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electronics.stackexchange.com

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5854

|buying|

<p>I think Digi-Key does this; check <a href="https://ordering.digikey.com/Help.aspx?WT.z_homepage_link=hp_BOM&amp;id=New%20BOM%20Wizard&amp;site=US&amp;lang=en" rel="nofollow">their BOM manager</a>.</p>

<p>I want to buy components from places like Farnell, Mouser, etc. But I then want to distribute them in kits, each kit would have maybe 10 of each component; the components are tiny 0603 types. </p> <p>The problem is, there are nearly 50 bags in each kit, and removing the required components from the right bag and rebagging them sounds like it will take a long time, and it seems wasteful as many distributors already have these bagging facilities. It's also not an option to make an order for each kit, because that's looking to be £50 each.</p> <p>So do any distributors offer the option of splitting each order into little bags? I've already shot off an email to Farnell about this possibility, but I'm not hopeful - I'm wondering if any distributors just offer it as an option on their website somewhere.</p>

Do any distributors pack in bags of 10 or so?

2010-10-30T00:11:02.033

5855

|avr|isp|

<p>Use a jumper or a switch so that you can physically disconnect the ICSP header. This way you can share the pins with other functions without worrying, and without having to fiddle with your other components.</p> <p>This seems like the most obvious and safest solution, and it's what I use.</p> <p>(My first answer was deleted, so I have tried to add more detail).</p>

<p>My usual method of reprogramming AVRs (so-far limited to ATtiny13 and ATtiny2313) is to disconnect the chip from the host circuit, plug it into another breadboard with all of the ICSP hookups in place, program, then replace. However, I keep hearing that one can program the chip in place (which is, I understand, the whole point of ICSP).</p> <p>Are there any special hardware considerations one has to take into account before programming the chip in situ? For instance, I worry that the ICSP process may damage circuit components connected to the same AVR pins which are used for ICSP. Does one occasionally need to add diodes or some other kind of buffering to protect these components?</p> <p>I know this question sounds kind of vague, and I guess it is - but I've not provided details of my particular circuit because I'm interested in more general rules of thumb. I.e. does one never have to worry about this, or does the answer really depend on the particular circuit the MCU is a part of?</p>

How do I plan for in circuit programming of an AVR?

2010-10-30T01:20:57.523

5858

|resistors|dac|

<p>If you have a spare PWM output on your micro, driving it into an RC filter will be the cheapest way to do this, and will take up very little space. This will be slower than the resistor arrays though. </p>

<p>I can either use an R-2R divider or a R = 2^N divider to get a 5-bit DAC.</p> <ol> <li>Which will be more accurate? R = 2^N I suspect, but;</li> <li>Which will be cheaper? I think R-2R because it can use standard values, but...</li> <li>I've heard R-2R have issues with monotonicity, when the output doesn't change for the same amount with each count. Would this be an isuse with 5-bit DAC - would any such monotonicity simply be overwhelmed by divider error?</li> <li>There's also the trade off of size, R = 2^N will be larger.</li> <li>Also there's the possibility of using an IC to do this. I'd be open to doing this as well, if it wasn't very big and could be interfaced over I2C.</li> </ol> <p>The DAC is going to be used to feed a comparator. The comparator will use this reference to compare against an incoming video signal.</p>

Best/cheapest way to cheaply get a 5-bit DAC: R-2R, or R = 2^N

2010-10-30T02:08:56.440

5871

|microcontroller|

<p>There is no need to use a DAC. Voltages are used to represent 1's and 0's by the convention that anything under 0.8V (AKA 'low') is a zero, and anything over 2.4V (AKA 'high') is a one. It's relatively simple to construct circuits that perform logic on these representative voltages. </p> <p>For example, a circuit can output something in the 2.4V to 5V range to represent '1' if either input is over 2.4V, or something less than 0.8V otherwise, and you have an OR gate. If it requires <em>both</em> inputs representing 1 in order to output 2.4V, you have an AND gate. An inverter just outputs a high when the input is low, and vice-versa. You can build simple gates like these with just a very few transistors, and perform combinatorial boolean logic. By using groups of bits to represent numbers, you can even build circuits to add numbers with combinatorial logic, no software required.</p> <p>Once you are working with gates, you can construct flip flops, and from them, registers and counters. Flip-flops allow you to store 1's and 0's from one point in time and use them later on. Registers and counters are circuits that perform functions on groups of bits that represent numbers. A register holds a number until you load a new number into it. A counter is like a register, but has another input that causes the stored number to increment. (Decrement is possible too). This puts you in the realm of state machines and sequential logic, still, no software required.</p> <p>Memory systems are a way to store massive numbers of bits. At a component level, some memory is built like a huge collection of flip-flops, but more commonly there is another technology (DRAM) that, while not exactly a flip flop, does the same thing.</p> <p>As a further step, you can build a system of sequential and combinatorial logic that can carry out operations depending on the bits stored in a memory system, including writing back new values to that memory system. Now you've arrived at the level of the processor, and everything the processor does, is just hardware carrying out lots of simple tasks. (microprogrammed cores notwithstanding). At this point, the particular combinations of bits that you put in the memory system can be considered machine language software.</p>

<p>This is about how micro controllers work in general.. </p> <p>The programming that we do is converted into 1's and 0's by the compiler and these machine understandable code are then loaded to the microcontroller.. </p> <p>How does the microcontroller respond to this.. I mean are these 1's and 0's converted into corresponding logic voltage (5v and 0) by DAC? If its like that, how does this small piece of silicon decide what to do with these various combinations of 5v and 0v?</p> <p>I understand that every single IC is made of logic gates and these gates are composed of transistors.. So how does these transistors respond to various combinations of 5v and 0v?</p> <p>What makes them look for these logics.. I mean how they monitor these instructions when they are powered on?</p> <p>So certainly there got to be an Operating System loaded into the mcu that tells it to process and how to process these instructions, isn't?..</p> <p>Next thing is.. consider a timer.. it is simply a register that increments by one after each clock cycle.. Isn't the OS again that instructs the mcu to increment after each clock? Am I right? In that case, in what language, all the code for a operating system is written? </p> <p>I can just proceed my work with programming the mcu for different tasks but today I was interested to know how my code is understood by this machine..</p> <p>Sorry that my question is lengthy to read.. please help me learn these basic things..</p> <p>Thanks in advance.. </p>

How do the Active High and Active Low signal work in Embedded Systems?

