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9888
|
|layout|decoupling-capacitor|
|
<p><img src="https://i.stack.imgur.com/TZeQ2.jpg" alt="enter image description here"></p>
|
<p>I'm making a board which will host an ATmega 162 microcontroller in PDIP package. Unfortunately, VCC and GND pins are diagonally arranged. From what I've read, the capacitors should be as close to the pins as possible for maximum effect. </p>
<p><img src="https://i.stack.imgur.com/hWgn1.png" alt="enter image description here"></p>
<p>Right now, I can see 3 ways to connect the capacitors. Run wires to the capacitors so that they are at equal distance from both pins, place capacitors near ground and run wire to VCC or place capacitors near VCC and run wire to ground. There's always the "none of the above" option too. </p>
<p>How do I make right decision in this case? Or is is irrelevant?</p>
|
How to connect decoupling capacitor when VCC/GND pins aren't close
|
2011-02-09T00:34:17.597
|
9896
|
|modbus|
|
<p><a href="http://jamod.sourceforge.net/" rel="nofollow">JaMod</a> is an open source Java implementation of the Modbus protocol. I've used it before to simulate a Modbus master device. I believe you could use it to simulate the slave device as well.</p>
|
<p>I'm looking for FOSS (for commercial use) VCL components for Delphi or libraries for Visual Basic/C/C++/C# ... basically, just something to abstract the h/w for development, although a h/w simulator might be useful for testing.</p>
<p>Does anyone know what is available? </p>
|
FOSS ModBus libraries/VCl?
|
2011-02-09T07:46:36.960
|
9899
|
|rfid|
|
<p>dren.dk has listed some great resources. I'm a bit bummed to see that the RFID IC is $30 alone. I have been using the <a href="http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/RFID/List/0/SortField/4/ProductID/688/Default.aspx" rel="nofollow">Parallax RFID read/write module</a> that interfaces via RS232, and have had good results with it so far, and it's only $13 more (currently $43 on sale) than the IC sold at SparkFun, so it might be more immediately integratable for you.</p>
|
<p>What I do <strong>not</strong> want is one of those RFID readers which attaches to serial or USB port and writes its input to stdin.</p>
<p>I am looking for cheap & nasty RFID reader which I can query over serial or USB; a bonus is if it is also an RFID writer but doesn't add too much cost.</p>
<p>Coding something like:</p>
<pre>
fopen(com1);
fwrite, com1, "hey, you, send me some input");
read(com1, ipit_value);
fclose(com1);
</pre>
|
Seeking cheap RFID reader / writer
|
2011-02-09T10:20:24.890
|
9912
|
|analog|temperature|thermocouple|
|
<p>You might want to look into:</p>
<ul>
<li><p>MAX31850/55/56</p>
<ul>
<li><p>1-wire version can be quite cheap ($3-5 in single quantities)</p></li>
<li><p>SPI can bankrupt you with 4-5$ range</p></li>
</ul></li>
<li><p>MCP9600</p>
<ul>
<li>if you need I2C, at pricey $5</li>
</ul></li>
</ul>
<p>It may help with the thermal sensing endeavours. Generally, searching Digikey for "thermocouple" an sorting by price can be enlightening.</p>
|
<p>I've tried a few options for reading the signals from thermocouples over the years. </p>
<p>The cheapest way (component cost) is likely to be DIY, and a lot of work involving lots of analogue stuff that I'm not good at! </p>
<p>I've tried the following:</p>
<p><a href="http://datasheets.maxim-ic.com/en/ds/MAX6675.pdf" rel="nofollow"><strong>MAX6675</strong></a></p>
<pre><code>1+ £14
25+ £9
100+ £5
</code></pre>
<ul>
<li>SPI Thermocouple solution</li>
<li>Very easy to use and results are returned with 0.1°C accuracy.</li>
<li>Very expensive</li>
</ul>
<p><a href="http://www.analog.com/static/imported-files/data_sheets/AD596_597.pdf" rel="nofollow"><strong>AD597</strong></a></p>
<pre><code>1+ £6
10+ £4
100+ £3
</code></pre>
<ul>
<li>Feed output voltage into microcontroller ADC</li>
<li>I've had good results with these</li>
</ul>
<p>Does anybody have any other recommendations? </p>
|
More Options for Reading Thermocouple Signals
|
2011-02-09T16:30:46.203
|
9915
|
|mosfet|esd|
|
<p>YES absolutely. </p>
<p>I made the mistake of putting 2N7000 in my designs before and worked on them in environments that were not well ESD protected. I have destroyed literally dozens of 2N7000's doing this. </p>
<p>The key issue for me is "how much" protection is necessary in designs. Especially for production when adding protection costs money. </p>
|
<p>CMOS inputs on microcontrollers and other ICs can be damaged by ESD discharges. Can the gate of a big discrete MOSFET (2N7000, IRF9530, etc.) be damaged by ESD discharges?</p>
|
Are discrete MOSFETs ESD sensitive?
|
2011-02-09T18:49:44.930
|
9922
|
|heat|
|
<blockquote>
<p>I would like to make a circuit that can heat up an object to a very high temperature, similar to an electric griddle or coffee cup warmer.</p>
</blockquote>
<p>If this is a hobby project or other one-off, why don't you repurpose an electric griddle or coffee cup warmer or iron or...? Your local thrift store has a ready-made supply of these.</p>
|
<p>I would like to make a circuit that can heat up an object to a very high temperature, similar to an electric griddle or coffee cup warmer. What kind of heating elements do they typically use and where can I buy them? They should be pretty easy to power with 120VAC right? I just need to be able to switch it on and off from an MCU.</p>
<p>Target temperature is ~200°C</p>
|
Heating an object with a circuit
|
2011-02-09T20:19:35.297
|
9930
|
|integrated-circuit|cmos|
|
<p>If you're looking for a free IC design book available on the web, I would recommend Hans Camenzind's book <em><a href="http://www.designinganalogchips.com">Designing Analog Circuits</a></em>. It's a pretty good resource that goes from the device building blocks to the large complicated circuits. It has plenty of drawings and is much more readable than any textbook I have.</p>
<p>His text is not encyclopedic, but you should be able to get enough examples to understand <strong>A</strong> way to build a diode so that you wouldn't be shocked by a new method. </p>
|
<p>Looking for some resources on the design of Integrated Circuit Designs as they can contain a range of components. I am interested in how they can produce diodes and resistors on the dies in the ICs. Are there any free resources available?</p>
|
IC Design Resources
|
2011-02-09T23:05:24.477
|
9935
|
|fpga|wireless|rf|video|
|
<p>I usign <a href="http://www.lyrtech.com/Products/SFF_SDR_development_platforms.php" rel="nofollow">A Small Form Factor Software Define Radio of Lyrtech</a>. You can do many applications for multiples kind of signals, It seems usefull.
This board has three modules: a Digital signal processing module, a conversion data module and a radio frecuency module.
The digital signal processing module has a virtex -4 (I would like other anyone with more resources) and a texas instrument Da Vinci DSP.
As you can see, it has a 1.6–2.2 GHz for high-band RF.
The only problem I see with this equipment is that could be expensive for your budget.
Hope this helps.</p>
|
<p>I want to build a FPGA based prototype for uncompressed video over wireless connection with one box being transmitter and other a receiver (to display). The transceiver speed for HD video (1080) is 3-4Gbps. But it would need an expensive FPGA board. I am thinking of VGA and I guess it needs around 1 Gbps (correct me if I'm wrong). </p>
<p><strong>What type of FPGA board should I use (preferably cheaper)?</strong></p>
<p>Also, I would need to interface the FPGA with an RF module. Are there any RF module available for that could be interfaced with FPGA and support 1Gbps speed?</p>
|
FPGA board for implementing wireless video
|
2011-02-10T06:24:31.517
|
9952
|
|pcb|connector|pcb-assembly|
|
<p>Go look at part search on <a href="http://www.hirose-connectors.com/" rel="nofollow">Hirose Connectors</a>, they have a lot of different choices to offer for the different stacking heights.</p>
|
<p>I need to stack two <a href="http://en.wikipedia.org/wiki/Printed_circuit_board" rel="nofollow">PCBs</a> together, but the stacking height is extremely critical. In terms of board-to-board connectors, the best I could come up with was SAMTEC GFZ series.</p>
<p>What other solutions can be recommended to stack two different PCBs? I need to have very low stacking height (less than 2 mm, the lower the better), and about 100 connections.</p>
|
Very low stacking height PCB connector
|
2011-02-10T15:56:21.787
|
9953
|
|filter|
|
<p>It's very difficult (or even impossible) to do such filter with a simple 2-pole analog filter, depending on your requirements (fp, fs, As).
Download and install <a href="http://focus.ti.com/docs/toolsw/folders/print/filterpro.html" rel="nofollow">FilterPro</a> (from Texas Instruments) and test some configurations. That's a very good and simple program. You enter the requirements of your filter, click on a button and then you get the circuit and the values for resistors and capacitors automatically.</p>
<p>Probably, with a digital filter you can achieve much better results. Take a look at IIR filters.
What's the application of your high pass filter? Maybe DC removal? If so, google for IIR+DC removal, you'll get plenty of results.</p>
|
<p>I want to design a very low frequency (<1Hz) high pass filter. I was thinking of using a 2 pole sallen-key opamp design with a pair of r's and c's. Is there anything special I need to consider when choosing component values/types. It looks as though the caps will need to be in the 100's of µF range.</p>
<p>Thanks</p>
|
Very low frequency (<1Hz) high pass filter design
|
2011-02-10T16:10:54.127
|
9956
|
|cable-assemblies|cases|
|
<p>SketchUp can be a little cumbersome in the beginning. I would urge you to stick with it. There are a lot of really great tutorials out there (start at <a href="http://sketchup.google.com/support/bin/answer.py?hl=en&answer=36207" rel="nofollow">http://sketchup.google.com/support/bin/answer.py?hl=en&answer=36207</a>). I'd spend just an hour or two really getting familiar with the tools and see how you feel. I'm in the same situation--hobbyist, so free/cheap is the best option. I hated that I could never get things to 'snap' or align properly. A few videos later, I'm fairly competent, and don't feel lost anymore. If nothing else, learn about inference and alignment. That should take some of the frustration out of it and make you more productive.</p>
<p>Sorry I don't have any alternatives, but I hope SketchUp works out for you. Good luck! </p>
|
<p>I often tend to build a prototype for a project and if I have something that's good enough I find a case that matches the prototype I've built. However, now I'm trying to do more of the design up front and would like to design the casing up front. The latest projects seem to involve more parts as well.</p>
<p>Which tools do you use? I would like something that could give me a 3D view of the assembly. As a hobbyist I'd like something that is free or cheap.</p>
<p>I'm looking at <a href="http://sketchup.google.com/" rel="nofollow">Google's SketchUp</a> now which seem useful but kinda cumbersome for my task.</p>
|
What's the best tool to design casings/boxes?
|
2011-02-10T16:51:23.080
|
9961
|
|soldering|usb|components|
|
<p>Flux! Use plenty of flux and it will magically work. </p>
<p>You don't need:</p>
<ul>
<li><p>a super-skinny soldering tip</p></li>
<li><p>hot air station</p></li>
<li><p>very thin solder</p></li>
<li><p>solder paste</p></li>
<li><p>desolder braid (helpful though)</p></li>
</ul>
<p>You do need:</p>
<ul>
<li><p>Flux</p></li>
<li><p>Magnification (you've got that covered)</p></li>
</ul>
<p>Flux up the pads really well, then apply heat and solder. Try to make a big ball that covers all the pads. Then remove solder by repeatedly cleaning the tip and touching it to the pads. This technique is similar to drag soldering. If in doubt add more flux.</p>
|
<p>I've got some really tiny leads on a USB port that I need to solder to a board.</p>
<p><img src="https://i.stack.imgur.com/iUUZy.jpg" alt="SMD mini USB port"></p>
<p>The local Hackerspace has a microscope that I'm going to see about using this for, but even a soldering iron is gigantic compared to these tiny leads. Does anyone have any tips (pun intended and unintended) for soldering these leads to a board?</p>
|
Soldering Tiny Leads?
|
2011-02-10T17:34:31.690
|
9965
|
|rf|transmitter|ham-radio|
|
<p>I found a <a href="http://www.expandedspectrumsystems.com/prod5.html" rel="nofollow">ten meter beacon kit</a> which got a writeup in <a href="http://www.ogdenarc.org/downloads/Beacon%20by%20N7JS.pdf" rel="nofollow">CQ Magazine (PDF)</a> a while back. It's 30 bucks, and looks like a quality product. Should be a fun build!</p>
|
<p>I want to build a <a href="http://en.wikipedia.org/wiki/Radio_propagation_beacon" rel="nofollow">Radio Propagation Beacon</a> but I would like to find an integrated circuit that does most or all of the work of the transmitter. </p>
<ol>
<li>Transmit to 28Mhz (Ham 10-meter band)</li>
<li>Allow me to feed it <a href="http://en.wikipedia.org/wiki/Continuous_wave" rel="nofollow">Morse code</a> audio and for it to transmit that. </li>
<li>As cheap and simple as possible, such as a single-chip solution.</li>
</ol>
<p>I'll write some code on an Arduino to produce the Morse code. It doesn't have to be high power, 200mw range is perfectly fine. </p>
<p>I do have an radio amateur license.</p>
|
How to build cheap radio propagation beacon?
|
2011-02-10T18:32:47.313
|
9969
|
|sensor|
|
<p>There is some discussion on this topic at this question: <a href="https://electronics.stackexchange.com/questions/18669/how-to-wire-up-a-3-wire-load-cell-strain-gauge-and-an-amplifier">How to wire up a 3-wire load cell/strain guage and an amplifier?</a></p>
<p>In <a href="https://electronics.stackexchange.com/questions/18669/how-to-wire-up-a-3-wire-load-cell-strain-gauge-and-an-amplifier/18769#18769">my answer</a> I discuss a project I built using a gutted bathroom scale and a Stellaris LM3S6965 evaluation kit to give the scale a web server that could be used to monitor the weight remotely. Since you don't really describe your project goals I don't know if that will be useful or not, but hacking a bathroom scale is certainly an option and it will likely be a lot cheaper and easier than building something with pieces you buy from the various hobby vendors, especially since their stuff always seems to have a very limited range while a bathroom scale is already designed to weigh people. From your description I could conclude that you should just buy a bathroom scale and weigh people and write the results down on a piece of paper but I assume you have something in mind that requires customize hardware and software or you wouldn't be asking.</p>
|
<p>I've seen this <a href="http://www.vernier.com/probes/probes.html?fp-bta&template=standard.html" rel="nofollow noreferrer">force plate from Vernier</a> and it requires another USB interface device. They have an SDK that will they allow us to communicate with the force plate.</p>
<p>Is there something that I can create on my own that also measures weight?
I think that I've seen a <a href="https://electronics.stackexchange.com/questions/3312/3-wire-digital-scale-strain-gauge-weight-sensor">strain gauge thread</a> on this forum.</p>
<p>There's this <a href="http://www.sparkfun.com/products/10245" rel="nofollow noreferrer">load sensor from Sparkfun</a> (mentioned in thread) but it maxes out at 125lbs.</p>
<p>I essentially want to create a plate for someone to step onto and be able to measure their weight.</p>
|
I want to be able to measure weight (typical range of human weight), what sensor can I use?
|
2011-02-10T20:00:30.500
|
9974
|
|eaglecad|footprint|
|
<p>PADS .asc file describes PADS board layout, not only component footprint. To transfer PADS footprint to another program (like EAGLE) so called .d file has to be exported from PADS (PADS Library Manager). There is a utility called Eagle2Pads (<a href="http://www.cadware.cz/index.php?lang=en&page=128" rel="nofollow">http://www.cadware.cz/index.php?lang=en&page=128</a>) for data conversion between EAGLE and PADS, both schematic and board layout, with components library bidirectional conversion tool to follow soon.</p>
|
<p>I have a <a href="http://www.linear.com/designtools/packaging/foot/DFN10DDB3X2.asc" rel="nofollow">.asc PADS file</a> that defines the footprint for a part I am using. Is there any way I can use this file with Eagle so that I don't have to make the package from scratch?</p>
|
Importing an asc PADs file into Eagle
|
2011-02-10T23:33:08.380
|
9982
|
|sensor|filter|gyro|compass|
|
<p>No, it's not a stupid question. Reweighting (or resampling) particles is non-trivial for any "fun" problem. Weighting is typically performed by computing the likelihood of the particle fitting the observation. See page 28 <a href="http://www.site.uottawa.ca/research/spot/index_fichiers/Theory%20and%20Implementation%20of%20Particle%20Filters.ppt" rel="nofollow">here</a>. This <a href="http://students.cs.byu.edu/~cs470ta/goodrich/fall2006/lectures/ParticleFilterTutorial.pdf" rel="nofollow">link</a> and this <a href="http://www.site.uottawa.ca/~mbolic/Miodrag_Bolic_files/published/bolic_T-SP-2004.pdf" rel="nofollow">link</a> give reasonable discussion on particle resampling.</p>
<p>These links assume you can easily compute the likelihood a particle corresponds to the observations. For ease, we typically assume the likelihood can be expressed as a normal distribution (i.e. with a mean and a variance). Since your observations are comprised multiple dimensions, you might use the multivariate version of the
<a href="http://en.wikipedia.org/wiki/Multivariate_normal_distribution" rel="nofollow">normal distribution</a>. </p>
|
<p>I am trying to implement a <a href="http://en.wikipedia.org/wiki/Particle_filter" rel="nofollow noreferrer">particle filter</a> for coupling gyro and electronic compass for better measuring device orientation. <sup>[<a href="https://electronics.stackexchange.com/q/9894/2118">related question</a>]</sup></p>
<p>I understand my <em>state vector</em> would contain the <em>absolute angle</em> and <em>turn-rate</em> and my <em>observation vector</em> contains the readings for the same from the compass and gyro. </p>
<p>In my transition model, I just use the constant <em>turn-rate</em> assumption plus random noise to move the particles to their next states. Then, <strong><em>when I get a set of readings (angle and turn-rate from the sensors) in the next time instant, how do I assign weights to the particles?</em></strong> Is there a systematic procedure to assign the weights for a state vector containing multiple variables or should I just calculate it based on the difference between the predicted value and the observed value for both compass and gyro?</p>
<p>i.e.: <code>weight(particle X) = RMS(angle(Particle X) - angle(sensor), rate(Particle X )- rate(sensor))</code>, and then normalize all the readings?</p>
<p>EDIT:</p>
<p>Let me explain my problem a little further. I am working on the basis that the electronic compass alone is subjected to magnetic interferences in the indoor environment and hence the gyro should be used along with it to improve the accuracy of orientation.</p>
<p>Now, these magnetic interferences will form the external/environment noise of the process and will definitely be non-Gaussian, since they are bound to be biased towards the side of the metallic structure. That is why I chose the Particle filter over say, the Kalman filter although it is the most preferred method. So when I really don't know the pdf of the noise, then how do I estimate the likelihood that a predicted value is equal to a real value (which would be its weight, right?) </p>
<p>Assuming a normal distribution in this case would not work, because it would give me wrong probabilities for particles. Atleast, this is what I understand; please correct me if I'm wrong.</p>
|
Calculating weights in a particle filter experiment using multiple state variables
|
2011-02-11T06:57:17.967
|
9983
|
|fpga|xilinx|rom|xilinx-system-generator|matlab|
|
<p>Use a ROM block (from the memory section of the Xilinx blockset).</p>
<p>It has a parameter called <code>Inital value vector</code> - put the name of the vector in there. Put <code>length(vector_name)</code> in the <code>depth</code> parameter. </p>
<p>Setup the <code>output type</code> tab to the fixed point representation you want to use. Bear in mind the sizes of RAM bclock you have available in the target FPGA when selecting the <code>number of bits</code>. For example, 2k elements of 9 bits fits just as well in a single RAM block as 2k elements of 8 bits (in case you, or other readers, aren't already aware of that).</p>
<p>Job done!</p>
|
<p>I want to put in a ROM a vector of values I have in the workspace. Does anyone know how to do it?
