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2270 | |arduino|arduino| | <p>Last time I looked the Sparkfun Speakjet shield did have stackable headers? Anyhoo aside from that moot point- It depends on how permanent your project is.</p>
<p>If you want to be able to use the Arduino again with different projects or shields - it's definitely recommended you get some stackable headers because of the cheap cost and ease of use. </p>
<p>If the project is relatively permanent and you don't intend on using the Arduino again in another project, soldering the wires on might be better for you, it will be cheaper in the short run and will be affective for making good connections - it's just fiddly to do and not the most professional looking way of hooking stuff up. </p>
| <p>I am just getting started with Arduino...I figure this is kind of a newbie question but here goes.</p>
<p>I have a Duemilanove and the Sparkfun Speakjet shield. I've got some breakaway headers (not the stackable headers) for connecting the Duemilanove with the Speakjet shield. But then I want to interface a bunch of other stuff like switches and LEDs to the Arduino pins that are not used by the Speakjet shield.</p>
<p>Is it required to get the stackable headers to wire up my switches and LEDs to the Arduino pins? Or is it advisable to just solder wires for my switches and LEDs onto the tiny nubs of the breakaway headers where they poke through the top of the Speakjet shield?</p>
| Tapping into unused Arduino pins with a shield in place | 2010-04-17T18:34:04.213 |
2272 | |capacitor|decoupling-capacitor| | <p>People typically give one explanation when asked what the function is of decoupling capacitors, but the truth is they fulfil several tasks. </p>
<p>Here is the list of things I am aware of:</p>
<p><strong>They reduce ground bounce</strong></p>
<p>Ground bounce is a phenomenon where a changing voltage difference across the ground plane negatively affects (mostly) analog and (sometimes) digital signals. For analog signals, like audio for example, this could manifest itself in the form of high pitched noise. For digital signals it could mean missing / delayed / fake signal transitions.</p>
<p>The changing voltage difference is caused by the creation and collapse of magnetic fields caused by changing current flows.</p>
<p>The longer the path the current flow has to follow, the higher the inductance associated with it and the worse the ground bounce becomes. Multiple current flow paths also exacerbate the problem, as well as the speed at which the current changes.</p>
<p>Current flow obviously occurs between a power supply and a connected IC, but somewhat less obviously also between "communicating" ICs. The current flow associated with two ICs looks like this; power supply -> IC 1 -> IC 2 -> Ground -> power supply.</p>
<p><em>A decoupling capacitor effectively decreases the length a current path by functioning as a power source, thereby decreasing inductance and thus ground bounce.</em></p>
<p>The previous example becomes; Cap -> IC 1 -> IC 2 -> Ground -> Cap</p>
<p><strong>They keep voltage levels stable</strong></p>
<p>There are two reasons why voltage levels fluctuate:</p>
<ul>
<li>Trace/wire inductance decreases the maximum rate of change of current through that trace/wire; a sudden increase in 'demand' for current will result in a drop in voltage; a sudden decrease in 'demand' for current will result in a spike in voltage.</li>
<li>Power supplies (especially those of the switching type) need time to respond and will slightly lag behind current demand.</li>
</ul>
<p><em>A decoupling capacitor will smooth current demand and reduce any drops or spikes in voltage.</em></p>
<p><strong>They CAN reduce EMI (transmission)</strong></p>
<p>When we talk about electromagnetic interference, we are either referring to the transmission of unintended electromagnetic interference or the receiving of intended or unintended electromagnetic signals that are interfering with the function of your device. Typically it refers to the transmission itself.</p>
<p>The placements of (decoupling) capacitors between power and ground planes changes the transmission coefficient across a range of frequencies. <a href="https://interferencetechnology.com/eliminating-the-myths-about-printed-circuit-board-powerground-plane-decoupling/" rel="noreferrer">Apparently</a> using only one value for your capacitors for the entire PCB as well as lossy / high resistance capacitors is the way to go if you need to reduce EMI, however this goes against common practice (which advocates an increasing order of capacitance the closer you are to the power supply). Most people don't really concern themselves with EMI if they make circuits for their hobby (though radio amateurs typically do), but it becomes unavoidable when you are designing a circuit for mass production.</p>
<p><em>A (decoupling) capacitor CAN reduce unintended electromagnetic radiation being produced by your circuit.</em></p>
<p><strong>To answer your remaining questions..</strong></p>
<blockquote>
<p>How do I know if I need one and if so, what size and where it needs to
go?</p>
</blockquote>
<p>Typically you place a decoupling capacitor whenever possible, choosing the smallest physical size with the largest value as close as possible to the power supply pin of the IC.</p>
<blockquote>
<p>Would an SN74195N 4-bit parallel access shift register used with an
Arduino need one? (To use my current project as an example) Why or why
not?</p>
</blockquote>
<p>It would probably work fine, but why bother with 'probably' if you can increase the odds by placing a component that costs a few cents, even a single cent in some cases?</p>
| <p>What is a decoupling capacitor (or smoothing capacitor as referred to in the link below)?</p>
<p>How do I know if I need one and if so, what size and where it needs to go? </p>
<p><a href="https://electronics.stackexchange.com/questions/2262/smoothing-capacitors-what-size-and-how-many">This question</a> mentions many chips needing one between VCC and GND; how do I know if a specific chip is one? </p>
<p>Would an <a href="http://pdf1.alldatasheet.com/datasheet-pdf/view/27391/TI/SN74195N.html" rel="noreferrer">SN74195N</a> 4-bit parallel access shift register used with an Arduino need one? (To use my current project as an example) Why or why not?</p>
<p>I feel like I'm starting to understand the basics of resistors and some places they're used, what values should be used in said places, etc, and I'd like to understand capacitors at the basic level as well.</p>
| What is a decoupling capacitor and how do I know if I need one? | 2010-04-17T23:47:47.080 |
2277 | |arduino|multiplexer| | <p>As rzrgenesys187 said:</p>
<blockquote>
<p>If pin C0 floats HIGH and C1 is
connected to AREF which is also HIGH,
then there shouldn't be any change.
Did you try connecting C1 to ground to
get zero when you run select_wire(1)?</p>
</blockquote>
<p>Yea, so it actually was switching the entire time.. however, there is a lot more distortion, so the wire connected to ground floated somewhere in the 10s. And AREF isn't high, so I don't understand how that works. AREF for me gave about the same values as ground when using</p>
<pre><code>analogReference(DEFAULT);
</code></pre>
<p>so not sure why, but AREF is giving me near-ground values... very strange, but the MUX does infact switch, so this question is answered.. and I actually never had any problems.. meh. </p>
<p>EDIT:</p>
<p>Actually, hooking straight into AREF does make it the input go high to 1023, so I have no idea why the input won't go that high with the MUX. maybe some kinda voltage limit, idk. I have to read up on it..</p>
<p>EDIT2:</p>
<p>Ok, finally think I'm figuring it out. Apparently breadboards leak a lot of current, so that if I was connected to C0 and it was reading C1, then a <em>lot</em> of voltage would leak to C1. Anyway though, connecting to AREF to C3 makes both inputs go high, so now I'm just even more confused. </p>
| <p>I am trying to get a Multiplexer to work with the Arduino. <a href="http://www.sparkfun.com/commerce/product_info.php?products_id=9056" rel="noreferrer">Description at sparkfun</a> <a href="http://www.sparkfun.com/datasheets/IC/cd74hc4067.pdf" rel="noreferrer">Datasheet</a></p>
<p>I thought the wiring was pretty simple and as a basic test, I have AREF connected to C1(multiplexer) and a floating wire connected to C0. Everything on the interfacing side maps almost 1 to 1 with the arduino. </p>
<p>I am using this simple code for switching the multiplexer</p>
<pre><code>void select_wire(char which){
digitalWrite(S0,which&0x01);
digitalWrite(S1,which&0x02);
digitalWrite(S2,which&0x04);
digitalWrite(S3,which&0x08);
digitalWrite(EN,0);
delay(1); //required?
}
</code></pre>
<p>and then I just read from the Analog pin at <code>S</code> on the multiplexer. My problem is that it is not switching! How do I fix this so that it will behave as intended and give a zero(or close) whenever I do <code>select_wire(1)</code> and read the analog pin? </p>
<p>Also, I am not using the Wiring "language" but I am using the Wiring library. I have also set all the appropriate <code>pinMode</code>s in the <code>init</code></p>
| Using Multiplexer with an Arduino | 2010-04-18T05:20:38.253 |
2289 | |usb|uart|microchip| | <p>It looks to me like the <a href="http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en546923" rel="noreferrer">MCP2200</a> is also supported as a CDC class device. In that mode bulk and isochronous transfers should also be supported.</p>
| <p>I was wondering how does the protocol mapping work between the USB side and the UART side when dealing with the Microchip MCP2200?</p>
<p>What sort of USB transfer type is used?</p>
<ul>
<li>bulk?</li>
<li>isochronous?</li>
<li>interrupt?</li>
</ul>
<p>Thanks for any clues!</p>
<p><strong>update</strong>: I found a bit more info <a href="http://www.lvr.com/usb_virtual_com_port.htm" rel="nofollow">Virtual COM port</a>.</p>
| USB-to-UART bridge: protocol mapping? | 2010-04-19T15:57:01.897 |
2294 | |led|automotive| | <p>Using a linear voltage regulator like an LM317T is a decent idea, but it means you're guaranteed to throw away 2 V, which is a little disappointing. You might instead try a low-dropout regulator like the LT3085-- with that, you'd only lose 0.275 V.</p>
<p>But in both cases, you'll be limited by the relatively low current limit of the regulator (1.5 A for the LM317T, only 500 mA for the LT3085). For a bike light, either would work fine, but I think you could build a more robust circuit without a regulator.</p>
<p>Here's what I'd suggest.</p>
<p>First, cap the voltage with a 13 V zener diode between power and ground. A zener diode is a diode that acts mostly like a normal diode-- a one-way valve. However, in the no-flow direction, it blocks current until you hit a certain threshold voltage. Once you hit that voltage, it opens up with very low resistance until you drop below the threshold again. It's great for capping voltage spikes. Be sure to get one that can handle the power you'll me pumping through it. Maybe start with a 5 W diode and then buy a fatter one if that burns?</p>
<p>Second, you need to limit the current through the LEDs. (If you did this part right, you might not even need the zener, but zeners are cheap.) LEDs burn out because they get too hot, and prolonged high current is what makes them hot. They can handle very high currents for short periods. Whatever LEDs you buy will have a current rating, like 20 mA at 4 V. There are no LEDs with voltages over roughly 5 V. The higher voltage LEDs you see advertised are either multiple LEDs in series or LEDs packaged with a current-limiting resistor. You can do better with discrete LEDs.</p>
<p>What you should do is put LEDs in series until you get close to your supply voltage-- maybe 3 of them, so you're trying to supply 3 * 4 V = 12 V, 20 mA. Then, take the remaining voltage between the cap (13 V) and the LED voltage (12 V) and pick a resistor that allows the right amount of current. In this case, 13 - 12 is 1 V, and you want 20 mA, so that's 1/0.020 = 50 ohms. I'd build one string like this and test it. Once that's working, build a few more. You can tweak the resistor value to make the LEDs a little brighter or dimmer (but don't burn them out).</p>
<p>Putting LEDs in parallel without giving each series string its own resistor is risky. LEDs are nonlinear elements-- raise the voltage a little near a certain threshold and the current changes dramatically. This means that they tend to not share current evenly. You might be able to pull it off if the LEDs are all from the same manufacturing run, but resistors are almost free; I wouldn't think it would be worth the savings.</p>
| <p>I would like to replace the bulb based tail/brake light and rear indicators/flashers on my bike with one integrated LED unit (flashers in brake light).</p>
<p>These are pretty expensive, and since I'm on a budget I'm looking at building one myself.</p>
<p>I've found some seemingly suitable 12v LEDs. I was hoping to use these to save me bothering with limiting resistors. However, one thing that bothers me is the max voltage rating of the LEDs and the rather unpredictable supply voltage. I've not yet measured it on my bike, but usually you would expect about 13v with the engine running. The absolute max voltage rating of the LEDs I'm looking at is 14v - do you think this is too close? Would the LEDs stand a higher voltage for short periods? (e.g. poss slightly higher V when at high engine revs when overtaking)</p>
<p>How would you protect against this? Would one resistor for the whole set of LEDs suffice? (one resistor supplying multiple parallel LEDs). Any suggestions on what kind of resistor to use? Perhaps it would just be better to use standard votage LEDs if I am forced to use resistors?</p>
<p>Anyway - any advice appreciated!</p>
| 12v LEDs and use on a motorbike | 2010-04-20T12:01:05.027 |
2304 | |power-supply|audio|voltage-regulator|noise| | <p>Not really an answer but an alternative.</p>
<p>For low current circuits you can use an AC adaptor without the rectifying bridge (the one that gives a low-voltage sine wave on it's output) or just a 220/110V->12V transformer and add two half-wave rectifiers (one diode for +12 and one for -12V). This way won't need two separate secondary windings on the transformer. Then you can regulate the voltage using one 7809 and one 7909 (but don't forget the capacitors on these).</p>
<p>PS. You could probably just remove some components from your adaptor but be extra careful when dealing with 220/110V circuits.</p>
| <p>I've got a battery powered synth that uses two 9v batteries to make a split rail power supply (±9 and ground). I'm trying to use a regular AC-DC power adaptor to replace the batteries. The adaptor outputs 12v and I'm regulating it down to 9v with the LM317 voltage regulator. To get the required -9v I'm using the ICL7660 CMOS voltage converter. The problem I have is with the noise created by the power supply, when i hook up the synth it works, but there's some oscillations and artifacts on the audio output. Does anyone know if there's a way I can filter out this noise?</p>
<p>here's the circuit so far -<br>
<img src="https://i69.servimg.com/u/f69/14/39/80/39/splitp10.jpg" alt="da circuit"></p>
| Can I Filter This Split Power Supply? | 2010-04-21T13:19:38.540 |
2311 | |soldering|surface-mount|surface-mount| | <p>Trapezoidal means that the edges of the stencil openings have a slope. This improves the solder paste distribution.</p>
| <p>When ordering a desktop stencil for laying down solder paste, there is an option to specify the stencil's aperture. Rectangular, home plate, trapezoidal...what's the difference between them? Is there one that is preferred for hand-populating surface mount parts?</p>
| Stencil apertures | 2010-04-21T20:14:37.157 |
2314 | |power|heat| | <p>One of the main issues with regulators like the LM7805 (and linear regulators in general) when you step down from large voltages is that a lot of the energy is dissipated as heat. If you are limited to passive cooling only and you have some significant power draw from your load, you might risk thermal overload.