2010-10-30T07:37:00.657

5882

|arduino|avr|avrdude|jtag|isp|

<p>I believe I may have found a two part solution for my particular problem. I currently own an Arduino Diecimila (which has the ATMEGA168 with the problem) and also a new Arduino Nano 3.0. I went ahead and flashed the Arduino Nano with the <a href="http://arduino.cc/en/Tutorial/ArduinoToBreadboard" rel="nofollow">ArduinoISP</a> firmware. I then picked up 3 28 Pin ATMEGA328P DIP chips for $5.00 each at the local electronics store.</p> <p>I used the ArduinoISP to flash one of the virgin chips with the Arduino Firmware using the above link with a crystal. I plan to now flash one of the other ATMEGA328Ps with the <a href="http://mightyohm.com/blog/2008/09/arduino-based-avr-high-voltage-programmer/" rel="nofollow">High Voltage Programmer</a> firmware. This chip along with a bit of wiring on a breadboard should allow me to reset all of the fuses on the original ATMEGA168. Once that is done, I will be able to use the Arduino Nano to reprogram the chip.</p> <p>Since the ATMEGA328Ps only cost $5 each, my end goal is to setup one 328 as an Arduino ISP programmer, setup the 168 as a HV Programmer, keep one 328 chip in my current Arduino Diecimila (upgrade!!), and I'll have one left over for whatever. I can then either switch chips on the Diecimila or build out a real board for the ISP and HV Programmer boards.</p> <p>I still have not tested the JTAG ICE MKII yet with a logic/oscilloscope. Not sure if it is the root of the problem or not. I will address this issue after I build the HV Programmer.</p> <p>I will report back on the success/failure of the HV Programmer. I just need to go get a few more 1K resistors to pull it off. Anyone ever tried the HV Programmer? Any other suggestions? If nothing else, hope this helps someone.</p>

<p>Two weeks ago, I pulled out my AVR JTAG ICE MKII and successfully burned a few C programs to my Arduino through AVRStudio 4 SP3. Everything was working very well.</p> <p>Life caught up to me and I did not touch the Arduino or JTAG until yesterday. I decided that I wanted to play with a few XBees. Downloaded XCTU to update firmware and what not. I realized I needed to reinstall Arduino firmware back on the Diecimila to use the Arduino-XBee shield to update the firmware. I attempted to load the original Arduino boot loader hex file via the JTAGICE2 with AVRProg in AVRStudio and ran into a problem that I have been unsuccessful in solving for the past 9 hours.</p> <p>I switched over to AVRDude so I could see verbose output. Every time I use AVRDude to program the ATMEGA168, I get the following:</p> <pre><code>avrdude: AVR device initialized and ready to accept instructions Reading | | 0% 0.00savrdude: Send: u [75] [20] avrdude: Recv: Reading | ################################################## | 100% 0.05s avrdude: Device signature = 0xffffff avrdude: Yikes! Invalid device signature. Double check connections and try again, or use -F to override this check. </code></pre> <p>I also received:</p> <pre><code>avrdude: jtagmkII_setparm() avrdude: jtagmkII_setparm(): Sending set parameter command (parm 0x03, 1 bytes): 0xa0 (1 bytes msg) avrdude: jtagmkII_setparm(): bad response to set parameter command: RSP_FAILED avrdude: jtagmkII_getsync(): ISP activation failed, trying debugWire avrdude: jtagmkII_setparm() avrdude: jtagmkII_setparm(): Sending set parameter command (parm 0x03, 1 bytes): 0xac (1 bytes msg) avrdude: jtagmkII_setparm(): bad response to set parameter command: RSP_DEBUGWIRE_SYNC_FAILED avrdude: failed to sync with the JTAG ICE mkII in ISP mode avrdude: jtagmkII_close() avrdude: jtagmkII_close(): Sending sign-off command: avrdude: usb_fill_buf(): usb_bulk_read() error error reaping URB: No such device avrdude: jtagmkII_recv(): Timeout receiving packet avrdude: jtagmkII_close(): timeout/error communicating with programmer (status -1) </code></pre> <p>While using the JTAGICE2, I was connecting its 6 pin header to the ICSP header on the Arduino. I would plug in my 12VDC wall wart first to the Arduino, then turn on the USB connected JTAGICE2, and then open AVRStudio or use AVRDude in DOS to attempt programming. Both programs never had a problem with the jtag itself...just the target. During the JTAGICE2 issue, I would use the following command:</p> <pre><code>arduino-0021...\avr\bin&gt;.\avrdude -C .\avrdude.conf -p m168 -c jtag2isp -P usb:64:b0 -vvvv -b 19200 -t </code></pre> <p>or</p> <pre><code>arduino-0021...\avr\bin&gt;.\avrdude -C .\avrdude.conf -p m168 -c jtagmkII -P usb:64:b0 -vvvv -b 19200 -t </code></pre> <p>After quite a few hours without success, I finally pulled out a Arduino Nano v3.0 (ATMEGA328P) and blasted ArduinoISP on it via the latest Arduino Wiring. Connected wires correctly according to the <a href="http://arduino.cc/en/Tutorial/ArduinoISP" rel="nofollow">Arduino.cc (First 'Schematic')</a> website and attempted to upload the bootloader to the Diecimila again. This time I tried the following avrdude command:</p> <pre><code>arduino-0021\..\avr\bin&gt;.\avrdude -C .\avrdude.conf -p m168 -c avrisp -P com4 -b 19200 -vvvv -t </code></pre> <p>I continue to receive the same error. The weird thing is that the last program I loaded 2 weeks ago on the Diecimila works perfectly fine. I just cannot get the darn thing off of there!</p> <p>The fact that the error mentioned that the Device Signature of the ATMEGA168 chip is 0xffffff worries me.</p> <p>Now I believe this problem may be occurring for a few different reasons:</p> <ol> <li>While programming the Arduino two weeks ago with AVRProg &amp; JTAGICEMK2, maybe fuses were set. I can however tell you that they were in whatever default state AVRProg uses as I NEVER screwed with the fuses tab at all. My most plausible explanation however, is that ISP has been disabled via fuse.</li> <li>Somehow hardware may have been damaged causing the programming capability to not work. I do not know of any damage I did but cannot rule that out.</li> <li>The JTAGICEMKII may be damaged...although receiving the same error using ArduinoISP should disprove that possibility</li> <li>During Google research, I read that the JTAG ribbon cable has major touchy issues. Not sure if this is a serious problem or not.</li> </ol> <p>Well I am officially at a loss. I hope I included all necessary information. I am running this setup off of a stable Windows 7 64bit PC using the latest Arduino, AVR ToolChain, and AVRStudio software available as of two weeks ago. In case it was my desktop computer, I also downloaded Arduino D/L and libusb-win32 on my Vista laptop, attempted AVRDude query using first DOS command and received the first error listed above. Do I just need to buy a new chip? I know they cost nothing but I would prefer to save it and learn from my mistake so I can fix it next time or avoid the problem all together.</p> <p>Do you have any suggestions that might help? Thanks in advance for your reply.</p>

Arduino Diecimila (ATMEGA168) + JTAG ICE MKII Hell..Did I Fry the Chip?