Thank you to all possible references, articles or comments.</p>
|
System Generator: How to make an implementation a mathematical function through a ROM
|
2011-02-11T07:36:53.557
|
9994
|
|charging|charger|lithium-ion|batteries|
|
<p>This is not what others will want to hear but you can actually PARTIALLY charge cells safely. If ~80% charge satisfies you that is. You need a voltage controllable supply, with or without current limiting. I say without because you can add that yourself - resistor pack / bulb or whatever limits the current, preferably something that fails open not short.
That being said, I bought a universal Li-Ion charger (mostly for mobile phone batteries) for 2 or 3 euros, new.</p>
|
<p>I have received some Li-ion batteries which were originally used in Asus A2 Laptop battery original one and I would like to know if it is possible to charge each cells independently with some device or just normal universal charger.</p>
<p>I Apologize if i asked in wrong section.</p>
|
How to charge Laptop Li-ion Battery cells manualy?
|
2011-02-11T11:50:18.887
|
9999
|
|amplifier|short-circuit|
|
<p>take a look at this circuit. you would need two one for each "side" of the amplifier.</p>
<p><a href="http://opencircuits.com/Basic_Circuits_and_Circuit_Building_Blocks#Current_Limit_or_Constant_Current_.28_Transistor_Based_.29" rel="nofollow">http://opencircuits.com/Basic_Circuits_and_Circuit_Building_Blocks#Current_Limit_or_Constant_Current_.28_Transistor_Based_.29</a></p>
|
<p>I am designing a little class AB amplifier for a small circuit. This circuit is biased such that it has low crossover distortion. Below is a schematic:</p>
<p><img src="https://i.stack.imgur.com/DT8FG.png" alt="enter image description here"></p>
<p>As you can see, I have inserted 68 ohm resistors in series with the power supply lines. This is such that when the output is shorted, the current is limited to about +/-200mA. In this demo, I have inserted such a short; a 10m resistor. However, in operation the resistors dissipate 1.5W each and in short circuit conditions about 2.5W, which means I have to use two big and expensive 5W resistors to remain within safe operating boundaries, and it also might cause problems for the power supply. </p>
<p>So I'm looking for some way to limit output current to about +/-100mA before the amplifier begins clipping (which the current solution manages), but without the "hack" of using resistors on the power supply lines. I was considering a comparator measuring the output current across a shunt resistor, but I wasn't sure how to achieve this for short circuits of both polarities. Also, I need the circuit to ideally work up to around 5 MHz, which limits the choice of components.</p>
<p>Edit: Thanks to russ_hensel and opencircuits.com, I devised the following current limiter (including amplifier), which actually works really well (it clips the output and doesn't make it sag or invert, like some limiting circuits.)</p>
<p><img src="https://i.stack.imgur.com/h6rYJ.png" alt="enter image description here"></p>
|
Short circuit protecting a class AB amplifier
|
2011-02-11T12:50:43.387
|
10024
|
|motor|arduino|
|
<p><a href="http://opencircuits.com/motor_driver" rel="nofollow">Many motor drivers</a> <em>can</em> directly drive a 1.5 volt motor from a 5 V (or more) power supply,
because they have built-in current limiters ("chopper circuit").</p>
<p>Alas, the <a href="http://www.ladyada.net/make/mshield/faq.html" rel="nofollow">Lady Ada motor shield FAQ</a> specifically says:
"Can this shield control small 3V motors? Not really, its meant for larger, 6V+ motors."</p>
<p>It appears to me that you <em>can</em> add a few power resistors to (inefficiently) drive a 1.5 V motor from the adafruit motor shield using the "L/R driver" system.</p>
<p>The <a href="http://www.stepperworld.com/Tutorials/pgCurrentControl.htm" rel="nofollow">"Current Control of Stepper Motors"</a> document describes the older, less efficient "L/R driver" system, and compares it to the more modern and efficient (but complicated) "chopper circuit".</p>
<p>This motor shield uses the L293D motor driver chip, which simply drives the output high or low, without any limit except its thermal protection limit.
To convert it to a L/R driver system:</p>
<ul>
<li>Ir: Find the rated current Ir (if it's not written on the motor and you can't find the datasheet, measure the motionless coil resistance Rcoil with a multimeter and calculate Ir = 1.5 V / Rcoil). If this is more than the 0.6 A that the L293D can provide, do the remaining calculations with Ir = 0.6 A instead. (Example: measure 3 Ohms; Ir = 1.5 V / 3 Ohms so Ir = 0.5 A).</li>
<li>Vdd: What is the voltage Vdd of your power supply? (Example: VDD = 5V, but lots of people prefer 12 V.)</li>
<li>P: Your power resistors need to dissipate up to P = Ir*(Vdd - 1.5 V)/2. (Example: P = 0.5 A * (5 V - 1.5 V)/2 = 0.88 W)</li>
<li>R: Your power resistors need a resistance of R = (Vdd - 1.5 V)/(2*Ir). (Example: R = (5 V - 1.5 V)/(2* 0.5 A) gives R = 3.5 Ohms).</li>
<li>Get or make 4 identical power resistors that have approximately the above resistance and at least the above power rating. (Example: a 5 W, 4.7 Ohm resistor will work nicely ... or a series of 4 quarter-watt resistors in series, each one 1 Ohm, produces a 1 W, 4 Ohm resistor, which will also work nicely.)</li>
<li>Connect one end of each resistor to one of the 4 halfbridge terminals on one side of the motor shield, the other end to one of the 4 pins of your bipolar stepper motor.</li>
</ul>
<p>I assumed your motor was a 4 wire (bipolar) stepper motor.
Does this L/R thing work for DC motors also?</p>
<p>The L293D datasheet says it requires something in the range of 4.5 V to 36 V to function properly, so I wouldn't bother trying to power the adafruit motor shield from anything less than 4.5 V.</p>
|
<p>Would it be safe to use a 1.5 volt motor with the adafruit motor shield? It is rated for 4.5 to 36 volt motors so I am unsure what will happen. Also, what would be a good way to determine the voltage of a motor if you have no information on it at all?</p>
|
Low voltage motor with arduino
|
2011-02-11T21:47:04.547
|
10028
|
|temperature|layout|heatsink|thermistor|
|
<p>I guess the cause of overheating is not power dissipation of your uC. That means you can just place thermistor close to uC and you'll get +-2C accurate readings. </p>
<p>Some uCs have internal thermistors connected to one of ADC input - check datasheet.</p>
|
<p>I'm going to be using a microcontroller and SDRAM IC in an enclosure that could, given some environmental variables that I have no control or knowledge of, get too hot for the devices to work properly. Redesigning the enclosure is not an option. However, I could notify the operator, if my microcontroller had a means of reading the temperature. </p>
<p>How can I monitor the temperature of a large IC? I'm using 54-pin TSOPs and 100-pin TQFPs. I've considered using a SMD thermistor and an ADC on the microcontroller, or using a prepackaged solution like <a href="http://ww1.microchip.com/downloads/en/DeviceDoc/21942e.pdf" rel="nofollow">this SOT-23-3 'active thermistor'</a>. However, with either of these methods, I'm not sure how to thermally couple the devices. I'd like to avoid having components on the back-side of the board if possible. </p>
<p>Other possibilities include adhering a device on some long leads to the center of the IC, or monitoring the current used by the device, and extrapolate the power consumed to get an estimate of the temperature. Both of these seem like hack jobs, while a thermistor or temp sensor seems much cleaner.</p>
<p>What single-sided layout will simultaneously give be the best thermal properties to cool my devices, and allow the sensor to be thermally coupled with the die of the IC? Or, are there other methods that I'm not considering that would be better?</p>
|
Measuring temperature of microcontroller and other large ICs
|
2011-02-12T00:24:41.190
|
10032
|
|simulation|vhdl|
|
<p>Both Xilinx and Altera provide their development environments for free. They are meant for designing the logic for placing on FPGA's and CPLD's, but you can simply use them in simulation mode. They let you place items on a schematic view like the above, and when you need more advanced components that are not built in, you can write their logic in VHDL.</p>
|
<p>in university we had our internal program called HLCCAD - it was very nice, and now I need to do design & debug some digital circuit and wondering what is current state of art software for that kind of things (price is out of consideration for now)? </p>
<p>I.e. I want to visually place components, and then simulate it.</p>
<p>Manually writing VHDL code & looking at simulation traceouts of specific nodes is not enough.</p>
<p>Any suggestions?</p>
<p>Update: Found <strong>Logisim</strong> - this is exactly what is needed. Are there any commercial alternatives with more horsepower?</p>
<p><img src="https://i.stack.imgur.com/mo0Xw.gif" alt="http://newit.gsu.by/projects/HLCCAD/webinfo/screenshot_ru.gif"></p>
|
Visual logic designer + simulation
|
2011-02-12T01:06:33.317
|
10034
|
|power-supply|capacitor|damage|
|
<p>Most likely the popped capacitor is causing stability issues (output going up and down as you described).</p>
<p>It should be replaced with a part with comparable voltage, ripple current, ESR and life ratings. Failure to choose an appropriate cap will likely result in the cap failing prematurely.</p>
<p>A properly protected power supply should not be damaged from a blown output capacitor. I wouldn't recommend operating it until the cap is replaced.</p>
<p>It seems odd to me that the power supply is capable of self-damage. With 25V caps the max output ought to be below 20V. </p>
<p>I would use a sharp utility knife to cut the part from the glue, then desolder it and replace it. Make sure you note the polarity.</p>
|
<p>I was experimenting with my universal laptop adapter (Meind 100W) and when I switched it to 34V mode (while official max is 24V) the capacitor (25V) popped (the top opened and some white fibers spread over the nearby parts).</p>
<p>The capacitor is glued to the board and is not easy to remove. When using the adaptor it slowly heats now.</p>
<p>When under load the output voltage of the adapter drops (and probably recovers after some seconds), so I have to set it to voltage that is higher than needed.</p>
<p>Questions:</p>
<ol>
<li>Is it safe to continue using that adaptor? Can it degrage further with time or it will remain stable?</li>
<li>How to unglue the damaged capacitor from board?</li>
<li>Should I use some additional safety measures (for example, external capacitor connected to output) to reduce the risk? (I'm not going to just buy another adaptor)</li>
</ol>
|
Is it safe to keep on using AC adapter with a damaged output capacitor?
|
2011-02-12T02:00:52.977
|
10041
|
|vhdl|floating-point|
|
<p>If this is not for synthesis, just do it directly:</p>
<pre><code>my_int <= integer(my_real * 1000.0);
</code></pre>
<p>If it's for synthesis, then W5VO's "hard way" answer is how you would implement it at the low-level, but I'd instead use David Bishop's synthesizable floating point library <a href="http://www.vhdl.org/fphdl/" rel="nofollow">fphdl</a> (standardized in VHDL-2008, but useable in any VHDL version) and then just write it similar to the above:</p>
<pre><code>my_sfixed <= to_sfixed(my_float * to_float(1000.0, my_float), my_sfixed);
</code></pre>
|
<p>I want to convert a floating point number to a integer number. Basically I have a floating point number between 1 and 0, with three decimal places, and I want to pass it to a integer number as if multiplied by 1000. I suspect there should be a more optimal way to do it than using the arithmetic multiply operation x1000.
I'm looking for a piece of code preferably.</p>
|
How to convert a floating point number to integer, using VHDL?
|
2011-02-12T07:46:04.663
|
10051
|
|hard-drive|
|
<p>According to the link to the SATA pinout of the forum page you linked to, pins 7,8,9 are all +5V, so that is just for one end of the diode. Presumably the other end is connected to pins 4/5/6 or 10/11/12 and you could replace it with a TVS diode of the same physical size and a rated voltage <strong>above</strong> 5V. Given that 5V ICs usually work at least 0.5V above or below the 5V spec, and the 5% tolerance of the TVS threshold, you should be safe with a 6.8V TVS diode. They are usually unipolar so getting it the right way round is important (otherwise you are reducing the 5V rail to 0.7V).</p>
<p>You can't measure the breakdown voltage of a TVS diode or zener using the resistance range of a meter. They are deliberately non-linear devices, so the resistance you measure depends on the voltage applied. The only way to measure the breakdown voltage with a meter would be to isolate the (working!) device, use a current limited adjustable voltage supply set to 1mA, increase the voltage until 1mA flows, then measure the voltage across the device. For smaller devices rated less than 5 watts, you probably need to use the pulsed version of this method to avoid heating the device up too much.</p>
|
<p>I hope the TVS diode (or something like this) of my HDD's PCB is gone, so I could fix this HDD easily, but I don't know where it is. Can you tell me how to measure it?</p>
<p>I <a href="http://forums.seagate.com/t5/Barracuda-XT-Barracuda-and/Need-PCB-Replacement-for-Momentus-7200-3-ST9320421ASG/m-p/40296" rel="nofollow noreferrer">read this</a> but I didn't understand, why 3 pins? I'm measuring the circuit resistance since I'm not measuring specifically the diode so I understand that if it's broken the resistance could be different than infinite, so how much should be the resistance?</p>
<p>My broken hdd history is here:
<a href="https://superuser.com/questions/242014/is-my-hdd-dead-forever">https://superuser.com/questions/242014/is-my-hdd-dead-forever</a></p>
|
How can I measure TVS diode for Seagate Momentus 7200.3?
|
2011-02-12T12:20:08.840
|
10052
|
|capacitor|oscillator|
|
<p>They have a technote paper on this subject, "Effect of Load Capacitance on the Crystal":</p>
<p><a href="http://www.mecxtal.com/pdf/te_notes/tn-021.pdf" rel="nofollow">http://www.mecxtal.com/pdf/te_notes/tn-021.pdf</a></p>
|
<p>I have a circuit board with an oscillator and I'm curious about why there is a capacitor hooked up to the output. The oscillator is a SWO series HCMOS Square Wave output crystal oscillator. The schematic of the oscillator connections is as follows. </p>
<pre><code> +3.3V
|
--------- | C=0.01uF
NC-| 1 4 |---------||-----GND
| |
GND| 2 3 |---------->Direct to FPGA input pin
--------- |
|
= C=15pF
|
GND
</code></pre>
<p>The <a href="http://www.mecxtal.com/clock_oscillator.php#XOs" rel="nofollow">data sheet</a> (select H22/H32/H53/SWO) does not reveal much, but there is a "Load" section that says the max load is 15pF. Specifically, it says:</p>
<blockquote>
<p>Load | 15 pF ; ( 30 pF and 50 pF load are also available for +3.3V and +5.0V VDD) </p>
</blockquote>
<p>In such a circuit, is the load the capacitor or the FPGA input pin? If the load is the capacitor, why is the load needed for the oscillator? What is its purpose?</p>
|
Why is a capacitor placed in parallel with oscillator output?
|
2011-02-12T14:52:28.120
|
10060
|
|power-supply|capacitor|ground|
|
<p>In the schematics they are put next to each other to avoid cluttering the functional part, but on the PCB they are usually spread out as follows:</p>
<ul>
<li><p>100nF are placed across the power supply of each ICs.</p></li>
<li><p>10µF is used for a group of ICs, often only one for the whole circuit, if it is not too big.</p></li>
<li><p>I've seen 10nF to decouple the analog supply, I suppose to be able to use a higher quality C0G capacitor without it getting much bigger. </p></li>
</ul>
<p>The total capacitance doesn't matter much.</p>
<p>As for the ground connection, there are probably two separate ground networks or planes, which need to be connected by a wire, and for technical reasons the schematic needs to contain that wire (so it is not forgotten).</p>
|
<p>I have a schematic for a commerical circuit board, and I was curious about the following:</p>
<pre><code> 1.2V
|
------------------------------------------
| | | | | | |
=10uF =1uF =.1uF =.1uF =.1uF =.1uF =.01uF
| | | | | | |
------------------------------------------
|
GND
</code></pre>
<p>What is this network for? I see that for all of the ICs there is a decoupling capacitor on the input voltages near the IC. The above, however, appears to just be caps connected between the supply and ground. What purpose does such a network perform, and how does one decide on the value Ctotal of the network? They all add up to Ctotal=11.41uF for the 1.2V supply. There is also a 3.3V supply with the same network, except that Ctotal=11.43uF. </p>
<p>There is also a ground-ground connection I am curious about.</p>
<pre><code> ------------------
| |
GND GND
</code></pre>
<p>What is the purpose of coupling ground to ground? </p>
|
Power and ground configuration in a schematic
|
2011-02-12T17:42:32.303
|
10062
|
|transistor-array|
|
<p>At 1.5A you want to be using MOSFETS,not darlingtons. Unfortunately the best MOSFETS come in SMD packages, but you'll find through-hole parts that will dissipate almost nothing at 1.5A</p>
|
<p>I am looking for a darlington array IC like the ULN2803a that can sink up to 1.5A. It needs to be in a DIP. Any recommendations? Its needed because i am driving a stepper motor and requires 1.2A per coil. I am controlling the stepper motor from a PIC. So if you have another solution let me know. </p>
|
Darlington Array IC that can sink 1.5A
|
2011-02-12T18:18:22.353
|
10063
|
|lcd|
|
<p>Compiled bin/hex files are very specific and can not be easily adapted to your specific situation. This means that the bin/hex file would have to be for the exact PIC you have along with all of the exact pins connected as was designed for in the original code.</p>
<p>Also many companies protect their code and compiled versions of their code very tightly. This means that there is a good chance that they wont just hand it over to you.</p>
<p>So, likely you wont find an answer to your question. Instead you should look to see if someone has released information on how to build what you are looking for. It will require that you are willing to be open to learning about firmware coding as you will have to touch it to work on a project like this.</p>
|
<p>I have seen some kits and boards for a Serial LCD based on the PIC16F648A.