Fear not, because if you are willing to put up with a bit more complexity and cost there is another option: <a href="http://www.national.com/appinfo/power/files/f5.pdf" rel="nofollow">Switching regulators</a>, specifically in this case buck converters, which work off of a completely different principle. Depending on what your other requirements are, like noise, stability, EMI considerations, you might look into some of the highly integrated switching regulator modules offered by TI, like the <a href="http://focus.ti.com/lit/ds/symlink/ptn78000w.pdf" rel="nofollow">PTN78000W family</a>. That part in particular is nice because of the adjustable output, so you can produce a variety of supply rails off of one part.</p>
<p>Cheers!</p>
| <p>I'm building a project that needs both 5V and 12V rails which will draw about 1A on the 12V and 0.5A on the 5V. I was thinking of using a 7805 to produce the required 5V but this could generate some significant heat. I am not so much asking if it is acceptable to use a 7805 (I just need a mini heatsink), but rather: are there any ways of doing it cooler? Any tips would be great.</p>
| What is the coolest way (using passive cooling only) to step 12V DC down to 5V DC | 2010-04-22T00:08:11.910 |
2318 | |shielding|wire|sensor| | <p>Are you sure the problem is noise coupling onto the cable? Is there any chance the ballast is producing a big enough magnetic field to saturate the sensor itself?</p>
| <p>What shielding techniques would be best suited for a digital sensor (3 wires - Pwr, Gnd, Sig) in a noisy environment (specifically fluorescent lighting)?</p>
<p>Twisted pair (trio in this case) works well for differential voltages, but I suspect it won't be effective here even though the current in the wires is balanced.</p>
<p>Does shielded wire require a separate ground wire, or is it acceptable to use the shielding as ground? Should the shielding be ground at both ends, or only at the PCB?</p>
<p>Edit: Sensor is connected to PCB via ~1m of cable.</p>
| Shielding Techniques for Digital Sensor | 2010-04-22T01:31:46.577 |
2324 | |microcontroller|avr| | <p>There are two main manufacturers of μC and the eternal dilemma Pic-Atmel. I cannot recommend to anyone what to choose, but I can explain the reasons that made me go for Atmel. Some of those reasons are unknown even to myself – maybe I liked more the way it sounds – but I felt more attracted to this family because it seemed to me much closer to the old Z80 microprocessor and that I used for several beautiful projects back when I was younger.</p>
<p>What can I say, if you decide to go in one direction, just stick to it and remain loyal to that family, according to the principle that it is better to know one thing completely than two things halfway.</p>
| <p>A recent question asked about the advantages/disadvantages of various types of MCU. AVRs seemed not even worth a mention given the answers. Why then does it seem to an outsider that AVRs are experiencing a rush of popularity? Is this solely due to the Arduino, or is there something else that makes the AVR an especially good microcontroller?</p>
| Why are Atmel AVRs so popular? | 2010-04-22T09:25:48.910 |
2332 | |rf|ethernet|wifi|network-interface| | <p>A very cheap way to add WiFi to a project, is to use a WiFi router as WiFi hardware. The router needs to be not-so-new in order to be cheap, and must support</p>
<ul>
<li>Serial/USB or JTAG ports on board</li>
<li><a href="http://openwrt.org">OpenWRT</a> (<a href="http://www.dd-wrt.com">DD-WRT</a> may work too, but I haven't used DD-WRT for this purpose)</li>
</ul>
<p>See OpenWRT <a href="http://wiki.openwrt.org/toh/start">supported hardware</a> page for information on what hardware is supported (note that DD-WRT supports more hardware). Router firmware already has a web server (for serving and admin page), a linux kernel (usually <a href="http://www.busybox.net/about.html">Busybox</a>), and most everything else you need to have a functional WiFi interface. Since OpenWRT is.. you know.. <em>open</em>, you can do whatever you want on the router side of the equation. </p>
<p>Many routers have USB connectors built in. Others have pads on the PCB that can be soldered to. This provides the router/microcontroller interface.</p>
<p>One solution is to get the router to do most of the interfacing for you (i.e. run a web server / web client, which the router/openWRT does already), and have your microcontroller just respond to get data requests or push data to the router via the serial/JTAG connection. </p>
<p>As an example the <a href="http://www.dlink.com/us/en/home-solutions/connect/routers/dir-601-wireless-n-150-home-router">D-Link DIR-601</a> can be found bought for about $5, has a serial port pads (some soldering required) and supports OpenWRT, albeit the flash space is a bit tight. Low power and small form factor this device surely isn't, but you cannot beat the price.</p>
| <p>I need low power wifi for a not-very-data-intensive application. What modules or chipsets should I look at? Other than low cost and low power, I have no restrictions. The cheaper the better.</p>
<p>This is for a high volume product, so both hobby level (since I can trace it back to an oem module) and oem level suggestions are welcome.</p>
| Cheapest way to add wifi to a project | 2010-04-22T15:36:10.857 |
2348 | |power-supply| | <p>If you're still looking for this type of power supply, I know that the older arcade style Xbox 360 Power Supplies (yes, they aren't the wall wart type, but they're still a wart on the floor) have an earth ground on the output connector.</p>
| <p>I am looking for an AC or DC output wall wart power supply
that provides an isolated output and brings out the earth
ground connection to the output.</p>
<p>Specs --</p>
<ul>
<li>Either single output or bipolar output</li>
<li>Any voltage 7V to 18V (preferable 7V)</li>
<li>100mA of current</li>
<li>Must be new and in production (no surplus)</li>
<li>Must have UL/CSA/TUV approval</li>
<li>Must be encapsulated or closed (no open frame designs)</li>
<li>Earth ground can be a separate connection or tied to
the power supply return.</li>
</ul>
<p>I haven't seen these made in a long while. All of the
wall-wart type supplies that seem to be made are isolated
and there is no earth ground.</p>
<p>Thanks for your help.</p>
| Looking for a Wall Wart Power Supply with an Earth Ground Connection on the Output | 2010-04-23T00:46:20.960 |
2369 | |linux|bootloader|arm| | <p>I have not much experience with bootloaders, but I can answer this question:</p>
<blockquote>
<p>How should I go about building/choosing a Linux distribution for this board?</p>
</blockquote>
<p>You should definitely use Debian as base of your system, because it's <strong>the most versatile Linux ever</strong>. It has a large package (application) collection for ARM and other architectures.</p>
<p>There are some distributions dedicated for ARM, but after 3 years of messing around with devices like Raspberry, BeagleBone etc. - I feel Debian has more packages working on ARM than ARM-specialized distros.</p>
| <p>I'm designing an embedded Linux board for use as a web-based controller. It will be based around an Atmel AT91SAM9G20, which uses an ARM926EJ-S core. Anyone have particularly good or bad experiences with bootloaders? More broadly, how should I go about building/choosing a Linux distribution for this board?</p>
| What's the best bootloader for an embedded Linux board? | 2010-04-24T20:04:30.963 |
2373 | |maximum-ratings| | <p>Technically, it is impossible to tell: switch manufacturers have to deal with the subtleties of arcing when designing circuits, and AC behavior is different than DC behavior. Arcs will be extinguished much more easily with AC (since voltage passes through zero) than with DC.</p>
<p>It's odd that the rating drops so much at 240VAC from the 6A rating at 125VAC. If the limiting factor were thermal behavior, I would expect the current rating would be the same. So I'm guessing they're probably using a particular test condition, like opening the switch with maximum rated current, assuming there's bouncing in the switch which may cause an arc.</p>
<p>Ask the manufacturer....</p>
| <p>I have a switch marked as having a max current of 2A at 240Vac, and 6A at 125Vac.</p>
<p>What would its max current rating be at 12Vdc?</p>
| What's the max current for this component? | 2010-04-24T22:01:38.443 |
2377 | |avr|attiny|programming|compiler| | <p>Devices like that are often programmed in assembler, resulting in smaller executables. It's worth making the effort and learning to use it.</p>
| <p>I'm trying to write a program for the ATTiny13. My problem is that it has huge size constraints. Well, when making my first Hello World program, it took 100 bytes of program space just to make a light turn on and off! Are there any options I can give to avr-gcc to shrink this size down? Also, what is in the crt0? I'm not too keen on AVR assembly so I don't understand it much.. </p>
<p>I do not want to have to drop to assembly for this project.. </p>
| ATTiny13 -- avr-gcc Hello World uses over 100 bytes? | 2010-04-25T02:19:27.283 |
2379 | |soldering|surface-mount|reflow|solder-paste| | <p>Solder paste drying out is not the problem. It's the fact that the flux is hygroscopic!</p>
<p>Now, this may not apply to all solderpaste, But I have left some unsoldered boards with paste on them lying about for varying amounts of time, and they become progressively more difficult to solder as time passes.</p>
<p>Basically, what happens is apparently the water flash-vaporizes, and literally causes the parts to go flying. I wound up having to use an old (dry) sponge to hold the parts down as they reflowed (this was the hot-plate reflow method).</p>
<p>I'm a bit mystified by the whole affair, as I would imagine the water would gradually boil off, not create a percussive effect powerful to actually launch 1206 parts about, but it is what happened.</p>
<p>This is with kester paste (variety is from digikey, don't know which specifically (not at my workstation at the moment).</p>
<p><strong>Edit</strong> - It looks like I'm currently using <a href="http://www.all-spec.com/products/KPS50005.html">Kester R500</a>. I prefer a more aggressive flux because I'm often doing unusual things to prototypes, and the boards are often a bit abused (the place I work has a terrible feature-creep problem). Other fluxes may behave differently.</p>
<p>Don't forget to wash your boards if you use a stronger flux.</p>
| <p>I'm soldering up some boards with smd parts, using a hot plate to reflow, and I'm (inevitably) realizing that I got some of the wrong parts. Now, is it better to leave the boards with smd components stuck on them (sitting in wet solder paste) until I can get the other parts, and then do the reflow all at once, or to reflow now, and then paste and heatgun (or just solder iron) the other parts in later? </p>
<p>I only have a few parts for which I need to do this, and I can stick the boards in a quiet refrigerator until I get the parts. I might not have ready access to a heat gun later, which is why this isn't a no-brainer (I'm imagining soldering iron+paste isn't the best way to do things, since I can't get to pads under the parts). Personally, I think the real question is whether reflowing twice negatively affects smd components, but context might prove it otherwise. </p>
| SMD solder now or later? | 2010-04-25T09:11:30.550 |
2381 | |power|schematics|connector| | <p>While this is resurrected due to Endolith's retagging, I want to clarify the reason that Pin 2 connects to the shield of the jack, but only when there's no plug inserted. You can do one of three things to wire this correctly: </p>
<ol>
<li>Only connect to pin 1.</li>
<li>Connect pins 1 and 2 together.</li>
<li>Connect pin 1 to your circuit's ground node, and connect pin 2 to another power connector (Black binding post for a banana jack, or battery ground terminal, for example.) Then, you can connect pin 3 to a red binding post or battery positive terminal, and have 2 power supplies without worrying about output contention. </li>
</ol>
<p>Method 3 is the reason that these plugs are designed the way they are.</p>
| <p>I am trying to include a DC jack on one of my PCBs. I am just setting up the footprints now, and I am not quite sure which pin is which. What do the symbols on the drawing mean?</p>
<p>I have included a snap of the schematic below, it has been taken directly from the <a href="http://www.farnell.com/datasheets/457135.pdf" rel="noreferrer">datasheet</a>.</p>
<p><img src="https://i.stack.imgur.com/iWcbg.png" alt="DC jack schematic"></p>
| Deciphering a DC jack schematic | 2010-04-25T12:25:00.503 |
2407 | |power-meter|resistors| | <p>Shunt resistors supposed to be used for DC, for AC suppose to use amper clamps which is the same current transformer.</p>
| <p>Looking for a shunt resistor for measuring power usage and was wondering if anyone had any experience with these. </p>
<p>It should be capable of handling 110V/20A in-home circuit.</p>
<p>EDIT: Energy monitors are the rage these days and I was thinking about putting a simple circuit together to try out. This would be used to measure a typical appliance or electronic device such as stereo or television. Similar to a Kill-a-watt or multimeter. I haven't really thought about accuracy as much as getting something to work well. I haven't thought this all the way through just thought maybe some here may have already "been there done that".</p>
| Best shunt resistor for power meter application? | 2010-04-27T20:40:55.380 |
2417 | |memory|integrated-circuit| | <p>Sandisk normally doesn't sell directly to individuals.
They sell directly to distributors, who in turn sell directly to individuals such as you and me.
If you want to buy this or any other Sandisk product, your best bet is to go to the
<a href="http://www.sandisk.com/business-solutions/find-a-distributor" rel="nofollow">list of Sandisk distributors</a>
and call up each one until you find one willing to take your money.</p>
<p>The <a href="http://www.dpreview.com/news/1006/10062301sandiskwormsd.asp" rel="nofollow">press release for the Sandisk WORM cards</a>
specifically lists contact information for obtaining these cards.
If you really want these specific cards mentioned in the press release, perhaps using that contact information might be a possibility?</p>
| <p>I've seen news articles talking about how SanDisk released Write Once Read Many (WORM) SD cards, but I can't find anywhere to buy them!</p>
<p>I'm thinking of building a project where I'll want to write reasonably small amounts of data (amounting to maybe 64 MB at most) to permanent storage, for retrieval via USB — can anyone think of a suitable IC for this?</p>
| Write Once Memory | 2010-04-28T15:01:14.633 |
2425 | |usb|choke| | <p>If your product sits "floating" on the USB cable, the common-mode choke is probably not necessary.</p>
<p>However, if your device is electrically attached through any other paths that could form a loop back to where your USB cable originates, you will have a potential for inductively picking up or generating noise that can affect the performance of your product, or other product attached to it. At that point, you will need the choke.</p>
| <p>I was looking over the schematic for the <a href="http://www.gumstix.com/store/app.php/products/229/" rel="noreferrer">GumStix Palo 43</a> and noticed they used a common mode choke coil on the data lines coming in from USB.</p>
<p>I understand how this design can help remove noise coming in on the USB lines, but I wonder if it is actually something I should start doing on my designs. The <a href="http://www.ftdichip.com/Support/Documents/DataSheets/ICs/DS_FT232R.pdf" rel="noreferrer">datasheet</a> for the FT232R has no mention of adding common mode choke coils, and I have used this chip before with out one.</p>
<p>So, would you recommend I change my USB design or keep it the way it is?</p>
| Are Common Mode Choke Coils needed on USB? | 2010-04-28T23:59:17.803 |
2428 | |components|markings| | <p>It is regarding the lead content or plating finish. Here is an excerpt from <strong>IPC/JEDEC J-STD-609</strong>:</p>
<blockquote>
<p>e0 - contains intentionally added lead (Pb)</p>
<p>e1 - SnAgCu (shall not be included in category e2)</p>
<p>e2 - Sn alloys with no Bi or Zn excluding SnAgCu</p>
<p>e3 - Sn</p>
<p>e4 - Preplated (e.g., Ag, Au, NiPd, NiPdAu)</p>
<p>e5 - SnZn, SnZnx (no Bi)</p>
<p>e6 - contains Bi</p>
<p>e7 - low temperature solder (\$\le\$ 150C) containing Indium (no Bi)</p>
<p>e8, e9 - unassigned</p>
</blockquote>
| <p>So after staring at a few ICs today, I was wondering what the "e3" or "e4" stands for on the top of an IC. For example, here is an e3: </p>
<p><img src="https://i.stack.imgur.com/hSgy4.jpg" alt="enter image description here"></p>
| What does the e3 or e4 printed on an IC mean? | 2010-04-29T07:49:13.640 |
2430 | |arm|3.3v| | <p>The problem with the term "TTL" is it's often used rather loosely. People often say "TTL" when they really mean 5V CMOS.</p>
<p>Real 5V TTL (74LS and similar) has 3.3V compatible input thresholds but has much higher input current requirements than any CMOS device does. So you need to make sure your 3.3V device can deliver enough current for the TTL inputs. This is probablly not a problem for driving a single gate but could become troublesome at high fanouts. </p>
<p>5V "TTL compatible CMOS" (74HCT and similar) inputs are fine to drive from 3.3V signals.</p>
<p>5V "traditional CMOS" (HEF4000 74HC and similar) inputs will usually be out of spec with 3.3V signals but in practice will often work despite this.</p>
<p>5V "CMOS schmitt trigger" inputs are very likely to fail to respond to 3.3V signals.</p>
<p>Be aware that different pins on the same device may have different specs. I've got caught out with this on PICs where many of the pins have TTL compatible input buffers but some have schmitt trigger input buffers.</p>
| <p>I need a quick heads up on a problem I am trying to solve at work. I'm trying to connect to a parallel data port on an interface module we use to access smart cards. The port has an 8bit input and an 8 bit output with associated strobe/ready pins. I have a microcontroller board with an ARM cortex (mbed.org) which would be perfect to interface to these ports to my PC for test purposes. The ARM board has loads of i/o but its a 3.3v part. I have used it with your typical 2 line LCD display (5v part) with no problem (I know the ARM i/o is 5v tolerant) and I can control the LCD no problem. What I'm wondering is, is it ok to assume that I can drive any 5v TTL level input from a 3.3v output pin ? I'm happy that I can read the 5v ttl levels as I said the ARM Cortex chip's documentation says it 5v tolerent. The connection will be very short (<10cm).</p>
| Is it possible to drive TTL inputs from 3.3v microcontroller | 2010-04-29T08:19:50.893 |
2440 | |current|batteries| | <p>I think another thing which might be confusing you is that we say the voltage in a conductor is always constant. While this is mostly true it is kind of a lie. All conductors still have a finite resistance. Because of this if you hook up a wire between the two terminals of a battery one end of the wire will actually be at a different potential then the other and the current in the wire will follow ohms law. I don't know if you've ever tried shorting the two terminals of a battery like this but because the resistance of the wire is so low ohms law gives a very large current which will heat up the wire and burn you. </p>
<p>Now the reason that we usually say that the potential in a wire is constant is because there are usually other components in our circuit whose resistance is much larger then the wires. Because of this most of the voltage will end up being dropped across the other components in the circuit and there will only be a very small voltage drop from one end of a wire to the other. So we can simplify our problems by saying that the voltage is constant in the wires.</p>
| <p>I am reading a basic electronics book: "There are no Electrons: Electronics for Earthlings" and I came across a clever passage about the fact that you need a closed circuit in order for current to flow. Here is the passage I am curious about:</p>
<blockquote>
<p>"This has always bothered me: If the negative terminals of batteries have excess electrons (a negative charge) and the positive terminals of batteries have too few electrons (a positive charge) and opposites attract, why can't I hook a wire between the negative side of one battery and the positive side of a different battery and get any current? This truth is it won't work. No current will flow. Had someone been able to explain that to me, I probably would never have written this book."</p>
</blockquote>
<p>Does anyone have a straight-forward answer to this question?</p>
| Current flow in batteries? | 2010-04-29T15:29:45.913 |
2443 | |microcontroller|pins|cmos| | <p>The idea of tri-state is to allow multiple output devices to share a single bus. For example, multiple RAM/ROM chips can be connected to a data bus. Only the selected chip will have active outputs (high or low), the other chips (not selected) will have all their outputs set to the hi impedence state (the third state). For outputs devices to share a bus they must be tri-state capable (usually controlled by chip-enable/direction pins). For microprocessors, micro controllers their hi impendence state allows other devices to use the bus (common for smart I/O devices, DMA etc).</p>
| <p>What does it mean to "tristate a pin" on a CMOS microcontroller?</p>
| "Tristate a pin" | 2010-04-29T18:29:59.780 |
2446 | |microcontroller|computers| | <p>You can absolutely build a computer using a micro-controller or even several micro-controllers. But your going to be limited to what your computer can do.</p>
<p>There are however other options than just using a micro-controller.</p>
<p>ARM Cortex has three different types of chips Cortex-A = Application processors, Cortex-R = Real-time processors & Cortex-M = Micro-controllers.</p>
<p>The above chips will have a Von Neumann, Harvard Architecture or a Von Neumann/Harvard Hybrid Architecture. The architecture used is't important if your following ARMS recommendation and using the correct Cortex-A/R/M chip for your purpose.</p>
<p>Then we have to look at what programming language we want to use (ASM, C, C++, ...) and what compiler (GNU, CLANG, ...) Note: Arm has there own free tool-chain that supports Asm, C, C++ that is based on LLVM/Clang I would personally use that and C++ because you can use the C++ standard library and mix in ASM and C Library's.</p>
<p>Then we have to take into consideration if we are going to use a General Purpose Operating System or A Real Time Operating System and if we are going to write that operating system our-selves or us one that already exists (Linux, BSD, FreeRTOS, ...)</p>
<p>Now here is what I would do.</p>
<ol>
<li><p>Research how to build your own Cortex-M0 development board, knowing
how to do this will give you a foundation for being able to make
your own Cortex-A development boards later.</p>
</li>
<li><p>Research Arm Assembly Language and Arm Cortex Architecture. Note: you
don't have to learn Assembly Language this will just give you a
really good understanding of how Arm chips work and make programming Arm chips in C++ much easier.</p>
</li>
<li><p>Research C++ programming on Arm Cortex chips and what C++ standards
and features you can use C++14, C++17, C++20 ...</p>
</li>
<li><p>Lastly research how to build a Real Time Operating System (RTOS) in C++</p>
</li>
</ol>
<p>You can find courses on udemy on howto do all of the things that I mentioned.</p>
| <p>We all have(mostly) 32-bit machines at our homes. But the 32-bit machines have a microprocessor in them. I was reading an article about the ARM Cortex. Its a 32-bit microcontroller. Now that intrigued a question inside me. Microcontrollers were made to decrease the external circuitry around a microprocessor, then the microprocessors became more powerful while microcontrollers remained in there 8 bit forms for too long a while. But now that we have 32-bit microcontrollers can't we have like a computer based around those things?</p>
| Can you base a computer around a 32-bit microcontroller? | 2010-04-29T19:05:46.150 |
2449 | |cpu| | <p>In superscalar processors we use register renaming to avoid WAW and WAR hazards and we prefer using ROB for RAW. so iff you assume we are using register renaming we will not be using ROB in WAR and WAW.</p>
| <p>I'm learning about superscalar CPUs and I had a question about that and data dependencies. Given the dependencies, RAW (read after write), WAR (write after read), WAW (write after write), when would the ROB (re-order buffer) NOT be used?</p>
| superscalar CPUs and data dependencies | 2010-04-29T19:52:46.087 |
2451 | |nixie|power-supply| | <p>Sure, it would work. </p>
<p>I have used a slight step-up transformer (120v to 130v) to drive a nixie supply. It also had a 6.3v filament tap which was really convenient for the 5v ttl logic supply. However, I used a full-bridge rectifier followed by a electrolytic capacitor to filter both supplies. Here's why I would recommend that setup over what you're suggesting:</p>
<ul>
<li>It's cheap. For $1.25, you can have decent regulation of your supply voltage. I'm assuming the isolation transformer is already accounted for.</li>
<li>You can/will see the nixie tubes flicker at 60 Hz.</li>
</ul>
<p>The motivation for fancier regulation circuits is to protect the nixie tubes. They are usually the focal point of any design using them, so it's in the designer's best interest to make sure nothing bad happens to the tubes. I've seen people drive nixie tubes with expensive regulated bench supplies, and read about people using unisolated circuits. Somewhere in that range is a cost-benefit-paranoia tradeoff. </p>
| <p>I've seen any number of nixie tube designs on the web that use regulated 170V supplies for the nixie tube anode.</p>
<p>Wouldn't it be possible to use unregulated, half-wave rectified 170V peak power for this? Yes, the illumination wouldn't be continuous, it would in fact flicker at 60Hz, but this is fast enough that it shouldn't matter to the human eye. The brightness would vary with line voltage, but since that doesn't usually vary more than a couple of percent, this effect also should go unnoticed to the casual observer.</p>
<p>The up-side of this would be that you could dispense with the relatively costly regulated supply, and use a simple 1:1 isolation transformer and a single rectifier diode to get the anode supply, since sqrt(2) * 120 gives very close to 170. </p>
<p>In fact, if you used SCR's to pull the cathodes to ground, you could do away with the rectifier, because when the AC reverses direction, the SCR will cut off just like a diode. A single current limiting resistor should suffice if placed on the anode side of the tube.</p>
<p>Would it work? If not, why not?</p>
| Isn't it overkill to use a regulated power supply for a nixie tube? | 2010-04-29T20:33:30.123 |
2452 | |digital-logic|analog|interface| | <p><a href="https://sound-au.com/project65.htm" rel="nofollow noreferrer">This circuit</a> uses an SCR to trigger the strobe. There is an optoisolator between the SCR and the trigger circuitry, so as long as the SCR is rated at a high enough voltage (400V in this case), you should be able to easily trigger the SCR through the optoisolator using TTL voltages without problems.</p>
| <p>Does anyone have a circuit that will trigger a strobe light to flash in response to a TTL logic signal? Specifically, if I have a strobe circuit capable of flashing 1000 times per second, it seems like it should be possible, under logic control, to get pairs of flashes at say, 5 msec apart, with the pairs separated by much longer intervals, e.g., 100 msec.</p>
<p>Most strobe circuits I've seen use some kind of relaxation oscillator to periodically trigger the flash tube. These are fine if all you want are single flashes at a not-too-specific rate.</p>
<p>I know there are camera flash units that will flash in response to a switch closure, but these don't usually recharge fast enough to put two flashes together in the space of 10msec or less. </p>
<p>My hunch is that if I dump the charge from a small cap into the primary of a trigger transformer, through a switching device of some kind, the tube can be made to flash. The problem is dumping the cap charge quickly enough to get the trigger spike, and not toast the semiconductor with the backlash from the transformer input.</p>
<p>The other concern is that since the trigger circuit basically produces nasty voltage spikes, how to go about isolating the control logic from the spikes.</p>
| logic triggerable strobe light circuit | 2010-04-29T21:01:11.423 |
2464 | |vga|pins| | <p>The colour channels are sent over 75Ω coax (it's an RF signal running with a high bandwidth - up to 250MHz - so it goes over coax). The ground pin next to each colour pin is the coax ground. It needs to be close to the centre pin to minimise impedance mismatch in the DB-15H connector (which is NOT a great connector for RF - it does not provide a coaxial join for the three colour channels).</p>
<p>Long runs of video cable (~30 metres) require low loss coax to function correctly. Poor cable quality results in degraded images (smearing and ghosting,etc).</p>
<p>Regards,
Tony Barry </p>
| <p>On a VGA connector, there are numerous 'ground' pins. Three of these are Red return, Green return and Blue return; But why does each color component have its own ground pin?</p>
| What are 'return' pins? | 2010-04-30T19:59:08.520 |
2482 | |usb|usb-device|host|lufa| | <ol>
<li><p>I don't think that V-USB supports host (OTG) mode and LUFA host mode will require at least an AT90USB646 which is quite expensive.</p></li>
<li><p>I don't know about a cheap micro that has 2 USB port but you may try using two. Just connect them via an UART and exchange the needed information.</p></li>
</ol>
<p>That said, davr is probably right that using a PS/2 keyboard would be simpler.</p>
| <p>Is it possible to run both USB Host and USB Device controllers on top of an AVR (ATMega64)?