2010-10-30T11:08:41.017

5884

|fpga|

<p>Yes, FPGAs are excellent for implementing massively parallel things. Many people have put 8 or more CPUs on a FPGA -- it's not merely "in principle".</p> <p>Check out the floorplan image in the article <a href="http://www.design-reuse.com/articles/21583/processor-noc-fpga.html" rel="nofollow">"A 24 Processors System on Chip FPGA Design with Network on Chip"</a> by Zhoukun WANG and Omar HAMMAMI.</p> <p>That floorplan makes it pretty obvious that that particular FPGA is pretty much packed full of stuff. The 24 CPU cores -- each one a 32 bit MicroBlaze CPU with 32 KByte total of local instruction and data memory -- fill up roughly half the FPGA (around the perimeter). The routing between the CPU cores and the 4 independent external buses pretty much fills up all the rest of the FPGA. (The external buses are each 64 data bits wide plus some control signals, each one leading to an independent DDR2 memory module).</p> <p>(This particular IC also includes two PowerPC 405 CPU hard cores in addition to the FPGA fabric -- Zhoukun and Omar apparently didn't bother using them).</p> <p>As other people here have pointed out, dividing "number of gates in a FPGA" by "number of gates in a CPU" is overly optimistic. In this case, 142,128 LUTs on a Xilinx FPGA Virtex-4 FX140 divided by about 1000 LUTs required for a minimum-size MicroBlaze gives (optimistically) 142 CPUs per chip. So are you disappointed that apparently "only" 24 CPUs fit in that FPGA fabric (not counting the two PowerPC 405 hard cores outside the FPGA fabric on that IC)?</p> <p>A 1 million gate FPGA divided by a 50k gate CPU gives (optimistically) 20 CPUs per chip. I think you will be lucky to squeeze even 4 CPUs onto that FPGA.</p> <blockquote> <p>"It is amazing what you can squeeze onto these parts if you design the machine architecture carefully to exploit FPGA resources. In contrast, there was a very interesting article in a recent EE Times by a fellow from VAutomation doing virtual 6502's in VHDL, then synthesizing them down into arbitrary FPGA architectures. Although the 6502 design used only about 4000 "ASIC gates" it didn't quite fit in a XC4010, a so- called "10,000 gate" FPGA. That a dual-issue 32-bit RISC should fit, and a 4 MHz 6502 does not, states a great deal about VHDL synthesis vs. manual placement, about legacy architectures vs. custom ones, and maybe even something about CISC vs. RISC..." -- <a href="http://www.fpgacpu.org/usenet/homebrew.html" rel="nofollow">Jan Gray</a></p> </blockquote> <p>The <a href="http://en.wikipedia.org/wiki/soft_microprocessor" rel="nofollow">Wikipedia: "soft processor" article</a> has more information on packing multiple CPUs on a single FPGA.</p>

<p>Let's say I have a 1 million gate FPGA. I've found a few processors on OpenCores which only require 50k gates. So would it be possible to make, say, an 8 core processor with such an FPGA? Or are there limits to FPGAs when it comes to implementing massively parallel things? </p> <p>Sorry if it sounds newbish, but I am a newb to FPGAs.</p>

Are FPGA's as powerful as the number of gates they have?

2010-10-30T11:45:41.730

5891

|flash|eeprom|durability|

<p>I suppose if your flash is broken, you can write a value to it but i doesn't take it correctly. For example, some bits are maybe unable to go low anymore which yields a different value.</p> <p>Some flash drives in PC's like SSDs have controllers that monitor the broken parts of the flash chips and saves the data to different spots and reports a decrease in capacity. It's just like a normal hard drive has about 0,5% of extra sectors when some turn out to be bad sectors. </p> <p>If you are speaking in normal EEPROM chips or memories that are embedded into MCU's or external, I am not sure if they got any error correction system built in. It might just write the value and not know it fails in doring so correctly.</p>

<p>What is the failure mode of flash memory? I've got some chips rated for 10,000 cycles - what happens after 10k cycles? Do the chips stop writing properly, do you get read errors, etc.? Does it also happen to EEPROMs?</p>

Failure mode of FLASH memory

2010-10-30T13:17:21.067

5899

|arduino|

<p>The <a href="http://www.adafruit.com/index.php?main_page=product_info&amp;cPath=17_21&amp;products_id=94" rel="nofollow">Adafruit audio shield</a> has a row of vias next to the headers so you can solder a connection directly on, I think it's a good approach for a shield with unused pins, but your right - a lot of shield designs just offer the headers.</p> <p>For my own shield designs I try to use stackable headers and I rarely bother with a prototyping area (normally out of laziness) - I guess you can always jam a <a href="http://www.ladyada.net/make/pshield/" rel="nofollow">proto board</a> right on top. </p> <p>I think shields are good tools for prototyping, but I agree they should probably add more prototyping areas, I also agree with Pingswept that designers probably over look this or can't be bothered.</p> <p>But the great thing is...they're open source and you can change them to suit, this probably won't make it any cheaper tho (unless it's a supper minimal design) but it will probably help to reduce the project's size.</p> <p>Maybe, if you don't have the opportunity to make the changes yourself, you could make some suggestions to the <a href="http://www.sparkfun.com/commerce/static.php?name=customer_service" rel="nofollow">chaps and chapettes at Sparkfun</a> - they're a friendly bunch. </p>

<p>I've done 5 or so Arduino projects now and am at the point where I think I'm outgrowing the whole pre-packaged platform/shield arrangement. It was great for lowering the barrier to entry of getting into microcontroller projects, and for quickly getting projects off the ground, but I'm really seeing the cost and implementation tradeoffs impacting me more and more these days.</p> <p>One question that has been bugging me is, why do shield designers and manufacturers leave so little room for other circuit elements in their design? Who really does a project that is literally just an arduino and a shield? Doesn't everyone hook up other inputs and outputs to fully realize the vision behind their project? </p> <p>If a shield only needs and uses 5 or so pins, why not omit the headers for the other ones, or better yet provide some blank through holes/pads connected to the unused underlying arduino pins for the user to utilize as they see fit?</p> <p>I know some shields do this to some extent. The Speakjet/voice shield from Sparkfun for example has a relatively large open prototyping section.</p> <p>It seems like shield designers almost go out of their way to make it more difficult than it needs to be to tap into the pins their design doesn't use, by calling for headers that seem to only serve as a mechanical connection to the arduino, surfacing with a tiny soldered nub you can tack a wire onto but can't make a solid mechanical connection? Or am I missing something basic in my soldering/construction skills? Is there a better way to utilize pins a shield doesn't need?</p> <p>I know about stackable headers...but wouldn't it be better to provide a more directly solder-friendly set of through holes for tapping into the unused pins?</p> <p>Again, maybe this is just reflective of where I'm at with my relationship with arduino right now...ready to get off the yellow brick road of arduino + shield = solution and into using the arduino strictly as a dev and prototype platform.</p>

Why do Arduino shield kit designers "consume" pins they don't use?