A have a few of the chips and a few LCDs. I'm not into PIC programming, does anyone have a link to the compiled software I can program my PIC chips with to make my own serial LCD?</p>
|
Need bin or hex file for Pic 16F648A Serial LCD
|
2011-02-12T18:20:15.257
|
10068
|
|pcb|drc|
|
<p>I'd get out my magnifying glass and scalpel, it doesn't have to be pretty so it's worth a try, just make light repeated scrateches next to the track, in a couple of minutes the grooves will ge deep enough to sever any contact. I've had mixed success with this method.</p>
|
<p>Okay, so I was a bit of an idiot while designing my PCB. The specifications of my PCB fab were 6/6 mil trace/space, and the boards did not meet this. So, below is the design for the PCB:</p>
<p><img src="https://i.stack.imgur.com/2hNfp.png" alt="Design file"></p>
<p>The trace going to C16 (a ground) is way too close to the pad which is connected through a trace to an inductor (it's a switch mode buck converter.) This basically connects the +3.3V line next to the filter capacitor to GND, shorting it. I verified this with the continuity test on my multimeter.</p>
<p>My PCB:</p>
<p><img src="https://i.stack.imgur.com/RuWb1.jpg" alt="PCB"></p>
<p>I have already bought 10 PCBs, so I'd like to know if it's possible to hack these and repair them. I'm okay with having to provide them with an external 3.3V source; in future, I'd like to get the converter working, but it's the rest of the circuit which is important.</p>
<p>Obviously I won't make this mistake in the next version... I might actually run the DRC. This is only for development.</p>
|
Is it possible to repair a PCB which has suffered a DRC failure?
|
2011-02-12T20:13:35.300
|
10073
|
|lcd|potentiometer|
|
<p>I'm working with RT162-7 based on HD44780 (seems compatible to your DEM 16217 SYH-PY).<br>
Connecting the contrast pin (V0) directly to 0 gives very reasonable contrast, even without a potentiometer or a potential divider.</p>
|
<p>I recently obtained DEM 16217 SYH-PY 2x16 character screen. <a href="http://www.display-elektronik.de/lcd-alphanumeric-table.htm" rel="nofollow">Here</a>'s the datasheet. As far as I can see, its contrast pin should be connected to voltage source over a potentiometer. How do I pick correct resistance of the potentiometer for this use?</p>
|
Which potentiometer to chose for LCD screen contrast?
|
2011-02-12T21:53:39.423
|
10074
|
|pic|
|
<p>If you look at <a href="http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en010236" rel="nofollow">their summary page</a>, you'll see the difference is in temperature tolerance/range:</p>
<pre><code>PIC16F873A-E/SP 28 SPDIP -40C to +125C
PIC16F873A-I/SP 28 SPDIP -40C to +85C
</code></pre>
|
<p>First post in Electronics and Robotics... I've been trying to order a DIP PIC off of Microchip (first time going directly off the website) for use with the RFM12, but I dont really know what all the variants are. </p>
<p>I'd like to get <a href="http://www.microchipdirect.com/ProductSearch.aspx?keywords=PIC16F873A" rel="nofollow">http://www.microchipdirect.com/ProductSearch.aspx?keywords=PIC16F873A</a> so that it would fit on a non-solder breadboard. Most confusing is E/SP and I/SP, what's the difference? I couldnt find anything online.</p>
<p>Thanks in advance!</p>
|
Difference between E/SP and I/SP and other variants
|
2011-02-12T21:57:44.223
|
10079
|
|adc|
|
<p>Incidentally, an approach I used once that seemed to work pretty well was to have a PIC output drive an RC circuit and feed that into one input of a comparator, while the other input of the comparator was the signal under test. Every 100us, I would sample the state of the comparator, set the output high or low as appropriate, and (if I set the output low) bump a counter. Every 4096 interrupts, I would copy the value of that counter and reset it.</p>
<p>The beautiful thing about this approach is that provided the input isn't changing, and provided the RC time constant is sufficiently high, and the input isn't too close to a rail, one can avoid any need for precision constant current sources or other such things. The system will output a ratiometric measurement of the input voltage compared to the output rails feeding the RC (e.g. if the input voltage is 3/4 of VDD, and the output swings fully to VDD or ground given the currents involved, the reading will be 3072/4096).</p>
<p>The biggest problem I've observed with this approach is that if the input changes significantly, the readings will be pegged for a little while, and the first reading after that will be meaningless. Still, it's a cheap approach and seems to work pretty well.</p>
|
<p>I'm curious as to why dual-slope analog to digital converters are used in most digital voltmeters, <a href="http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=11023&mid=11&lang=en&pageId=79" rel="nofollow">like one of these</a> when a delta-sigma converter <a href="http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en025692" rel="nofollow">like one of these</a> easily exceeds the specifications of any of the other dual-slope converters sold by Microchip, and in fact many other suppliers, especially given the low price point of the chip (about $4 in low quantities.) Is there a reason I am missing?</p>
|
Dual slope converter vs. delta-sigma converter?
|
2011-02-13T00:01:00.817
|
10082
|
|laser|constant-current|
|
<blockquote>
<p>Can it work this way: We start from, let's say, a 1.5 V supply, use a FET to connect diode to the supply for 50 ns and sense the peak current. Then we slowly increase the supply until we reach the required peak current. Will that work?</p>
</blockquote>
<p>Yes it will work, but if it gets too much current you may burn it out, to little current and it will not lase.
Max current is usually 10 to 15 percent above its min lase current.(depends on laser)</p>
<p>some good info <a href="http://www.repairfaq.org/sam/laserdps.htm#dpstoc" rel="nofollow">here</a> and an interesting chapter <a href="http://www.repairfaq.org/sam/laserdps.htm#dpsmld" rel="nofollow">here</a>
and <a href="http://www.repairfaq.org/sam/laserfaq.htm#faqtoc" rel="nofollow">full table of contents</a>they also have some driver references and schematics</p>
<p>I learned a lot from that site about how to drive some re-purposed red laser diodes that I had laying around. </p>
<p>I personally would start off with the lowest current possible, move it up till it lases and then calculate 10% above lasing current and make that your safe constant current, pulsed current can be higher.</p>
|
<p>I need to build supply for ~20 laser diodes (~150 mW each), and the question is why can't we just use a constant current power source for each of them? </p>
<p>A similar question for pulsed mode operation: if I would need, let's say, 50 ns pulses, is it correct that I just need to stabilize the current in these periods or is it again more complex? </p>
<p>Can it work this way: We start from, let's say, a 1.5 V supply, use a FET to connect diode to the supply for 50 ns and sense the peak current. Then we slowly increase the supply until we reach the required peak current. Will that work?</p>
<p><strong>Any practical experience? Any comments on the last paragraph?</strong></p>
|
Why is a laser supply so tricky?
|
2011-02-13T01:02:42.320
|
10087
|
|eaglecad|
|
<p>You need to change the width of your ground polygon. The polygons are actually made up of many wires drawn to make a continuous surface. If you zoom in on a polygon that is drawn in a non-solid pattern (like an inner layer on a 4 or greater layer board) you can see what I mean.</p>
<p>When you draw the polygon you can choose the size of the wires used, just the same as when drawing wires. You can also change it after the fact using change->width, if I remember correctly.</p>
<p>You probably want to make the width no greater than the width of your IC pads.</p>
|
<p>The thermal reliefs of my ground polygon to one of the pads of my footprint are just simply weird! I dont know what causes it? It seems to me that the lines leading up from the polygon to the pads are just too thick and are out of proportion to the pad. </p>
<p><img src="https://i.stack.imgur.com/kSOEh.png" alt="enter image description here"></p>
|
Weird Thermal Reliefs in Eagle PCB
|
2011-02-13T05:36:51.053
|
10092
|
|transistors|relay|
|
<p>Relays can be set up to activate so many different voltage levels without adjustment. This is why they are so often seen in industrial controls. For instance say I design a controller for a valve that requires switched +15V to work. Then the company switches the valve to a current controlled style where the output has nothing to do with a fixed voltage level. This is a simple change for a relay(really no change) and probably a complex one for a MosFET.</p>
|
<p>Rather basic, I'm afraid, but when would you use a relay, and when would you use a transistor? In a relay the contacts wear out, so why are relays used at all?</p>
|
Relay vs. Transistor?
|
2011-02-13T12:30:11.660
|
10098
|
|soldering|transistors|
|
<p>The difference in the structure of MOSFETs and BJT is that the former have a thin insulation layer. I don't know if this is easier damaged than the rest of the crystal when heating it. But I would <em>most strongly advise</em> you to get a temperature controlled soldering station. If you leave your iron unused for a minute the temperature will rise to levels components won't like.<br>
Also, most likely a temp controlled station will have proper earthing which is even more important than temperature when soldering MOSFETs.</p>
|
<p>I'm soldering through the hole MOSFETs in to a PCB and I don't have a temperature controlled soldering iron. So will I need to heat sink the legs as I solder them to stop internal damage. I as this as bipolar transistors are damaged from heat. </p>
|
Are MOSFETs Sensitive to heat while soldering?
|
2011-02-13T15:17:33.977
|
10104
|
|robotics|
|
<p>Arduino is a wonderful hardware and software system to learn robotics. I would like to suggest to start with this one. FYI, I am CTO of a robotics company.</p>
|
<p>My brother is a senior in High School. When he visited our college. I've took him to a robotics event (inter college robotics competition). He got to see various bots designed by college students and got mesmerised. Now he too wants to design bots like that.</p>
<p>I told him programming is necessary. He already knows little bit and I'm helping him in becoming proficient. But I've no clue regarding this field. </p>
<p>Can any one kindly suggest a path & tiny projects to improve his interest.</p>
|
Getting started with robotics
|
2011-02-13T16:43:25.550
|
10105
|
|spectrum-analyzer|
|
<p>I use a spectrum analyser made from a <a href="http://ossmann.blogspot.com/2010/03/16-pocket-spectrum-analyzer.html" rel="nofollow">kid's toy</a>.</p>
<p>These are £4.99 in my local toy shop.</p>
<p>It's been handy for determining the operating frequencies of wireless sensors.</p>
|
<p>I'm trying to learn more about building RF circuits and I want to buy a spectrum analyzer. I've looked around on ebay, and a lot of them are really expensive. I'm a student, so I don't have a lot of money to spend on it. What's a good model to buy since I'm just starting out? </p>
|
What's a good spectrum analyzer to learn with?
|
2011-02-13T16:44:38.220
|
10106
|
|operational-amplifier|
|
<p>To perfectly amplify a square wave, you'll need an op-amp with infinite bandwidth.</p>
<p>What is the square wave used for? You probably don't need to keep all of those harmonics.</p>
|
<p>I want to amplify a 4 MHz triangle or square wave by 2 using an op-amp. Do I need an ~8 MHz op amp, or a much higher rated (and more expensive) device to handle the harmonics?</p>
|
If I'm amplifying a triangle or square wave, does the GBWP of my op-amp need to be higher?
|
2011-02-13T16:45:10.670
|
10107
|
|power-supply|batteries|solar-cell|inverter|battery-charging|
|
<p>It's mostly a myth that it's <em>much more</em> efficient to power DC appliances like laptops on a full end-to-end DC system rather than using an inverter and then the existing AC-DC converter instead<sup>1</sup>.</p>
<p>Let's take a look at your first question:</p>
<blockquote>
<p>1) How inefficient is it to boost 12V to 120V and then back to 12V as
in using a traditional car power inverter to power a laptop (i.e. the
12V car battery power is boosted to 120V by a power inverter and then
back to 12V by the laptop's power supply)?</p>
</blockquote>
<p>It depends on your hardware, but it's not <em>too</em> terrible. You have two primary conversions: the DC -> AC conversion in the inverter and the AC -> DC conversion in the power supply for the appliance.</p>
<p>Most modern quality inverters are over 90% efficient and many approach 95% efficiency over a large part of their operating range. Very cheap or small inverters may be worse, perhaps in the low 80s and even good inverters are often less efficient when operating at very low power relative to their rated power.</p>
<p>For the AC -> DC side you'll find more variance. Some quality converters e.g., those supplied with some name-brand laptops approach 90% efficiency, but many others are in the 70% to 80% range. Very small AC -> DC converters, such as those found in USB plugs tend to be slightly less efficient than converters will fewer space constraints.</p>
<p>Overall then, you're looking at a best-case loss of perhaps 15% (a 95% efficient inverter with a 90% efficient power supply) to a worst-case loss with a reasonable inverter of perhaps 40% (an inverter in the high 80s combined with a 70% power supply<sup>2</sup>. </p>
<p>Now consider also that the "end-to-end" DC path will generally also need a DC-DC conversion unless the device happens to operate exactly at the voltage (say 12V or 24V) of your DC system. This conversion is likely to be, at best, as efficient as one of the above conversions. At worst, if you buy one of the various adjustable buck/boost converters with wide input and output ranges, the efficiency might be considerably lower if it is operating outside of its ideal range. So ignoring all the other factors, it is even possible that the full DC route is already less efficient than AC!</p>
<p>Still, let's assume that the full DC path is theoretically somewhat more efficient than the DC-AC-DC path, by perhaps 10%. Here are downsides of a full DC path that might outweigh that small advantage:</p>
<ul>
<li>Something like a home (or RV or whatever) as you mention in point (2) will already have existing 120V wiring: power appliances on a full DC system would require either locating those appliances very close to battery bank, or running a second DC wiring system at considerably effort (adding wiring to an existing house is a lot harder than doing it as it's being built - unless you don't mind ugly). Furthermore, you'll run into issues such as no standard outlet for DC power (the cigarette lighter is probably the closest widely supported thing, but unsuitable for many purposes).</li>
<li>Lower voltages are inherently less efficient than higher voltages for transmission: both because a given absolute voltage drop represents a higher relative fraction of the total voltage, and because proportionally more current is needed to deliver the same power. This effect is roughly quadratic: a 12V system suffers approximately <em>100 times</em> the voltage drop as wires of the same gauge at 120V of the same gauge to deliver the same power. An example: over 10 feet 14 AWG household wiring, for a load of 120W, a 120V system needs 1 amp and suffers a voltage drop of 0.042% - basically a rounding error. A 12V appliance of the same power would need 10 amps, and suffer a voltage drop of 4.2% - so over 10 feet of 14 AWG you've already lost about as much power as you'd lose in a good inverter. In a house, you could easily have wiring runs of 50 or 100 feet, resulting in DC voltage drops that make the system unsustainable - even with a small 120W load. In practice, you'd need to use a significantly larger gauge of wire to counteract this: a significant cost which could instead just be spent on more solar panels or batteries. </li>
<li>AC is the default: almost every appliance you buy will by default come with an AC plug. There are all sorts of appliances where you can <em>also</em> buy a DC version, but often with a greatly reduced selections. Yes, you <em>can</em> buy a DC powered fridge, but you pretty much have to choose from the 1 or 2 weird models at your local solar/battery store. These are often twice the price of a fridge you'd buy anywhere else, and based on some old model that may inherently be less efficient. The same for DC powered fans, TVs, coffee makers, whatever. Yes, they exist, but the market is currently minuscule as the selection follows. You'll waste more money and be less happy with what you end up with than you'll ever save in "AC conversion losses". The one approach that does work here is getting things that run on AC but have an external AC-DC power brick: you can skip the brick and connect your DC system up directly (but again the voltages are usually weird things like 17V, 21V, etc, so you still end up needing a conversion).</li>
</ul>
<p>So I'll be what seems like the lone voice here and say that any sort of large or medium sized "DC system" doesn't really make sense just to save on conversion losses when you are hooking up off-the-shelf appliances. 120V AC is actually a pretty reasonable method of power distribution, especially since it's the <em>default input</em> for almost everything you'd buy. The conversion losses are fairly small with modern equipment, and you usually can't avoid conversion losses entirely even with a full DC system.</p>
<hr>
<p><sup>1</sup> I'll sometimes call this the DC-AC-DC approach.</p>
<p><sup>2</sup> Of course, you can push the worst case much further if you seek out a really inefficient inverter (but this is under your control) and find some device with a terrible (or just old) SMPS or linear regulator that is very inefficient.</p>
|
<p>This question has two parts:</p>
<p>1) How inefficient is it to boost 12V to 120V and then back to 12V as in using a traditional car power inverter to power a laptop (i.e. the 12V car battery power is boosted to 120V by a power inverter and then back to 12V by the laptop's power supply)?</p>
<p>2) Is there any way to power a laptop directly from a 12V car battery? This would be useful not only for use in a car, but also for a solar-powered home that runs on 12V batteries. If there is a significant gain in not going through the boost/buck cycle of power inverters, then it would seem wise to power laptops and other 12V devices directly from battery power. I realize that laptops have different power supply ratings and some require more than 12V, but it seems rather wasteful to boost everything to 120V before bringing it back down.</p>
|
Powering laptop from 12V sources without inverter
|
2011-02-13T17:03:19.293
|
10121
|
|arduino|diodes|driver|
|
<p>From the <a href="http://www.sparkfun.com/products/315" rel="nofollow">comments @ sparkfun</a> (Specifically <a href="http://www.sparkfun.com/users/333" rel="nofollow">superbrad</a>):</p>
<blockquote>
<p>The L293D has internal flyback diodes, which catch what would
otherwise be high voltage inductive noise (sometimes even in the
kilovolts). With the SN754410, you must use external flyback diodes in
your H-Bridge.</p>
<p>Even though you might feel like you can get away with it, it's a VERY
bad idea to use the SN754410 without a flyback diode. It's not just
the driver you have to worry about, it's your entire circuit (MCU,
accelerometers, expensive XBee, etc.). Eventually, your luck will run
out, even if you don't turn it on and off frequently.</p>
</blockquote>
|
<p>I am considering buying one of the hbridge drivers referenced in the below tutorial, but when I looked at the comments underneath the second hbridges sparkfun page, kickback diodes were referenced and how one of the drivers has internal diodes but the other doesn't. I will be working with motors no more than 8V and much less than 1 A of current. Which of these drivers should I use and should I use kickback diodes with it also?<br>
<a href="http://itp.nyu.edu/physcomp/Labs/DCMotorControl" rel="nofollow">http://itp.nyu.edu/physcomp/Labs/DCMotorControl</a></p>
|
Motor drivers and kickback diodes
|
2011-02-14T05:21:25.510
|
10129
|
|power-supply|batteries|ground|
|
<blockquote>
<p>The potential is relative. Ground is an arbitrary designation.
<em>—Fake Name</em></p>
</blockquote>
<p>This is something I worked out recently, only then realising why the <a href="http://en.wikipedia.org/wiki/Hydraulic_analogy" rel="nofollow">hydraulic analogy</a> was causing me cognitive dissonance. If a "voltage supply" was a waterfall, the image of a 12m top-to-bottom waterfall stuck in the middle of the sky, somewhere above my 5m waterfall which started 5m above the "ground" just didn't make any sense.</p>
<p>And then I tied the negative pin on my Arduino (powered by a 12V wall wart) to the drain on the transistors I was using to switch current to my LED strips and the circuit worked.</p>
|
<p>For the sake of not incorrectly connecting my power supply and damaging my board I'm going to ask a relatively dumb question. Is ground on my board the negative terminal on my battery? Explicitly should I connect the ground to the negative terminal of the battery?</p>
|
When a battery is your power source, what is ground?
|
2011-02-14T15:28:46.527
|
10139
|
|avr|lcd|
|
<p>I like the way you do serial port debugging, and the comments at each stage.</p>
<p>It appears that your display, like every other small character <a href="http://techref.massmind.org/Techref/lcds.htm" rel="nofollow">LCD display</a> I've ever held in my hands, uses the <a href="http://techref.massmind.org/Techref/io/lcd/44780.htm" rel="nofollow">Hitachi 44780 interface</a> standard.
May I ask why you aren't using some pre-tested <a href="http://www.arduino.cc/playground/Code/LCD" rel="nofollow">off-the-shelf LCD library code</a>?</p>
<p>Would something like the following work for you?</p>
<pre><code>// WARNING: untested code. And therefore riddled with bugs.
#define SCREEN_ENABLE 4
#define SCREEN_READ 2
#define SCREEN_RS 1
// LCD #defines copied from http://techref.massmind.org/techref/io/lcd/44780.htm
#define LCDClearDisplay 1
#define LCDCursorHome 2
#define LCDOff 8 ;0x08 turn the display (and the cursor) off.