Specifically, what I'm looking for is to receive data from a usb keyboard, and simultaneously sending keystrokes to a PC.</p>
<p>From what I've seen, both VUSB & LUFA stacks support USB host modes, but they work with a single usb port only.</p>
<p>Any help is appreciated!
Thanks!</p>
| Dual Role USB device on AVR | 2010-05-01T23:28:09.513 |
2490 | |cpu|computer-architecture| | <p>The control signals are generated by the Decode stage. If I remember correctly (it's been like seven years...) the control signals are then passed through the pipeline registers between each stage, so they propagate down the pipeline with the rest of the instruction's data.</p>
<p>I think the question is actually asking how many cycles it takes to generate the control signals. For a single-cycle and pipelined implementation, it only takes one cycle to decode the instruction (for the pipeline, the results of the decode are passed to each stage in succession once generated).</p>
<p>However, the multi-cycle processor will generate different control signals during each cycle.</p>
| <p>Are the control signals for a given instruction generated within a single cycle
for the pipelined, the multicycle as well as the single-cycle implementations of the MIPS32 datapath? </p>
<p>I think they are for the single cycle implementation but not for the pipelined and multicycle implementation.</p>
| When are MIPS control signals generated? | 2010-05-02T16:51:36.950 |
2491 | |usb|logic-analyzer|digital-communications| | <p>This is what you need <a href="http://www.totalphase.com/products/beagle_usb480/" rel="nofollow">http://www.totalphase.com/products/beagle_usb480/</a>, it is a USB 2.0 protocol analyzer, comes with software that will parse out USB traffic, and will be much easier to use than a logic analyzer. I have one of these for I2C/SPI and it works well, plus, Bunnie uses it <a href="http://andrew.huang.usesthis.com/" rel="nofollow">http://andrew.huang.usesthis.com/</a></p>
| <p>Is it possible to passively listen on low speed USB communication?</p>
<p>Suppose I connect a logic analyzer to D+ or D- line, will I see a valid data?</p>
| Passive listening to USB communication | 2010-05-02T22:22:23.023 |
2495 | |connector|usb|robotics| | <ul>
<li><p>Mill-max makes spring probe strips and buttons (See <a href="http://www.mill-max.com" rel="nofollow">http://www.mill-max.com</a> )
If you had two little PCBs you could put use the spring probes to hit large
pads. You would need to apply constant pressure to insure the contacts
stay mated. </p></li>
<li><p>There are conductive elastomer strips in a variety of sizes. The elastomer
would connect two PCB pads. </p></li>
<li><p>Spring probes for in-circuit testing could work too. </p></li>
</ul>
<p>I would look at the Mill-max contact strips first.</p>
| <p>I'm designing a robot gripper that needs to pickup an electronic device (the size of half a laptop) and move it around. The problem is that when the device gets picked up, I need to establish a USB connection (the device has one of those small USB connectors.</p>
<p>I was thinking about designing a PCB with an SMD right angle USB connector in one side and a few fat pads on the other. I would manually attach the connector to the device before the robot picks it up, and I would have some sort of spring on the gripper to make the USB connection. Something like the ones used in the SD cards, but bigger.</p>
<p>Question is: do you have another suggestion or know what component to use to make the electrical contact?</p>
| What type of connector to use for pressure contact? | 2010-05-03T00:31:08.117 |
2513 | |pic|memory|flash| | <p>Some 16-bit PICs have an 8/16-bit parallel port with up to 11 address lines. The <a href="http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en520629" rel="nofollow">PIC24FJ16GA002</a> is an example.</p>
| <p>I've been considering using a NANDrive by SST in a new design, however I wasn't sure how complicated it would be to connect a PIC to the ATA interface on the NANDrive. I did a quick Google search and found a couple of forums with people who had done it, but I was wondering if anyone here had experience with it and could suggest a standard software library for PIC C18 that implements ATA.</p>
| ATA Interface for PIC | 2010-05-04T21:00:47.887 |
2527 | |pcb|power|led| | <p>Looking at the board there is not much there besides the LEDs and a couple of parts which I am guessing are resistors. It look like there are two groups of 9 LEDs and then a current limiting resistor. So measure the voltage across the resistors and use ohms law to work out the current. Each group should not pull more than around 50mA so I am guessing the board in total will be less than 100mA. Looking at a <a href="http://www.vishay.com/docs/81012/tsal7200.pdf" rel="nofollow">data sheet for an IR led</a> for 100% on you should not exceed 20mA or you will be damaging the LEDs.</p>
| <p><strong>Disclaimer</strong>: I have very little (almost none, really) electronics experience.</p>
<hr>
<p>I purchased a set of IR illuminator boards off of eBay. The only information that the seller provided was that the board had an operating voltage of 12 VDC and that the board has a built-in auto protection circuit that prevents damage from high voltage.</p>
<p>I have two questions. One directly related to this PCB, and one general:</p>
<ol>
<li>How can I figure out how much current these boards will draw?</li>
<li>Suppose the seller omitted the required voltage information. How would I go about figuring out how much juice a certain board needs without frying it?</li>
</ol>
<hr>
<p>The board in question is sold by a lot of eBay sellers. <a href="http://cgi.ebay.com/New-18-Infrared-LED-Lamp-Bulb-Camera-5mm-12V-/130388274468?cmd=ViewItem&pt=LH_DefaultDomain_2&hash=item1e5bbf2d24" rel="nofollow">Here's</a> one listing with decent pictures.</p>
<hr>
<p><strong>EDIT</strong>: Thanks for your answers everyone; you were all helpful.</p>
| How to Determine a PCB's Power Requirements? | 2010-05-05T16:36:26.110 |
2535 | |potentiometer|cleaning| | <p>They do make a WD40 Contact Cleaner Spray that works well. No Residue, Totally evaporates. Alcohol based. <a href="https://www.walmart.com/ip/WD-40-Specialist-Electrical-Contact-Cleaner-Spray-11-Oz/37971472?wmlspartner=wlpa&selectedSellerId=2419&adid=22222222227026211114&wl0=&wl1=g&wl2=c&wl3=52479953471&wl4=pla-84042622871&wl5=9029483&wl6=&wl7=&wl8=&wl9=pla&wl10=113134491&wl11=online&wl12=37971472&wl13=&veh=sem" rel="nofollow noreferrer">https://www.walmart.com/ip/WD-40-Specialist-Electrical-Contact-Cleaner-Spray-11-Oz/37971472?wmlspartner=wlpa&selectedSellerId=2419&adid=22222222227026211114&wl0=&wl1=g&wl2=c&wl3=52479953471&wl4=pla-84042622871&wl5=9029483&wl6=&wl7=&wl8=&wl9=pla&wl10=113134491&wl11=online&wl12=37971472&wl13=&veh=sem</a></p>
| <p>I have a couple of potentiometers that haven't been touched in quite some time. In fact, probably not in 15 years. So now they produce noisy output, presumably from oxides or some other crud that has built up on the contact surfaces. </p>
<p>Outright replacement might be an option, but these are quite large relative by current standards, they are in fact about the diameter of a quarter and are probably 1/4" inch thick, real 1970's technology. Might be hard to get the same form factor.</p>
<p>Certain retailers used to carry this stuff that came in a can like wd-40, complete with a little red tube for injecting the stuff into exactly this kind of part. You'd squirt a tiny amount into the noisy pot, wiggle the knob 2-3 times, and no more noisy output. So there's the proof of concept that it can be done, but this magic stuff seems to have vanished from the shelves.</p>
<p>It had to just be some kind of solvent, like xylene or something. Any ideas on what would clean the corrosion (dust? dirt? <em>fungus</em>?) off a potentiometer, without damaging it?</p>
| How to clean a potentiometer? | 2010-05-06T02:41:27.800 |
2559 | |servo|remote-control|robotics| | <p>They claim that it's similar to the HS-55, which has a 180 degree span.</p>
<p><a href="http://www.servocity.com/html/hs-55_sub-micro.html" rel="nofollow">http://www.servocity.com/html/hs-55_sub-micro.html</a></p>
| <p>Does anybody know what the rotational span of the <a href="http://www.sparkfun.com/commerce/product_info.php?products_id=9065" rel="nofollow">ROB-09065 servo</a> from SparkFun?</p>
<p>And even better, is there a datasheet available anywhere?</p>
| Rotation span of SparkFun ROB-09065 servo | 2010-05-07T15:26:45.690 |
2567 | |amplifier|audio| | <p>What you actually want is to <em>reduce</em> or <em>attenuate</em> the voltage down to headphone levels. A voltage divider(or L-Pad as audiophiles call them) will do that just fine, and only needs two resistors. The only downside is that the resistors might get a little warm so use ones that are rated for 10 watts or so.</p>
<p>I'd say a use a ten ohm and a one ohm and put the headphone out across the one ohm.</p>
<p>Lots of people are making "L pad headphone attenuators", I'm sure the audio nerds know more than I do about them.</p>
<p>I've also heard of transformers being used.</p>
| <p>My motor-scooter has a built in radio, with a small speak either side of the front panel, below the handlebars. It's a JonWay, i.e. cheap Chinese, so I suspect the radio is more suited to developing countries where helmets are not yet mandatory.</p>
<p>For me to listen while wearing a helmet, I need zero traffic, or a headphone jack, and I'd like to do the jack myself. I may not find the radio board without too much dismantling, but the speakers are very accessible, so I may have to grab my input signal directly from them. </p>
<p>My electronics knowledge has all but evaporated after 15 years of non-use, so all I can start with is that I'll need a high impedance input, to make the increased load on the amp negligible, and my own power amp stage. Where do I go from here? I would like to do a rough design myself, maybe make the amp component a kit, but nothing ready made.</p>
| Piggy-backing off power amplifier outputs | 2010-05-08T13:43:32.213 |
2569 | |robotics|autonomous| | <p>I did some more digging and found out this PDF on MIT OCW. Its the course notes for Underactuated systems. I have not yet read the whole book but it is a nice resource to understand concepts of walking as most of the legged locomotion problems require underactuated control. You can find it here <a href="http://ocw.mit.edu/OcwWeb/Electrical-Engineering-and-Computer-Science/6-832Spring-2009/CourseHome/index.htm" rel="nofollow">1</a></p>
| <p>Recently I have been watching Robert Full's talks on TED. He has some obscenely interesting works on robot locomotion. This has intrigued my curiosity and I have been trying to understand his works. I have tried to read many papers on these type of works but I have been unable to understand as I don't have the basics of these things.</p>
<p>Can anyone please direct me to a resource (ebooks, websites, video/audio lectures, forums etc.) where I can understand the basics of Robot Locomotion and gait functions?</p>
| Resources to understand robot locomotion and Gait functions | 2010-05-08T14:53:57.410 |
2573 | |current-source| | <p>Depending on your load you may be able to just force the
SET pin to GND. </p>
<p>If you pull the SET pin to GND the LT3080
will force the OUT pin to 0V. The internal schematic shows
that the SET pin connects to the positive input of the control
amplifier and the OUT pin connects to the control amplifier
output (through a transistor buffer). The OUT
pin follows the voltage on the SET pin. </p>
<p>Use an N channel FET to short the SET pin to ground.</p>
| <p>I would like to use a LT3080 as a current source (see <a href="http://www.linear.com/docs/25276" rel="nofollow">datasheet</a> page 17 in Typical Applications Section). However, I need to be able to shut it off. Since $$I_{\text{out}}=10\mu\text{A} \times R_{\text{set}}/R_{\text{out}}$$ it seems just a matter of shorting \$R_{\text{set}}\$ with a PMOS. The problem is that for all PMOS devices I've reviewed the best I've found for zero gate leakage current is 1uA, and at high temperatures 10uA, so depending on the temperature it will suck all the current from the 10uA current source, thereby killing the output current when it is not supposed to. </p>
<p>I thought of using a PNP but the problem is that \$V_{\text{ce(sat)}}\$ will be comparable to the 0.5V-1V I intend to drop accross \$R_{\text{set}}\$, so it will not shut off \$I_{\text{out}}\$ effectively. The only solution I have at the moment is to shut off the input voltage. Any ideas?</p>
| Shutdown for LT3080 current source | 2010-05-09T03:08:39.187 |
2585 | |avr|bootloader| | <p>You <em>can</em> jump into bootloader and start reprogramming the application part, but that's probably a bad design. Consider what happens if an update fails or gets interrupted: now your app area is trashed, and since half your bootloader effectively lives there, it's probably trashed too. So you've effectively bricked the device. </p>
<p>You want to structure the bootloader as an independent program.</p>
<p>See this FAQ: </p>
<p><a href="http://www.avrfreaks.net/forum/faq-c-writing-bootloader-faq?name=PNphpBB2&file=viewtopic&t=79206" rel="nofollow noreferrer">http://www.avrfreaks.net/forum/faq-c-writing-bootloader-faq?name=PNphpBB2&file=viewtopic&t=79206</a></p>
| <p>According to the datasheet, the ATMega168 can only execute self-programming instructions when running code from the bootloader block.</p>
<p>Once the bootloader is complete and the application starts, can the application then jump back into a subroutine in the bootloader block and have it write to the flash?</p>
<p>Or, is it the case that once the program leaves the boot block it's not allowed to self-program again until after a reset?</p>
| AVR self-programming | 2010-05-11T10:54:24.133 |
2590 | |lm335|diodes|zener|temperature| | <p>Are you sure you have it connected properly? If you are getting 4.83V at V+ and
4.88V at your supply it sounds like you have an open circuit.</p>
<p>Check the pinout against the datasheet. On page two they are showing the <strong>bottom</strong> views
of the package.</p>
| <p>I'm relatively new to electronics, and I'm trying to make a thermometer using a LM335 temperature sensor. By reading the datasheet I thought it was simple, connect up 5V to a resister, then to the V+, connect up V- to GND, and I should get somewhere just below 3V when reading the V+ pin. </p>
<p>However, when I do this, I'm actually getting 4.08. I've tried two different sensors, so I'm reasonably sure that it's not just a DOA.</p>
<p>Any ideas about what I could be doing wrong? What I can do to try to work it out?</p>
| LM335 doesn't seem to work | 2010-05-11T23:15:05.523 |
2591 | |ethernet|sbc| | <p>This PhidgetSBC2 board has <em>everything</em> you need, including a full Debian Linux distribution (allowing you to add whatever packages you would like).</p>
<p>Only downside is it is a bit more expensive.</p>
<p><a href="http://www.phidgets.com/products.php?category=21&product_id=1072" rel="nofollow">http://www.phidgets.com/products.php?category=21&product_id=1072</a></p>
| <p>I want to get started with embedded development and for my first project I thought of making a caller-ID type of appliance.</p>
<p>Here's why I want a SBC for this:</p>
<ul>
<li>I want to be able to locally serve this data (i.e., caller log) via HTTP</li>
<li>I thought of maybe extending this appliance and adding an answering machine of some sort at a later time, so I guess I'll need "advanced" modem capabilities</li>
</ul>
<p>From what I understand, all I really need is a SBC and a USB modem.</p>
<p>Can someone recommend the cheapest and most lightweight SBC that would be able to fulfill these requirements?</p>
<p><strong>EDIT</strong>: <a href="http://andahammer.com/micro2440-oem/" rel="nofollow">This board</a> looks cheap enough. Though it's only the "brains" of what I'm after. How hard would it be to hook up OEM ethernet, USB, and serial connectors to something like this?</p>
| SBC Recommendations | 2010-05-11T23:45:19.973 |
2603 | |arduino|bootloader| | <p>The idea behind the Arduino bootloader is that you don't need any <strong><em>specialty</em></strong> hardware or circuits to re-program them, compared to the initial programming of it, or older microcontroller, which often need a dedicated programmer (like PicKit2 for PIC MCUs). The bootloader allows programming over a basic serial connection.</p>
<p>Of course, at the time, you needed the serial link, typically a rs232 converter from TTL to RS232. Then serial ports being phased out, usb to serial became ubiquitous, allowing for that to replace a max232 or similar. And now, the use of USB enabled Atmel microcontroller allow even that to be unnecessary, so a single ic with minimal passive parts could provide the Arduino functions and USB to Serial. Now you only need a usb cable and a few passive to upload a sketch. The initial programming of the bootloader still requires traditional ICSP programming.</p>
| <p>I have been struggling with making an Arduino for a while (was successful in making a breadboard version using an <a href="https://en.wikipedia.org/wiki/In-system_programming" rel="nofollow">ISP</a> programmer cable). They say that the Arduino bootloader is made so that no external circuitry is required to program the <a href="http://www.atmel.com/devices/ATMEGA8.aspx" rel="nofollow">ATmega8</a>. But when I looked into the schematics there is the normal circuit required for the serial connection. Then what does the bootloader actually do?</p>
| I don't get the Arduino concept | 2010-05-12T12:12:04.797 |
2612 | |open-source|licensing| | <p>Here is a <a href="http://multimedia.cx/eggs/poking-at-youtube/" rel="noreferrer">nice article by Multimedia Mike (ffmpeg/mplayer)</a> about the second trick you mentioned (exploring corner cases). There are no GPL violations on YouTube side, but it is fun nevertheless.</p>
| <p>Let's say I have an open source project with a license that prohibits commercial uses. Then comes along a commercial product with <em>striking</em> similarities in functionality/hardware. </p>
<ol>
<li>How would I go about inspecting the commercial product to see if they are using parts of my source code?