2010-10-30T16:59:28.210

5904

|voltage|transistors|basic|

<blockquote> <p>"<em>The problem is that the LED circuit really needs 6V to run,</em>"</p> </blockquote> <p>No, you're lucky that the LED needs 6V! If it wouldn't it would go up in smoke as your circuit doesn't have any form of current limiting. </p> <p>You're using the transistor in common collector, aka voltage follower. In common collector the Arduino will see the load's resistance \$\times\$ \$H_{FE}\$ as the impedance at the base, so for instance a 100\$\Omega\$ emitter resistor may show as a 10k\$\Omega\$ at the base. That's why you can do without a series resistor connected to the base. </p> <p>If you would just have a common LED on the emitter, however, you only have the LED's voltage drop (2V?) + the base-emitter junction (0.7V) between the Arduino's output and ground. That's less than the Arduino's output level, the base current would skyrocket, and the collector current even more so. Goodbye, LED. </p> <p>Now this LED of yours, which needs 6V. 6V is a weird voltage for any LED, so I assume it has a few LEDs in series with a series resistor built-in. If the LEDS' combined voltage is higher than 4.3V this circuit won't work: the transistor's emitter has to be at 4.3V maximum otherwise there can't flow any base current, hence no collector current either. </p> <p>The solution is to use the transistor in common emitter, like is most often done to switch a load from a positive control voltage. Place the LED between collector and +6V, and place a series resistor between the Arduino output and the base. If the LEDs are 25mA a 1mA base current will do for most small signal transistors, so use a 4k7 resistor.</p>

<blockquote> <p>Why is my transistor only driving 5V instead of 6V? How can I fix it?</p> </blockquote> <p>I have a 6V, 25mA circuit running some LEDs. I can control them by connecting and disconnecting the positive terminal of the battery pack.</p> <p>I want to control them with an Arduino. So I added an NPN bipolar junction transistor with the base attached to the arduino's digital output pin and the collector-emitter acting like a wire from the positive terminal of the battery to the LED circuit. I also connected the Arduino's ground to the battery's negative terminal, but the Arduino is powered off a separate power supply.</p> <pre><code> o---------o ##### | | # # |/ /+\ # A #--| ( ) # R # |&gt; \-/ # D # | ####### | # U # | # # | # I # o-# LED #-o # N # # # | # O # ####### | # # | #####--------------o </code></pre> <p>The problem is that the LED circuit really needs 6V to run, while the Arduino's digital pins only output 5V. I don't quite understand why, but even though the collector is attached to 6V, the emitter is not really driving 6V, even when the base is on at 5V.</p> <p>It's a little hard for me to debug, since the circuit is all diode-y, so if it doesn't get enough voltage that part just turns off in a non-ohmic way. Part of the circuit only needs 5V to function, and it works, but the longer series of LEDs only works when I connect the base to a 6V source.</p> <blockquote> <p>What is going wrong, and just as importantly, how do I fix it?</p> </blockquote>

Transistor with two voltage levels, Vb ≠ Vcc

2010-10-30T20:19:39.363

5912

|heatsink|linear|voltage-regulator|

<p>While researching the same question for a SOT-223 package switching transistor, I stumbled on the ON Semiconductor Soldering and Mounting Techniques Reference Manual (find it here: <a href="http://www.onsemi.com/pub_link/Collateral/SOLDERRM-D.PDF" rel="nofollow">http://www.onsemi.com/pub_link/Collateral/SOLDERRM-D.PDF</a>). This is a compiled set of articles on thermal and mounting considerations and includes dozens of footprints for common package types (including SOT-223). It also includes articles on how to prepare PCB heatsink mounts, thermal grease, and other techniques that I had not considered before. The document was recently revised, July 2014.</p> <p>I found it worthwhile to look through. </p>

<p>I want to use a linear regulator for some application, it's in a SOT-223 (not SOT-89) package. How do I keep it cool, preferably without a bulky heatsink? The regulator may be dissipating 2-3W of heat. I've heard that you can use copper traces under the regulator on the PCB to keep the regulator cool; does anyone have any references on this? </p>

How to keep a linear regulator cool without an actual heatsink?

2010-10-30T23:50:27.347

5914

|pic|video|android|

<p>I've been doing something like this over the course of about 4 of the last 6 months (I worked on some other stuff in between). Building my own Linux board has been a tremendous learning experience, but it's also been quite challenging.</p> <p>Here are some things I wish I knew before I started:</p> <ol> <li><p>Generally, BGA packages mean you have to use fine-pitch traces and vias, and you it's difficult to assemble the boards yourself. Even if you were to succeed in soldering a BGA yourself, if you had a problem, you wouldn't know if it was due to bad soldering or bad design. The worst problem, though, is that this makes iterating on your design expensive-- around $1000 and 15 business days per rev if you live in the US.</p></li> <li><p>For the love of William Shockley, start with a reference design with Android support (well, just Linux in my case). My board is based off the Atmel AT91SAM9G20 eval kit; that's saved me a great deal of headache.</p></li> <li><p>Use the U-boot bootloader. It's the dominant one, which means that you can get support in more places.</p></li> <li><p>Before you start laying out a board, think very carefully about how to position the components to minimize trace length. I did this to some extent, but not as much as I should have.</p></li> <li><p>Buy the dev kit that is most similar to what you're planning to build, and build the bootloader and kernel from source. That will teach you a lot. If you're serious about video, I would probably try to validate whatever hardware platform I chose before laying out a board.</p></li> </ol> <p>Good luck.</p>

<p>How can I create an device running Linux (Android OS) with video output?</p> <p>PS. I don't want to use an existing very sophisticated dev board, I want to create one.</p> <p>Thanks!</p>

MCU + Linux + Video?