#define LCDOn 12 ;0x0C Turn on the display, but without a cursor
#define LCDCursorOn 14 ;0x0E Turn on the cursor (as an underline) as well as the display
#define LCDCursorBlink 15 ;0x0F Turn on a blinking block cursor as well as the display
#define LCDCursorLeft 16 ;0x10 Move the cursor left by one character
#define LCDCursorRight 20 ;0x14 Move the cursor right one letter
#define LCDShiftLeft 24 ;0x18 Shift the entire display left one character
#define LCDShiftRight 30 ;0x1C Shift the entire display right one character
#define LCDGoto 128 ;0x80 Add the location of the character position
; to which you wish to move the cursor
void screen_enable(void){
_delay_us(2);
PORTE |= SCREEN_ENABLE;
_delay_us(2); // must be at least 140 ns
}
void screen_disable(void){
PORTE &= ~SCREEN_ENABLE;
_delay_us(2);
}
void Screen_Execute(void)
{
screen_enable();
screen_disable();
}
/** wait until screen is no longer busy */
void screen_busywait(void)
{
char busy = 0x80;
DDRA=0x00; // all inputs, to avoid fighting the screen outputs
while(busy){
// read busy flag
PORTE |= SCREEN_READ; // read
PORTE &= ~SCREEN_RS; // instruction: read busy flag and address
screen_enable();
// read busy bit while the Enable bit is high
busy = PINA & 0x80;
screen_disable;
//BLINK_LED(500);
}// wait until no longer busy
// switch to "normal" "MCU writes to display" mode.
PORTE &= ~SCREEN_READ; // write
DDRA=0xFF;
}
void screen_send_instruction( char instruction ){
PORTA=instruction;
PORTE=0x00 + SCREEN_RS; // RS high: instruction
DDRE=0xFF;
DDRA=0xFF;
Screen_Execute();
};
void Screen_init(void)
{
//BLINK_LED(1000);
SEND_STRING("Starting initialization\r\n",0);
// see http://techref.massmind.org/techref/io/lcd/44780.htm
_delay_ms(15);
SEND_STRING("Step 1 executing.\r\n",0);
screen_send_instruction( 0x30 );
_delay_ms(250);
SEND_STRING("Step 1 complete.\r\n",0);
screen_send_instruction( 0x30 );//second time
_delay_ms(5);
screen_send_instruction( 0x30 );//third time
_delay_ms(1);
SEND_STRING("Step 2 start.\r\n",0);
screen_send_instruction( 0x38 ); // 8 bit interface, 2 line display, normal font
SEND_STRING("Step 2 complete.\r\n",0);
SEND_STRING("Step 3 start.\r\n",0);
//BLINK_LED(1000);
screen_busywait();
screen_send_instruction( LCDOff );//screen off
SEND_STRING("Step 3 complete.\r\n",0);
screen_busywait();
screen_send_instruction( 0x06 );// Entry mode: increment
screen_busywait();
screen_send_instruction( LCDClearDisplay );//cursor goes to home and screen is cleared
screen_busywait();
screen_send_instruction( LCDCursorOn );//screen on and underline cursor on.
SEND_STRING("Step 4 start.\r\n",0);
//BLINK_LED(1000);
screen_busywait();
screen_send_instruction( 0x14 );//Move the cursor right one letter (why????)
SEND_STRING("Step 4 complete.\r\n",0);
SEND_STRING("Step 5 start.\r\n",0);
//BLINK_LED(1000);
screen_busywait();
screen_send_instruction( LCDCursorBlink );//Turn on a blinking block cursor as well as the display
SEND_STRING("Step 5 complete.\r\n",0);
}
</code></pre>
<p>p.s.: Rather than use 11 pins of your MCU to control the display, some people sacrifice a little speed to gain back some of those pins: some control the LCD display with 7 pins of the MCU in 4-bit mode, others <a href="http://techref.massmind.org/techref/io/lcd/Shift1.htm" rel="nofollow">control their LCD display with 1 pin of the MCU</a>.</p>
|
<p>I have a <a href="http://www.display-elektronik.de/DEM16217SYH-PY.PDF" rel="nofollow">DEM 16217 SYH-PY</a> 2x16 character LCD and I have problems initializing it.</p>
<p>I'm using AVR Studio 4. The 8 datalines are connected to port A of the microcontroller while the 3 control lines are connected to port E. Enable is PE2, R/W is PE1 and S is PE0. Port A connections are DBn to PORTAn. As far as I can see from the datasheet, no instructions seem to take more than 2 ms. For some reason, busy flag check isn't working correctly, so I used 2 ms delay instead.</p>
<p>At first, I wanted to have an LED blink after each step, but it turned out to be much better to have output at a serial port.</p>
<p>Here's my code:</p>
<pre><code>#include <avr/io.h>
#include<util/delay.h>
#include "LED.h"
#include "Terminal.h"
void Screen_Execute(void)
{
_delay_us(2);
PORTE=PORTE | 4;
_delay_us(2);
PORTE=PORTE ^4;
_delay_us(2);
//_delay_us(2);
}
void Screen_busy(void)
{
_delay_ms(2);
//is the screen busy?
//PORTE=PORTE | 2;
//DDRA=0x7F;
//Screen_Execute();
//while ((PINA & 128))
//{
//Screen_Execute();
//BLINK_LED(500);
//}// wait until zero
//DDRA=0xFF;
//PORTE=PORTE ^ 2;
//Screen_Execute();
//no longer busy
}
void Screen_init(void)
{
//BLINK_LED(1000);
SEND_STRING("Starting initialization\r\n",0);
DDRE=0xFF;
PORTE=0x00;
DDRA=0xFF;
PORTA=0x30;
_delay_ms(250);
_delay_ms(1000);
SEND_STRING("Step 1 executing.\r\n",0);
Screen_Execute();//voltage stabilized
_delay_ms(5);//first output complete
SEND_STRING("Step 1 complete.\r\n",0);
//PORTA=0x30;
//Screen_Execute();//second time
//_delay_us(110);//end
//PORTA=0x30;//third time
//Screen_Execute();
SEND_STRING("Step 2 start.\r\n",0);
//BLINK_LED(1000);
Screen_busy();
PORTA=0x38;//two lines, 8 bits, 5*7 characters
SEND_STRING("Step 2 execute.\r\n",0);
Screen_Execute();
SEND_STRING("Step 2 complete.\r\n",0);
SEND_STRING("Step 3 start.\r\n",0);
//BLINK_LED(1000);
Screen_busy();
PORTA=0x08;//screen off
SEND_STRING("Step 3 execute.\r\n",0);
Screen_Execute();
SEND_STRING("Step 3 complete.\r\n",0);
SEND_STRING("Step 4 start.\r\n",0);
//BLINK_LED(1000);
Screen_busy();
PORTA=0x14;//cursor goes to home and screen is cleared
SEND_STRING("Step 4 execute.\r\n",0);
Screen_Execute();
SEND_STRING("Step 4 complete.\r\n",0);
//Screen_busy();
//PORTA=0x04;//
//Screen_Execute();//end of init
//Screen_busy();
SEND_STRING("Step 5 start.\r\n",0);
//BLINK_LED(1000);
PORTA=0x0F;
Screen_Execute();//cursor blinks, screen works
SEND_STRING("Step 5 execute.\r\n",0);
Screen_busy();
SEND_STRING("Step 5 complete.\r\n",0);
}
</code></pre>
<p>My problem is that after initialization, cursor appears on a random position on the screen.</p>
<p>When I try to do initialization as described in the documentation, by sending the <code>PORTA=0x30;</code> line 3 times, it doesn't work. Also, if I try to use tighter timing, it again doesn't work. </p>
|
Need help initializing display on ATmega162
|
2011-02-14T16:56:34.953
|
10142
|
|troubleshooting|
|
<p>Switching power supplies use an inductor which can emit high-frequency noise. You can't do much about it, apart from replacing it. You could try disassembling the unit and injecting hot-melt glue into the inductor windings. That might dampen the vibration.</p>
|
<p>The powerbrick for my computer emits a high pitched whine. What could be causing the noise? Any way I can stop or reduce it? </p>
|
Power brick with a high pitched whine
|
2011-02-14T17:08:02.627
|
10146
|
|pcb|eaglecad|
|
<p>Ok, I've found a solution to this problem.</p>
<p>The answer is to place the centre pad in the package with "stop" and "cream" turned off, then manually draw in rectangles for the "stop" and "cream" layers over the pad as they would've appeared anyway.</p>
<p>The physical end result is the same, but placing vias on the pad doesn't produce DRC errors.</p>
|
<p>I'm using some QFN devices in a PCB I'm designing using the Eagle PCB software. The QFN packages have a centre pad that is grounded and intended to help with thermal dissipation.</p>
<p>When creating the package, if I have the centre pad as an actual pad then I get DRC errors when I come to place vias on the pad to connect it through to the ground plane on the opposite side of the board.</p>
<p>Another possibility would be to leave the centre pad off the package and draw it in on the board, but this is a pretty unsatisfactory solution.</p>
<p>What's the best way of dealing with this problem?</p>
|
Vias on QFN centre pad in Eagle PCB
|
2011-02-14T17:56:34.503
|
10149
|
|current|multimeter|
|
<p>Multimeters use a precision shunt resistor to measure current indirectly (known R, measure V, calculate I). Typically a low current range (uA to low mA) will have a larger resistance shunt resistor to generate a larger voltage drop. </p>
<p>As a result, this larger resistance is no longer negligible at higher currents and begins to cause a measurable voltage drop. Additionally, the power dissipation can begin to cause resistance change and eventually it will kill the resistor. Typically, a fast-blow fuse protects the shunt resistor from continuous over-current. </p>
<p>If you're wondering if running 10mA through the meter while in uA mode will damage it, the answer is most likely "no". If you run 300+ mA through the meter, then you will probably be in danger of blowing the fuse. If you try to use the meter as a volt-meter and forget to switch the leads, and connect it to a supply capable of dumping a lot of instantaneous power, you might be able to blow the shunt resistor before the fuse blows.</p>
|
<p>My multimeter only has one 400mA fuse protecting the µA and mA range (and a 10A fuse protecting the amp range.) Is it possible to damage the microamp range by feeding milliamps through it? </p>
|
Can I burn out my multimeter's µA range by using a few mA of current?
|
2011-02-14T19:23:04.040
|
10153
|
|arduino|soldering|
|
<p>Before you begin designing PCB's, you may want to familiarize yourself with a circuit simulation program such as PSPICE. I would recommend getting PSPICE version 8 (student edition), which you can easily find for free. It's older, but it has an easier-to-learn interface and does everything. From there, you can design a circuit, and then run simulations on it to ensure proper functionality. There are tons of PSPICE tutorials out there and it is commonly used in college electronics courses. Once you've designed a circuit in PSPICE, it can be exported to a PCB layout program.</p>
|
<p>I have a decent (equivalent of introductory college level) with circuit design, all on breadboards, as well as programming on a variety of microprocessors and a couple FPGAs. I'm just wondering where would be a good place to go on from here in more advanced and higher level circuit designs, but I'm not sure if I'm at the point where I should make the jump to PCB layouts, or is there an intermediate step that's recommended? I was highly considering making something like Arduino on pcb.</p>
<p>I've also never actually used a soldering gun, and that's something I know I should learn, but I'm not sure really what kind of devices are good to learn that on, and circuits to do stuff like that.</p>
|
I've done breadboards and programming, where is a good place to move on?
|
2011-02-14T20:38:25.947
|
10157
|
|avr|speakers|
|
<p>Thank you for posting and linking to exactly which sound-maker you are trying to use: the <a href="http://www.hitpoint.com.tw/main.php?product=acoustic&db=ac_pb&type=dc&id=10" rel="nofollow">PB-12N23PW-05Q</a> self-oscillating buzzer.
(If you had a raw piezo disk, or a coil speaker, we would use a different drive circuit).</p>
<p>If you insist on using a NPN such as the BD237, you need to add a external resistor between the MCU and the base of the NPN, as joeforker mentioned: 1 KOhm should be adequate.
But no matter what resistor or silicon NPN transistor you use, you will end up with (at best) a V_ce_sat voltage drop of around 0.6 V, so the voltage across the buzzer is about 4.4 V -- which is technically outside the "guaranteed-to-work" "4.5 to 5.5 V" operating range in the buzzer datasheet.</p>
<p>If I were you, I would probably throw out the NPN and replace it with a MOSFET.
A cheap 2N7000 has an on-resistance of 5 Ohm; at 25 mA that gives a voltage drop of .125 V.
(More expensive MOSFETs have an order of magnitude less (better) on-resistance).</p>
<p>The MOSFET should work in the circuit you posted -- it doesn't need a resistor.</p>
<p>I am surprised that you are getting a different sound.
The kinds of mistakes I am likely to make (and so the first things I would check) are:</p>
<ul>
<li><p>Did I put the buzzer in upside down?
(This doesn't matter much for a raw piezo disk, but it does matter in a self-oscillating buzzer like yours).</p></li>
<li><p>Hook the buzzer up to a bench power supply, and see what it sounds like in the 4 V to 5 V voltage range. Perhaps it's supposed to sound like that at that (5V - transistor drop) voltage?</p></li>
<li><p>What is the actual voltage across the buzzer and across the transistor?
I might check this with an O'scope, since it's quite possible that we have an <em>average</em> current of 25 mA, as shown on the graph, but peak pulses of much higher current -- perhaps such a high instantaneous current that your so-called "5 V" power supply is briefly pulled down to such a low voltage that your ATmega resets.
If that is the case, you'll need to add some bypass capacitors and perhaps a ferrite bead or resistor.</p></li>
</ul>
|
<p>I have a <a href="https://www.mgelectronic.rs/ProductFilesDownload?Id=4123" rel="nofollow noreferrer">PB-12N23PW-05Q</a> buzzer and I'm trying to use it with ATmega 162. I can't connect it directly to pin, because from what I've read from 162's datasheet, it can source at most 20 mA. The buzzer takes 50 (or around 25, if we take a look at the graph), so I don't think I can just directly connect it to the microcontroller. </p>
<p>My initial idea was to connect it to a transistor and use the transistor as a switch. Unfortunately, it didn't work. I used BD237 and my idea was that the microcontroler will pull the pin connected to the base high and the transistor will operate the buzzer. In my setup, I had buzzer connected to Vcc, buzzer's negative port connected to collector, GND connected to the emitter and 162 connected to the base. Transistor is of NPN type. Somewhere I read that this way some problems related to the voltage drop on the transistor can be mitigated, but to me it looks like the voltage drop is the main problem here. </p>
<p>Here's the schematic. The mc is used instead of switch on the real thing.</p>
<p><img src="https://i.stack.imgur.com/etLrO.png" alt="buzzer circuit schematic"></p>
<p>Right now, I'm looking for other ideas on how to connect the buzzer. </p>
|
Control 5 V buzzer using 5 V microcontroller (which can't drive it directly) and a single 5 V power supply?
|
2011-02-14T21:01:28.990
|
10158
|
|batteries|lipo|
|
<p>A buck conveter and multicell battery charger is way to complicated for a school project.
I work developing hardware and im telling you, that would take you a long time.
If you dont need more than 4 v use as many cells as you want in parallel. Parallel batteries are inherently ballanced. Use a simple dc power supply @4.1v to charge them. Make sure not to discharge them lower than 3.5 so their life time is not affected.
Dont charge them higher than 4.1v, and dont leave them charging once they reached 4.1v
If you're designing a robot ease your time in mechanical and software improvements.
Good luck</p>
|
<p>I am planning on a <strong>1 cubic inch robot</strong> as my next project in robotics and the biggest challenge I am facing is on the battery. Lithium polymer seems to be the best option in terms of weight and the required current output and rechargeable!</p>
<p>The requirement in circuit is around 400mA with 3.5V, After searching a lot in Internet I could best get to this <a href="http://www.all-battery.com/polymerli-ionbattery37v240mah602025.aspx">battery</a> which fits my dimension and voltage requirements.</p>
<p>But its still low on current so I plan on using them in parallel. I read that Li-ion and Lipo batteries are very sensitive and might damage the battery or cause fire if used incorrectly So I need some help on this!</p>
<ol>
<li><p>Can I use them in parallel ? Is that the right and safe thing to do ?</p></li>
<li><p>If I use them in parallel then can I charge them to in parallel ? or do I need some special balancer circuit ?</p></li>
<li><p>Can somebody help me with a decent charger circuit for this cell ?</p></li>
<li><p>Anybody knows a better battery than this one that I can use in my application?</p></li>
<li><p>Any other points/suggestions that will help me on this project that I missed out ?</p></li>
</ol>
|
Need help with LiPO batteries
|
2011-02-14T21:17:22.910
|
10185
|
|eda|
|
<p>I spoke to Mentor support. They make the HyperLynx family of tools. They confirmed they need not be unique. Use the parser to verify your IBIS models; which I did and it didn't complain. Also they are not shorted even if they have the same name.</p>
|
<p>I don't see any reference in the <a href="http://eda.org/pub/ibis/ver5.0/ver5_0.pdf" rel="nofollow">specification</a> that says so, but then I don't see anything that says otherwise. Other sections do talk about uniqueness, so I'm guessing they don't need to be unique.</p>
<p>EDIT: 2/18/11: I'm using Mentor's HyperLynx simulation software.</p>
|
Do IBIS signal names need to be unique?
|
2011-02-15T01:00:12.603
|
10190
|
|wireless|infrared|
|
<p>The Nordic nRF24L01 RF chips have a 33mW power consumption in Rx mode and much less in Tx. Not really answering your IR question, but I thought I'd mention them because you can buy ready made USB dongles which would speed up your development. It does also mean that line of sight isn't an issue!</p>
|
<p>My next robotics project is a "1 cubic inch robot" and I am planning to add a 2 way wireless communication between my robot and a computer. Since for that size Power is a big bottleneck the best I could come up is a IR transceiver. So how can I achieve this ?</p>
<p>If I use a 38khz receiver then I might end up receiving the same transmit signal ? what Is the best option I can use in my application ??</p>
|
2 Way IR communication for my robot
|
2011-02-15T04:46:02.233
|
10223
|
|motor|dc-motor|
|
<p>Potentiometers are terribly inefficient for controlling power loads, since significant power is burned up in the potentiometer itself. Under the right load conditions, <em>most</em> of the power sourced by the power supply will be burnt in the pot. </p>
<p>This doesn't matter too much if you're only dealing with small loads and have a mains supply, and can deal with the heat from the potentiometer. But if your power source is a battery, this inefficiency translates directly to shortened run time between battery charging.</p>
|
<p>I've used small high speed dc motors by just wiring them to a battery and potentiometer, but i've heard a lot of talk in these forums about motor controllers and h-bridges, and I don't fully understand when they are needed.</p>
<p>My question is: I want to run a geared motor like one of these:</p>
<p><a href="http://www.surpluscenter.com/item.asp?item=5-1571&catname=electric" rel="nofollow">http://www.surpluscenter.com/item.asp?item=5-1571&catname=electric</a></p>
<p><a href="http://www.hobbyengineering.com/H2013.html" rel="nofollow">http://www.hobbyengineering.com/H2013.html</a></p>
<p>Do I need a motor controller, arduino motor shield, or h-bridge to do so? Or can I just wire up a 6/12 volt power supply and use a pot to control the speed? I realize I won't be able to run it in reverse this way. Would I be able to just use a switch to reverse the polarity and run it forwards/backwards?</p>
|
Controlling a geared motor
|
2011-02-15T19:15:12.853
|
10225
|
|wire|antenna|tv|
|
<p>Here are the effects that I would expect from switching between the coat hanger wire and the wire in CAT5:</p>
<ul>
<li>(Obvious) The wire in CAT5 will not retain its shape as well as a coat hanger wire. It will also not be as rigid. If you were planning on fastening the whole thing to a board, this wouldn't matter.</li>
<li>Thinner wire will have a narrower bandwidth than thicker wire. The closer you get to an ideal wire (zero diameter, zero ohms), the higher the "Q" of the antenna. This is more significant when you are using really thick wire (or a birdcage dipole structure) and really thin wire. Additionally, I don't think your topology is very Q sensitive, so impact should be minimal.</li>
<li>Thinner wire will have higher resistance. Since you are receiving, impact will be minimal.</li>
</ul>
<p>There are several other very minor effects that you might expect, but ultimately you won't notice an electrical difference, and it would be difficult to measure the difference. The 300-75 ohm transformer is only needed if the antenna is designed to be 300 ohms. Since you didn't post any documentation, I can't comment on that.</p>
|
<p>I want to make a fractal antenna to replace an old set of rabbit ears. All the guides I've seen have used a thicker wire (metal coat hangers seem popular). While I don't have any hangers, I do have an absurd amount of cat-5 that I have been harvesting whenever I need wire. If I pull a length of wire out, would the thinness of the wire restrict its ability to pickup a good signal? Thanks and pardon the relative low bar on this question.</p>
<p><strong>Note:</strong> I will be untwisting them and stripping them at the appropriate junctions. I also have a 300->75ohm transformer already.</p>
|
Can a small gauge wire be used in a fractal antenna?
