworth filter.</p>
<p>Most time-domain implementation bake the dt term into the PID parameters (Kp/Ki/Kd).
Most z-domain implementations don't. dt is put into the equations that take Kp, Ki, & Kd and turn them into a[] & b[] coefficients so your calibration (tuning) of the PID controller is now independent of the control rate. You can make it run ten-times faster, crank out the a[] & b[] math and the PID controller will have consistent performance.</p>
<p>A natural result of using FDE is that the algorithm is implicitly "glitchless".
You can change the gains (Kp/Ki/Kd) on-the-fly while running and it is well-behaved - depending on the time-domain implementation this can be bad.</p>
<p>A lot of effort is usually spent on time-domain PID controllers to prevent integral wind-up. There's a simple trick with the FDE form that makes the PID behave nicely, you can clamp it's value in the history buffer. I haven't done the math to see how this affects the behavior of the filter (with regard to Kp/Ki/Kd parameters), but the empirical result is that it's 'smooth'. This is exploiting the 'glitchless' nature of the FDE form.
A feed-forward model contributes to prevent integral wind-up and the use of the D term helps balances the I term. PID really doesn't work-as-intended with a D gain.
(Slewing setpoints is another key feature to prevent excessive wind-up.)</p>
<p>Lastly, Z-transforms are an undergrad topic not "Ph.D."
You should have learned all about them in Complex Analysis.
This is where the university you go, the instructor you have, and the effort you put into learning the math and learning how to use the tools available can make a significant difference in your ability to perform in industry. (My Complex Analysis class was horrible.)</p>
<p>The defacto industry tool is Simulink (which lacks a computer-algebra-system, CAS, so you need another tool to crank out general equations).
MathCAD or wxMaxima are symbolic solvers you can use on a PC and I learned how to do it using a TI-92 calculator. I think the TI-89 also has a CAS system.</p>
<p>You can look up z-domain or laplace-domain equations on wikipedia for PID & low-pass filters. There's a step here that I do not grok, I believe you need the discrete-time-domain form of the PID controller then need to take the z-transform of it.
The laplace transform should be very similar to the z-transform and is given as PID{s} = Kp + Ki/s + Kd·s
I think the z-transform would better account for the Dt's in the following equations.
Dt is delta-t[ime], I use Dt as not to confuse this constant with a derivative 'dt'.</p>
<pre><code>b[0] = Kp + (Ki*Dt/2) + (Kd/Dt)
b[1] = (Ki*Dt/2) - Kp - (2*Kd/Dt)
b[2] = Kd/Dt
a[1] = -1
a[2] = 0
</code></pre>
<p>And this is the 2p2z FDE:</p>
<pre><code>y[n] = b[0]·x[n] + b[1]·x[n-1] + b[2]·x[n-2] - a[1]·y[n-1] - a[2]·y[n-2]
</code></pre>
<p>DSP's typically only had an multiply & add (not a multiply & subtract) so you may see the negation rolled into the a[] coefficients.
Add more b's for more poles, add more a's for more zero's.</p>
| <p>I've seen many PID articles, such as <a href="http://www.eetimes.com/design/embedded/4212241/Case-Study-of-PID-Control-in-an-FPGA-?cid=NL_Embedded&Ecosystem=embedded">this</a>, use a Z transform of the generic PID equation to derive some crazy difference equation which can then be implemented in software (or in this case an FPGA). My question is, what is the advantage to such an implementation versus the traditional and much more intuitive, <a href="http://igor.chudov.com/manuals/Servo-Tuning/PID-without-a-PhD.pdf">PID without a PhD</a> type implementation? The second seems easier to understand and implement. The P term is straight multiplication, the integral uses a running sum and the derivative is estimated by subtracting the previous sample from the current sample. If you need to add a feature such as Integral Windup protection, it is straight forward algebra. Trying to add Integral Windup protection or other features to a difference type algorithm, such as linked above, seems like it would be much more complicated. Is there any reason to use such an implementation, other than the "I'm a bad ass who likes to do Z transforms for fun" type bragging rights that go along with it?</p>
<p>EDIT: The PID without a PHD article I linked is an example of the simpler implementation that uses a running sum for the integral term and the difference between consecutive samples for the derivative term. It can be implemented with fixed point math in a deterministic manner and can include real time time constant information in the calculation, if desired. I'm basically looking for a practical advantage to the Z transform method. I can't see how it could be faster, or use less resources. Instead of keeping a running sum of the integral, the Z method appears to use the previous output and subtract the previous P and D components (to arrive at the integral sum by calculation). So, unless someone can point to something I'm missing, I will accept AngryEE's comment that they are essentially the same.</p>