<ul>
<li>I realize I could do an image dump, but is that really useful, or easily obfuscated?</li>
</ul></li>
<li>Are there any simple tricks I could use, such as adding strange corner case behaviors, that would allow me to easily detect if anyone has copied the source verbatim, and are not overly obvious?</li>
</ol>
<p>Bonus legal question: can I somehow subpoena the source code, if so what do I need to have to present 'reasonable doubt'?</p>
| How do I detect open-source licence violations by companies? | 2010-05-12T22:14:14.113 |
2632 | |datasheet| | <p>All of the above answers are good and valid. I especially like the point about being humble and looking hard at what you might have missed. </p>
<ul>
<li>The only point I have to add is to look at Errata.</li>
</ul>
<p>Often we read datasheets and specify parts for our design, quite early on in the project.</p>
<p>It can be a month at the very least before we actually have a fully populated board. :) During such time, often chip manufacturers find slight issues with their parts, and update the Errata for these parts. Most often than not, they usually specify a workaround for the problem which we might need to incorporate in our design.</p>
<p>Unfortunately, I learnt the hard way, after months of trying to debug an issue, read the datasheet over and over, and then found that I had not read the errata. :) </p>
| <p>After my embarrassing mistake by having the <a href="https://electronics.stackexchange.com/questions/2590/lm335-doesnt-seem-to-work">component in backwards</a>, I'm wondering if anyone has advice for the newbie (or expert) on reading datasheets.</p>
<p>What conventions are there which aren't obvious.</p>
<p>What's the first thing you should check when something's not working.</p>
<p>What can I safely ignore and what should I worry about?</p>
<p>Anything else?</p>
| Any advice on reading datasheets | 2010-05-14T11:03:37.023 |
2641 | |fpga|cost|softcore| | <p>first of all you want to run linux on a core. How about <a href="http://www.linux-arm.org/LinuxKernel/LinuxM3" rel="nofollow">running it on an ARM</a> like some other suggestions in this thread. MCU are good at running OS but it gets kind of wasteful of FPGA resource building an MCU. MCUs can fit into a much smaller silicon area when custom designed for that and can thus be produced more cheaply. Then there are other explanations about FPGAs being really good at parallel processing -kind of true although logic operations don't feel like processing exactly. Like you point out powerful FPGAs get expensive, and indeed power hungry. So a low cost platform that can run linux and DSP needing the benefits of parallelism for fast IO etc. Take a look at <a href="https://www.xmos.com/products/silicon/xa-series" rel="nofollow">XMOS parallel processor</a> </p>
| <p>How cheap do FPGAs get? I know they're more expensive than microprocessors of comparable capability, but I wonder if there exist FPGAs that could contain a Microblaze soft core running Linux, while leaving gates available for implementing DSP functionality (media codecs, for example) at a cost competitive with, say, a Cortex A8 ($20-30 in qty. ~100).</p>
<p>(Apologies if my terminology is non-idiomatic i.e. wrong. Please comment with corrections, or edit directly.)</p>
| Cheapest FPGAs? | 2010-05-14T17:21:59.663 |
2648 | |rf|radio| | <p>Please be aware of DCF 77 reading some introduction text.
Indeed DCF 77 it's a specific modulation protocol (AM) were the modulation signal have a subordinated phase shift as the way to transmit the digital information.
Due to the working frequency (77,500 Hz) the propagation tends to follow earth curvature so the signal reach long distances.
Although the modulation complexity there are some ease circuits to extract hours and minutes with discrete components to differentiate or integrate the pulses.
The results are conditioned by distance, eight and electromagnetic environment.
I'm at about 2,500 Km (line of sought) with an acceptable signal in summer time after that depends of climacteric conditions.
I've two DCF and two GPS. If you need an acceptable compromise price vs features I would suggest you start with a LIDL DCF clock. </p>
| <p>I'm looking to better understand basic RF receiver circuits, and I thought building a basic AM 77.5 kHz receiver seemed like a good challenge. I do however have had quite a challenge in finding any resources on this. Do you know any good starting points for the basic circuits involved in building this, in discrete components if possible, as I would like to understand the details of the system?</p>
<p>If I understand correctly it should be possible without any kind of phase locked loop, and just with "simple" envelope detection as it is low frequency amplitude modulation?</p>
<p>Don't worry about the actual demodulation, I'm going to sample the signal and do it digitally. This is what I know how to do. ;) So I'm only looking for the RF to baseband part.</p>
<p>Thanks in advance.</p>
| DCF77 (AM 77.5 kHz) receiver in discrete components? | 2010-05-15T11:03:01.680 |
2649 | |arduino|communication|74hc595|io| | <p>You should scope it anyway to ensure its performing correctly but here is the thought process/math you need to take into account to determine transmission line effects.</p>
<ul>
<li><p>Edge rise and fall time, in opposition what some have posted here, the frequency of the signal does not matter at all when determining when you need to take transmission line effects into account. It is generally true that high frequency signals have faster rise/fall times but low frequency signals can also have very fast rise and fall times if they are being driven at low frequency by a transceiver with a high slew rate. As always use the slowest rise/fall times possible to stay within spec for the parts you are using, you can reduce the rise and fall times with an RC filter at the source. In general you need to consider transmission line effects if the length of the wire is greater than Tr/(2*Td) with Tr = to the signal rise time at the source and Td = to the propagation delay per unit length of the cable you are using. You may also need to properly terminate the signal lines on shorter cables if the load is highly capacitive, this is kind of difficult to calculate upfront as there are many items with capacitive effects in such a system. If you have this problem you will notice ringing (under and over shoot on edges) in the signal.</p></li>
<li><p>Current in the cable, this will be defined in the spec sheet of the receiving IC as the input current. This combined with the resistance of the cable will tell you if the voltage drop is acceptable given the specs of the receiving IC. This only an average current value. The actual peak current can depend on the type of termination used and needs to be considered when deciding if the driving IC can handle the load or if you need a line driver. The peak current should only last as long as the round trip propagation delay of the circuit. </p></li>
</ul>
<p>If you need to take the transmission line effects into account you also need to know the characteristic impedance of the cable and the output impedance of the driving IC.</p>
<p>If you do need to handle the transmission line effects there are a few options for termination style. The only two i would consider are source termination and AC biased end termination.</p>
<p>In source termination you need to place a resistor as close as possible to the driving IC with value equal to the characteristic impedance of the cable minus the output impedance of the driving IC, you may have to tune this a bit to hit spec dead on as the impedance of the cable connectors will also impact the system and as always place the driving and receiving IC's as close to the connectors as possible to reduce reflections. This is probably the easiest method and probably the best method in this case. Peak current will be (Vhigh - Vlow)/(2*Z0) with Z0 = to the characteristic impedance of the cable.</p>
<p>In AC biased end termination you connect to the signal line as close to the receiving IC as possible a resistor in series with a capacitor with the capacitor tied to ground. The value of the resistor should be the characteristic impedance of the cable, the value of the capacitor is determined by the frequency of the signal (the R and C form a low pass filter). The peak drive current is the same as for source termination. The average drive current is dependent on the duty cycle of the signal, if its very close to 50% then it will be roughly equal to to the input current of the receiving IC, if it is over 50% the average drive current will be higher. As the R and C form a low pass filter this termination style will filter out some high frequency noise.</p>
<p>Couple other things to keep in mind:</p>
<ul>
<li><p>Using twisted pairs for a single ended signals does not reduce noise pick up at all. It does result in a more consistent characteristic impedance for the transmission line. This may make the output look better if you really should have properly terminated the signal but didn't. It does nothing to reduce outside EM noise on the line.</p></li>
<li><p>Use of shielded cable on a single ended system is iffy at best. You can often create a situation where outside noise capacitively couples to the shield resulting in current flow on the shield which then couples to the signal wire. I wouldn't bother using a shielded cable unless your using differential signaling. Also the usefulness of a shield on high frequency noise is dependent on the inductance to ground, low inductance paths usually require special connectors. </p></li>
</ul>
<p>You can use very much the same thought processing on any line be it a cable or a 2 inch PCB trace.</p>
| <p>My current project involves using 74HC595 shift registers to control an LED display, however the display could be up to 5 or so metres away from the Arduino board. The plan is to use some DB9/RS232 cables between a box with the Arduino, and an enclosure with the display. Would the length be too long for the digital signal to travel from the digital out pins to the shift register without degradation?</p>
| How long between Arduino digital pin and IC? | 2010-05-15T11:53:36.973 |
2653 | |ham-radio| | <p>You might want to look into the ARRL QEX publication (http://www.arrl.org/qex). Aimed more at experimenters/builders. QST is also good, but is a balance between building and operating.</p>
| <p>It's been quite a while since I heard about amateur (ham) radio. I think it's a good hobby to dabble into to develop an understanding of communication technology and electronics. But whatever research I have done to date turns up things that describe it for someone who buys ready made radios. I want to dive into the electronics and understand how all of it works, I don't want to think too abstractly.</p>
<p>Can anyone please guide me to some website or book which can guide a beginner to get started in radio technology but also provide at least a basic understanding of how everything works and how to get your hands dirty? I know I have to get a licence and I am preparing for the exam.</p>
| Getting started in Ham radio | 2010-05-15T13:01:39.557 |
2669 | |schematics| | <p>In IEC-land (Europe and the Commonwealth), two overlapping circles usually means an (AC) transformer.</p>
<p>From Australian Standard AS 1102.106 <em>Graphical symbols for electrotechnical documentation - Part 106: Production and conversion of electrical energy</em>:</p>
<p><img src="https://i.stack.imgur.com/Iu8Q8.png" alt="enter image description here"></p>
<p>Where the transformer is a three-phase type, there are often some extra qualifying symbols added which denote the vector groups of the windings.</p>
<p><img src="https://i.stack.imgur.com/0Z287.png" alt="enter image description here"></p>
| <p>The attached screenshot is from a schematic in a datasheet. I know that the flat-topped arrow is a diode, but I don't know what the pair of looped circles are. Can anyone help me out? If there's a good online symbol reference, please share the link!</p>
<p><img src="https://i.stack.imgur.com/vVIYH.jpg" alt="unknown symbol"></p>
<p>Thanks!</p>
| Identify this symbol: two circles overlapping | 2010-05-17T13:01:38.880 |
2675 | |batteries|basic|power| | <p>Connecting two identical batteries in parallel will often increase the lifetime by a factor of at least two, and may increase the lifetime by even more than that (not only will the batteries be drawn down about half as fast as would be a single battery, but they may allow a device to keep working past the level of depletion that would cause a device to fail if only using a single battery). There is, however, an important caveat: if one battery is stronger than the other, it's possible that the stronger battery may try to push power into the weaker one. If the batteries are not rechargeable, such action may be detrimental to both batteries; even if the batteries are rechargeable, they may be damaged if they are connected while the difference in charge is too great.</p>
<p>Connecting batteries in series will cause them to push more voltage into the device they are using. The effect of this may vary with the device:</p>
<ul>
<li><p>Some devices will be damaged or destroyed</p></li>
<li><p>Some devices will work better with the higher voltage, but draw more current (possibly leading to shorter battery life than if using one battery, but perhaps allowing one to get more work done in that time).</p></li>
<li><p>Some devices will work about the same at any battery voltage above a minimum threshold, and draw about the same current regardless of voltage. All of the batteries in series will get depleted at the same rate regardless of how many there are, but the level of depletion required to make the device unusable will be extended by having more batteries in series. For example, a device which will become unusable when its input voltage falls below 5.5 volts could be used with four AA batteries that were less than ~10% depleted, or six that were up to 90% depleted. Using more batteries in such a situation may be economical, up to a point, though if one had twelve batteries one might achieve optimal economy by using three groups of four (along with a couple of dummy cells or a jumper wire) until they no longer worked, and then using two groups of six.</p></li>
<li><p>Some devices use a constant amount of power, and will in fact use less current when supplied with a higher voltage. Putting more batteries in series when using such devices will be economically advantageous provided that the voltage is not increased beyond the device's ability to handle it.</p></li>
</ul>
| <p>If I've got a device that uses a single battery, and with that single battery, the device lasts an hour, and I want the device to last for two hours, I'm assuming I can wire two batteries up and it should work. But how? Do I want to double the voltage (so serial) or double the current? (so parallel.)</p>
<p>Either way, if the device takes two batteries normally, and I want to double the running time, I do a combo of 2 parallel series of 2 serial batteries, right? But if I want to triple the run time, is that 3p2s or 2p3s?</p>
<p>Thanks.</p>
| How do I connect two identical batteries to increase the consumer lifetime? | 2010-05-17T16:25:13.513 |
2679 | |cases|cad|software| | <p>I make my cases with Rhinoceros. It’s absolutely not expensive (1200€) but very powerful. It is used by designers (cars boats etc), architects, etc.</p>
| <p>What software is generally used in industry to design cases for pcb boards?</p>
| 3d modelling software for case design | 2010-05-17T19:25:51.523 |
2694 | |pic|batteries| | <p>If possible measure the voltage of an AA Alkaline battery just after it has been loaded by your normal load (device) and you stopped the load current, when it drops below 0.9V per AA battery your batteries are depleted. I do this is many products I designed and it works perfect. Normal Alkaline batteries will recover after a load has been removed but this takes time depending on the load current. Sometimes this can be minutes or even hours depending on temperature and load current. Measuring it during steady use with a small current you will have to take a higher voltage depending on your current but normally 1.2V is OK for a device using only 5mA.</p>
| <p>I have a small circuit using a PIC18F14F50 microcontroller chip which is logging data into an external EEPROM chip over an i2c interface (which I can then read back later over the USB interface). One sample is recorded every 15 minutes and doesn't need to be particualrly accurately timed.</p>
<p>It's ok if samples are missed or mis-timed while batteries are being changed, but it's not great if the batteries expire and no data is recorded for several days until someone notices.</p>
<p>So I'd like to warn the user when the battery is low in plenty of time for them to replace them. The average current is under 2mA and I'm running in from 3 AA alkaline batteries in series to give 4.5volts so I'd expect them to last quite a number of days.</p>
<p>But I'm wondering how to detect that the battery is low? I presume the voltage will drop as the batteries reache the end of life. I'm thinking that this PIC has a 1.024v reference voltage so I can divide down the supply voltage and feed it to an analogue input and when the divided voltage drops below that trigger a warning.</p>
<p>But I don't know enough about batteries to know how well this will work? And I don't know what voltage to choose that would indicate that perhaps 10-20% battery life is left. Will that even work at all? Is there a better approach?</p>
<p>This doesn't need to be at all accurate, I just want to give a good warning in plenty of time without getting people to disard batteries that still have life left in them.</p>
<p>As my current usage is fairly constant, would a simple timer be reasonable if I can work out how long the batteries last on average and then pick 85% of that time before I give the warning? Or does battery life vary more than that?</p>
<p>Any thoughts would be welcome.</p>
| Battery life monitor on PIC circuit | 2010-05-18T13:56:56.353 |
2704 | |arm|linux| | <p>There are two another choices there: <br><br>
1. Vybrid VF3xx ARM Cortex-A5 family from Freescale (now NXP), main features: 266MHz, 1.5MB on-chip SRAM, 2x Ethernet + L2 switch, <strong>LQFP176</strong>. <br><br>
2. RZ/A1 ARM Cortex-A9 family from Renesas, they have few ICs with LQFP package (176, 208, 256 pins), and large on-chip SRAM (3MB-10MB), 400MHz.<br><br>
You can get it from DigiKey for example.</p>
| <p>What is the cheapest ARM processor with an MMU so I don't have to use uCLinux?