|
2011-02-15T19:32:42.397
|
10229
|
|analog|design|integrated-circuit|
|
<p>The only thing I can think of outside of what is mentioned above would be to dive into a program like <a href="http://en.wikipedia.org/wiki/Electric_%28software%29" rel="nofollow">Electric</a>, teach yourself how to use it (hopefully with guidance from an experienced engineer), make some kind of awesome and before unseen circuit, and finally get it in the hands of someone who matters and has the ability to hire you.</p>
<p><a href="http://youtube.com/jeriellsworth" rel="nofollow">Jeri Ellsworth</a> took a similar path with digital (granted, which has lower entry costs and less need to be near the process node and device physics) but did not have any education. She stated in <a href="http://twit.tv/tri3" rel="nofollow">a recent interview</a> that it was all because of mentors. So in the event you think it's something you'd really want to do, that'd be a first step. Even with a MS, a good mentor will get you farther than anything else IMHO.</p>
|
<p>I've asked other questions about having a career in electronics without an EE degree. I'm wondering specifically about being an analog IC designer. What would it take to land a position doing that before having that degree? What would convince an employer to hire me despite lacking that piece of paper? What kind of employer would I best off sending my resume and other info to?</p>
|
Earning a living in analog IC design w/o an EE degree
|
2011-02-15T22:15:56.187
|
10235
|
|components|protoboard|
|
<p>You can also buy <a href="http://www.mill-max.com/images/products/pdf/metric/195M.pdf" rel="nofollow">dedicated pins</a> that allow you to solder on one side (usually bifurcated) and wire wrap on the other. The pins have a shoulder that you can jam into the PCB through hole to secure it. </p>
<p>Basically, if you want to attach a component to a wire wrap board that component has to be connected to a wire wrap pin. Whether that's a dedicated terminal, a single piece of a strip socket, a repurposed DIP socket, or a component carrier plugged into a DIP socket - that's your choice.</p>
<p>As an aside, unless you're dealing with exotic components or have a stash of wire wrap stuff, wire wrap components seem pretty expensive. Digikey wants $3 to $7 for a 16 pin DIP socket. You might be better served by doing point-to-point wiring on a Veroboard.</p>
<p>Edit to add:</p>
<p>OK, given the specific example of a voltage regulator, how would you add that? Let's assume this is a TO-220 or similar package. There are three leads that need to be connected, so you need to connect them to three wire wrap pins. Exactly how you do this depends on what kind of wire wrap pins you have:</p>
<ul>
<li><p>Terminal pins (bifurcated or not): I'd solder the pins to the component, then plug the whole thing into the perfboard, then wire-wrap to the pins.</p></li>
<li><p>DIP socket: plug the three leads into 3 adjacent socket pins (bending if necessary), then wire-wrap to those pins.</p></li>
<li><p>SIP or discrete sockets: same as DIP sockets.</p></li>
</ul>
<p>If this were a TO-92 with an off-pitch triangular lead layout, you might have to "normalize" the leads to fit the 100 mil pitch of the perfboard. Just use good pliers to make it fit (or cheat and get the 3 leads started into 3 holes, and use the perfboard to leadform it - this is what I'd do).</p>
<p>Other tips:</p>
<p>Don't forget that you can cut skeletonized wire wrap sockets apart to make discrete socket pins/SIP socket strips.</p>
<p>You might have to glue the wire wrap sockets in place, especially when using single-pin connections.</p>
|
<p>I used to use a breadboard, and it would hold the components put into it. A wire wrap board is different. The components are don't seem to be secured to the board. How are they supposed to be secured to the board?</p>
|
How to secure components to a wire-wrap board
|
2011-02-16T00:53:49.037
|
10239
|
|digital-logic|
|
<p>(look at the circuit below)In this case you have to push E,F,G,H in sequence without touching Button B,C,D</p>
<p>The diode for logic gate are for self-locking after one logic gate get out put.</p>
<p><a href="https://i.stack.imgur.com/kY01S.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/kY01S.jpg" alt="enter image description here"></a></p>
<p>*from Make: electronics experiment 21 </p>
|
<p>I am trying to figure out how to create a combination lock using logic gates, so that a password must be input (let's say pressing numbered buttons) in the correct order.</p>
<p>I understand logic gates completely, and have some of a grasp on flip-flops and latches, but I'm definitely getting stuck on how to use them in the right combination.</p>
<p>So as an example, if there are 3 buttons (call them 1, 2, & 3), I would like to be able to set a password such as 1 2 3 1 (hardcoded is fine), where they have to be input in that exact order, otherwise you have to start at the beginning again (1 2 3 3 3 3 1 will not work).</p>
<p>Any tips, links, hints on this?</p>
|
Creating a combination lock using logic gates?
|
2011-02-16T02:03:08.417
|
10244
|
|software|simulation|math|
|
<p>SNAP - symbolic, semisymbolic, and numerical analysis of electronic circuits</p>
<p><a href="http://snap.webpark.cz/indexa.html" rel="nofollow">http://snap.webpark.cz/indexa.html</a></p>
<p>very useful</p>
|
<p>Does any of the common circuit simulation software provide the system equations? Deriving a system of 1st-order differential equations for a circuit by hand is kind of a pain. And yes, I know that the simulators will actually run the simulations for me, but there are some cases where I'd really be interested just to see what the equations are. Which, if any, circuit simulators would provide them?</p>
<p><strong>EDIT ..</strong></p>
<p>What I am specifically looking for here is, I would like to be able to enter my circuit into the software, just like you would do for simulation, but besides run the simulation, I'd <em>also</em> like to have the software show me the equations that it has derived and uses to run the simulation - the system of differential equations that says what the rates-of-change of the system state variables are. This could be a system of equations or it could be in matrix form, doesn't matter.</p>
|
software for obtaining differential equations for circuit simulation
|
2011-02-16T03:25:48.830
|
10249
|
|serial|uart|
|
<p>Just to clarify the various comments about synchronisation at the bit level, I have sketched some example bit patterns (not very well!). First, remember that the async bitstream consists of a logic-low start-bit, a number of data-bits (typically 7 or 8), an optional parity-bit and a number of logic-high stop-bits (typically 1 or 2). The data-bits are sent LSB first. Parity is not that often used as the integrity it provides is minimal compared to a vertical checksum as markrages has recommended. The most common format is 8 data-bits, no parity and one stop-bit.</p>
<p><img src="https://i.stack.imgur.com/zsYMT.png" alt="Async serial examples"></p>
<p>The first trace shows a pair of 0x55 bytes - the green and red rectangles representing the start and stop-bits respectively. As you can see, this is a square wave so the receiver can't tell which low bit is the start bit, since every low bit is preceded by a high bit (which could be a stop bit). Which ever way the receiver looks at it, this represents a pair of 0x55 bytes but only one way has the correct framing. This was the basis of my earlier comment.</p>
<p>The second trace represents a pair of 0x10 bytes. However, the receiver may see the bits marked by the triangles as framing bits and (incorrectly) decode a pair of 0x04 bytes.</p>
<p>The third trace represents a pair of 0xFF bytes. There is no ambiguity here as all the low bits are genuine start-bits - hence JustJeff's earlier comment.</p>
<p>A typical sequence is as markrages says in his answer. Traditionally, 0x01 (Start-Of-Header) or 0x02 (Start-Of-Text) have been used as a start byte but a pair of 0xFF bytes is more reliable as JustJeff says. You might also want to put a 'stop-byte' at the end. Traditionally, 0x04 (End-Of-Transmission) and 0x03 (End-Of-Text) have been used for this purpose. Finally, always check your receivers framing-error status!</p>
|
<p>I just have a few general questions that those with more experience could easily answer. </p>
<p>I am working with an arduino, and interfacing with various devices such as the PC that I use to write the arduino C code, which is obviously plugged in via USB, and I have had success with a serial link to an iphone by connecting the tx/rx pins. </p>
<ul>
<li><p>What sort of data integrity guarantees are there for the serial link? For example if the cable connecting two devices becomes frayed or damaged, what sort of changes might I expect my data stream to undergo? Could it start receiving garbled data, or will it just cut off? </p></li>
<li><p>Is its functionality fully encapsulated by a byte stream? Suppose I want to relay 16-bit numbers. My first and only instinct is that I must come up with my own protocol (big-endian or little, for example) to pack my data into a byte stream and write to the port? It functions more or less like a network socket (minus the concept of packets) does it not? </p></li>
</ul>
|
Serial (UART) communication
|
2011-02-16T04:04:54.343
|
10254
|
|crystal|generator|
|
<p>Sounds like an interesting project.</p>
<p>All microcontroller datasheets I've read so far all have the same crystal oscillator configuration -- a single inverter in the <a href="http://en.wikipedia.org/wiki/Pierce_oscillator" rel="nofollow">Pierce oscillator</a> configuration.</p>
<p>It will make no difference to the precision of a Pierce oscillator whether you use such a microcontroller or a SSI discrete logic chip to drive the crystal -- it's a simple inverter either way.</p>
<p>While most of the Pierce oscillators I've seen use exactly 2 capacitors, one per crystal pin, some people insist that <a href="http://techref.massmind.org/techref/clocks.htm" rel="nofollow">the right way to built a Pierce oscillator</a> is with 4 capacitors, one to ground and one to VCC at each crystal pin.</p>
<p>Sometimes I wonder if a "gentle" sine-wave oscillator such as a <a href="http://en.wikipedia.org/wiki/Wien_bridge_oscillator" rel="nofollow">Wien bridge oscillator</a> would be better at driving a crystal than the digital on/off of a Pierce oscillator.
Perhaps you could build a couple of each kind of circuit and compare them.</p>
<p>Wikipedia claims that <a href="http://en.wikipedia.org/wiki/crystal_oscillator#Stability_and_aging" rel="nofollow">thermal noise influences the stability of crystal oscillators</a>.
Would putting one of your crystals in a little <a href="http://en.wikipedia.org/wiki/Thermoelectric_cooling" rel="nofollow">Peltier cooler</a> at a constant cold temperature work any better than the more common approach, putting the crystal in a little oven at a constant hot temperature?</p>
<p>The <a href="http://opencircuits.com/24%22_Wall_Clock" rel="nofollow">Spark Fun Wall Clock</a> has a few pointers on getting a clock to read GPS time.</p>
|
<p>I am building clock with ultimate precision.</p>
<p>There are few known ways to improve precision: temperature controlled environment and multiple crystals. I am implementing both.</p>
<p>I was going to use 5 crystals on separate uC's (2$ each in retail). But then I've thought: maybe I can just build crystal generators on inverters (2 generators per 0.2$ chip), and feed multiple 32khz signals to single uC?</p>
<p>Will the precision of inverter-based generators be inferior to uC-based ones?</p>
<p>Obviously inverters look very attractive - in the same budget I can have 2-3 times more crystals.</p>
|
Multiple crystals
|
2011-02-16T09:36:37.753
|
10265
|
|power-supply|mains|
|
<p>I'd guess that it's an unregulated power supply, meaning you'll see the 21V under the rated load (1.2A). 26V is its open circuit voltage.</p>
|
<p>I have an AC/DC power supply (from the UK). It is labelled 230V/50hz. As far as I know, electric in Mainland britain is 240V/50hz. Indeed, the unit did correctly power the Korg keyboard in the UK. The DC output is labelled 21V / 1.2A. (The Korg piano is indeed labelled 21V input on the back.)</p>
<p>Now I have the same power supply in France. As far as I know, France is also 230V/50hz. When I plug the power supply in the wall in france (obviously using a 50 cent plastic plug adaptor - of course NOT using any sort of transformer, etc).</p>
<p>Using a good multimeter, in France the output from the power supply is 26 volts (around 25.9 to 26). Is that normal? Why not just 21?</p>
<p>(Unfortunately I never tested the output, in the UK.) Now, the electric piano is actually not working. ie, I did plug the power supply in question in to the Piano and no result, nothing comes on.</p>
<p>Does anyone know:</p>
<ol>
<li><p>Why is it showing 26 rather than 21 as labeled?</p></li>
<li><p>Do you reckon I may have blown a fuse in the piano, due to the 26 versus 21? Or, perhaps not a fuse, just permanently ruined it? Conversely, is it likely just some other unrelated problem with the piano?</p></li>
<li><p>To rephrase: If the piano says 21V on the back, would 26 V be too hot, or no problem, typically?</p></li>
</ol>
<p>It's an expensive pro piano and a real nuisance! It is a mystery that it is showing 26V. It's almost impossible to find a replacement power supply, and, that may well not be the problem. </p>
<p>A further question for you experts:
would an alternate supply, eg,
<a href="http://www.webducommerce.com/alimentation-21v/chargeur-alim-secteur-21v-1-7a-36w-p-3485.html" rel="nofollow">http://www.webducommerce.com/alimentation-21v/chargeur-alim-secteur-21v-1-7a-36w-p-3485.html</a>
with a HIGHER amperage rating, actually be OK?? Should you try to match the amp rating, or us the point that it must be "at least" 1.2A in my example? Thanks again, pro geniuses!</p>
|
21V power supply -- 26V output with different mains?
|
2011-02-16T17:46:17.717
|
10282
|
|fpga|microblaze|
|
<p>regarding functionality MB vs ARM Cortex-M3, basically the Cortex-M3 contains a ARMv7-M CPU and that means it's based on ARMv6-M. Check out some screenshots showing off mainstream features. MB will definitely be better integrated on Xilinx FPGA fabric and its 'in the field' since many years. For more info on MB, search UG081 - MicroBlaze Processor Reference Guide.</p>
<p>Kind regards</p>
<p><a href="https://i.stack.imgur.com/dILcA.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dILcA.png" alt="ARMv7-M Architecture"></a>
<a href="https://i.stack.imgur.com/js9H4.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/js9H4.png" alt="Xilinx MB Key Features"></a></p>
|
<p>Is the Microblaze soft cpu better than the Cortex M3 soft cpu in terms of functionality?</p>
<p>Given all the buzz about the ARM based processors, I was wondering if to implement an ARM processor on my FPGA or if I should stick to the Microblaze that comes with it.</p>
<p>Is there any major difference in terms of performance or functionality that I should consider?</p>
|
Is the Microblaze soft cpu better than the Cortex M3 soft cpu
|
2011-02-16T19:24:29.190
|
10291
|
|resistors|multimeter|resistance|production-testing|
|
<p>I great trick I learned from reading the HP 3478A DMM Service manual (section 3-119 extended ohms operation) is to first measure a 10M resistor, and then put the 10M in parallel with the unknown high resistance and measure the parallel value. The formula unknown=(reference value * measured parallel value) / (reference value - measured parallel value) does the trick. As an example, say you used a 10 ohm reference, and say you are measuring a 10 ohm unknown. The two 10 ohm resistances in parallel would measure 5 ohm, so running the formula gives 10 * 5 = 50 and 10 - 5 = 5, and 50 / 5 = 10 ohms. This works for any reference value, and the measured value will always be less than the reference value. Some of the other answers point out some of the limitations of any high resistance measurement. You also run out of digits of measurement precision at some point.</p>
|
<p>I've got an issue that appears to be caused by damaged resistors that are either open circuited or of too low a value due to contamination. The problem is that they're gigaohm resistors, so to a multimeter, they're <em>always</em> open-circuited. How can I measure the resistance, or, at least, test the continuity?</p>
|
How to measure gigaohm resistors?
|
2011-02-16T22:12:15.197
|
10296
|
|led|resistors|voltage-regulator|potentiometer|joule-thief|
|
<p>By coincidence I was looking for a bycycle dynamo operated LED lamp. White LEDs require about 3.6V, but because the supply varies from the speed you cycle (6V max, AC) I had to put a bunch of electronics in there for it anyway. Furthermore I wished high effiency, I don't want to be cycling for a resistor converting my power into heat.. So I started looking.</p>
<p>Also note that if you get a 1.4V battery, if you drain it, the voltage will slowly drop to about 1V. At 0.8V it's completely dead. You may want to consider to have a working product at 1.2V or 1.1V for example, also if you want to support rechargeable batteries.</p>
<p>For that you really need a DC/DC converter to boost a voltage up. The LT1932 is probably even more suitable for your purpose. It converts a low voltage to a constant current (which you need for a LED). It's a bit expensive (because 1) it's linear technologies, 2) you're trying to do something low-voltage), but it is able to drive a single LED from 1V. It also has a SHDN pin so you can control it:</p>
<p><img src="https://i.stack.imgur.com/Hw4HM.gif" alt="LT1932 typical circuit"></p>
<p>It can drive several white LEDs (they require over 3V drop each) from 2V input. This figure shows 4 white LEDs, so that's why it needs 2.7V minimal. I don't know how it will behave if you put only 1 LED in there, but I think it will work just fine. </p>
<p>All you need for this driver is shown there. Rset sets the current through the LEDs(in the datasheet is probably a table). It drives the LEDs in this example with 15mA. And as said, LEDs are controlled by current not by voltage. The resistor you normally use only sets a 'fixed' current (for a certain voltage you apply on the system). This regulator is set to a certain current with the resistor Rset, and then you're done. If you put another LED in series, it will adjust the voltage so the current stays the same. Ofcourse, this has limits, but you won't reach that I suppose. </p>
<p>There are more of these IC's and are quite handy. You probably find more examples that are cheaper, but might not be able to work from 1V.</p>
|
<p>I would like to mount a <a href="http://www.vishay.com/ir-emitting-diodes/list/product-81011/" rel="nofollow noreferrer">TSAL6400 led</a> on a single AA size battery box, with a simple ON/OFF switch. My problem is that the LED needs exactly 1.35V to function at its rated brightness. At this voltage it uses 100 mA current.</p>
<p>I would like to use Sanyo Eneloop batteries. I've measured them and they have 1.405V one day after charging. I think they will drop to about 1.395V @ 100mA.</p>
<p>I've followed the LED tutorials, which all say I have to wire a resistor in serial with the LED. My problem is that if I calculate, that resistor needs to have (1.4-1.35)/0.1 = 0.5 Ohm resistance.</p>
<p>My question is that what would you recommend me to do this project? I would like to make the box as little as possible, I'm planning on mounting everything directly on a single AA box.</p>
<ul>
<li>Shell I use two 1 Ohm resistors in parallel, to get a 0.5 Ohm resistor?</li>
<li>Can I possibily use some micro turn potentiometers for my problem? It would be the best solution, as then I could just use different batteries, as all I would need to do is to set it after changing batteries. I am mostly interested in this solution. Can someone explain to me what is the best way to get 1.35V from 1.4V-1.6V sources using a simple potentiometer?</li>
<li>Maybe it's an overkill, and I really don't know how to use them, but can I use a voltage regulator for this purpose? I mean is there a voltage regulator which is small and can provide as little as 0.4V drop?</li>
</ul>
<p>UPDATE:
I've made some measurements on my LED:</p>
<ul>
<li>1.184 V - 12 mA</li>
<li>1.315 V - 75 mA</li>
<li>1.345 V - 93 mA</li>
<li>1.357 V - 100 mA</li>
<li>1.380 V - 110 mA</li>
</ul>
<p>The last one is when I connected it directly to a Eneloop AA battery. By definition it's overdriving, but I don't know how dangerous it is for the LED.