2010-10-31T00:02:22.743

5931

|pic|debugging|

<p><a href="http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&amp;nodeId=1406&amp;dDocName=en537580&amp;redirects=icd3" rel="nofollow noreferrer"><strong>MPLAB ICD 3 In-Circuit Debugger</strong></a></p> <p><a href="http://ww1.microchip.com/downloads/en/DeviceDoc/51292S.pdf" rel="nofollow noreferrer">Header Specification</a></p> <blockquote> <p>WHY DO I NEED A HEADER TO DEBUG?</p> <p>Some PIC® microcontrollers, particularly low pin count devices (with 20 pins or less), generally must use a header for debugging. This is done to free up I/O lines for your application and to make production parts more affordable. Optional headers are also available for high pin count devices (with 64 pins or higher).</p> <p>Debugging requires a two-line connection (plus VDD, VSS and VPP) to communicate with the device. In a high pin count device, losing a few I/O lines is generally not a problem for most designs. But in a low pin count device, it can be a critical problem. Imagine having to do an 8-pin design where there are only 5 I/Os, having used up 2 I/Os just for debugging!</p> <p>Notes about Headers</p> <p>Some 8-, 14- and 18-pin devices use <strong>small header boards</strong> with a special MCU for debugging. This special MCU has extra pins for MPLAB ICD 3 communication and therefore allows the use of all pins on the part for the application. The header board is not used or needed for programming. However, when debugging these devices the header must be used.</p> </blockquote> <p><img src="https://i.stack.imgur.com/3SmFm.png" alt="alt text"></p> <p><img src="https://i.stack.imgur.com/jr8Nd.png" alt="Figure 1"></p> <p><img src="https://i.stack.imgur.com/A8lcp.png" alt="Figure 2"></p>

<p>In a recent question on <a href="https://electronics.stackexchange.com/questions/5861/what-pic-should-i-use">which PIC to use</a>, one answer mentioned that a particular PIC had the feature that of debug hardware being built in, so that a special debug header was not needed. What is a debug header?</p>

In relation to a PIC, what is a debug header?

2010-10-31T13:45:09.480

5935

|capacitor|

<p>Don't forget Charge Conservation. (It's sorta like forgetting energy conservation!)</p> <p>You cannot create charge by rubbing with a cloth. You can only separate the opposite charges which were already there. Which means, the negative charge on the plastic has an exactly equal positive charge on the (slightly conductive) cloth. This is commonly lost through your hand and to ground.</p> <p>So, to 'charge' a capacitor, stop dumping the opposite charge into ground. Instead wear thick rubber gloves, so the cotton cloth becomes one terminal, the plastic pipe the other.</p> <p>One method for transferring charge from an insulating surface is by induction, via "Faraday's Ice Pail." You'd need two steel mixing bowls. Place them on insulators (glass or plastic.) Connect them to corresponding plates of your Leyden jar. Charge your two objects and place them in the bowls. Disconnect one capacitor terminal, then the other, et voila!</p>

<p>By rubbing a cotton cloth along a PVC pole, static electricity is generated. How can this be used to charge a capacitor? </p> <p><a href="http://home.earthlink.net/~lenyr/stat-gen.htm">http://home.earthlink.net/~lenyr/stat-gen.htm</a> is what I'd like to do, but it doesn't explain how it should be wired up.</p>

Electrostatically charging a capacitor

2010-10-31T15:47:30.113

5943

|oscilloscope|noise|

<p>I don't have a PC scope but a real bench oscilloscope.</p> <p>When running normally I see around 500µV noise on all settings about 5mV/div, and about 1mV noise on the 5mV/div setting. The noise is uniform across all channels.</p> <p>This noise is not significant for any of my uses so far. </p> <p>It's also not unusual for the scope to read ±1mV dc offset when there is zero input; some scopes have this calibrated out but expect a slight drift over time. Mine's quite old (manufactured '93), so I get around -3mV offset.</p>

<p>Following <a href="https://electronics.stackexchange.com/questions/5466/is-a-single-channel-oscilloscope-enough-for-most-purposes">this question</a>, I purchased a <a href="http://www.audon.co.uk/dso2090.html" rel="noreferrer">DSO-2090 USB oscilloscope</a>.</p> <p>When I power it up, I see lots of small fluctuations in the waveform, whether connected to nothing, a battery source, itself (small waveform generator on the back) or by shorting the ground clip.</p> <p><img src="https://i.stack.imgur.com/k8BaK.png" alt="Oscilloscope Noise" /></p> <p>(<a href="https://i.stack.imgur.com/k8BaK.png" rel="noreferrer">See the large version</a>)</p> <p>In the screenshot above, the CH1 is connected to a small, battery powered circuit of mine. CH2 does not have the probe connected at all.</p> <p>I have spoken to a colleague about this and was told that I should see a flat line so I am worried I have purchased a faulty unit.</p> <p>My question is whether or not background noise like this is normal in an oscilloscope?</p> <h1>Edit 1</h1> <p>Added 1kHz waveform example as per comment:</p> <p><img src="https://i.stack.imgur.com/mbhpI.png" alt="1kHz" /></p> <p>(<a href="https://i.stack.imgur.com/mbhpI.png" rel="noreferrer">See the large version</a>)</p>

How much background "noise" is normal on an oscilloscope

2010-10-31T19:48:12.393

5948

|.net-micro-framework|arm7|

<p>GHI EMX seems to have a bigger number of peripherals and IO ports. If you're looking for using lots of sensor at the same time its the better choice.</p> <p>Although I like the built in accelerometer in Tahoe 2.</p>

<p>Which board is better overall for .net mf development, the Tahoe 2 or the GHI EMX module?</p> <ol> <li><a href="http://devicesolutions.net/Products/TahoeII.aspx" rel="nofollow">Tahoe 2</a> </li> <li><a href="http://www.ghielectronics.com/product/129" rel="nofollow">GHI EMX</a></li> </ol> <p>I'm looking at a general purpose board for plugging in different types of sensors (at once) and using functions like the NIC and SD file io.</p>

Which board is better overall for .net mf development, the Tahoe 2 or the GHI EMX module?

2010-10-31T23:16:49.217

5951

|pcb|pcb-fabrication|via|

<p>The "aspect ratio" defined as = board thickness / unplated drill dia is important. If it is too high, you may have via barrel cracking due to expansion when soldering. Typically a value of 6 is considered safe. E.g with 1.5mm (60 mil) board thickness, a drill size of 10 mils, which means after plating, about 8 mils plated hole dia.</p>

<p>Is there a standard for via sizes, or can you make them any size you want?</p> <p>(I'm going to be using traditional PCB houses to manufacture my PCB's.)</p>

Standard via sizes?

2010-10-31T23:29:00.687

5953

|.net-micro-framework|

<p>Since you have decided to go with a development platform that is all inclusive the number of require components will be rather small.</p> <p>On the software side, I believe you will need Visual Studio.</p> <p>On the hardware side, this will depend mostly on what sensors you will want to integrate with and through what interface. In almost all circumstances I would suggest getting "Expansion connectors that expose GPIO, I2C, SPI and UART signals" These are different protocols that you will be using to interface with your sensors.</p>

<p>assuming I have already purchased a .net mf board such as a tahoe II, what other items are required?</p> <p>Obviously sensors will vary on the projects I'm doing, but what stuff will I need for every project?</p> <p>Edit: Okay so maybe I got excited and didn't provide enough detail. Assuming I have a board such as the Tahoe 2 and a computer and a cable to hook it up and copy programs across. What other items do I need (examples circuit boards, transistors, soldering iron, etc) what are the required items that each project is likely to need.</p> <p>Update:<br> <strong>Basic Hardware Parts list</strong><br> •Leds<br> •Resistors<br> •Caps<br> •Transistors<br> •Solderless breadboard<br> •Solid core wire<br> •Crocodile clamps<br> •External power supply (5V for Meridan boards)<br> •Multimeter<br> •Some sensors<br> •Network Cable </p> <p>GPIO, I2C,SPI and UART all supported.</p> <p><strong>Software</strong><br> Visual Studio 2010 (express or a retail edition)</p>

Can someone give me a basic parts list of required items for .net micro framework development?