Bonus for non-bga and integrated RAM/Flash</p>
| Cheapest ARM with an MMU | 2010-05-19T00:46:52.763 |
2708 | |arduino|switches|microcontroller|avr| | <p>Use a Hall Effect sensor and a magnet on the door. If the sensor picks up a magnetic field, the door is shut. No magnetic field - not shut.</p>
<p>Now you can periodically poll the sensor at whatever rate you want (something long...like 250 ms?). Once you detect no magnetic field, you can start tracking time.</p>
| <p>I'm trying to build a latching switch connected to a door and would appreciate ideas.</p>
<p>The switch is connected to a microcontroller input pin, and I'd like it to operate as follows: When a person opens and closes the door, it latches on. It remains on until it is reset in software. </p>
<p>The basic idea is to time how long since the door was opened and closed again, and do something based on that. Once I have done this, I can reset the switch again. It does not matter if the door is opened or closed several times.</p>
<p>I'm not sure where to start, so any ideas welcome.</p>
| Latching switch ideas | 2010-05-19T02:03:34.160 |
2710 | |camera| | <p>Another possibility is that it is a "non-repeating pattern" used to establish register between two cameras.</p>
| <p><img src="https://i.stack.imgur.com/Pq1Mi.jpg" alt="alt text"></p>
<p>I came across a test pattern a few years back in a robotics laboratory that I remember being told was some sort of test pattern to train cameras for robotic vision. It was like some sort of checkerboard pattern but it was not a uniform pattern.
The image is my best rendition of it. Does anyone know what this type of pattern is called and what its use is?</p>
| What is this test pattern used for? (Computer vision, camera distortion mapping) | 2010-05-19T02:41:25.687 |
2718 | |video|embedded| | <p>The parallel digital video port (DVP) is a SGI thing. See <a href="http://techpubs.sgi.com/library/manuals/3000/007-3594-001/pdf/007-3594-001.pdf" rel="nofollow">here</a> for the spec.</p>
| <p>My boss recently asked me how difficult it would be to design a product that could continually record fairly low quality video and store the last few hours in some form of internal memory. I have never done any development with video before. Where would be a good place to start my design?</p>
<p>Do you have any suggestions for an MCU? I have been using Silicon Labs MCUs lately for other designs.</p>
<p>What would be the best camera type to use to keep the project as simple as possible?</p>
<p>What format would be best to store the video in?</p>
<p>Would I need a video codec or is that only need for a device that supports playback? This device would probably just need to be able to transfer the video to a PC for playback.</p>
<p>Any insight you can offer would be much appreciated!</p>
<p><strong>ADDED:</strong>
I have been looking on digikey at CMOS Image sensors. I see that there are several on there made by a company called OmniVision. These data sheets say that "The captured data can be transferred either by a standard parallel digital video port (DVP) or by a single-land MIPI high-speed serial interface".<br>
I have never heard of either of those. How do you go about getting that into an image file? using C?</p>
| Where do I start with embedded video? | 2010-05-20T11:50:23.113 |
2725 | |reverse-engineering|magstripe| | <p>@kellenjb and @pingswept:</p>
<p>Your comments were on the mark.</p>
<p>My eventual setup was to hook the probe up to pin 1 and the scope's ground to pin 3.</p>
<p>I found that this produced peaks/valleys of around 10-20mV with about 1-2 ms between "0" peaks (1s are half this width) depending on the card and speed of swipe. It's very obviously data in the format described in @pingswept's PDF.</p>
<p>I found setting the scope to trigger in single shot mode at around 7 mV did an excellent job of capturing the data.</p>
<p>Now all I need to do is transcribe and translate it.</p>
<p>Thanks guys.</p>
<p>As an additional note, not all hotel swipe cards I tried worked. Only one out of the three I had around produced any data. My AAA and Costco membership cards both worked, though.</p>
| <p>I got given a piece of electronics to take apart that has a magnetic swipe card reader built into it.</p>
<p>Upon taking it apart the card reader itself (which appears very much like a tape deck head) seems to have 5 pins, only three of which have wires attached in the current circuit (I'll call these 1 through 3 and will ignore the disconnected pins).</p>
<p>Pin 2 is obviously the ground, as it's connected to the outer case (this was also obvious from the circuit board it was attached to).</p>
<p>Resistance from pin 1 to pin 3 is about 65 ohms. 1-2 and 2-3 are OL.</p>
<p>I tried putting +5V (limited by a 1k ohm resistor) across 1 with 3 hooked up to my oscilloscope, but the voltage was a steady +5V with no change when I swiped a card.</p>
<p>Same results for +5V through 3 with 1 hooked up to the scope.</p>
<p>Oscilloscope does not show any voltage through ground (pin 2) when voltage is applied to 1 or 3.</p>
<p>So I'm sort of stuck.</p>
<p>I tried googling around, but so far I haven't really found much information on how the mag stripe readers actually work that gives me a better idea of how I might provoke a reaction from this thing.</p>
<p>Do any of you guys have any thoughts or suggestions?</p>
| Pinout of a 3 wire magnetic card reader | 2010-05-21T04:56:33.493 |
2729 | |arduino|system| | <p>"Real" serial ports use the EIA-RS232 standard of +/-12v volts which allows quite long cables. Lots of embedded gear uses the TTL logic levels of 0/5v, as this is much simpler but can only be run a metre or so. Sometimes you can cheat and connect TTL outputs to an RS232 input, even though this violates the RS332 spec. I wouldn't recommend going the other way and connecting 12v to a defenceless uC expecting 5v, though. </p>
<p>The reason for the use of 12v and -12v is noise immunity---5v serial lines only work over short distances before the noise overwhelms the signal, while RS232 can run up to 10m or more.</p>
<p>Traditionally the line drivers/receivers used to convert TTL to RS232 require +/- 12V power. This is the main reason there is a -12v line on a PC power supply. For 5v only systems, the Maxim MAX232 is the defacto standard for RS232 interfacing--this chip uses capacitor charge-pumps to generate +/- 12v from a single 5v supply.</p>
<p>If you aren't up to building a MAX232 interfacing circuit you can buy one pre-built from futurlec for about $5: <a href="http://futurlec.com/Mini_RS232_TTL_5V.shtml" rel="nofollow">http://futurlec.com/Mini_RS232_TTL_5V.shtml</a></p>
<p>I can provide a work-alike single-sided PCB layout for a TTL<->RS232 converter, if anyone is interested, as I built one a while ago to use when prototyping serial interfaced projects.</p>
| <p>I have a DSC-1555 Alarm system that I am trying to wire up to an Arduino-Mega the problem I've run into is that the DSC uses 12v TTL to the Console and the Arduino uses 5v TTL.</p>
<p>I was just guessing to use some resistors but I want to double check before trying.</p>
| Wiring a Arduino to a 12v TTY | 2010-05-21T16:39:30.587 |
2734 | |power-supply| |
<p><img src="https://i.stack.imgur.com/SswML.png" alt="schematic"></p>
<p><sup><a href="/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fSswML.png">simulate this circuit</a> – Schematic created using <a href="https://www.circuitlab.com/" rel="nofollow">CircuitLab</a></sup></p>
<p><em>Figure 1. Regular 9 V PSU wall-wart. Figure 2. Modified for +9/0/-9 V.</em></p>
<p>You can easily modify a standard 9 V wall wart supply as shown in Figure 2. Ripple voltage will be worse and max current on each supply will be half of original specification so I'd recommend some large caps or voltage regulators to eliminate hum.</p>
<p>If you want to keep a standard jack on the PSU then convert it to an AC PSU by removing the rectifier and capacitors and put the diodes and caps into your project case.</p>
| <p>I am working on a simple audio mixer project. The op-amps I am using (LM741) take +9V and -9V inputs. I am currently getting this by wiring two 9V batteries together, connecting + on one to - of the other, and grounding the pair. This seems to work, but I would now like to switch to a power supply. I can find a bunch of 9V power supplies, but they all only have the one polarity. Is there an easy way to get +9V from a center-negative power supply? I figure I probably need an inverter circuit or something, but I don't really understand what I'm doing.</p>
| +/- 9V DC Power Supply | 2010-05-22T21:13:35.437 |
2749 | |servo|torque|remote-control|datasheet| | <p>I believe the general interpretation of "/" is that it stands for "per", and that the unit following the slash is always treated as a single whole unit.</p>
<p>m/s = meters (per 1) second<br>
A/h = amperes (per 1) hour<br>
0.8 kg / cm = 0.8 kilograms (per 1) centimeter (of lever length or gear/pulley radius)</p>
<p>These are also understood as inverse ratios, such that 1/2 of the second unit will be balanced by twice of the first unit, etc.</p>
<p><a href="https://i.stack.imgur.com/Luzav.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Luzav.png" alt="Shaft of servo represented as a lever."></a></p>
<p>The center of the servo shaft is like the fulcrum of a lever and the shaft radius is the same as the length of the lever where the mass is lifted. The maximum mass the lever can lift depends on where the load is suspended from the lever, which is the same as the radius of the shaft / gear / pulley.</p>
| <p>I've recently bought some cheap TowerPro SG-50 rc servos from ebay. They seem to work quite well, and despite their small size they are quite strong.</p>
<p>But how "strong" are they actually. The datasheet specifies:</p>
<blockquote>
<p>Stall Torque: <code>0.8 kg / cm</code></p>
</blockquote>
<p>What does that mean. I guess that stall torque is the amount of torque that needs to be applied in the reverse direction of the rotation, before the servo stalls. But what does the unit <code>kg / cm</code> mean?</p>
| Stall torque for servo, kg/cm? | 2010-05-25T14:49:58.877 |
2759 | |inverter|ups|power| | <p>I ended up trying a true sine inverter, and that seemed to do the trick. I guess the ups did not like the square wave from the inverter.</p>
| <p>First off, I am aware that plugging an UPS into an inverter is a bit redundant. The only situation I can think of it being useful is in a car when you want full amps for cranking over the motor but still want to run equipment. Anyhow, besides the silliness of why would you plug a UPS into an Inverter, my question is why it will not work. I have been using a motor master 3000 watt modified sine wave inverter with an APC Back-UPS RS 1500VA. When it is plugged in the UPS gives a wiring fault error. I was thinking it may be that the Inverter is not grounded properly so I tied the earth ground pin from the UPS to the buildings ground and still the UPS say’s there is a wiring fault. I heard people say that UPS’s do not like inverters in the past, but the troubling part that I have is that I had the ups working off a Robin Subaru R1700i inverter series generator without any issues. Anyone out there have any thoughts on this matter? </p>
| Plugging a UPS into an inverter | 2010-05-26T18:01:19.517 |
2771 | |motor|motor-controller|autonomous|brushless-dc-motor| | <p>I know this is a very old question from 2010, but for the sake of other people with the problem today, brushless drone and model motor controllers now commutate the motor by sensing the back emf of the winding. There is no hall effect sensors, so you just have to reverse any 2 of the 3 motor wires.</p>
| <p>Can you run a <a href="http://en.wikipedia.org/wiki/Brushless_DC_electric_motor">BLDC motor</a> backwards without damage?</p>
<p>Is it OK to drive a model airplane BLDC engine backwards while landing, so it gets a little "reverse thrust" and come to a stop a little quicker on the runway?</p>
<p>Is it OK to drive a model helicopter BLDC motors backwards so it can hover upside-down?</p>
<p>Or do I need to design the hardware so that it never drives the motor backwards, under any circumstances, no matter what the pilot on the ground does at the transmitter?</p>
| Can you run a BLDC motor backwards without damage? | 2010-05-27T20:55:17.677 |
2790 | |batteries|temperature| | <p>If your device works continuously, don't worry about the performance of lithium batteries at charging and discharging. they just have a lower capacity which you can check in their data sheets. But if you using battery some in a while and you will have a voltage drop in the start because of passivation. The only way to avoid this problem is to take a higher current in start, for example, with a resistor, and then continue with regular condition.</p>
| <p>I'm building a small, low-power device that will be used inside a standard consumer refrigerator (approximately 2°C). I've had trouble with Alkaline batteries at low temperatures, and was wondering if anyone has any recommendations for cells to use under these conditions. How do Lithium coin cells hold up, for instance? The datasheets I've found for them don't seem to take temperature into account.</p>
<p>Update: it looks like I'll have to source ~50mA for short bursts, so the low-end lithium manganese dioxide cells I've been using aren't going to cut it. Any other suggestions?</p>
| Small batteries for use in cold (but not freezing) environments? | 2010-05-28T18:18:59.423 |
2797 | |charlieplexing|microcontroller|avr|breadboard| | <p>I'm only a beginner at all of this, so take this with a grain of salt, but I'd have a totally different approach.</p>
<p>I'd use a 7447 decoder instead. This would use 7 pins (4 for the output, and 3 to select the display), but it would be much simpler than having to work out the combinations to charlieplex and would give a brighter output too.</p>
| <p>I was making a breadboard demo for a Microcontroller class. Basically my project is to make a score keeping device. I want to drive 4 seven segment displays using an atmega8. I read about charlie plexing and understand that it will enable me to drive all the 4 displays using a single port. I understood the theory but can't really figure out how to make the charlie plexing circuit on a bread board. Can anyone please help? </p>
| CharliePlexing on a breadboard | 2010-05-29T18:56:38.390 |
2811 | |frequency-measurement|measurement|microcontroller|attiny|avr| | <p>Using prescalers even GHz measurement can be achieved. This is simple 40MHz frequency meter with ATMEL AVR AT90S2313: <a href="http://www.myplace.nu/avr/countermeasures/index.htm" rel="nofollow">http://www.myplace.nu/avr/countermeasures/index.htm</a></p>
<p>Here are some other similar projects:</p>
<p><a href="http://www.ikalogic.com/freq_meter_2.php" rel="nofollow">http://www.ikalogic.com/freq_meter_2.php</a></p>
<p><a href="http://www.saturn.dti.ne.jp/~khr3887/lfcd_e.html" rel="nofollow">http://www.saturn.dti.ne.jp/~khr3887/lfcd_e.html</a></p>
<p><a href="http://www.circuitlake.com/rs232-frequency-meter-and-pulse-generator.html" rel="nofollow">http://www.circuitlake.com/rs232-frequency-meter-and-pulse-generator.html</a></p>
<p><a href="http://www.ulrichradig.de/home/index.php/avr/frequenzcounter" rel="nofollow">http://www.ulrichradig.de/home/index.php/avr/frequenzcounter</a></p>
<p><a href="http://www.triplespark.net/elec/analysis/FreqCnt/" rel="nofollow">http://www.triplespark.net/elec/analysis/FreqCnt/</a></p>
<p><a href="http://www.cappels.org/dproj/30MHzfmeter/30MhzFmtr.html" rel="nofollow">http://www.cappels.org/dproj/30MHzfmeter/30MhzFmtr.html</a></p>
<p><a href="http://www.qsl.net/pa3ckr/bascom%20and%20avr/rfcounter/index.html" rel="nofollow">http://www.qsl.net/pa3ckr/bascom%20and%20avr/rfcounter/index.html</a></p>
<p><a href="http://www.sump.org/projects/counter" rel="nofollow">http://www.sump.org/projects/counter</a></p>
<p><a href="http://digilander.libero.it/alfred73/eprojects.htm#1300%20Mhz%20Frequencymeter%20with%20prescaler" rel="nofollow">http://digilander.libero.it/alfred73/eprojects.htm#1300%20Mhz%20Frequencymeter%20with%20prescaler</a></p>
| <p>I need to measure the frequency of square-wave that can vary between 0 and 1MHz, and has a resolution of 0.25Hz.</p>
<p>I havent decided on which controller yet but It will most likely be one of the 20pin Attiny's.</p>
<p>Normally how I would measure lower frequency signals would be by using two timers one configured in timer capture mode to interrupt on say the rising edges of the external signal and another timer set up to interrupt every second therefore the former timers counter register value after 1 second would be equal to the frequency of the signal.</p>
<p>However this method obviously wont work for capturing signals ranging between 0 and 1MHz with a resolution 0.25Hz for this I would need a 22Bit counter (AFAIK 8bit micros only have 8/16bit counters).</p>
<p>One Idea I had was to divide the signal before applying it to the micro but this would be impratical as the signal would have to be divided by 61 therefore the frequency could only be updated every 61 seconds where I would like it to be every few seconds.</p>
<p>Is there another method that would allow the frequency to be updated say every 4 seconds?</p>
<hr>
<p><strong>Update:</strong></p>
<p>The simplest solution is to use an use an external interrupt or a timer capture to interrupt on the rising edge of the signal and have the <code>isr</code> increment a variable of type <code>long int</code>. Read the variable every 4 seconds (to allow for frequencies down to 0.25Hz to measured).</p>
<hr>
<p><strong>Update 2:</strong></p>
<p>As pointed out by JustJeff an 8bit MCU will not be able to keep up with a 1MHz signal so that rules out interrupting on every rising edge and incrementing a <code>long int</code>...</p>
<p>I have chosen the method suggested by timororr. Once I get around to implementing it Ill post back and share the results. Thanks to all for your suggestions. </p>
<hr>
<p><strong>Progress Report:</strong></p>
<p>Iv'e started to test some of the ideas presented here. Firstly I tried vicatcu's code.
There was a obvious problem of TCNT1 not been cleared after the frequency been calculated -not a big deal...</p>
<p>Then I noticed when debugging the code that about every 2 to 7 times the frequency was calculated timer 1's (the timer configured to count external events) overflow count would be short by two.
I put this down to latency of Timer 0 ISR and decided to move the if statement block form the ISR to the main (see snippet below) and just set a flag in the ISR.
Some debugging showed that the first measurement would be ok but with every subsequent reading Timer 1's overflow count would be over by 2.
which I can't explain -I would have expected it to be under not over...</p>
<pre><code>int main()
{
while(1)
{
if(global_task_timer_ms > 0 && (T0_overflow == 1))
{
global_task_timer_ms--;
T0_overflow = 0;
}
.....
}
}
</code></pre>
<p>Next I decided I would try to implement timrorrs suggestion. To generate the neccesary interval (of approx 15ms between each timer_isr interrupt) I would have to cascade the two 8-bit timers
as the only 16-bit timer on the Atmega16 is being utilized to capture the rising edges of the external signal. </p>
<p>I thought this solution would work and be much more efficient as most of the overhead is shifted to the timers and only one short isr left for the cpu to handle.
However it wasn't as accurate as I had hoped, measurements shifted back and forth by approx 70Hz which I wouldn't mind at high frequencies but its definitely not acceptable at lower frequencies.