<img src="https://i.stack.imgur.com/XHWDh.png" alt="LED measurement"></p>
|
how to drive a 1.35V led with a 1.4V AA battery
|
2011-02-16T22:57:15.690
|
10317
|
|led|
|
<p>I haven't tried this myself, but I read an application note saying it is practicable to connect strings of LEDs in parallel and omit all those load-sharing resistors providing there are AT LEAST 4 LEDs in each string. It said that, when connected like this, LEDs tend to naturally share the current. (Of course, we are talking about LEDs of the same type.) So I understand them to be saying that if you had, say, 6 parallel strings, and each string comprised 4 LEDs in series, then if you pump 180mA through the lot, it will pretty well divide itself with ~30mA through each string. Easy enough to test this, especially if you include a small test resistor in series with each string and use it for current-sensing. If the currents are almost identical, you can remove the resistors! Careful with CURRENT sources though, if you really push the boundaries and any string goes open-circuit, then all of its current will divide as extra current through the other strings, maybe in turn burning them out! The more strings you have, the lesser the risk. (I'd only do this for cheap LEDs, not the $40 room-lighting LEDs!)</p>
<p>As every hobbyist knows, specialized ICs and modules are notoriously hard to get hold of in small quantities. But a boost module I know to be available by mail order is the BoostPuk 4019 from LUXdrive. It won't work down to single AA cell voltages, but because of this thread's general subject title, hobbyists with a similar need are likely to be reading this. Check out the LUXdrive 4019 and other handy driver modules here: <a href="http://www.ledsupply.com/led-drivers.php" rel="nofollow">http://www.ledsupply.com/led-drivers.php</a></p>
|
<p>I have twenty LEDs that I want to light up. I planned out a few possible circuits, which I describe below along with a few questions. Would any of them not work, and why? Anything else I should be taking into consideration but haven't? The LED has the following specs:</p>
<pre><code>Vmin: 2.8V
Vmax: 3.5V
If: 20 mA
</code></pre>
<p>From what I understand, the Vmin is essentially the same as Vd in <a href="http://upload.wikimedia.org/wikipedia/commons/a/a5/Diode-IV-Curve.svg">this</a> diagram, so the current will be 0 until it reaches that voltage. Is this correct?</p>
<p>If the LEDs are connected in series, that means that I'll need 20*2.8V=56V in total to get current passing through every LED. I calculated the approximate amount of power necessary (60V*0.02A=1.2W) and compared it to the amount that can be provided by a typical AA battery, which I've been told usually provide around 800mA of current (1.5V*0.8A=1.2W). Seeing as they're the same, I'm pretty sure it'll be possible to step up from a single AA to what's needed to light the LEDs. So far, I know of the SEPIC, which I'm reading up on right now. Is there a better way of accomplishing this? Possibly without needing inductors?</p>
<p>Another solution I've considered is connecting them in parallel, which I recall reading somewhere that it's a bad idea unless there's a resistor in series with each of the LEDs. Two AA batteries in series would be enough in this case, providing a 3.0V potential across each branch. Since the LED takes 2.8V, the resistor would take up the remaining 0.2V, and to get a 20mA current, I'll need a (0.2V/0.02A=10ohms) 10 Ohm resistor.</p>
<p>I could also plug it into an adapter which converts the AC electricity from the outlet to 15V (the current rating on the adapter means the maximum it can give and not the amount it'll always give, right?). In this case, I could separate the LEDs into four groups of five (which is convenient given their layout), each LED in a group of five is connected in parallel to each other, and the four groups are connected in series. That would give a voltage of (15V/4) 3.75V across each group of five, and since the LEDs in the group are in parallel, they'll each get 3.75V too. The current needed would then be (0.02A*5) 100mA. The voltage across the resistor in series with the LEDs is (3.75V-2.8V) 0.95V. The resistance needed would then be (0.95V/0.02A) about 50 ohms.</p>
|
Powering twenty high intensity LEDs
|
2011-02-17T01:24:52.947
|
10322
|
|voltage|
|
<p>I'll try to explain it as I understand it...there is no +ve and -ve, its only a denotation of two directions. Voltage means Potential "difference". i.e, it is not a quantity, but a comparative value, in a direction. If you like a direction, then its +ve, if you don't like it then its -ve. An apple falls from the tree to the ground, both the ground and the branch of the tree exert a certain pull on that apple, but the ground exerts "X" amount more than the branch, the ground wins. Then Jupiter decides to take a cosmic stroll and climbs 2 feet above the tree, now the apple flies up. Actually there is no up and down, there never was. If the sight of an apple flying up distresses you, you say down is where earth is so towards the earth is the +ve "direction", and up is where Jupiter is so flying to Jupiter is -ve "direction".</p>
<p>In the same way there is no +ve and -ve in electrical engineering, its just a denotation of two directions (scalar not vector in the case of electronics), one we prefer, one we don't so much but still use it to our benefit.</p>
|
<p>Just a general electronics question: What is negative voltage, like -5 Volt?</p>
<p>From my basic knowledge, power is generated by electrons wandering from the minus to the plus side of the power source (assuming DC power here). Is negative voltage when electrons wander from + to -?</p>
<p>Why do some devices even need it, what is so special about it?</p>
|
What is negative voltage?
|
2011-02-17T02:40:51.527
|
10327
|
|components|standard|
|
<p>A pin header with pins that slide into connectors with sockets would use class letter CP that stands for "connector adapter". That is if you have two PCBAs with female sockets on each board and they are ref des A1J1 and A2J1, and you have a header with male pins sticking out the top and bottom then the header would use class letter CP. Depending how you associate the coupler on your schematic diagrams would determine which parts list the coupler (connector) goes on.</p>
<p>If you have a pin (male) header on one board and a socket (female) header on a second board, where the two boards connect directly together, then arbitrarily call one board most movable and the other most fixed. (I would call the pin header by class letter P and the socket header by class letter J. How you show the assembly being put together on the assembly drawing might give you a clue as to which board is most movable and which is most fixed.</p>
<p>If you have two RF cables that connect together but each has an N-male connector, then a double female N connector, to connect the cables together, would use class letter CP (connector adapter)
--Regards, Larry</p>
|
<p>What prefixes should be used on reference designators for components of various types? I think we can all agree that "R##" refers to a resistor, "C##" refers to a capacitor, and "L##" refers to an inductor. Beyond that, it appears to be a mishmash of conventions. </p>
<p>I've seen both "IC" and "U" used for chips. "Q", "T", and "M" have been used for transistors and MOSFETs. Ordinarily, "D##" is used for diodes, but LEDs and Zeners get special treatment on some boards. </p>
<p>What standards are available for reference, and who endorses them? JEDEC, ISO, IEEE, and other standardization bodies are welcome references (though I'd prefer an inexpensive standard), but I'm also curious to see what's used at various companies other than my own. </p>
<p>Edit: What I'd really like to see is a list <strong>in an answer here</strong> which complies with the standard (even if it's just a quote).</p>
|
Standard nomenclature for component types
|
2011-02-17T04:17:07.813
|
10329
|
|pic|microprocessor|tcp-ip|network-interface|
|
<p>I've worked a lot with the Microchip TCP/IP Stack and I've found in most cases it's easier to have your server connect to the PIC and request data rather than have the PIC post the data to the server.</p>
|
<p>I'm currently working with the flyport from OpenPicus, it has 24FJ256GA106 PIC processor in it and I was looking for the best way to send information from the flyport to a server. </p>
<p>I want to know how can I send this data? In a packet form to the server? Does anyone know where I can find information on accomplishing this?</p>
<p>I already have previous experience with .Net programming and was hoping to have it pushed to a SQL server. However, getting the data sent would be enough information to get me started.</p>
|
Working with PIC to send data to server
|
2011-02-17T04:42:26.530
|
10368
|
|stepper-motor|
|
<p>Running a stepper motor at under its rated current will affect <strong>both</strong> its maximum speed and torque (both holding and dynamic), though depending on the driver type, it mostly affects the torque.</p>
<p>Firstly, The stepper motor driver you are linking <strong>requires power rails of 7-30V</strong>. Its <em>logic</em> interface is 5 or 3.3v.</p>
<p>Furthermore, your stepper motor is 3.6 ohms per winding, so even with 3.3V rails, your motors are going to pull ~900 ma, which will cause power rail brownouts.</p>
<hr />
<p>Fortunately, in this context, the stepper motor controller IC provides <em>chopped current limiting</em>, which is a technique which limits the maximum amount of current it runs through the stepper motor. Therefore, you can run the stepper motor you have off the wall-wart you have, a the cost of reduced torque.</p>
<p>In a system which uses <em>current chopping</em>, the voltage largely determines the motors maximum speed, and the current the torque. There is interactions, but they are fairly small in effect size (assuming you are not at extremely low voltage or current), proportionate to the effect of changing the relevant characteristic directly.</p>
<p>I urge you to carefully study the <a href="http://www.sparkfun.com/datasheets/Robotics/A3967.pdf" rel="nofollow noreferrer">A3967 datasheet</a> (the A3967 is the stepper motor IC the linked driver uses).</p>
<p>Furthermore, the designer of that stepper motor driver provides a fairly decent introduction into the concepts of how the device works <a href="http://schmalzhaus.com/EasyDriver/" rel="nofollow noreferrer">here</a>, which, from your question, I don't think you have really read. You should carefully read it before you hook anything up, lest you damage one of your parts.</p>
<hr />
<p>Additionally, the stepper motor driver you link <em>already has a voltage regulator</em>, so you do not even need the voltage regulator you included in your post (<a href="http://www.sparkfun.com/products/114" rel="nofollow noreferrer">SFE sku: PRT-00114</a>).<br />
See the schematic for the Stepper Driver <a href="http://www.sparkfun.com/datasheets/Robotics/EasyDriver_v43.pdf" rel="nofollow noreferrer">Here</a>. The voltage regulator is IC2.</p>
|
<p>I have a <a href="http://www.interinar.com/vexta-pk266-02a.html" rel="nofollow">stepper motor</a> and it is rated at 2 amps per phase. I also have a <a href="http://www.sparkfun.com/products/10267" rel="nofollow">stepper driver</a> which is rated at 750 miliamps per phase. To make matters worse I have a wall wart power supply rated as 9V @ 650miliamps. That power is converted by a <a href="http://www.sparkfun.com/products/114" rel="nofollow">voltage regulator PCB</a> down to a usable 3.3 V at an unknown amperage. </p>
<p>My question is, what effect will underpowering the motor have?<br>
Will it affect the speed of the motor or just holding torque?</p>
|
Underpowering a stepper motor
|
2011-02-18T03:09:41.270
|
10369
|
|stepper-motor|
|
<p>If you visit the web sites of companies that manufacturer quality stepper motors, you'll likely find documentation giving the theoretical way to calculate this. You'll need to know a lot about the mechanical load, and be prepared to do a fair amount of math. But if you are designing a printer to sell at a loss and make it up on ink... it's worth optimizing these things so you can use the cheapest motor that can meet your ramp speed requirements.</p>
<p>But in the more likely case, if you are building a one-off robot or hobby CNC machine or whatever, chances are you are going to buy the biggest motors you can get a good deal on (or you've already extracted them from that ancient printer), and then crank up the ramp-rate until you find it unreliable, then back off whatever safety factor you desire.</p>
<p>A well engineered and adjusted high voltage chopping drive amplifier will be necessary to get the maximum performance out of the motor without damaging its magnets.</p>
|
<p>How can the required ramp-up speed for a stepper motor which is attached to its drive system be determined?</p>
<p>Given that a stepper motor requires ramping-up to full velocity, and that ramp speed must be slow enough so that the motor doesn't simply vibrate in place, is there a known method for determining the ramp-up speed?</p>
|
Determining the ramp-up speed for a stepper motor with its drive system
|
2011-02-18T03:13:06.773
|
10370
|
|fpga|radio|
|
<p>There is a four part series "Software radio for the masses", linked from <a href="http://www.arrl.org/software-defined-radio#f-widget-29624" rel="nofollow">the ARRL</a>, which explains all this basic information, including the different ways of doing software defined radio.</p>
<p>Once the signal is digitized, it's processed using DSP techniques. You can find more details about them in "Signals, Samples and Stuff: A DSP Tutorial" articles, also linked from above mentioned page.</p>
<p>Oscillators in SDR can be of any kind, from crystal, to PLL controlled VCOs, to direct digital synthesis (DDS), to numerically controlled oscillators (NCO, CORDIC) done entirely in software or FPGA.</p>
|
<p>I've done some reading on software defined radios and while the concept is clear I have yet to grasp how the signaling is actually done. I've researched the Analog to Digital IC's that are involved in the process and they say that the support sampling rates of 500Mhz or more (is that even correct?) My question is: How is the modulation and demodulation acheived in a software deined radio?</p>
<p>EDIT: I was assuming that there was some sort of voltage controlled oscilator involved, however I can't find the literature.</p>
|
Theory of operation for a software defined radio
|
2011-02-18T03:23:50.737
|
10371
|
|arduino|sensor|sound|
|
<p>The best way is to perform <a href="http://en.wikipedia.org/wiki/Fast_Fourier_transform" rel="nofollow">an FFT</a> on the microphone input. <a href="http://technology911.com/v/sr0ewZHu9jg,arduino-realtime-fft" rel="nofollow">FFT software</a> is available for the Arduino.</p>
|
<p>I'm trying to find a sound sensor that can give feedback on all the frequencies of sound and their levels.</p>
<p>The sensors I'm finding in my search however only support level of sound it seems.</p>
<p>Is it possible to get the level of individual frequency ranges from one sensor, or does it require multiple senors?</p>
<p>I'm new to this so don't know the exact terminology, but essentially I want to create something that can respond to a set of different frequencies of sound independently, not just how loud the sound is.</p>
<p>Ideally the sensor would be made to work with Arduino, but I'm not afraid of something that it is more complicated.</p>
|
Sound Sensor that can give feedback on the amplitude of different frequencies?
|
2011-02-18T03:40:40.437
|
10375
|
|atmega|rs232|max232|
|
<p>The RS232 specification requires a signal voltage of between -3 and -30V for a logical '1', and a signal voltage of between +3V and +30V for a logical 0, input impedance is around 3k and output impedance should be around 300 ohms.</p>
<p>If you're going to implement a fully complient interface then yes, you will need something like the MAX232 - or an alternative, like the MAX3221 which does come in a quite small TSSOP package.</p>
<p>Alternatively you could utilise one of the handshaking lines from the DTE (PC or similar) to supply the negative voltage and use a simple transistor level changer to handle the signal inversion (from the MCU) and level shifting. This does however require that the DTE is configured such that it's handshaking lines are in a suitable state.</p>
<p>Another option is to take advantage of the fact that most equipment these days implements RS232 using something like a MAX232 device. While these are fully complient with the specification they also extend things so that the input levels are basically +2.8 to +30 for a logical '0', +1.4 to -30V for a logical zero (from memory) - in other words the receivers actually include TTL signal levels. So you can just invert the signal on the UART pins and pass it out directly to the DTE device. This technique is used on quite a few devices including many handheld GPSes. I'm not saying you be 100% compatible but you'll find this works more often than not.</p>
<p>You still need to invert the UART signals (unless you're bit-banging the pins yourself), two inverters should be smaller than the MAX232 plus associated circuitry, but probably not by much.</p>
|
<p>I am trying to interface my ATmega chips to the computer using a serial interface. I have read that this can be done directly by connecting the appropriate pin between the chips and the serial pin. But it is advised that I use a MAX232 chip. What is the purpose of this chip and do I really need to use it?</p>
<p>I ask this because in a project I am making, there is a big size constraint and the chip might take up valuable space.</p>
|
Do I have to use a MAX232 chip?
|
2011-02-18T04:47:23.363
|
10394
|
|atmega|programmer|
|
<p>First, initial programming of AVR chips can not be done with RS232 serial RX/TX. This means that every chip with boot loader in it was either pre-programmed in the factory, or someone else has used some other way of programming to do it (SPI, JTAG, PDI).</p>
<p>My suggestion is to build a cheap 1$ parallel programmer with just few resistors, and then program some boot loader into the chip with RS232 or FTDI driver. That way programmer is not needed any more.</p>
|
<p>Hey people, I need to program the ATmega8 chips via serial. I understand that for doing that I would need to install a bootloader on the chip. And to install a bootloader, I would need a parallel port programmer. Am I right? Or can I just hookup the chip with an MAX232 to make a programmer? I am really confused right now. The best answer here would be a circuit.</p>
<p>UPDATE</p>
<p>He people I just found this <a href="http://www.qubbeks.puslapiai.lt/images/articles/AVR_programmer/avr_programatorius_schema.jpg" rel="nofollow">http://www.qubbeks.puslapiai.lt/images/articles/AVR_programmer/avr_programatorius_schema.jpg</a>. Do you think this is the kind of circuit which won't require any bootloading?</p>
|
Programming Atmega with serial port
|
2011-02-18T12:08:51.593
|
10396
|
|pcb|capacitance|
|
<p>Calculating the capacitance between two tracks edge to edge is not so easy, because it's not the parallel plate scenario so it's all fringing fields. <a href="http://chemandy.com/calculators/rectangular-capacitor-calculator.htm" rel="nofollow">This calculator</a> is for tracks over planes, with fringing taken into account. The same site has an inductance calculator which you should also take into account. Obviously both will depend on the length of track.</p>
<p>In terms of how much is too much, it will be clear when your pulses start to show a rounding effect which alter the received width of the pulses. So it depends on the tolerance of the receiver, at what point does it fail to receieve the signal correctly? You end up with a budget: the receiver tolerance has to allow for transmitter tolerance plus the transmission distortions.</p>
<p>In the end, you probably have to prototype it to find out, because it's not just the PCB track-ground capacitance that could affect the signal, there is capacitance between IC pins.</p>
|
<p>I'm routing some traces which carry high speed UART at 1.8432 Mbaud. The traces will be routed on the same layer as a power or ground plane (because it's a 2-layer design.) This will introduce capacitance.</p>
<p>My questions are:</p>
<ul>
<li>How much capacitance on average will a 6 mil trace with 6 mil spacing on each edge have? If there isn't a general rule, is there a way to calculate it?</li>
<li>How much capacitance is too much capacitance?</li>
</ul>
|
Trace-to-plane capacitance?