2010-10-31T23:43:45.297

5954

|power-supply|sepic|

<p>I've built a SEPIC and published this page about it, there's even a description of how to build a the inductor without unobtainium: <a href="http://dren.dk/carpower.html" rel="nofollow">http://dren.dk/carpower.html</a></p> <p>... but the inductor design is pretty hackish, so it's not going to win any medals for production use.</p>

<p>I have a 6V to 20V input I want to convert to 12V at 1 amp maximum continuous current. The output must be the same polarity as the input, so that pretty much means a SEPIC is the only way to go... However, I've been looking around and all solutions I've seen thus far require many components and a lot of surface area; I'm looking to minimise surface area as far as possible, and to do this I don't mind sacrificing a bit of efficiency. Does anyone have any suggestions?</p>

12V @ 1A from a 6V to 20V input

2010-11-01T00:19:43.277

5960

|capacitor|

<p>We had a couple .1uF electrolytic go on backwards on a PCB due to the solderer not realizing they were polarized caps(we did not mean to order them).</p> <p>This caused very odd problems only solved by adding large decoupling capacitors to power(10uF). It was very odd but only had around 20 extra mA being pulled at 5V. We found out we had put them on backwards, swapped them and there was no need for the extra caps on power.</p> <p>My long and short of it, I am not sure how I would have told in the same situation that this happened.</p>

<p>I'm trying to debug a friend's <a href="http://shop.41hz.com/shop/item.asp?itemid=8&amp;catid=">AMP6 audio amp kit</a>. It seems that an electrolytic smoothing cap on the output of a 5 V regulator has been soldered in backwards. This seems bad, but the component is going to be a little tricky to desolder because of its physical location. Because of this, I'm trying to be certain that this is the problem before attempting the job.</p> <p>Before it explodes, how does a backwards cap behave? Like a 100 ohm resistor?</p>

What's the resistance of an electrolytic cap soldered in backwards?

2010-11-01T05:38:19.313

5967

|capacitor|video-transmitter|

<p>Bypass capacitor is just another name for a decoupling or smoothing capacitor. This probably means that the board has a voltage regulator on board and decided to have you be the one to provide the capacitor for it instead of on its own board.</p> <p>With a RF module that can output a good amount of power, I would expect for a cap this large to be a necessity.</p>

<p>I'm using an Airwave 663 module. It's a 5.8GHz FM video + stereo audio transmitter module. Here is the datasheet: <a href="http://www.airwave.com.tw/specification/RF%20modules/AWM663TX.pdf" rel="nofollow">http://www.airwave.com.tw/specification/RF%20modules/AWM663TX.pdf</a></p> <p>It is apparent that the module requires a 470uF 16V capacitor on the BYPASS pin. Compared to the other components on my board, this is absolutely massive. But I can't find any specification anywhere about what this capacitor does and whether or not this capacitor can be made smaller.</p> <p>If anyone here has dealt with similar modules, what was your expereience?</p>

Airwave TX "BYPASS" capacitor

2010-11-01T10:11:43.450

5970

|pcb|surface-mount|pad|

<p>Make sure the pads don't have any vias in them. I have seen some component footprints that have vias on their pads and I don't realize it until it comes to fab. </p> <p>I have also seen footprints in our corporate database that have been made with keep out markers that go to all layers causing DRC errors when I put components top to bottom.</p> <p>Probably unlikely any of these are your issue, but at least something to check.</p>

<p>Is it possible to put SMT components on both sides of the board with the pads touching? I don't want the pads to be electrically connected, but my PCB program (gEDA PCB) warns that they are shorted. Is there any way to avoid this?</p>

SMT pads on both sides of the board

2010-11-01T10:55:08.303

5980

|audio|usb-host|

<p>I'm curious about the <a href="http://www.maximintegrated.com/datasheet/index.mvp/id/3639" rel="nofollow">MAX3421</a>, but I can't seem to find anyone who's actually used it! It looks like it might be an easier solution than the Vinculum.</p>

<p>Are there any microcontrollers which are able to act as a USB host for audio devices? Basically I'd like to create an interface which allows my to connect my USB headset to the analog microphone/headphone jacks of my PC (so it doesn't appear as a separate sound device to the OS).</p> <p>However, I have no idea if cheap microcontrollers are powerful for that or if there are any microcontrollers which support usb-audio. Googling wasn't very helpful; most controllers supporting usb-host only support mass storage devices...</p>

Microcontroller acting as USB host for an audio device

2010-11-01T13:42:09.637

5990

|antistatic|

<p><a href="https://i.stack.imgur.com/5Uq4x.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5Uq4x.png" alt="metal-in shielding bag"></a></p> <p>Both sides of the antistatic bag are coated by antistatic agent, we tested it in our factory. Interior and exterior resistance are &lt; \$10^{11} \Omega \$. Metal-in Static Shielding Films are designed for products requiring protection against Electrostatic Discharge(ESD). Static shielding bags provide properties intended to protect electronic devices and assemblies from Electrostatic Discharge(ESD) and to avoid charge accumulation on the bag that could be damaging to ESD susceptible devices and assemblies.</p>

<p>From Wikipedia:</p> <blockquote> <p>To create the anti-static effect, the black or silver bags are slightly conductive</p> </blockquote> <p>and</p> <blockquote> <p>A device should not be powered while in an antistatic bag, because the conductivity of the bag could cause damaging short-circuits between parts of the device.</p> </blockquote> <p>So I deduce that those bags are conductive in the interior surface. What about the exterior surface?</p>

Do antistatic bags have conductive interior, exterior or both?