I didnt spend two much time analysing the problem but Im guessing the timer cascading arrangement is not so accurate
as I have implemented a similar arrangement to timrorrs suggestion on a far slower 8051 controller that had 2 16-bit timers and the results were quite accurate.</p>
<p>I have now gone back to vicatcu's suggestion, but I have moved the frequency calculation into the Timer 0 isr <em>(see snippet below</em>), this code has produced consistent and reasonably accurate measurements.
With a little calibaration accuracy should be approximatly +/-10Hz.</p>
<pre><code>ISR(TIMER0_OVF_vect)
{
TCNT0 = TIMER0_PRELOAD; //Reload timer for 1KHz overflow rate
if(task_timer_ms > 0)
{
task_timer_ms--;
}
else
{
frequency_hz = 1.0 * TCNT1;
TCNT1 = 0;
frequency_hz += global_num_overflows * 65536.0;
global_num_overflows = 0;
frequency_hz /= (TASK_PERIOD_MS / 1000.0);
task_timer_ms = TASK_PERIOD_MS;
}
}
</code></pre>
<p>If anybody has any other suggestions Im open to them although but I rather not have to use ranges...
Im also no longer to intent on getting 0.25% resolution, there doesnt seem much point with the level of accuracy that I have at the moment.</p>
| Measuring 0 - 1MHz ( 0.25Hz resolution) Squarewave using an MCU | 2010-05-30T15:14:57.473 |
2820 | |arduino|bootloader|avr| | <p>The clock setting of ATMega*8 chips are defined by the fuses. I'd rather use the same clock settings for the arduino chip and the AVR or you application may not work properly (especially if you use serial communication, etc...).</p>
<p><a href="http://www.micahcarrick.com/05-12-2006/avr-tutorial-clock-source.html" rel="nofollow">This page</a> contains useful information on the subject as well as links to the relevant parts in the datasheet.</p>
| <p>hey i have some chips with the arduino bootloader on it and some chips without. I want to use them using the same circuit. The confusion I have is with the clock the arduino uses 16MHz external and avr has its internal will it cause a problem if I use them in the same circuit?</p>
<p>I was thinking, I just add the clock, the arduino chips will use the crystal and the other chips will not. Am I right?</p>
| AVR external clock problem | 2010-06-01T16:26:58.880 |
2827 | |manufacturing|integrated-circuit|cost|development| | <p>For large quantities you work with distributors. Distributors are important, not just for ordering parts, but also for <strong>support</strong>. When I have to select parts the fact that there's a distributor with <strong>knowledgeable FAEs</strong> plays an important role. </p>
<p>Prices are the <strong>result of negotiations</strong>. It helps if you and the distri know each other, a purchase history will probably get you a more interesting price. Loyalty pays off. My experience with Belgian distris is that it's a small world, sales engineers from one distri know colleagues from another one, and they often know more about your orders with other distris than you would appreciate. </p>
<p>Working with a few big distris who have a big portfolio can have the practical advantages of one-stop shopping, but you can also negotiate <strong>package deals</strong>.<br>
On one occasion I negotiated a very good price, but that was for 100k controllers/year, which we didn't need. The deal was closed at this price however, because we also needed a few other microcontrollers, and taken those together we reached the 100k turnover. </p>
<p>Bottom line: every supplier-customer situation is different, that's why you won't get a firm quote for large quantities. It's all about negotiating. </p>
<p><strong>edit</strong><br>
That was for ICs (that's what endolith asked). Common passives like 0603 10k\$\Omega\$ resistors we don't even take in stock, but we let the subcontractor that populates the PCBs use them from their own stock.</p>
| <p>I know of <a href="http://www.findchips.com/">findchips.com</a>, <a href="http://www.oemstrade.com/">oemstrade.com</a>, <a href="http://octopart.com/">octopart.com</a>, and the like. But even the lowest prices on these sites are still higher than the prices on BOMs I get from China. How do you realistically estimate the cost of an IC purchased at high quantities for manufacturing purposes?</p>
| How do you find high-quantity prices for ICs? | 2010-06-02T15:05:13.857 |
2829 | |pcb|pcb-fabrication|surface-mount| | <p>My favorite is Advanced Assembly in Colorado. They are an assembly house (as I guess we can all surmise by the name) but they have ties with board houses. When I quote boards I alway have them quote first because they are the only place that the assembly itself isn't more expensive than the bare boards...unless you pick the one day turn option which is ridiculous money. They also take my loose parts and don't require reels, but everything is machine placed, unlike the guy down the road from me who will take the loose parts and place them with not quite so good quality.</p>
| <p>Can anyone recommend a good place to go making PCB's? I'm particularly interested in places that also offer assembly, because this makes SMD parts an option. </p>
<ul>
<li>GoldPhoenix is an option, but not the cheapest.</li>
<li>Anyone used OurPCB?</li>
<li>Any order time is OK- there is no particular rush, and the slowboat from China is just fine.</li>
</ul>
| Recommended PCB houses / Assemblers | 2010-06-02T15:52:30.517 |
2831 | |microcontroller|embedded| | <p>I must admit, I haven't had much use with a lint of some sort on a microcontroller/microprocessor project.</p>
<p>On my current embedded project, which uses C++ on a Linux-based PC/104 SBC, we've used <a href="http://sourceforge.net/apps/mediawiki/cppcheck/index.php?title=Main_Page" rel="nofollow">cppcheck</a> (works with C too!). It works pretty well, although it has issues with complicated class inheritance trees. And it has provided some value - it's good for checking for potential locations where memory leaks could occur. But most of the things it noted were stylistic - use preincrement instead of postincrement in for-loops, that sort of thing.</p>
<p>I also used an <a href="http://www.jslint.com/" rel="nofollow">online lint for Javascript</a> when developing applications for an enterprise software system. It was absolutely invaluable there, as there were no debugging tools to check for syntax errors in that setup.</p>
| <p>I currently develop embedded systems using a number of different compilers, the most common coming from IAR systems.</p>
<p>My love of hardware is what drives doing embedded systems and firmware. I however seem to lack quite a bit in software engineering.</p>
<p>I have read many times that a good Lint is invaluable for code. I would like to know if anyone on here uses a Lint, which Lint it is, and how much it helps in detecting errors.</p>
| Embedded System LINT use | 2010-06-02T16:11:34.067 |
2841 | |linux|sbc| | <p>(Kind of a repeat from my answer to the previous question, but with a new board.) I'd go for the <a href="http://www.embeddedarm.com/products/board-detail.php?product=TS-7553#" rel="nofollow">Technologic Systems TS-7553</a> for $135-- slightly cheaper than the Beagleboard, and just as good. I haven't actually used the 7553, but I've used its predecessors, the TS-7500 and TS-7550, and they're good. The only requirement it might not meet out of the box is booting over Ethernet, but I know it can be configured to do so (at least via TFTP or NFS).</p>
<p>(Maybe this goes without saying, but I have no connection to Technologic Systems at all. I've just used some of their boards.)</p>
| <p>I realize this is nearly a dupe of <a href="https://electronics.stackexchange.com/questions/2591/sbc-recommendations">SBC Recommendations</a> , but I have slightly different specs in mind.</p>
<p>Does anyone know of a single-quantity SBC with the following features?</p>
<ul>
<li>32 bit CPU, something common e.g., x86, ppc, arm, atom</li>
<li>capable of running some fairly modern variant of Linux</li>
<li>built-in 100Mbit/s ethernet interface (preferably with RJ-45 jack)</li>
<li>built-in RS-232 or RS-232C serial port (DB-9 connector desirable but not critical)</li>
<li>capable of booting an arbitrary OS/application from FLASH</li>
<li>capable of booting an arbitrary OS/application from ethernet</li>
<li>capable of booting over serial port desirable, not critical</li>
<li>must have at least one USB 2.0 port. more::=better</li>
<li>must operate from a single-voltage DC supply (not more than 28V, not more than 25W)</li>
<li>prefer Not to have PS/2 keyboard & mouse interfaces</li>
<li>prefer Not to have any graphics capability</li>
<li>built-in SPI, I2C, or general-purpose discrete I/O bonus</li>
<li>price point under $250</li>
</ul>
<p>The mission for this SBC is to sit on my network and operate custom I/O hardware. Heaviest possible use case required would be to support a USB web-cam and serve low-bandwidth (CIF) video through a custom server app. Definitely not required to run databases, web servers, web browsers, middle-ware, ESB, or anything like that. Intended s/w platform C/C++, and maybe, just maybe, J2ME or J2SE.</p>
<p>The best match I've found so far is the <a href="http://beagleboard.org/" rel="nofollow noreferrer">BeagleBoard</a> , but this falls short by having graphics capability (not needed) in place of ethernet capability (mandatory). I know you can add a USB based ethernet adapter, but ideally there would be a better match that would render this not necessary. There are also some atom-based 'car PCs' that are near misses, mainly for power supply reasons. </p>
| linux sbc recommendations | 2010-06-03T03:03:42.550 |
2854 | |embedded|rtos| | <p>Licensing is another difference to keep in mind when selecting an open source RTOSs. Especially if you plan to use the RTOS in a commericial project. Most open source RTOSs have a modified GPL license. The license modification usually specifies that you do not have to your proprietary code that links with the GPL RTOS (but you still have to release the RTOS files with your modifications).</p>
<p>NuttX (and probably others) have a non-restrictive, modified BSD license. With the BSD license, you can essentially take the code and use it as if it were own with no obligations other than retaining the licensing and copyright information within the files.</p>
| <p>While reading Linux User's Journal today, I stumbled across <a href="http://www.linuxjournal.com/article/10785#mpart4" rel="noreferrer">a little blurb</a> about <a href="http://nuttx.org/" rel="noreferrer">NuttX</a> RTOS. I checked out their <a href="http://nuttx.org/" rel="noreferrer">website</a> and was fairly impressed with it's feature set and it's ability to put it in an 8052! I find it interesting that it supports POSIX which is something I have helped worked on for one of my clients in-house RTOS. This one seems a little more feature rich than the in-house RTOS.</p>
<p>Has anyone else heard of NuttX and has given it a try? If so, how does it compare to other RTOS's such as <a href="http://www.freertos.org/" rel="noreferrer">FreeRTOS</a>?</p>
| Has anyone evaluated NuttX RTOS? | 2010-06-03T21:12:49.483 |
2864 | |resistors|safety|zener| | <p>I've seen a 1/4-watt 1K resistor explode when one end got connected inadvertently to line voltage while the other end was connected to a ground-referenced circuit. Interestingly, all the current that went through the resistor also went through an ADC input on a Microchip PIC (16C73 if I recall) but the processor chip suffered no apparent damage.</p>
| <p>I don't have an explosion chamber, so I cannot test critical values.</p>
<ol>
<li>If you explode resistors with too high current-voltage combination, does it damage your equipment, such as multimeter and DC-supplier, even in the explosion chamber?</li>
<li>How do I notice when a critical point for resistors is achieved, not touching the hot component?</li>
<li>I want to test a <a href="https://en.wikipedia.org/wiki/Zener_diode" rel="nofollow">Zener diode</a> for increasing voltage. I have a great amount of different diodes, but I have no idea which ones are Zener diodes. Which resistors and Zener diodes should I use and how do I find the right ones without exploding them?</li>
</ol>
| At what current and voltage do typical resistors explode? | 2010-06-05T14:26:26.040 |
2869 | |resistance|colour-coding| | <p><a href="https://i.stack.imgur.com/ShVgv.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ShVgv.jpg" alt="enter image description here" /></a>After hours of painstaking work of trying to figure out exactly how wide the gaps are on either end, I noticed there was a light print on the package which held the resistors together. That had the Ohms printed.</p>
<p>For some of you, this might save a lot of time.</p>
| <p>I know the values of resistors if they are gold-colored at the end. When both ends are the same, such as brown-o-p-brown and red-x-y-z-red, I am in problems. <strong>How to know which side has the last colour and which side is the starting end?</strong></p>
| Resistors with ends of the same colour | 2010-06-05T18:16:00.747 |
2875 | |power-supply|dc|safety| | <p>You can have a look at <a href="http://tuxgraphics.org/electronics/201005/bench-power-supply-v3.shtml" rel="nofollow">this kit from tuxgraphics</a>.</p>
<p>It may not have all the features yon want, but for a DIY power supply, it may be a good start.</p>
| <p>My school uses HY 3005D-3 but I want to do it myself to save on $. Before opening it, I ask for tips about: not-to-break-it, cheap DC supply and DIY-materials (not that I know them soon). So how to build, to get cheap DC Power supply with such adjusting knobs?</p>
| DIY Beginner's DC Power Supply? | 2010-06-05T23:11:00.663 |
2878 | |gps| | <p>I recently purchased a couple of GPS modules for a project I'm working on. You didn't specifically mention Arduino, but I bought the <a href="http://www.adafruit.com/index.php?main_page=product_info&cPath=17_21&products_id=98" rel="nofollow">GPS logger shield</a> from Adafruit with an EM-406a module. I'm not using an Arduino, but I figured it was a compact solution that had two things I wanted (GPS and removable storage). The EM-406a had no problems getting a satellite lock inside my office. I also got the <a href="http://www.sparkfun.com/commerce/product_info.php?products_id=8146" rel="nofollow">Copernicus DIP Module</a> from Sparkfun so I could breadboard with it. No problems so far - just read the datasheet and remember to pull XRESET and XSTANDBY high.</p>
| <p>I have decided to play in the world of GPS modules. I have read the <a href="http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=127" rel="nofollow" title="GPS Buying Guide">GPS Buying Guide</a> from Sparkfun, but still am not sure which unit I want to go with. I am leaning toward the <a href="http://www.sparkfun.com/commerce/product_info.php?products_id=8975" rel="nofollow" title="LS20031">LS20031</a>, do any of you have any experience with GPS modules? Any advice you would like to add to the chiphacker community?</p>
| GPS Suggestions | 2010-06-06T03:48:24.033 |
2896 | |motor-controller| | <p>For an AC motor, you can reduce the voltage to reduce the speed. As a quick hack, you could try running it off 120 V AC; if that speed is good, you're done.</p>
<p>Otherwise, you could try a triac, which chops the voltage for part of each AC cycle, making the average voltage lower, or you could use a variable transformer, like this: <a href="http://www.electroniccity.com/shopping/pricelist.asp?prid=1147" rel="nofollow">http://www.electroniccity.com/shopping/pricelist.asp?prid=1147</a></p>
| <p>This is a AC 220v 60W 0.2A fan I recently bought to replace my old bathroom vent that gave up some time ago. The problem is that the new one doesn't come with a built in speed controller like the old did, so the fan is running really loud. The people at the store tell me to go to another store to buy a speed controller but I have only found dimmers or expensive industrial speed controllers. I studied electronics some years ago and have been looking for a way to build such a speed controller, the question is how. My first guess is to control the speed by reducing the watt or amp. Any help would be welcome.</p>
<p>Some schematics that came with the unit (The instructions are in German):</p>
<p><img src="https://i.stack.imgur.com/vvldD.jpg" alt="Schematics"></p>
| What is used to control AC motor speed? | 2010-06-07T18:01:11.113 |
2898 | |cases|mount| | <p>For extruded aluminum, find the local distributor for aluminum structural framing in your area. Try 8020.net in the US and Bosch-Rexroth in Europe. You might also try <a href="http://www.frontpanelexpress.com">frontpanelexpress.com</a>, though their stuff might be too big.</p>
<p>Here are some options to mount the PCB:</p>
<ol>
<li>The slots</li>
<li><a href="http://www.pemnet.com/fastening_products/prod_desc.php3?cat=Fasteners+for+PC+Boards">PEM studs</a> (you'd need a fabricator to press these in for you)</li>
<li>Bolts and standoffs (try Digikey)</li>
</ol>
<p>For the PEM studs, check out the KSSB family-- they're designed specially for mounting PCBs without extra fasteners.</p>
| <p>I want to make a case for a PCB using extruded aluminum. (Such as the IPOD nano shown below, and the portable amp under it).</p>
<ol>
<li>How do I mount the PCB inside the alumimum extrusion? (I know some come with slots but are there different options?</li>
<li>Who are some good suppliers of extruded aluminum? (bonus if they do milling on small quantities too)</li>
</ol>
<p><img src="https://i.stack.imgur.com/z2Reh.jpg" alt="Example"></p>
| Mounting a PCB in an Extruded Aluminum case | 2010-06-07T21:54:21.637 |
2903 | |licensing| | <p>In many cases, a reference design will show you how to use a manufacturer's own device. So, they only stand to gain if you use the design and buy their devices.</p>
<p>However, I am not a lawyer.</p>
| <p>Can I use a reference design from a data sheet in a commercial product without attribution/licensing of any sort?</p>
| Are reference designs assumed to be license free? | 2010-06-08T19:19:46.543 |
2904 | |music|filter|schematics| | <p>Take a look at <a href="http://en.wikipedia.org/wiki/RC_circuit" rel="nofollow">http://en.wikipedia.org/wiki/RC_circuit</a> under the Parallel circuit section.</p>
<p>That circuit allows you to adjust the resistance (with a pot) and adjust the capacitance by opening or closing switches. So, you can have any combination of switches open or closed to get a different effective capacitance.</p>
<p>The capacitor between Black and Red is just always added with the switched capacitors.</p>
<p>The pot and capacitor at the end is a Snubber, find more info at <a href="http://en.wikipedia.org/wiki/Snubber" rel="nofollow">http://en.wikipedia.org/wiki/Snubber</a></p>
| <p>Here's a link to the (crummy) schematic: </p>
<p><img src="https://i.stack.imgur.com/Y0uFR.png" alt="enter image description here"></p>
<p>It's a filter/phase shift designed by the experimental electronic musician David Tudor, for use in destabilizing audio feedback loops.</p>
<p>The circuit seems unclear to me, and I don't understand the signal flow, or the use of capacitors here. </p>
<p>Thanks!</p>
| Can anyone figure out this (David Tudor) circuit? | 2010-06-08T19:29:04.757 |
2907 | |diodes|datasheet|markings| | <p>I contacted Newark and their answer is: "Our part# does not mean anything in relation to the specs on the manufacturer part.". So it is apparently about book-keeping.</p>
| <p>My diode is:</p>
<blockquote>
<p>VISHAY GENERAL SEMICONDUCTOR 1N4004-E3</p>
<p>Diode</p>
<p>Diode Type:Standard Recovery;
Repetitive Reverse Voltage Max,
Vrrm:400V; Forward Current, If(AV):1A;
Forward Voltage Max, VF:1.1V; Forward
Surge Current Max, Ifsm:30A; Operating
Temperature Ran 78K2120;</p>
</blockquote>
<p><a href="http://at.farnell.com/jsp/search/browse.jsp;jsessionid=YTEEQOAO1ZSPQCQLCIPJMMQ?N=0&Ntk=gensearch_002&Ntt=1N4004&Ntx=mode+matchallpartial&suggestions=false&ref=globalsearch&_requestid=660188" rel="nofollow">Source, please, search for 78K2120.</a></p>
<p><strong>Questions</strong></p>
<ol>
<li>What does "78K2120" mean?</li>
<li>According to the new reply, it is an identifier but what does it mean? Why is it chosen? Does it contain some information except being a random identifier?</li>
<li>Is there some standard, seen too many manufacturers just throwing similar lines but with different meaning?</li>
</ol>
| Marking for Operating Tempature Range on Diode's data sheet? | 2010-06-08T23:55:02.973 |
2908 | |ac|dc| | <p>If you set your multimeter to DC(V) and then measure an AC(V) it will not cause damage, neither will the opposite.</p>
<p>If you measure it with both, and one says 5 V, then that is what signal you have. 5V AC wave will not be anything on DC measurement, but will be 5V with AC turned on.</p>
| <p>My circuit is almost identical to <a href="http://en.wikipedia.org/wiki/File%3aRC_Filter.png" rel="nofollow">the Wikipedia</a> but with 5V in, 1pF cap, 4 pieces of IN4004 diodes. I am not certain whether it is AC or DC here and there (actually I do but not want to break my multimeter). Is there some safe way to test its type? My multimeter has only separate modes for AC and DC but not a common mode for both of them. <strong>So how to find out unknown voltage type?</strong></p>
| Measuring Voltage of Unknown Type | 2010-06-09T01:19:40.387 |
2910 | |capacitor| | <ol>
<li><p>Some caps -- such as nearly all electrolytic capacitors and tantalum capacitors -- are polarized. Such caps use some sort of chemical reaction between an anode and a cathode made of two different kinds of materials to form a thin insulating layer. When you hold one of these caps in your hands, you will see a "-" mark by the pin intended to stay more negative, or a "+" mark by the pin intended to stay more positive.