|
2011-02-18T12:45:37.767
|
10405
|
|microcontroller|library|tcp-ip|encryption|
|
<p>Consider these embedded SSL libraries:</p>
<p><a href="http://www.yassl.com/yaSSL/Products-cyassl.html">http://www.yassl.com/yaSSL/Products-cyassl.html</a></p>
<p><a href="http://polarssl.org/">http://polarssl.org/</a></p>
<p><a href="http://www.matrixssl.org/">http://www.matrixssl.org/</a></p>
<p>And maybe <a href="http://gitorious.org/tropicssl/">http://gitorious.org/tropicssl/</a></p>
<p>Tropicssl and polarssl originated from <a href="http://www.ohloh.net/p/xyssl">http://www.ohloh.net/p/xyssl</a></p>
<p>Tropicssl and xyssl are BSD licensed, whereas as all the others are GPL with an option for a proprietary license for $.</p>
|
<p>I am wanting make an embedded device that can communicate with a web-server in a secure fashion. My preference would be for it to use standard SSL so the web-server views my device similar to a web browser.</p>
<ul>
<li>Are there any prebuit libraries for
the embedded side to do this?</li>
<li>What about an IC that can handle the
handshaking and decryption for me?</li>
<li>If not how would I go about doing
this myself?</li>
</ul>
|
SSL from a Microcontroller
|
2011-02-18T16:14:42.570
|
10406
|
|audio|transistors|noise|bjt|
|
<p>For audio purposes I often use the IF3602. Its over $40 each and has a huge lead time, but is the lowest voltage noise FET I've ever seen: < 1 nV/rHz at audio frequencies and has a large input impedance.</p>
<p>A good BJT PNP is the SSM2210. With a few of these in parallel you can get an input referred noise of ~0.5 nV/sqrt(Hz) from 0.1-10000 Hz.</p>
|
<p>I found myself looking for a low-noise PNP transistor the other day.</p>
<p>I couldn't find any parametric searches that listed noise performance. Even from the transistor manufacturers. You can search by beta, \$V_{ceo}\$, and \$I_{c}MAX\$. All these searches seem to return a table of every general-purpose part in the manufacturer's portfolio. Not helpful.</p>
<p>This circuit needs to have low-noise at audio frequencies. RF transistors seems to be better characterized for noise, but they aren't necessarily low-noise at audio frequencies.</p>
<p>The best I have found was <a href="http://www.diyaudio.com/forums/solid-state/17285-ultra-low-noise-transistors.html" rel="nofollow">a forum thread at DIYaudio</a>, but the recommendations tended to be old-school, even obsolete parts. I'm looking for a mass produced transistor in SOT-23 or smaller.</p>
<p>So recommendations are welcome, but I'd really like to see a selection tool or parametric search that includes this information.</p>
|
Low-noise audio-frequency BJT?
|
2011-02-18T16:14:57.573
|
10411
|
|audio|switches|
|
<p>Uso 4066 analog switches. These make perfectly good audio analog switches (<a href="http://www.national.com/ds/CD/CD4066BC.pdf" rel="nofollow">See This</a>) and have been used even in high-end audio (my old Quad 44 preamp uses similarily specced chips). These have been around for a long time and there may be better moderen equivelents. You would need a good few to build up a large matrix but they are easy to drive from ttl/cmos, 5v/3.3v etc.</p>
|
<p>Modular synths have recently piqued my interest, but patch cords are hell. I have been thinking of some intelligent way to route signals - something microcontroller-driven and remembering different presets. I came across analog crosspoint switches - they are used to switch high-frequency signal, television and the like, and have 16 inputs and 16 outputs. They, however have unnecessarily high bandwidths (60+MHz) and prices ($30+/chip) for this.</p>
<p>I'm looking for a 16x16 switch (or a good way to implement one), suitable for modular synth use, and not having dedicated inputs and outputs - just 16 points which can be freely connected to one another.</p>
|
Crosspoint switch matrix for audio frequency signal?
|
2011-02-18T17:09:37.413
|
10413
|
|reverse-engineering|
|
<p>As to how the discovery is done in the US. No spies necessary. If your device happens to do something that looks infringing a patent (like has the same purpose or looks implementing something with some specific time or energy consumption or exposes some suspiciously similar buggy behavior) then in the US the patent holder can file a lawsuit claiming that you maybe infridge their patent and then the court orders to retrieve all possible documentation from you for further analysis. If that happens and there's any trail in your stored documents (blueprints, agendas, e-mails, whatever) you're likely to be found guilty in patent infridgement. This is the number one way - a suspicion is enough for requiring full blown documents disclosure. And of course patent holders will sometimes do analysis of actual chips and other devices.</p>
|
<p>I have seen patented hardware designs at the level of generic digital block such as shift registers, flip-flops and adders. If a chip maker were to include such a design deep within an ASIC, how can patent holders uncover copyright infringement? Do patent holders really go around planting industry spies to get blueprints, or engage in etching open mass produced chips to deduce internal logic?</p>
<p>On another note, is it ethical to glean ideas from patents and include it within commercial products?</p>
|
Patented hardware architectures
|
2011-02-18T17:18:02.310
|
10416
|
|rs232|max232|
|
<p>From the <a href="https://datasheets.maximintegrated.com/en/ds/MAX202E-MAX241E.pdf" rel="nofollow noreferrer">data sheet for the ESD protected version</a> under <em>Applications Information</em> (page 13):</p>
<blockquote>
<p>The MAX202E, MAX206–MAX208E, MAX211E, and MAX213E require 0.1µF capacitors, and the MAX232E and MAX241E require 1µF capacitors, although in all cases capacitors up to 10µF can be used without harm.</p>
</blockquote>
<p>and</p>
<blockquote>
<p>Use larger capacitors (up to 10µF) to reduce the output impedance at V+ and V-. This can be useful when "stealing" power from V+ or from V-.</p>
</blockquote>
<p>The <a href="https://datasheets.maximintegrated.com/en/ds/MAX220-MAX249.pdf" rel="nofollow noreferrer">data sheet for the non-ESD-protected version</a> doesn't include this information.</p>
<p>From reading the data sheets, I find the following differences between the MAX202E and MAX232E:</p>
<pre><code> MAX202E MAX232E
Icc mA 8 - 15 5 - 10
Iclk kHz 230 140
Caps µF 0.1 1
</code></pre>
<p>Otherwise, they seem to be the same.</p>
|
<p>this is just a quick and dirty question. I don't understand the purpose of the 1 \$\mu\$F caps in the MAX232 circuit. What do they do, exactly? Can they be skipped? Can they be swapped with 10 \$\mu\$F caps?</p>
|
Can I use 10\$\mu\$F caps in a MAX232?
|
2011-02-18T17:47:53.063
|
10431
|
|components|
|
<p><a href="http://www.houseofconnectors.com/berg-strip.htm" rel="nofollow">http://www.houseofconnectors.com/berg-strip.htm</a></p>
|
<p>I'm trying to attach certain components to my prototype board. However they have short pins, so it is hard to wire-wrap to them. Someone showed me something that you can insert the pins into to make them longer. They come in strips which can be divided. He called it something that sounded like "borgstrip", but that's not what it is. What is it called?</p>
|
What is the name of this electronic component
|
2011-02-18T19:44:28.017
|
10433
|
|multiplexer|
|
<p>A big difference between analog and digital multiplexers is that the former can be used <strong>bidirectionally</strong>, while the latter are <strong>unidirectional</strong>. That means that analog multiplexers can also be used as <strong>demultiplexer</strong>, while for digital you need separate ICs for that.
There are also several types, depending on the number of in/outputs: </p>
<p><strong>multiplexers (non-exhaustive)</strong><br>
8-input: <a href="https://assets.nexperia.com/documents/data-sheet/74HC_HCT151_Q100.pdf" rel="nofollow noreferrer">74HC151</a>, <a href="https://assets.nexperia.com/documents/data-sheet/74HC_HCT251.pdf" rel="nofollow noreferrer">74HC251</a>,<br>
dual 4-input: <a href="https://assets.nexperia.com/documents/data-sheet/74HC_HCT153.pdf" rel="nofollow noreferrer">74HC153</a>, <a href="https://assets.nexperia.com/documents/data-sheet/74HC_HCT253.pdf" rel="nofollow noreferrer">74HC253</a>,<br>
quad 2-input: <a href="https://assets.nexperia.com/documents/data-sheet/74HC_HCT157.pdf" rel="nofollow noreferrer">74HC157</a>, <a href="https://assets.nexperia.com/documents/data-sheet/74HC_HCT257.pdf" rel="nofollow noreferrer">74HC257</a>. </p>
<p><strong>demultiplexers (non-exhaustive)</strong><br>
3-to-8 inverting: <a href="https://www.diodes.com/assets/Datasheets/74HC138.pdf" rel="nofollow noreferrer">74HC138</a>,<br>
3-to-8 non-inverting: <a href="https://assets.nexperia.com/documents/data-sheet/74HC_HCT238.pdf" rel="nofollow noreferrer">74HC238</a>,<br>
dual 2-to-4: <a href="https://assets.nexperia.com/documents/data-sheet/74HC_HCT139.pdf" rel="nofollow noreferrer">74HC139</a>.</p>
|
<p>I am almost completely new to electronics. Recently I was reading about an 'analog multiplexer' I know what a multiplexer does, and how it works, but is there such a thing as a 'digital multiplexer' that would just give +5v when a channel was on?</p>
<p>Pardon if my question is malformed, I just started in on electronics two days ago.</p>
<p>REPHRASE:<br>
OK, so the difference is that a 'digital' multiplexer will just output +5/0, and an 'analog' multiplexer will just pass the input signal with as little distortion as possible ?</p>
|
Analog Multiplexer?
|
2011-02-18T22:03:10.547
|
10435
|
|pcb|
|
<p>I had same issue. I was trying to replace a bad cap and noticed they're all glued down to the circuit board with epoxy. Carefully cut the joint where the epoxy touches the bad piece with a dremel and try "rocking" the bad piece side to side with some pliers. </p>
|
<p>How to remove that capacitor from the board?</p>
<p><a href="http://vi-server.org/vi/_/cap1.jpg" rel="nofollow noreferrer">capacitor http://vi-server.org/vi/_/cap1.jpg</a></p>
<p>In the <a href="https://electronics.stackexchange.com/questions/10034/is-it-safe-to-keep-on-using-ac-adapter-with-a-damaged-output-capacitor">question about damaged power supply</a> I was told to use "a sharp utility knife", but it don't cut that thing (is it epoxy?). Also tried old not-so-sharp scalpel (it can punch that things if pressed hard, but not cut).</p>
<p><a href="http://vi-server.org/vi/_/cap2.jpg" rel="nofollow noreferrer">knife http://vi-server.org/vi/_/cap2.jpg</a></p>
<p>What other methods of removing it can you propose?</p>
<p><strong>Update</strong>: Mission accomplished:<br />
<a href="http://vi-server.org/vi/_/cap3.jpg" rel="nofollow noreferrer">removed capacitor http://vi-server.org/vi/_/cap3.jpg</a></p>
|
How to remove glued capacitor from the board?
|
2011-02-19T01:13:59.573
|
10438
|
|robotics|analog|
|
<p>As this question was resurrected by a misguided answer, let me take the opportunity to elaborate. </p>
<p>I actually bumped into <a href="https://en.m.wikipedia.org/wiki/Mark_Tilden" rel="nofollow noreferrer">Mark Tilden</a> for a few years in a row as a regular contributor to the Telluride Neuromorphic Workshop, from the time when he was still in Los Alamos until after he joined the WoWee Toys team. </p>
<p>Mark’s ideas are at the most informal edge of what’s considered <a href="https://en.m.wikipedia.org/wiki/Neuromorphic_engineering" rel="nofollow noreferrer">Neuromorphic Engineering</a>. His extremely simple robotic circuit creations (which he named BiCore Nervous Networks) are examples of the types of emergent behaviors that can be elicited when mechanics model themselves and interact with non-linear feedback system elements. At the time these ideas had already made it into orbit and the news, with his extremely simple circuits <a href="https://www.eetimes.com/document.asp?doc_id=1139665" rel="nofollow noreferrer">being used to keep a satellite aligned to the Earth magnetic field</a>, with a minimalist power expenditure. Do note that <a href="http://pweb.netcom.com/~mthorn/satbot00.htm" rel="nofollow noreferrer">this was in the mid 1990’s. </a></p>
<p>Although the guy is definitely a pioneer, his ideas lacked much of the academic rigor that is expected in science, and were always deemed more of a curiosity within a field that is thought of as a curiosity itself. These ideas seem to lack the theoretical foundation that would make it possible to build on top of (do note, that this is the same way as Neural Networks were perceived in the 1970’s). </p>
<p>At <a href="https://en.m.wikipedia.org/wiki/WowWee" rel="nofollow noreferrer">WowWee</a> he scaled up his insect creations which they called B.I.O. Bugs (we had dozens of these roaming around at the workshop), and the toy company (already a Hasbro subsidiary) became well known when it introduced first the Robosapien line and later a line of simple flying robots with the DragonFly.</p>
<p>Unfortunately, precisely because of the lack of theoretical foundation, these analog “insect brain” ideas were hard to work with, scale, and reliably integrate within a mass-market cost-driven application. It is my understanding that these initial toys actually used micro controllers programmed to emulate the analog behavior. </p>
|
<p>Years ago, I saw a program on TV about this guy who spent his free time building analog robots that looked and behaved very much like insects. I've been trying, without success, to find that or similar information.</p>
<p>Basically, I'm just looking for examples of how complex life-like behavior can arise in a system that has no "smarts", no thoughts, and no stated goals. It just happens that its component parts cause it to behave in a goal-seeking manner that appears life-like. Analog robotic insects seem like a great example of that type of phenomenon.</p>
<p>If anyone can point me to information about analog insect-like robots, that would be excellent.</p>
<p>If anyone can guess the specific TV program I'm talking about, that would be even cooler!</p>
|
Where can I find good examples of analog insect-like robots?
|
2011-02-19T02:04:39.893
|
10457
|
|dac|
|
<p>As others have pointed out, you have a high pass filter in the way. This may be in the DSP logic generating the output, but it's probably also in the form of a DC-blocking capacitor.</p>
<p>If you trace the circuit from the output jacks back to whatever IC is functioning as the DAC, you maybe be able to find and shunt the capacitor. </p>
<p>Depending on what kind of output you need, another trick might be to build yourself an AM radio... ie, you could use a diode and a capacitor (from signal to ground) to build an envelope demodulator and lowpass filter. You then modulate your signal by multiplying your samples by a carrier signal consisting of 1, -1, 1, -1, etc. There will be some distortion, but you should be able to get low frequencies out.</p>
<p>Also be aware that in using the audio input as a storage scope, you run the possibility that the problem is on the input instead, or there in addition to on the output.</p>
|
<p>I have created a wav file (sampling rate of 44.1kHz at 32-bit floating point precision) consisting of 44.1k samples at 0.0 followed by 44.1k at 1.0. After which the file is played out from line-out using Media Player Classic and looped back into line-in. The resulting waveform is captured and inspected using Audacity.</p>
<p>The output waveform goes from 0.0 to 1.0, holds it there for a number of samples and some how "decays" back to 0.0. What is going on? And how do I recreate the desired step waveform where it will persist at 1.0 for the second half of the waveform?</p>
<p>The brand of the sound card used in question is Realtek, PC is an Acer TravelMate 4720.</p>
<p>PS: This may seems like a PC question but I suspect it has more to do with sound electronics used on sound cards.</p>
|
PC sound generation of step waveform
|
2011-02-19T16:20:57.607
|
10464
|
|wire|rs232|cables|db9|
|
<p>I just had the same thing.</p>
<p>There is this cable which I've been using for about half a year now. I was convinced that it only had 3 wires. However, when I opened it today, I discovered it has 5 wires as well.</p>
<p>They are connected as follows:</p>
<p><strong>Male side:</strong></p>
<ul>
<li>pin 1 = brown + also connected to pin 8</li>
<li>pin 2 = red</li>
<li>pin 3 = orange</li>
<li>pin 4 = yellow + also connected to pin 6</li>
<li>pin 5 = black</li>
</ul>
<p><strong>Female side:</strong></p>
<ul>
<li>pin 1 = connected to pin 8</li>
<li>pin 2 = orange</li>
<li>pin 3 = red</li>
<li>pin 4 = yellow + also connected to pin 6</li>
<li>pin 5 = black</li>
</ul>
<p>I opened the cable because it was broken. And I noticed that the brown wire was disconnected on the female side. I assume that it needs to be connected to wire 1 though.</p>
<p><strong>Well, the basic 3 wires are there and in right position:</strong></p>
<ul>
<li>pin 5 to pin 5.</li>
<li>pin 2 and pin 3 are crossed.</li>
</ul>
<p><em>I had expected a simple loopback with pins 1,4,6 and pins 7,8 connected.</em></p>
|
<p>I stripped a DB9 extension cable which I will use to connect to a DB9 connector on one end and an RJ45 on another. I need to make connections to pin 2, 3, and 5 on the DB9 side.</p>
<p>When I stripped the DB9 wire, I was surprised to find 5 wires, since there are 9 pins in a DB9 connector. Why are there 9 pins but only 5 wires?</p>
<p>One of the wires is unshielded. Why is that? The other wires are red, brown, orange, and black. Which pins do these go to?</p>
|
Questions about wires in a DB9 cable
|
2011-02-19T21:55:42.640
|
10473
|
|power-supply|
|
<p>From your readings, the middle terminal is isolated from the others, and I would surmise that it's either <em>earth</em> ground (if your AC adapter has a ground terminal on it) or simply disconnected, so it can be ignored. For DC power all you need are two terminals, one each positive and negative.</p>
<p>What's what most people call "ground" is determined in context of the circuit you're powering, and it's <em>usually</em> negative--here, the right terminal.</p>
|
<p>I have an AC adapter jack that has three terminals, L(eft), M(iddle), and R(ight). If I plug in the power supply and connect the plug to the jack, these are the readings I get from the multimeter.</p>
<pre><code>L(red probe) M R(black probe) = +5V
L(black probe) M R(red probe) = -5V
L(red probe) M(black probe) R = 0V
L M(red probe) R(black probe) = 0V
</code></pre>
<p>So is the middle terminal ground? Or is ground the the right terminal? I heard that I only need to use two of the terminals when supplying power to components. Is this true?</p>
|
Which one is ground?
|
2011-02-20T02:34:25.643
|
10478
|
|low-power|indicator|
|
<p>If you want red, green, yellow, and black, you could perhaps get a set of automotive door-lock actuators, and mount them at right angles to each other. Have a yellow square that's always visible, and have the actuators slide red and green filters to either cover or uncover the square (both filters uncovering the square would yield yellow; red and green both covering would yield black; one or the other alone would yield that color). Automotive door-lock actuators are designed to operate off twelve volts, but they would probably work acceptably at lower voltages; they would simply take longer to switch colors.</p>
|
<p>The project I am working on requires a color indicator which shows the current state (either red, green, or yellow).</p>
<p>Ideally the indicator would have a large surface area so you can quickly glance at the device and determine the state. 2" x 2" would be nice.</p>
<p>The device is battery powered and would ideally be able to operate for months at a time without recharging.</p>
<p>What would be the best solution to use for this kind of application?</p>
|
What is the best low-power color indicator?
|
2011-02-20T04:03:24.813
|
10481
|
|avr|programmer|
|
<p>If you have a parallel port, try the <a href="http://www.xs4all.nl/~sbolt/e-spider_prog.html" rel="nofollow">SP12 programmer</a>. I used to use it without any problems, with just three resistors mounted inside a DB-25 shell.</p>
<p>I now use an Atmel Dragon, it's only $50 and you get in-circuit debugging as well programming. It also supports all the AVRs.</p>
|
<p>I have been trying to make a serial programmer for AVR chips. I have been using this schematic as reference, <a href="http://www.elektronika.lt/_sys/storage/2004/05/06/avr_prog.gif" rel="nofollow noreferrer">http://www.elektronika.lt/_sys/storage/2004/05/06/avr_prog.gif</a>.</p>
<p>I made the circuit and have checked that the connections are correct. Here is a picture of it on breadboard</p>
<p><img src="https://i.stack.imgur.com/kZNSg.jpg" alt="CKT on Breadboard"></p>
<p>The problem is it doesn't even get detected in linux.</p>
<pre><code>rick2047@Sophiya:~$ setserial -g /dev/ttyS*
/dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4
/dev/ttyS1, UART: unknown, Port: 0x02f8, IRQ: 3
/dev/ttyS2, UART: unknown, Port: 0x03e8, IRQ: 4
/dev/ttyS3, UART: unknown, Port: 0x02e8, IRQ: 3
rick2047@Sophiya:~$ dmesg |grep ttyS
[ 0.220488] serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
[ 0.221036] 00:08: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
rick2047@Sophiya:~$
</code></pre>
<p>In window there is a com3 and com1 but cannot connect to com3, it says check your port settings.</p>
<p>I checked the bios and there is only a Serial Port A in the peripherals section. Does that mean I can use only one serial? My monitor is an old CRT which runs on serial cable. </p>
<p><strong>UPDATE</strong>
The monitor is on VGA. So why does this not work?</p>
<pre><code>rick2047@Sophiya:~$ avrdude -p atmega8 -P /dev/ttyS0 -c ponyser -V -U flash:w:test1.hex
avrdude: AVR device not responding
avrdude: initialization failed, rc=-1
Double check connections and try again, or use -F to override
this check.
avrdude done. Thank you.