2010-11-01T15:22:21.307

5993

|transistors|hall-effect|

<p><em>pingswept</em> is right about the amplification, but he cuts a few corners. First, if you amplify a 0V-5V signal, the amplified signal range still starts at 0V! We'll need to fix that. The <a href="http://www.elkor.net/pdfs/i-Snail-V_Current_Transducer_0-5VDC_Output.pdf" rel="nofollow">i-Snail</a> is self-powered, which means it needs a minimum current to be able to output a voltage. So at no current the voltage will be effectively 0V, but it's possible that the lowest effective output voltage is, say, 5mV. The datasheet doesn't say. For the given sensor that would mean a 50mA primary current. </p> <p>To amplify this low kind of level you need a rail-to-rail input-output opamp. A 100x non-inverting amplifier would amplify the 5mV input to 500mV. That's still too low to drive the transistor, but we can use a comparator to compare this with a threshold of, say, 100mV. Many comparators have open collector outputs, but those can often sink less than 20mA, so you'll want to drive the NPN with the comparator after all. </p> <p>Alternatively you can skip the amplifier and directly input the i-Snail's signal to the comparator, and set the threshold to 5mV. Keep in mind however that this will be near the comparator's offset voltage, so you may have to trim that. It also depends on the minimum voltage the i-Snail delivers or the minimum level you want to detect. In the given example of 50mA that would be 6W at 120V AC.</p>

<p>I have an <a href="http://www.eztronics.nl/webshop/catalog/product_info.php/cPath/33_39/products_id/281" rel="nofollow">i-Snail-VC-50</a> sensor with an output of 0-5V. I'd like to connect this output to the base of a <a href="http://www.datasheetcatalog.org/datasheet/philips/BC546_547_3.pdf" rel="nofollow">BC547</a> transistor, which powers an LED with an external 5V power source. What I want to achieve, is that the LED lights up as soon as the sensor output voltage rises above 0V (most of the time, the output will be either 0V or within the 0-1V range).</p> <p>How could I achieve this, making sure that no components get damaged if the sensors output is at its maximum (6.5V)?</p> <p>I know transistors are current driven, so perhaps a voltage driven mosfet (I have some <a href="http://robofun.ro/docs/irfz48n.pdf" rel="nofollow">IRFZ48N</a>'s at my disposal) would be better suited for this task?</p>

How to drive a BC547 using a 0-5V sensor output?

2010-11-01T15:40:55.503

5996

|arduino|solar-cell|

<p><a href="http://www.rachelselectronics.com/categories/open-source-hardware/" rel="nofollow noreferrer"><strong>SolArduino v1</strong></a></p> <p><img src="https://i.stack.imgur.com/hswgu.png" alt="Board"></p> <p><img src="https://i.stack.imgur.com/g3F3u.jpg" alt="PCB"></p> <p><a href="http://www.rachelselectronics.com/2010/09/solar-piston-v1/" rel="nofollow noreferrer"><strong>Solar Piston v1</strong></a></p> <p><img src="https://i.stack.imgur.com/NVco0.png" alt="Schematic"></p>

<p>suppose I want to keep an Arduino powered during the night, and recharge it during the day with a solar cell. What kind of circuit do I have to make, how many and which type of batteries, and what size of solar panel do I need to keep it going?</p>

powering arduino via solar cells

2010-11-01T16:38:49.580

5998

|pcb|design|physical-design|

<p>Mike is right: less mass is better, since the part will exert less force on the soldering when vibrating. So the SMT will be better, even when PTH has a larger soldering contact. (An 0402 resistor <a href="http://www.resistor.com/assets/pdf/0402std.pdf" rel="nofollow">weighs</a> only 1 milli-gram). </p> <p>When I was in college we learned that in very high-vibration environments they would use <strong>wire-wrapping</strong> instead of soldering. But that's many moons ago, and I guess soldering techniques have improved since. The space shuttle didn't exist yet (talking about high-vibration)</p>

<p>This is more of a opinion question than a information question. I am designing some boards that will be working near decent sized actuators, so I ask you, what is more resistant a 0805 SMD or a 7mm thru-hole resistor?</p>

SMD vs. Through-hole components in high vibration environments

2010-11-01T17:05:39.150

6009

|pcb|geda|

<p>When you want to wave solder (not much done anymore) QFP parts you simply <em>have</em> to place them at a 45 degree angle. If you place them orthogonally the solder wave will short all the pins transversal to the wave. 45 degrees allows to place <em>solder thieves</em> that take any excess solder.</p>

<p>I've seen some PCB's with components mounted at multiples of 45 degrees (45, 135, etc.) I recently discovered my PCB program (gEDA PCB) supports these, though it isn't a GUI function and you have to run a command. When is it appropriate to mount at these angles? And what about angles of 30 degrees and 60 degrees, or arbitrary angles? </p>

When is it appropriate to mount components at a 45 degree angle?

2010-11-01T20:23:11.170

6017

|pcb|analog|radio|

<h2>Creating Delay</h2> <p>To create a delay you want to pick a filter with a large <a href="http://www.microwaves101.com/encyclopedia/groupdelay.cfm" rel="nofollow">group delay</a> at your frequency range.</p> <p><a href="http://www.microwaves101.com/encyclopedia/groupdelayfilters.cfm" rel="nofollow">Microwaves101 explains it to some extent</a>.</p> <h2> Why a longer line helps </h2> <p>If you are using a longer line and dropping your noise floor you are actually creating a very basic <a href="http://www.microwaves101.com/encyclopedia/isolators.cfm" rel="nofollow">isolator</a>. Now the microwaves101 explanation of an isolator is a tied to an easy to implement microwaves component, the <a href="http://www.microwaves101.com/encyclopedia/circulators.cfm" rel="nofollow">circulator</a>. Now this is a relativly complicated device to think about implementing if you are used to frequencies that Microwave engineers consider DC(like 500kHz). The device that approximates an isolator for you is a diode. If you connect power to a line with a diode that is idea, any reflections/ringing/feedback will be blocked and dissipated by the diode.</p> <h3> What the Cable Does. </h3> <p>As you increase the cable length, you increase cable loss. Lets say you have a number like 1dB loss (which is a gain of -1dB). If reflections are your primary source of noise then a reflection off of your load will travel back to antenna and then back to the load again. This means just from the cable you have caused a 3dB loss(half power). This neglects the fact that the reflection is a rather large loss on both interfaces also. This "isolates" in the respect that as the line gets longer your reflected signals have a larger and larger loss, at-least 3 times what your signal feels.</p> <h3> How Do I Fix It?</h3> <p>This is probably a sign that your load, whatever you are measuring with, is miss-matched, A decent match, giving a reflection of around -20dB coupled with the loss hitting the antenna again should leave your reflections relatively small.</p> <p>You can fix this with a tuning network, which adds discrete components nearby to attempt to create the correct impedance. You can correct this by fixing any flaws in your layout also. Probably both (based on experience with my own boards).</p> <p>Another way to approach this is to really cheat with your line connecting the boards. If you are operating over a small frequency range(ie. Able to treat the signal as a single frequency), then you can use stub tuners(which have been mentioned in this thread, just not by name) where the length of the stub acts as a capacitor or inductor(this is very frequency and fab dependent). You can also have a lot of fun by using a length of cable that is a quater-wavelength long. This means that when a signal is reflected, it will return to the antenna with a 90 degree phase shift, then return to the load completing a 180 degree phase shift. This cancels itself out in stead state(not perfectly, but it gets the job done).</p> <h3> Summing it Up</h3> <p>At least you jumped in head first. There are a number of other things that can cause a miss-match, with more application specifics they can be looked into also. For example, a COAX cable causes a missmatch due to its shield having currents on the outside and inside that do not sum to the inner conductors current. I hope this has helped some, and I hope microwaves101 can be of some help. It is by far not the perfect learning resource, but someone is trying.</p>