If a polarized cap is ever "reverse biased" more than 1 V to 1.5 V (typical), it drives that chemical reaction in reverse, eating away at the thin insulating layer, leading to a short between the two pins.
Not only is that capacitor no longer working,
after that, any significant voltage -- forward or reverse -- could make that "capacitor" overheat and in some cases explode.
The person drawing the circuit and connecting the capacitor in a circuit must make sure the "+" end goes towards the more positive voltage, and the "-" end goes towards the more negative voltage, at all times, to prevent catastrophe.
See the Wikipedia article Greg pointed out for more details.
Other caps -- such as nearly all ceramic capacitors, paper disk capacitors, and mica capacitors -- are non-polarized.
Such caps typically use an anode and a cathode made of identical metal, and they work just as well with "reverse biased" voltage as forward biased.
They don't have either "+" or "-" mark, because they don't need one.</p></li>
<li><p>& 3. You never "need" a polarized cap. Practically all physical circuits would work just as well, and perhaps better, if the polarized caps were all replaced with non-polarized caps of the same capacitance and voltage rating.
The opposite is not true -- you often can't replace non-polarized caps with polarized caps.
Some circuits require a capacitor that can handle a high positive voltage at some times and a high negative voltage at other times (polarity reversal), which requires a non-polarized capacitor.</p></li>
</ol>
<p>The only reason people use polarized caps is because they often cost much less than non-polarized caps of the same capacitance and voltage rating.</p>
<p>However, when drawing a schematic, you should always draw a "+" sign on one side of a cap whenever you intend that that the cap always has positive voltage applied to it, it never suffers polarity reversal.
That helps the people reading the schematic understand what you meant.
That gives people putting together the physical circuit the <em>option</em> of using polarized capacitors, even though many times it is more convenient to use non-polarized capacitors in the place of the polarized capacitors clearly marked on the schematic.
It also tells people putting together the physical circuit, should they choose to use a polarized capacitor, which way around the polarized capacitors should go.
It also communicates to repair people that, if they measure a negative bias voltage, that something has gone horribly wrong.</p>
<p>The schematic you show -- with the clearly marked "+" polarized capacitor -- would work just as well with a non-polarized capacitor.
The "+" on one end of the capacitor is telling us that that end is expected to never be negative relative to the other end.
It's also telling us that we have the <em>option</em> of using a polarized or nonpolarized cap in that location when we build that circuit.</p>
| <p><em>Question emerged from my last question about small caps' markings, better to open new question so not become bloated.</em></p>
<p>Heard term polarization in the context of light but not with caps. Googling revealed the effect: <a href="http://en.wikipedia.org/wiki/Dipolar_polarization">Dipolar Polarization</a>. Not sure whether it is the right effect but at least it mentions cap.</p>
<p><strong>1. What does the term "polarized" mean?</strong></p>
<p><strong>2. Why should I use "polarized" cap instead of non-polarized cap?</strong></p>
<p><strong>3. Why does the circuit need a polarized cap? <a href="http://en.wikipedia.org/wiki/File:RC_Filter.png">http://en.wikipedia.org/wiki/File:RC_Filter.png</a></strong></p>
| What does polarization mean in "polarized cap"? | 2010-06-09T01:54:40.440 |
2918 | |pcb|eaglecad|routing| | <p>Also, you often find placement and routing guidelines in the datasheet of ICs that require some external peripheral components. I think it wasn't mentioned yet.
And from my experience i wouldn't suggest using the autorouter. It was said that its good for beginners, but IMO the opposite is the case. There are so many "best practices" that most autorouters have no knowledge of.</p>
<p>Since i was confronted with getting a PCB to be EMV approved forthe first time, i know haw important the attention to details is and how most autorouters would mess those details up.</p>
| <p>Can anyone offer any useful strategies on going from a rat's nest to a routed PCB?</p>
<p>(I'm using Eagle and aiming to make single/double sided PCBs at home)</p>
<p>Drawing the schematic is fine, but when it comes to routing the tracks, it feels like unravelling a giant ball of wool.</p>
| Advice on going from rat's nest to routed PCB | 2010-06-09T15:07:02.867 |
2925 | |prototyping|wire|breadboard| | <p><strong>Fast</strong></p>
<ul>
<li><p><em>"Male to Male Solderless Flexible Breadboard Jumper Cables"</em> that you connect to your breadboard and let say female sockets in your Arduino/Lauchpad/etc.</p></li>
<li><p>Also try <em>"Female to Female Jumper Cables"</em>. They are pretty useful in fast prototyping.</p></li>
</ul>
<p><strong>Cheap</strong></p>
<ul>
<li>Buy network cable such as Cat 5/6 and take out the wires, more <a href="https://electronics.stackexchange.com/questions/621/stranded-vs-solid-wire/623#62">here</a>. It is a reusable and cheap solution. Yet there are different types of RJ45-headed cables: one of mine is stranded copper (cannot cut it with my tools) and one is solid wire (soft). The last fits to breadboard but try to see the cables first, large differences in quality. </li>
</ul>
| <p>I need breadboard wire for fast prototyping. It can apparently be 22AWG or 24AWG, acccording to <a href="https://electronics.stackexchange.com/questions/621/stranded-vs-solid-wire/624#624">this reply about stranded VS solid wire.</a> Because it is for prototyping, I am not looking for expensive wires with excellent electrical shielding and such things -- just simple wires to plug into breadboard and reuse it fast: connect, reconnect, etc without getting them broken. Where do you get your solid experimenting wires?</p>
<p><strong>Example</strong></p>
<blockquote>
<p>Huge price differences: <a href="http://fi.farnell.com/tyco-electronics-raychem/fldwc0311-0-25-0/wire-0-25mm-black-100m/dp/797972?Ntt=TYCO+ELECTRONICS+/+RAYCHEM+-+FLDWC0311-0.25-0+-+FLEXLITE+WIRE+0.25MM+BLACK+100M" rel="nofollow noreferrer">Farnell Finland 66.7EUR</a>, <a href="http://cpc.farnell.com/tyco-electronics-raychem/fldwc0311-0-25-2/flexlite-wire-0-25mm-red-100m/dp/CB04715?Ntt=WIRE+0.25MM+RED+100M" rel="nofollow noreferrer">Farnell UK CPC 23Pounds</a>, cannot find in eBay or Dealextreme, nearly out of stock in CPC Farnell. </p>
</blockquote>
| Cheap solid equipment wire for breadboard from online shop? | 2010-06-09T16:52:59.767 |
2931 | |power-supply|protection| | <p>A graph will illustrate the difference between classical current limiting and foldback. </p>
<p><img src="https://i.stack.imgur.com/6RF2J.gif" alt="foldback current limiting"> </p>
<p>During normal operation of the PSU you move along the horizontal part of the graph: the voltage remains constant at variable current. Once the current exceeds the maximum allowed the voltage drops but the current remains (left graph), which may cause damage to the circuit, and also causes a high dissipation in the PSU itself.</p>
<p>With foldback current limiting, when the maximum current is exceeded the voltage still drops, but the current is decreased to a safe value. (right graph) </p>
<p>(note: \$I_{SC}\$ means short-circuit current) </p>
<hr>
<p><strong>edit</strong> (overvoltage protection)<br>
Overvoltage protection means that the device suppresses spikes on the input voltage, so they can't disturb the output. This is often done by a VDR (Voltage Dependent Resistor, aka Varistor). The VDR is placed parallel to the input and will conduct if the input voltage exceeds normal values.</p>
| <p>I am looking at buying a 24V power supply. Two of the options are these:</p>
<ul>
<li><a href="http://www.automationdirect.com/adc/Shopping/Catalog/Power_Products_%28Electrical%29/DC_Power_Supplies/24VDC,_DIN_Rail_Mount_%28RHINO_PS,_PSB,_PSC,_PSM,_PSP_Series%29/PSP24-060S">PSP24-060S 24 VDC 2.5A (60W) power supply</a></li>
<li><a href="http://www.automationdirect.com/adc/Shopping/Catalog/Power_Products_%28Electrical%29/DC_Power_Supplies/24VDC,_DIN_Rail_Mount_%28RHINO_PS,_PSB,_PSC,_PSM,_PSP_Series%29/PSB24-060-P">PSB24-060-P 24 VDC 2.5A (60W) power supply</a></li>
</ul>
<p>The first offers <em>"foldback short circuit protection"</em> and <em>"overvoltage protection,"</em> but it is $85 dollars. The second is much cheaper but does not mention these.</p>
<p>What are these types of protection, and how important are they? Are they worth an extra ~$50? Thanks!</p>
| What is "foldback short circuit protection" in a power supply? | 2010-06-09T20:25:13.547 |
2935 | |flipflop| | <p>Common JK flip flops, such as the 7476 have both preset and clear inputs. These force the state of the FF asynchronously, i.e., without waiting for a clock edge. You can use a simple R-C circuit and a schmitt trigger buffer (or inverter) to give you a short (e.g., 50usec) active-low pulse at circuit power on, and feed this signal to the 'preset' inputs of the FF's that should start at '1', and to the 'clear' inputs of the FF's that need to start at 0. (The unused preset or clear of each FF should be pulled up to prevent erratic operation.) The spec sheet for the particular part will tell you how short this pulse can be made.</p>
| <p>I am studying for my digital electronics final and one of the major topics is flip flop counters. I need to know how to get the asynchronous counter to preset to 2 before counting to 10. I know how to make it reset (With some well placed NAND gates), but I cant figure out how to get the counter to preset to 2 after reseting. Any help would be much appreciated. Thanks! </p>
| Flip flop counters | 2010-06-09T21:05:17.563 |
2940 | |diodes|rectifier| | <p>I'm going to go out on a limb and take a guess that your other question about reading AC and DC relates to this question ..</p>
<p>If you're feeding regular AC through a full-wave rectifier (the four diodes you mention), the resulting waveform may well give you funny readings on ordinary DVMs. The waveform will resemble the absolute value of a sine wave, and still has enough AC character that a $50 DVM will likely show you a significant reading, albeit an incorrect one. </p>
<p>Using a DVM to try to figure out a circuit like this gets you into the murky territory of the 'true RMS' problem. DVMs are all over the map with regard to how well they perform at giving correct RMS readings. And even if you have a meter that's dead on, this number may not tell you what you really want to know. In situations like this, an oscilloscope is the preferred instrument, and you can get PC/USB based ones for under $100 that will perform admirably at AC line frequencies.</p>
| <p>I rectified about 14V AC to about 12V DC but 6 V AC simultaneously with 12V DC at the end! It was verified by two different tests, 2W10 is apparently just an unit jammed with 4 diodes. Rs means large resistors.</p>
<p><strong>Test 1:</strong> 2W10 rectifier, Rs ---> OUT: 12.7 V DC and 6.0 V AC</p>
<p><strong>Test 2:</strong> 4 pieces of "IN4004 pec616", Rs --> OUT: 12.0 V DC and 6.0 V AC </p>
<p><img src="https://i.stack.imgur.com/ZkYWi.png" alt="enter image description here"></p>
<p><strong>Questions</strong></p>
<ol>
<li>Why do I get both V AC and V DC? I expected only V DC. </li>
<li>How can I filter V AC out? </li>
<li>Can V AC be a problem in circuits that only needs the 12 V DC?</li>
</ol>
| Circuit with V AC and V DC after rectification | 2010-06-10T02:18:32.447 |
2944 | |relay|ttl|pnp|transistors| | <p>29.4V is only 2% from 30V, and most power supplies have tolerances up to 5%, so that 29.4V might as well be 30.9V.<br>
<em>JustJeff</em>'s solution is based on a TTL output with open collector, which sounds like a good idea to cope with the high voltage. If you read the datasheet, however, it shows the 30V output as <strong>Absolute Maximum Ratings</strong> (AMR). AMR is for exceptional conditions, you're not supposed to operate continuously at those values. So you can't use an open collector output directly. </p>
<p>The alternative is a common push-pull output driving an NPN transistor, which in turn drives the TIP32A. Despite being a Darlington the TIP32A has an extraordinarily low \$H_{FE}\$: 50 at 1A. </p>
<p><img src="https://i.stack.imgur.com/luktk.png" alt="enter image description here"></p>
<p>So, supposing you need 1A the base current has to be at least 20mA. That's the NPN's collector current. A <a href="http://www.nxp.com/documents/data_sheet/BC847_BC547_SER.pdf" rel="nofollow noreferrer">BC847C</a> has an \$H_{FE}\$ of 400 minimum, so that will need 50\$\mu\$A base current. That's OK, TTL can source far less than it can sink, but the 50\$\mu\$A is less than the 400\$\mu\$A it can deliver. </p>
<p>Let's pick a base resistor of 22k\$\Omega\$, that will give a base current of 195\$\mu\$A. A 1000\$\Omega\$ resistor between the NPN's collector and the TIP32A's base will allow about 28mA, enough to get the 1A, and a current the NPN also can deliver with the given base current. </p>
<p>In this setup you usually add a pullup resistor between the TIP32A's base and emitter, so that the NPN's leakage current won't switch it on. But the TIP32A has resistors built-in, and the NPN's low leakage current of <5\$\mu\$A will only drop 40mV, far too little to switch it on. </p>
<p><img src="https://i.stack.imgur.com/sBZWS.png" alt="enter image description here"> </p>
<p>If you want 3A from the TIP32A it needs at least 100mA base current and you'll need a Darlington for the NPN as well, like the <a href="http://www.nxp.com/documents/data_sheet/BCV27_BCV47.pdf" rel="nofollow noreferrer">BCV47</a>.</p>
| <p>I can not wrap my head around the fact how I can drive a relay (24V, 160ohm) with an tip32a PNP transistor which has TTL inputs from a controller.
I can easily calculate my resistors when I use the NPN variant (tip31a), but I cannot conceive how to switch the transistor off with just TTL.
The relay will be powered from 29.4V and has a resistor in series to give the appropriate 24V for the relay. And of course there is a diode over the relay.</p>
<p>Any tips will be greatly appreciated, but please note that I at the moment can not use any transistor but the tip32a.</p>
| Switching relay with a PNP and TTL levels | 2010-06-10T05:10:08.317 |
2952 | |power|power-supply|safety| | <p>I've measured the overload behavior on a bunch of phone chargers, from high-quality to super-cheap. They are designed with a constant-voltage/constant-current (CVCC) output. The idea is to provide a constant voltage (typically 5 V) until it reaches the maximum current (e.g. 1 A). At that point, the current will remain constant and the voltage drops. Once you reach a short circuit (or very close), the charger will shut down entirely until the short is removed. At that point it will continue to work properly.</p>
<p>I measured the curve below on a Samsung charger under varying load. You can see that the voltage stays constant until it starts to overload. At that point the voltage drops but the current stays constant. Finally, it shuts down entirely. See more curves on my website <a href="http://www.righto.com/2012/10/a-dozen-usb-chargers-in-lab-apple-is.html" rel="nofollow noreferrer">here</a>. The curve is much more ragged for a super-cheap charger, but the idea is the same.</p>
<p><a href="https://i.stack.imgur.com/qzzEk.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qzzEk.png" alt="Oscilloscope output showing the voltage/current curve." /></a></p>
| <p>I'm experimenting with PIC microcontrollers and various related circuits both on plugboards and simple homemade PCBS.</p>
<p>I'd like to use various old AC power adaptors I have lying around to power my circuits instead of relying on batteries all the time. I have several old mobile phone chargers for example that give out 5v with 500-1000mA of available power. ( I realise they are likely unregulated and I'd need a regulator circuit or similar).</p>
<p>My worry is that that they are very cheaply made so what happens if I accidentally short circuit one or try to draw 1000mA from a 500mA supply.</p>
<p>Are they likely protected against such abuse in any way even if only by an internal fuse? Or are they likely to be severely damaged or worse overheat and catch fire or something? Or will they simply deliver their maximum current and continue working?</p>
<p>None of this is likely to happen, but I want to be safe?</p>
<p>I doubt this affects the answer but this is the UK with a 240v mains supply.</p>
| What if I overload a cheap AC adaptor? | 2010-06-10T15:43:10.457 |
2961 | |batteries|voltage-regulator|monitor| | <p>1 ... Mark's answer is correct but may not fully answer your question.