</code></pre>
|
Serial programmer not working, what are the possible problem sources?
|
2011-02-20T05:42:44.377
|
10485
|
|stepper-motor|
|
<p>Turning the system while energized will cause high currents to flow, but disconnecting it while operating will cause high voltage as the motor's magnetic field collapses. The high voltage is probably what will damage the driver. It is designed to handle high currents.</p>
<p>But turning a stepper like that is generally a bad idea. From <a href="http://www.cs.uiowa.edu/~jones/step/physics.html" rel="nofollow">Jones on Steppers</a>:</p>
<blockquote>
<p>It is also worth noting that the best way to demagnetize something is to expose it to a high frequency-high amplitude magnetic field. Running the control system to spin the rotor at high speed when the rotor is actually stalled, or spinning the rotor at high speed against a control system trying to hold the rotor in a fixed position will both expose the rotor to a high amplitude high-frequency field.</p>
</blockquote>
|
<p>I have a <a href="http://www.interinar.com/vexta-pk266-02a.html">stepper motor</a> and I've noticed that when I turn the spindle with the motor lead wires touching each other, that the motor strongly resists my efforts to turn it. When the wires are not touching each other the motor turns more freely. I have inferred from this that the current that is induced from my attempts to turn it is so strong that once it is feed back into the motor, it resists the turning motion. </p>
<p>Now that I have connected the motor to a <a href="http://www.sparkfun.com/products/10267">driver</a>, it is my expectation that turning the spindle would not cause damaging current to be feedback into the driver to destroy it. I am concerned that turning the spindle would damage the driver because the driver's documentation states that disconnecting the motor while the system is on will damage the driver IC.</p>
<p>My question is: Can turning the spindle while connected to the driver cause damage to the driver?</p>
|
Induction voltage from a Stepper Motor
|
2011-02-20T19:51:41.920
|
10487
|
|power-supply|potentiometer|switch-mode-power-supply|dac|
|
<p>The feedback pin is expecting a DC error voltage, with some usual stuff (ripple, noise, etc.) riding on it. The analog voltage loop is bandwidth-limited so that only useful information is used to determine the duty cycle of the converter.</p>
<p>The easiest way is to use a DAC output and a series resistor to either sink or source amount of current out of / into the FB node. The size of the injection resistor will determine the adjustment range. The FB reference voltage is 1.23V, so as long as the DAC can go above and below that reference, you can control the voltage both up and down.</p>
<p>This is the digital equivalent of having the bottom resistor adjustable.</p>
|
<p>I want to make a battery powered, adjustable SMPS for use in situations when I cannot have an outlet near me, so I would like some more information or suggestions about this topic. The SMPS chip I am basing this off is a <a href="http://www.national.com/profile/snip.cgi/openDS=LM2733" rel="nofollow noreferrer">LM2733</a>.</p>
<p>The power source would be a LiPo, voltage output 3V to 25V, and at most 500mA.</p>
<p>There are a few ways I think I can control a SMPS chip digitally: one is a digital pot controlled with a MCU via SPI or I2C. A 1024 step pot would give me 20mV stepping, which is more than enough. What I saw in datasheets is that the pots are only able to go up to 5V for the digital resistor. <em>Would that be a limiting factor in such a design?</em> This way seems the simplest and least demanding way from what I see.</p>
<p>Another way would be using a DAC, but I am not sure if it would need to go faster than the switching speed of the SMPS, because in data sheets I always see the voltage dividers before the output capacitor. Problem is that I do not know what the feedback pin wants to see. <em>Does it want the entire ramp up and down from the inductor and compare it to the reference voltage, or does it just find the average voltage of each cycle?</em></p>
<p>I know it is similar to <a href="https://electronics.stackexchange.com/questions/6510/using-a-digital-potentiometer-with-a-smps">{this question}</a>, but I'm looking for some more information or discussion.</p>
|
Different ways to digitally control an adjustable SMPS
|
2011-02-20T20:48:47.583
|
10490
|
|arduino|wireless|sparkfun|
|
<p>If your data is infrequent bursts, then you should be able to resend it at a lower data rate, using any micro controller which has two UARTs and enough memory to store an entire burst. You could probably even do it with some tiny single-UART parts by bit-banging the slow side.</p>
<p>As long as you can resend on the slow side before new data comes on the fast side, I don't think you should have any problem. And your delays should be deterministic within a few clock cycles so you may not need the timestamp (or does that wireless link do resend on error?)</p>
|
<p>I'm building a MindFlex-based EEG. Basically, I'm sniffing a 9600bps bus, analyzing the data with an Arduino*, and sending it to Processing/Java for display. To make it absolutely isolated from mains power, I want to make it wireless, but the only wireless gear I can afford (<a href="http://www.sparkfun.com/products/8946" rel="nofollow">transmitter</a>, and its matching <a href="http://www.sparkfun.com/products/8949" rel="nofollow">receiver</a>) transmits at 2400bps. I think that if I move the Arduino into the headset, I can make a SoftSerial connection at 2400bps to operate the transmitter, then use hardware serial at 9600bps to talk to the headset. That way, I can hook up a reciever to a FTDI USB-TTL adaptor and send the data to Processing.</p>
<p>Will that work? If it helps, new data comes from the headset about once per second, and I plan on implementing a timestamp into the data from the Arduino, so lag shouldn't be too much of an issue. I also cannot afford XBees, Bluetooth, or anything else.</p>
<p>*Before anyone says anything, if wireless works, I will use an Arduino Pro Mini, and if it doesn't I'm going to use a BoArduino - I'm not throwing an entire Uno at this project. </p>
|
Wireless UART Speed Shift
|
2011-02-20T23:25:23.490
|
10498
|
|arduino|serial|
|
<p>With SoftwareSerial you use <code>overflow()</code> to check for overflow...</p>
<pre><code>if ( myport.overflow() ) {
// The input buffer overflowed
}
</code></pre>
<p>See: <a href="https://www.arduino.cc/en/Reference/SoftwareSerialOverflow" rel="nofollow">SoftwareSerial: overflow()</a>.</p>
|
<p>Can I detect whether bytes are getting dropped by the Arduino Serial driver because of buffer overflow (i.e. if I'm not keeping up with my input stream)? If so, how?</p>
|
Arduino Serial Buffer Overflow
|
2011-02-21T05:37:35.583
|
10500
|
|avr|usb|sleep|
|
<p>IIRC electrically you just have to toggle the pull-up resistor connected to D+ (or was it D-) so I would try manually setting and clearing (with a small delay in between) the DETACH bit in the UDCON register.</p>
<p>In both the LUFA and V-USB libraries there were no problems with disconnecting and reconnecting to USB from software. I guess USB_Init did this by itself in those.</p>
|
<p>I am using an AVR at90usb1286-based <a href="http://www.pjrc.com/teensy/" rel="nofollow">Teensy++ 2.0</a> to periodically read data from a few sensors. In its final form, my project will act based on the sensor inputs. For now, I log the results to the USB port.</p>
<p>Because the measurement interval is relatively long I am placing the microcontroller in powersaving sleep between measurements and using the watchdog timer to wake up periodically. This works just fine, but after waking up the USB connection does not work anymore and I have found no way to get it back</p>
<p>I am using PJRCs <a href="http://www.pjrc.com/teensy/usb_debug_only.html" rel="nofollow">Debug Only USB library</a> together with their host-side component <code>hid_listen.exe</code>.</p>
<p>Because of its debug function, I would like the solution to impact as little as possible the structure of the code.</p>
<p>I have tried three strategies so far:</p>
<ol>
<li>Entering powersaving sleep (SLEEP_MODE_PWR_SAVE) without any special precautions. I get an "USB Device Not Recognized" error from windows7 and no additional communication is possible.</li>
<li>Entering a sleep mode that keeps the USB active (SLEEP_MODE_IDLE). In this mode the USB keeps functioning, but the sleep is interrupted pretty much immediately.</li>
<li>Entering powersaving sleep (SLEEP_MODE_PWR_SAVE) and trying to re-initialize the USB afterward by calling <code>usb_init()</code>. This does not seem to have any effect.</li>
</ol>
<p>Here is a simplified application that shows the problem, adapted from <a href="https://www.mainframe.cx/~ckuethe/avr-c-tutorial/#watchdog" rel="nofollow">this lesson 13</a></p>
<pre><code>#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/wdt.h>
#include <avr/power.h>
#include <avr/sleep.h>
#include "usb_debug_only.h"
#include "print.h"
ISR(WDT_vect, ISR_NAKED){
_WD_CONTROL_REG = _BV(WDIE); // must reset interrupt after trigger
/* do other work inside the watchdog interrupt? */
PIND = _BV(PD6); /* toggle the pin */
reti();
}
int main(void){
DDRD = _BV(PD6);
PORTD = _BV(PD6);
/* watchdog setup goo */
wdt_enable(WDTO_1S);
_WD_CONTROL_REG = _BV(WDIE); /* generate watchdog interrupts */
usb_init();
sei(); /* enable interrupts */
while(1){
set_sleep_mode(SLEEP_MODE_PWR_SAVE);
sleep_mode();
print("a");
usb_debug_flush_output();
/* Do stuff after the watchdog wakes us up */
}
}
</code></pre>
<p><strong>Questions</strong></p>
<p>Considering the given hardware, what are good strategies to put the controller into a sleep state while maintaining some form of debug output capability?</p>
<p>I am not concerned about power consumption, as the USB will be inactive in battery-powered production mode. However, I do wish to be able to get some debug output while I'm writing the program...</p>
|
AVR (at90usb1286) sleep and USB
|
2011-02-21T11:22:36.857
|
10504
|
|sensor|temperature|calibration|
|
<ol>
<li>Using mix of distilled water and crasched ice (much of ice = almost no floating) You will get relatively easily 0 deg C with uncertainty below 0.2 deg C (0.005deg C achievable). Insert sensor 15 cm minimum, better 20..25cm (to cool sensor cable), and mix mixture from time to time. Wait few minutes until readings stabilize. </li>
<li>90 deg 'C : borrow 50..100'C thermometer with 0.1deg /div or 0.2dev/div resolution from chemical laboratory. Put both thermometers close to each other to pot with hot water. Mix water with spoon. You should get uncertainty below 0.3deg. Boiling point of water can give similar accuracy, but is more difficult to get, and as mentioned by others, requires corrections for altitude and barometric pressure at sea level (or barometric pressure at Your laboratory).</li>
</ol>
|
<p>I am using an LM35 temperature sensor, which produces an output of 10.0 mV/°C. My circuit will handle temperatures up to around 90C</p>
<p>What can I do to check the LM35 output, and maybe fine tune it for accuracy? Are there any non hazardous easy to obtain chemicals that boil below 100C?</p>
<p>Or if I am forced to change the circuit to handle temperatures up to 100C would sticking the suitably waterproofed sensor in a pan of boiling water be sufficient to calibrate it?</p>
<p><strong>Note</strong></p>
<p>I am not looking for 0.1C accuracy, 0.5 will do.</p>
<p><strong>Update</strong></p>
<p>All interesting answers, thanks, but the simplest solution seems to be changing the circuit to allow 100C as a close enough calibration point</p>
|
How to calibrate a temperature sensor
|
2011-02-21T13:02:29.840
|
10513
|
|capacitor|resistors|components|storage|
|
<p>I use those cabinets, too. I need to keep them at an optimum volume. I spread the same-kind parts into many cabinets according to their values, as if the cabinets were empty. Than do same thing for different kind, superposing to the previous placing. Meanwhile optimizing their places for easier distinguishing. Despite sometimes I need to pour the parts into table :-) generally it works nice.</p>
|
<p>I've got one of <a href="http://www.treston.com/index.php?article_id=1826&__from_id__=3072&product_group=5110">these cabinets</a>, which I intend to use for storing electronic components:</p>
<p><img src="https://i.stack.imgur.com/PZrV8.jpg" alt="enter image description here"></p>
<p>It has 24 drawers (each 175 x 69 x 37mm).</p>
<p>Every drawer can be subdivided into up to six compartments by installing dividers.</p>
<p>Can you suggest a good system for organizing resistors, capacitors and suchlike into the limited number of drawers that's available?</p>
|
Organizing electronic parts?
|
2011-02-21T17:39:51.563
|
10528
|
|microcontroller|avr|c|keyboard|
|
<p>Yes, a <a href="http://en.wikipedia.org/wiki/Keyboard_matrix_%28music%29" rel="nofollow">matrix with diodes</a> is exactly how it is done.</p>
<p>I'm going to assume you select select one column at a time by driving it low, let all the other columns float (open-collector) (or drive all the other columns high),
and your <a href="http://geekhack.org/showthread.php?t=9181" rel="nofollow">row input pins have pull-up resistors</a>.</p>
<p>In principle, super-brief keytaps would be missed if the MCU doesn't select that column during the entire interval from the time the key is pressed until the time the key is released.
In practice, humans are so slow that even when they try to quickly tap a key,
a typical keyboard encoder with a fairly slow MCU will scan through every column dozens of times during that interval.
The typing speed world-record is 1075 keystrokes over the course of 1 minute.
That's an average of slightly more than 1 keystroke per millisecond on average.
Almost certainly some keys were held down longer, and others shorter,
but as long as you're not trying to beat the world record,
I suspect that a keyboard scan time of 100 microseconds is more than fast enough.
A 16 MHz processor should be able to scan every column in 100 microseconds or less fairly easily.
In fact, some low-quality buttons have "keybounce" for so long that you may get several (false) key-presses and key-releases when a human tries to push the button one time, requiring extra complexity in hardware or software to make sure it is interpreted as a single keypress.</p>
<p>Most keyboard encoders simply scan the keyboard over and over (polling), selecting only one column at a time.</p>
<p>Low-power keyboard encoders drive <em>all</em> the columns low,
set up an interrupt to wake them up if <em>any</em> row goes low,
and then go to sleep.
When they wake up, they scan the keyboard over and over (polling),
selecting only one column at a time,
until no keys are being pressed,
then go back to sleep.</p>
|
<p>For my first hardware hack I'm taking a stab at a 'mechanical keyboard from scratch' (where scratch means individual components).</p>
<p>I plan to use a teensy++ board (16MHz) and was wondering about how to scan for key presses, so far I was thinking of using a grid (matrix) for the keys, every row is an out pin and every column is a in pin, the switches connect them (along with a diode for limiting the direction of current to lessen ghosting).</p>
<p>So there would be a scanning cycle, during which a column is set to high (or low, depending) and then every row is tested for this value. My question concerns whether or not this would be accurate enough, it means that the switch has to be closed at the exact moment that row and column are checked otherwise the key wont be registered at all. Is this how it is done or is there some much better approach?</p>
<p>There is also the issue of key bounce, so either a delay between checking the same key (could be a result of the scanning loop) and/or a counter where a certain key to be activated a number of times.</p>
|
'keyboard from scratch' registering key presses
|
2011-02-22T01:12:31.560
|
10535
|
|high-voltage|battery-charging|
|
<p>We did this about 22 years ago ,when solar cells were much more expensive and less efficient .The unit was birdsnested and bench tested using a middle of the road fence energiser.It did trickle charge a 12V SLA battery.The reasoning was that 10J was typical for an electric fence and they beat at roughly 1 pulse per second .This implies that you could harvest say up to 1 watt without dropping the fence peak volts too much .I used a transformer out of a dead electric fence backwards.There were some power electronic components between the transformer low voltage winding and the battery but nothing expensive exotic or tricky .The bench tests implied good grounding which is not unreasonable because many electric fences have the bottom wire grounded anyway.This never went into production because there was not sufficient demand at the time.</p>
|
<p>Many farms use electric fences to discourage animals breaking through to neighbouring paddocks.</p>
<p>These electric fences have regular (say once per second) high-voltage spikes of between around 100 V and 120 kV.</p>
<p>Would it be possible to "harvest" this as a power supply for remotely-deployed electronics? e.g. a coil wrapped round the electric fence wire, with a high resistance to ground, trickle-charging a battery.</p>
<p>Ideas welcome.</p>
|
Harvest power from an electric fence
|
2011-02-22T02:20:58.537
|
10538
|
|voltage-regulator|
|
<p>If you want to stay with linear there's the <a href="http://www.national.com/ds/LM/LM123.pdf" rel="nofollow">LM323</a>. I can deliver up to 3A, and can dissipate up to 30W, thanks to a TO-3 package. </p>
|
<p>I have been looking at a lot of different regulators. Generally speaking switching regulators will give me a wide range of input voltages at the out put amps I am looking for with added efficiency. However, the simplicity of a linear regulator is really appealing for the project that I'm looking at. The problem that leaves me with is that most linear regulators will do between 0.5 and 1.5 amps. Is there a way to hook up two regulators so that they provide my 5 volts with their combined amp output like with batteries?</p>
|
Regulator solution for 5 volts at +2ish amps
|
2011-02-22T03:53:50.997
|
10546
|
|communication|rs232|mbed|
|
<p>If you have the mbed module - <a href="http://mbed.org/handbook/Serial" rel="nofollow noreferrer">check this page out</a></p>
<p>the easiest code for it to test would be</p>
<blockquote>
<p>include "mbed.h" <br>
Serial device(p9, p10); // tx, rx<br>
int main() {<br>
device.baud(19200);<br>
device.printf("Hello World\n");<br>
}<br></p>
</blockquote>
<p>Hope this helps</p>
|
<p>I'm using an external power source to power an MBED module. I have the UART transfer and receive ports connected to a MAX232 level switcher in order to make the signals compatible with RS232. From there the wires go to an RJ-45 connector, which goes to a DB9 connector that is connected to a USB-DB9 converter. This is connected to the laptop.</p>
<p>With this setup, I should be able to program the CPU to write text which will appear in a terminal program like HyperTerminal in Windows, correct? I've tried several things, but haven't been able to get any input in HyperTerminal. What's a simple program I can use to test my setup?</p>
|
Using a laptop to communicate with an MBED module
|
2011-02-22T07:05:42.093
|
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