<p>FINAL EDIT:
Thanks for the responses. I think I've learned a bit about each but in the end, think Angry is correct in that it is just a matter of preference. The two forms:</p>
<p>$$ u(k) = u(k-1) + K_p(e(k) - e(k-1) + K_i T_i e(k) + \frac{K_d}{T_i}(e(k)-2e(k-1)+e(k-2)) $$
$$ e(k-2) = e(k-1), \quad e(k-1) = e(k) $$
$$ u(k-1) = u(k) $$</p>
<p>or</p>
<p>$$ \mbox{sum} = \mbox{sum} + e(k) $$
$$ u(k) = K_p e(k) + K_i T_i\cdot \mbox{sum} + \frac{K_d}{T_i}(e(k)-e(k-1)) $$
$$ e(k-1) = e(k) $$</p>
<p>will evaluate to essentially the same thing. Some mention the first can be implemented in a DSP or FPGA faster, but I don't buy that. Either could be vectorized. The first requires two post operations, the second requires one pre and one post operation, so it appears to even out. The first also requires 1 more multiplication in the actual calculation.</p>
| What is the advantage of a Z transform derived PID implemenation? | 2011-01-21T00:11:08.873 |
9253 | |eaglecad|pcb-design| | <p>I don't think there's an easy way around this. I would open up the <em>resistor-power.lbr</em> library on its own, in the library editor, open up the first footprint (ACO1), change the major grid to <em>10mm</em>, then go through each one and note those that are close. There's usually some kind of logic to the footprint names and numbers -- for this library, it appears the <em>letter prefix denote a width</em> class and the <em>number denotes length</em>. <sup><strong><em>EDIT1:</strong></sup> I went and did this, and none are 47mm wide.</em><br>
<sup><strong><em>EDIT2:</strong></sup> After looking at the datasheet, it appears it is 47mm long and only 9mm wide, which fits <strong>HPS947</strong>. (<strong>KH216-8</strong>, <strong>RS10-38-39</strong>, and <strong>RWM8X45</strong> also seem to fit... sorta.)</em></p>
<p>In almost every PCB design you will be making your own parts. I find it useful to make a new EAGLE library for every project, and copy all used part into it. The easiest way to make a new part, if it's just a variation of another, is to copy symbols and possibly even footprints into a new layout, then edit them. For this part, you can copy the <em>power-resistor.lbr > R</em> symbol by opening it up as if you were going to edit it, selecting the whole thing with the <strong>Group</strong> function, then copying the group with the <strong>Copy</strong> function (click <strong>Copy</strong> button, right-click previously grouped symbol, select <em>"Copy: Group"</em>. This puts the whole thing into your <em>Paste Buffer</em>: </p>
<ul>
<li><img src="https://i.stack.imgur.com/ILNd6.png"> <em><-- (that button)</em></li>
</ul>
<p>Open up a new library, <em>example.lbr</em>, then create a new symbol <em>(Library > Symbol)</em>. Click the <strong>Insert Paste Buffer</strong> button <em>( ^-- that button)</em>. The copied symbol should come up, labels and all -- click on the crosshairs to line it up with the symbol anchor. I usually make my own footprints simply to remove all doubt in the library specs, but they can be copied using the same method. Another way to copy a part is to copy the entire library and rename it, then edit the entire thing. <strong><em><a href="http://www.sparkfun.com/tutorials/110" rel="nofollow noreferrer">Sparkfun also has a pretty good tutorial on making parts.</a></em></strong></p>
<p>Also, when I make my own parts, I fill out the caption so I won't have to browse the footprints directly in the future!</p>
| <p>I am working on my very first PCB design using Eagle. In my design, I will be using a <a href="http://www.mouser.com/Search/ProductDetail.aspx?R=CP001010R00JE14virtualkey61300000virtualkey71-CP001010R00JE14" rel="nofollow">10W 10 Ohm power resistor</a>. Since it isn't a "standard" size, I'm having trouble finding the component in Eagle. In particular, it has a width of 47mm.</p>
<p>No component in rcl.lbr is long enough. resistor-power.lbr seems pretty promising, but many of the components don't have measurements. And I'm not sure what the closest equivalent is. For example, KH216-8 seems like it is roughly the right size. And it happens to have a measurement. So is it, uh, "safe" to go with that?</p>
<p>How could I view the dimensions of a component if it's not in the description?</p>
<p>Are there any other techniques I can use when trying to find a library part that approximates the component I've chosen?</p>
| How to tell size of Eagle library component? | 2011-01-21T04:21:21.207 |
9259 | |jtag|debugging| | <p>My debugger for a Coldfire does some initialization of the SDRAM controller and other low-level registers that is normally done by the bootloader. Check to see how your debugger initializes the chip.</p>
| <p>I am using WindRiver JTAG Debugger to debug my code.