The following provides a formula for calculating R2 for a given Vbattery.</p>
<ul>
<li>R2 = (Vb - 2.5) x R2 / 2.5</li>
</ul>
<p>See below for details.</p>
<p>2 ... The circuit as shown is "dangerous" because it takes advantage of a "shortcoming" of the 2N7000 MOSFET which is not present in all MOSFETS.<br>
Substitution of a FET with a lower turn on gate voltage (Vth or Vgs_th) may lead to an alarm that is always on or that draws some current at all times.</p>
<p>Unlike a bipolar transistor or MOSFET the TL431's Cathode (positive terminal) is NOT pulled to or even near ground voltage when the device is on. A typical specification sheet advises that anode voltage of a TL431 will fall to approximately no lower than it's gate voltage of 2.5V when turned on. In practice the voltage may be almost a diode drop below this (about 1.9V) but no data sheet ever advises this and it cannot be relied on.</p>
<p>With 2.5V applied to its gate a 2N7000 MOSFET is turned off. Typically 3V is required to cause it to conduct somewhat and 4V or more is needed for reasonable conduction.</p>
<p>Datasheet: <a href="http://bit.ly/DS_2N7000" rel="nofollow">http://bit.ly/DS_2N7000</a></p>
<p>The TL431 changes from non conducting to conducting when its gate is raised to or above its internal reference voltage of 2.5 Volt.
Vb (Vbattery) is divided by RA & R2 and applied to the gate.</p>
<ul>
<li>Vgate = R2/(R1+R2) x Vb</li>
</ul>
<p>OR when the gate is JUST at the trip point</p>
<ul>
<li>R2 = (Vb - 2.5) x R2 / 2.5</li>
</ul>
<p>The writer has nominated 6V as the low battery point for 2 cells and at 9 volts when 3 cells are used. The "best" trip point depends somewhat on loading. Heavily loaded cells have a lower loaded voltage for a given state of discharge. I would personally suggest a slightly higher trip point unless cells are heavily loaded if maximum cell life is desired.</p>
<p>Sensibility check:</p>
<p>Plug the available data into the above formula to see if it gives his answers.</p>
<p>R1 = 2.49k, Vb = 6V, </p>
<ul>
<li><p>R2 = (Vb- 2.5) x R2 / 2.5</p></li>
<li><p>= (6-2.5) x 2.49k / 2.5 = 3.49k</p></li>
</ul>
<p>He has chosen the next highest standard value of 3.57k . </p>
<p>So results are the same. QED.</p>
<p>Note that the required tolerances are somewhat less than implied by the precision of the resistors used. </p>
| <p>Hey, I came across this Low Volatage Shunt regulator on a Hobby RC forum, I am trying to figure out how the resistor Values are Calculated, </p>
<p><a href="http://www.rcgroups.com/forums/attachment.php?attachmentid=210702" rel="nofollow">http://www.rcgroups.com/forums/attachment.php?attachmentid=210702</a></p>
<p>the one shown here, uses a TL431 regulator and a 2N700 transistor connected with Lithium Polymer batteries of value 11.1v or 7.4v, the circuit trips the alarm at a particular voltage in this case it is 9v when an 11.1v battery is used and 6v when a 7.4v battery is used. If anyone can help this would be super awesome thanks</p>
| Low Voltage Shunt Regulator | 2010-06-10T18:37:28.133 |
2962 | |power-supply|operational-amplifier|datasheet| | <p>First, what you call "drop-out" can be found on page 3 of the <a href="http://www.ti.com/lit/ds/symlink/lf347-n.pdf" rel="nofollow">datasheet</a> as <strong>output voltage swing</strong>. At \$\pm\$ 15V power supply the output voltage swing for the LF347 is minimum \$\pm\$ 12V. </p>
<p>Voltage is not absolute, but rather relative to some reference point. If \$V_+\$ is 30V higher than \$V_-\$ for the opamp this might be a dual, \$\pm\$ 15V supply as well as a single +30V supply. It works exactly the same. It's you who decides where the reference, ground, lies.<br>
Single supply opamps are often used with low supply voltages, like +5V. You'll have to keep output voltage swing in mind; if the output doesn't come closer than 2V from the rails a 5V opamp's output will be limited to +2V to +3V. Therefore low-voltage opamps are often <strong>RRIO</strong>, for Rail-to-Rail I/O. Outputs will go to a few tens of mV from the rails, and input signals close to the rails will be handled correctly as well. Non-RRIO will accept any input voltage as long as it's between the rails, but voltages close to the rails won't be amplified correctly.</p>
| <p>I'm trying to pick an op-amp and I'm having trouble figuring out if the op-amp needs a positive and a negative power supply or if I can connect it to ground and the positive supply.</p>
<p>What do I need to look for in the datasheet?</p>
<p>Also, where do I find the "drop-out" of the output compared to the rail voltage?</p>
| OpAmps - Single Supply or Dual? | 2010-06-10T18:45:15.863 |
2967 | |sound|frequency| | <p>You could hook it to the output line of a PC serial port, set the port for 4800,n,8,1 and transmit 0x55 bytes at it all day. If you draw out the waveform you'll see that back to back 0x55 bytes will result in a square wave at half the bit rate. Using 8,n,1 settings means it takes 10 bits to send a byte, so at 4800bps, that's 480 chars/second, so each 0x55 that you send would get you a hair more than 2msec of 2400Hz square wave.</p>
<p>If it is indeed 'electromagnetic' then it really shouldn't matter about the polarity, but you should use limiting resistors to keep from exceeding the voltage ratings. To keep the peak-to-peak voltage down where it would be with a single-ended 5V square wave, you'd need to trim the +/-12V swings of the serial port down to +/-2.5V .. or if you had an RS-232C port (i.e., already TTL level) you wouldn't have to mess with resistors at all.</p>
<p>Actually, if this part is like a tiny dynamic speaker (which the 40ohms suggests), then you should probably worry more about keeping under the <em>current</em> maximum. It's doubtful that the internal insulation would be remotely close to breakdown at 8V, but it is probable that the fine gauge wire would melt if you push too much current through it. If you have to use resistors, start large and work your way down.</p>
| <p>I desoldered a component, HY-05 Electro-magnetic sound generator, from a broken motherboard. Its DCV is 3~8V, operating frequency 2400 plus or minus 200 Hz. I can get a small metallic sound with the operating voltage probably because the frequency is wrong. How can I adjust the frequency in the power supply of 50Hz? If the question is bizarre, it may be that the component is just broken.</p>
| How to get higher frequency from DC power supply? | 2010-06-10T21:02:17.603 |
2992 | |voltage-measurement|measurement|microcontroller|ac|high-frequency| | <p>Several ways to measure peak-to-peak voltage with a MCU:</p>
<ul>
<li><p>undersampling: Directly sample with an ADC, even though you know you are getting less than once sample per cycle of the signal. This requires (a) the signal repeats over and over the same waveform, and any changes to that pattern occur relatively slowly, and (b) the actual sample-and-hold part of the ADC has a high enough bandwidth, even though you only get one sample once every few cycles of the signal, and (c) the exact sampling instant of the sample-and-hold doesn't always hit the same point on the repeating signal, but drifts along it, eventually hitting the highest peak and later the lowest valley of the signal. (Often this drift happens without you having to do anything; but to guarantee it will always work, you may need to <em>lower</em> your sampling rate with some signals). High-speed digital oscilloscopes often use this undersampling technique to inspect amazingly high frequency signals.</p></li>
<li><p>use maximum peak detector and minimum valley detector to hold the maximum and minimum voltages on sampling capacitors long enough for you to sample them. Either use a resistor on each capacitor with a "long enough" RC time constant that the change in voltage from the actual maximum to your ADC sample is insignificant, or use a transistor on each capacitor to reset the voltage immediately after you sample it. If you can estimate the diode voltage drop in software, the simplest hardware is a diode-capacitor-resistor peak detector and a diode-capacitor-resistor valley detector ... but using an op-amp precision peak detector rather than a single diode may be simpler than trying to estimate the diode voltage drop.</p></li>
<li><p>use a DC blocking capacitor, followed by a diode to ground (to clamp the minimum voltage to 0) and a diode to a peak detect sampling capacitor. The voltage on that capacitor gives you the peak-to-peak voltage directly. Somehow estimate and compensate for the diode voltage drops in software, or else use op-amps to compensate for them in hardware, similar to the peak detector.</p></li>
<li><p>use a frequency mixer (analog multiplier) to shift high-frequency signals down to an easier-to-handle frequency well inside your ADC's capability. (Like undersampling, this assumes the signal repeats over and over the same waveform, and any changes to that pattern occur relatively slowly).</p></li>
</ul>
<p>I'm not sure why you want a precision rectifier. I assume you really meant "precision peak detector" (which is admittedly almost the same circuit).</p>
<p>A RC filter with a long RC time constant will give you the average voltage of the signal.
As pingswept says, it's probably best to use a fixed cutoff frequency (for the peak detect, valley detect, and the average detect) to handle the high frequencies with analog circuits, and deal with low frequencies in software.</p>
<p>As long as the MCU is sampling the highest peak voltage and lowest valley voltage,
consider also reporting the midway voltage halfway between the two --
this is not always the same as the true average voltage of the signal.</p>
| <p>I need to measure the peak to peak voltage and DC offset of a 1Hz to 1MHz sine/triangle wave. The signals amplitude varies between 0 and 2Vpp and the offset can vary between -2v and +5v. I will be using an Atmega16 to do the A/D. The Atmega16 has an 8 channel 10-Bit ADC with 50-200KHz sample rate @10-Bit resolution. Taking multiple samples for cycle is obviously out of the question.</p>
<p>What I was thinking of doing was to sample two different versions of the signal eg connect the signal to both a negative peak detector and a precision rectifier and connect those circuits outputs to two different ADC channels and then from result of these conversions (ie the negative and positive peaks) calculate the the vpp and DC offset. Obviously the signals will need to scaled and level shifted before being applied to the controller.</p>
<p>Im not really sure if this will work at all, there must be a far simpler and more sophisticated way to do this that I haven't thought of.</p>
| Measuring VPP and DC offset of a 1Hz - 1MHz signal using MCU | 2010-06-12T13:00:41.883 |
3008 | |arduino|floating-point| | <p>Arduino Mega hardware SPI pins are not located in the same place as on the ordinary Arduino. You will need to change the library.</p>
| <p>I recently acquired a number of components including an Arduino Mega microcontroller and a uM-FPU V3.1 Floating Point Co-processor.</p>
<p>Using a breadboard I have built the circuit shown on Page 2 of the document uMFPU-V3_1 Arduino.pdf from the Micromega website.</p>
<p><img src="https://i.stack.imgur.com/thaq8.jpg" alt="enter image description here"></p>
<p>I am having some difficulty in getting the circuit to function as expected.</p>
<p>PC details: Window Vista 64,
Microcontroller: Arduino Mega (genuine),
Arduino IDE: Version 0018</p>
<p>The documentation (uMFPU-V3_1_Arduino.pdf) says to download the support files (uMFPU-V3_1-Arduino.zip) and place the folders (Fpu, FpuSerial, Spi) in the hardware/libraries subdirectory of the Arduino application directory.</p>
<p>It seems that the directory structure of the Arduino IDE has recently changed? Earlier versions of the IDE apparently had the libraries located as suggested in the document above, but the current version 0018 of the Arduino IDE seems to have the /libraries subdirectory located directly in the Arduino application directory. </p>
<p>The sketches provided in the documentation (sample.pde, graph.pde etc.) seem to only compile in the IDE version 0018 with the FPU libraries placed in the new directory location.</p>
<p>With the libraries in the new location, the example sketches (sample.pde, graph.pde etc) can be compiled without error and uploaded to the Arduino. At the moment, when the sketches run on the microcontroller, the Arduino IDE Serial Monitor only responds with the message 'Sample' or 'Graph' and nothing else. There is no indication of a connection to the FPU with version details, no display of the results of FP calculations or even the message 'uM-FPU not detected'.</p>
<p>I also have tried using older versions of the Arduino IDE (0016) (with the libraries placed in the location suggested in the documentation) on another computer with Windows XP (not 64bit) and the result seems to be the same.</p>
<p>Hopefully someone may have some ideas or suggestions about where the problem may be? Could it be a faulty FPU chip or the Arduino board itself?</p>
| Arduino Mega/uM-FPU coprocessor | 2010-06-14T12:21:50.253 |
3012 | |development| | <p>"The problem is not with starting things, but continuing them." I recognise that in some of my students. My advice is to find some end goal that motivates <em>you</em>. Just some hints:</p>
<ul>
<li>entering a robot competition (and win!)</li>
<li>setting up a StackExchange type of website for breeding stick insects</li>
<li>writing an compiler for </li>
<li>creating some electronic/embedded product and actually sell it on your website</li>
<li>protecting your dorm room with the best anti-burglar system ever created</li>
</ul>
<p>Some 15 years ago I wanted build a laer tag system, and I wanted to introduce the kids of the local electronics club to PIc programming. So I</p>
<ul>
<li>created a PIC programming langauge and compiler (Jal)</li>
<li>creaded a PIc programmer (Wisp, now Wisp648)</li>
<li>started selling PIC chips because the local electronics store was way too expensive</li>
</ul>
<p>One or two of the elctronics kiddies indeed programmed a few PIc chips, but I never got around to build the laser tag system. That's just to show that once you have a goal there is plenty to do!</p>
| <p>My New term is going to start a couple of weeks from now. And as it goes in colleges here the first few months of the semester are easy. I have lots and lots of spare time to learn something new. I like to learn things by myself. But have not done much since a couple of months due to submissions and finals. I would like to dive into something exciting to learn this new semester.</p>
<p>My main interests are into uControllers, intelligence, analog electronics and robotic locomotion. Can you please recommend something which would take a few months to learn and would add to my engineering skills?</p>
<p>Regards.</p>
<p><strong>Edit</strong><br>
My really lazy question has provided the community with a nice list of things to do once you have some knowledge under your belt. The problem is not with starting things, but continuing them. I faced that problem and also many before or after me. I propose we continue adding to this list. Here is a small summary of what I gathered.</p>
<ol>
<li>Start with BEAM robotics: It has been a very facinating branch of robotics which uses only descreet electronic elements and it also has possiblity of adding intelligence using Nv Nets. But the problem is its still in its research phases and there are not many resources. I had to use the web archive to get to some papers and I dont think thats a very good sign.</li>
<li>Making your own PCBs: This is different and you wont get to learn this in class. So if you have to access to cheap PCB manufacturer I propose this to you.</li>
<li>Learn C: C is one of the oldest and most widespread languages and still used in industry</li>
<li>Learn ARM</li>
</ol>
| What should I learn? | 2010-06-14T21:38:07.960 |
3018 | |embedded|radio|antenna| | <p>First, I agree with Joby, you should probably start in a simulator. The reason is simple, there is a large cost to program every device on a network with new software and then collecting data about the cause of a failure can be very hard when it just stops working.</p>
<h2> TinyOS</h2>
<p>On that note, you possibly know this already, or you have accepted routing protocols and you want to test how they function in a real world situation. This is very doable. <a href="http://docs.tinyos.net/index.php/CC2420" rel="nofollow">Lets start by clicking over to all of the information on their wiki about their stack</a>. This explains what decisions they made when implementing the stack and how it was designed to allow you to easily change out their protocol with your own communications stack.</p>
<p>It looks like they have done a great job of properly implementing a stack and you should be relatively able to replace the protocol with what you need. Now the challenge here is what I have run into when implementing a wireless protocol. If the algorithm is complex, it can be very very hard to find the root of a problem. At my job we implemented a proprietary 900MHz protocol, let me forewarn of two problems we hit.</p>
<h2>Possible Problems</h2>
<p>Processing power, try to stay up with how much time you are burning. We found when we started using complicated load equations, and I use the term complicated with reference to how fast an MSP430 runs, the lag on the system and it's response was prohibitive to using a great algorithm.</p>
<p>When we did make errors in our implementation we found that a minor error could stay invisible for hours, days or in one case weeks. This should be solved by using a tried and proven algorithm. The problem we had was our algorithm worked well, but in a certain case the load on the microcontroller was so great it caused large problems, which we exacerbated by our systems response.</p>
<p><a href="http://docs.tinyos.net/index.php/TOSSIM" rel="nofollow">Take the time to play with your code in the simulator that tinyOS has</a>.</p>
<p>Let me know if there is anything I can add or make more clear. if you put it in a comment I can try to edit in more info.</p>
| <p>I would like to load TinyOS on CC2420 radio motes to operate on certain communication protocols (e.g. epidemic routing, probabilistic routing, etc.). However, I have no prior experience in programming motes to perform the protocols I want. I'm just wondering about the most applicable resources for reference and how difficult (if not impossible) was implementing such mentioned protocols. It would be great to hear from you. Thanks in advance!</p>
| Implementing Communication Protocols on CC2420 motes powered by TinyOS | 2010-06-15T04:04:03.247 |
3042 | |voltage|scaling|negative| | <pre><code> +5V
|
.-.
| |
| |2K 2K_
'-' .----|___|----.
| | |
| | |
'--------o |
| +Pwr |
| |\| |
.----|-\ |
| >-----o----Output
input--------------------|+/
|/|
-Pwr
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
</code></pre>
<p>This will make 2.5V become 0V, 0V becomes -5V, and 5V stays 5V.</p>
<p>The circuit posted by Kortuk will invert the input resulting in a mapping from [0v -> 5v] to [+5v -> -5v] instead of [0v -> 5v] to [-5v -> +5v].</p>
<p>Here is a <a href="http://www.falstad.com/circuit/circuitjs.html?cct=$+1+0.000005+10.634267539816555+50+5+50%0Aa+256+240+384+240+0+15+-15+1000000+4.849953000939981+4.85%0A172+256+256+208+256+0+6+4.85+5+0+0+0.5+%252B+Voltage%0AO+384+240+432+240+1%0Ar+256+224+160+224+0+2000%0Aw+256+224+256+144+0%0Aw+384+240+384+144+0%0Ar+256+144+384+144+0+2000%0AR+160+224+112+224+0+0+40+5+0+0+0.5%0A" rel="nofollow noreferrer">simulation</a>.</p>
| <p>Can anyone explain how one would convert one voltage range to another? I'm going to need to convert a range of 0 to +5 volts into a range of -5 to +5 volts. How would this be accomplished? Thanks!</p>
| Converting/scaling a voltage range ([0v - 5v] to [-5v - +5v]) | 2010-06-16T16:03:27.750 |
3048 | |relay| | <p>You can see a list of advantages and disadvantages here: <a href="http://en.wikipedia.org/wiki/Solid_state_relay#Advantages_over_mechanical_relays" rel="nofollow">http://en.wikipedia.org/wiki/Solid_state_relay#Advantages_over_mechanical_relays</a></p>
<p>In your case, whatever. Both solutions work. It will depend on the variable that you take into account, such as price, life cycle, etc.</p>
| <p>Anyone familiar with relays mechanical or otherwise? I would like to be able to switch on/off up to 250W (120V) load using a microcontroller.</p>
<p>Will be used to control lighting to an aquarium.</p>
| Which relay - Mechanical or Solidstate? | 2010-06-16T20:00:06.140 |