Whenever I run the code with Debugger connected, Code works correctly but If I disconnect it, It fails to even Start!</p>
<p>Has anyone faced such kind of Problems?</p>
| Code Running from Debugger but Not Without it | 2011-01-21T08:54:04.893 |
9264 | |uart| | <p>And just a footnote, DMX (for stage and theater lighting), usually sent over RS-485 using microphone cables or twisted pair, is at 250,000 baud. This is not a "standard" speed and to the best of my knowledge, the only chipsets that support it are the FTDI even though DMX is a common and popular protocol.</p>
| <p>I know 9600, 19200, 38400, 57600, 115200 and 1.8432 Mbaud, but no others. Why are these values used, and is it simply doubling each time or is there something more complex going on (for example, 38400 quadrupled is not 115200 baud?) </p>
<p>The reason I ask this question is I'm designing something which may have to interact with a variety of different baud rates. It will initialise in 9600, and then switch to a specific baud rate. But I can't support arbitrary rates because the dsPIC33F I am using does not support arbitrary rates as it is limited to a 16-bit BRG down counter. It's similar in this regard to many other processors.</p>
| What standard UART rates are there? | 2011-01-21T13:14:28.590 |
9271 | |schematics|best-practice| | <p>I think the closest equivalent is to develop the production test
fixture and test script for your circuit as soon as possible. Make
sure you test all important functionality. The test fixture emulates
whatever user interface and sensor hardware are attached to the
circuit. The "design verification" test script will probably have
more tests and take longer than the production test script, where you
are mostly testing to see that the pieces are connected together
properly.</p>
<p>So when you are making changes to the firmware or the circuit
itself, you can occasionally run the design verification test against
it to make sure you haven't caused any regressions. It is also
helpful to make reduced test scripts to test one aspect of the
circuit's performance, for example testing response across supply
variations, or a particularly tricky state machine that would require
two pages of instructions for a human to attempt. These shorter
scripts are to save time and give better test coverage than the full
script. But you always run the verification test before committing
changes to the schematic or firmware. For final released design run the verification test across temperature.</p>
| <p><a href="http://en.wikipedia.org/wiki/Daily_build" rel="nofollow">Daily build</a> in software is taking the source code, compiling it and generating the executables, then running that nightly. This is considered a best practice since it catches errors that prevent the build sooner rather than later, which makes it easier to fix. And if the build works, then others can make sure they aren't introducing errors.</p>
<p>What would be the equivalent for a schematic design? Clearly I can't build the PCB, but there might be something more than generating the netlist.</p>
<p>Edit 1/21/11: Also a <a href="http://en.wikipedia.org/wiki/Smoke_testing#Software_development" rel="nofollow">smoke test</a> is running some tests against the build. Again, not possible. I like the DRC (design rule check) idea, I'm thinking of checks such as that.</p>
<p>Edit 1/24/11: I was think of the schematic since that's what I do, rather than the PCB.</p>
| What is equivalent to a daily build (and smoke test) for schematic designs? | 2011-01-21T16:49:36.430 |
9272 | |fcc| | <p>If you build it for yourself, it would fall under 15.23 so FCC authorization isn't required, but you still need to design/build it in a way so that it doesn't disrupt telecommunications. See <a href="http://edocket.access.gpo.gov/cfr_2010/octqtr/47cfr15.23.htm">http://edocket.access.gpo.gov/cfr_2010/octqtr/47cfr15.23.htm</a></p>
| <p>Is FCC certification required for something you put together for personal use or only for something you actually sell to someone else?</p>
| Is FCC certification required for something that is not sold? | 2011-01-21T16:51:20.180 |
9279 | |bjt|emitter-follower| | <p>If you drive the base positive enough (assuming an NPN) what happens is the transistor 'saturates', and the collector voltage will dip to just a couple tenths above the emitter. In this mode, the base-collector junction is actually forward biased, instead of reverse biased as is usually the case.</p>
| <p>I've been playing with voltage swings in a basic emitter-follower circuit. If I swing the input too large in the negative cycle, the base-emitter junction is reverse-biased and the transister goes into cutoff mode. I can see the clipping in the output and this makes sense to me. With the collector, however, I've noticed that I can swing higher and not see symmetrcial clipping. Eventually I do see the clipping.</p>
<p>Is there a rule of thumb, like with the base-emitter junction, for managing base-collector junction? May I use VC-VB=0.6/0.7 V for this relationship too?</p>
| BJT transistor junctions: base-collector | 2011-01-21T18:46:23.720 |