<p><strong>The Background</strong></p> <p>My main background is embedded software but I have had to debug the analog circuitry myself so I've picked up a little bit here and there, enough so to describe the problem in a coherent way to someone who could give me a solution. At my work, I was on a project where we were developing a hand-held radar transceiver that operated in the single Ghz frequency range. One particularly thorny issue that we never resolved was the antenna connectors we used introduced ringing artifacts in the receive signal. To prove this as a source we would put 50ohm terminators instead of the antennas and would observe a significant decrease in the noise in the signal. We also observed decreasing noise as we introduced progressively longer lengths of cable between the Tx/Rx connector and their respective antennas. So the initial conclusion was to introduce delay between the connectors and their antennas to dissipate the ringing and make our lives easier on the Rx side.</p> <p><strong>The Problem</strong></p> <p>So the real problem is how do we implement that delay, preferable 15-20ns worth, where space is our main constraint (the last board we built was two dual-side 10cm x 10cm boards, one for the electronics and the other for the antennas with the aforementioned connectors between the two boards)? I had once suggested drawing out trace paths between the connectors and antennas in the same manner as illustrated in <a href="https://electronics.stackexchange.com/questions/4168/what-is-this-squiggly-trace-for">this question</a> except that's for digital signals and my limited experience with analog signals has taught me that analog RF signals are a lot more pickier than digital signals. Never did get to try out my idea and now the project is on hold for lack of funding.</p> <p><strong>The Question</strong></p> <p>So if nothing else I'd like an answer to whether using PCB traces for large analog RF delay is a feasible idea and what pitfalls would need to be considered. Is this even a common practice or does the RF world rely on special circuits to do that function? Another project which I was involved in had the same problem and used a gated switch as a solution which worked but added quite a bit more components (guesstimate of 25% extra space required). I'm mostly looking for a general argument about how this problem could be approached but references would also be appreciated (even if its way above my head!). Thanks.</p>

Feasibility of introducing RF delay via PCB trace?

2010-11-01T21:49:57.270

6027

|inductor|

<p>What they're telling you with the saturation current is that above 1.6A, the core can't take any more magnetic flux, and this translates into a change in the effective inductance when the current gets into that realm. You can put more current through the winding, and you do get more flux as a result, but the effective permeability of the core drops off.</p> <p>The effect won't be a sharp break, either; you would start to see some of the effects as you get near the saturation point. If you apply a pure sine wave voltage across the coil that would result in less than 1.3A peaks, the current will also be sinusoidal, but if you run the voltage up to where the peak currents would reach saturation, the current waveform will have a significant harmonic component.</p>

<p>I have a 15µH 1.6A inductor, <a href="http://uk.farnell.com/bourns/sdr0604-150yl/inductor-smd-15uh-1-6a/dp/1828004" rel="nofollow noreferrer">this one</a>.</p> <p>The <em>operating current</em> is 1.3A, but the <em>saturation current</em> is 1.6A.</p> <ol> <li>What is the difference between these? </li> <li>Will the inductor work properly at less than 1.3A or less than 1.6A? </li> </ol>

How important is saturation current for an inductor?

2010-11-01T23:02:47.010

6028

|oscilloscope|

<p>Just an idea... Measure with two probes and use the add function for the two channels :)</p>

<p>I'm building a 3.3V 400mA power supply around an ultra fast buck reg (3 MHz or 1.6 MHz, LM2734Z/X.) According to simulations, the ripple will be &lt;2mVp-p. The noise floor of my scope is about 500µVp-p on 5mV/div (the minimum setting), so how do I measure such a small signal? </p> <p>I'm thinking I'm going to need an amplified probe of some kind, but I suspect these will be very expensive. </p> <p>I was thinking of fine tuning the trigger and using the averaging function to remove the noise from the signal, but would this be adequate for power supply ripple? Scope is a HP 54501A, 100 MHz -3dB b/w, 10 MS/a digitising, quite an old scope but only cost £150.</p>

Measuring low ripple on a power supply with an oscilloscope

2010-11-01T23:05:36.413

6029

|capacitor|inductor|

<p>You aren't talking about a battery, but an RF receiver. When you add the antenna and ground connections, you are receiving energy that is broadcast by a transmitter. The resonant frequency of your tank should match the frequency of the transmitter. If you're going to harvest energy, I guess you would target 60/50 Hz, unless you have a stronger source nearby.</p> <p><a href="http://en.wikipedia.org/wiki/Wardenclyffe_Tower#Theory_of_wireless_transmission" rel="nofollow">Nikola Tesla started to build such a transmitter</a> for communications and experiments on power distribution, but his financing was coming from people who had a vested interest in the power generation systems of the day. When he mentioned the possibility of broadcasting power that anyone could pick up for free, then his funding dried up. So, it took another forty years to lay a transatlantic cable to make reliable communications with England happen.</p>

<p>I am curious about a resonant LC circuit. Assuming a perfect inductor and capacitor, would it be possible to tap off the energy in the oscillations to use it as a battery? Literally, it would be an AC battery. With a bridge rectifier and filter cap would this act as a DC battery?</p> <p>(This is just theoretical stuff - I doubt you could get useful energy from an LC circuit as it would dissipate too quickly due to losses in the inductor and capacitor, plus to store any reasonable amount of energy would probably require a massive inductor and capacitor.)</p>

LC circuit: can it act as an "AC battery"?

2010-11-01T23:19:14.577

6034

|theory|kirchhoffs-laws|

<p>It depend of how many nodes/meshes your circuita has. However, you can use online calculator for any linear 2X2 system:</p> <p><a href="http://www.cirvirlab.com/simulation/kirch_2_real.php" rel="nofollow">http://www.cirvirlab.com/simulation/kirch_2_real.php</a></p>

<p>When I solve questions, I usually get confused between when to use the Kirchhoff's Voltage Law (KVL) and when Kirchhoff's Current Law (KCL). Please help.</p>

How do I decide whether to use Kirchhoff's Voltage Law or Kirchhoff's Current Law?

2010-11-02T02:33:00.693

6037

|education|

<p>If you are are bachelor in software, then its OK to have associate or bachelor level in electronics. Don't overspend your time on master degree, unless your current education was poorly sourced and you are questioning it. </p> <p>I had 3.5 years in electronics, then switched to computer sicence. Stayed in boring financial industry doing software for 20 years, then returned to robotics and industrial automation with some luck in job search. </p>

<p>I've been working in software for way too long, dislike it for a number of reasons, and would like to shift completely into electronics engineering work. I'd prefer analog, microwave, optoelectronics or maybe some specialty yet to be invented, but any electronics is better than any software. I have more talent and interest in electronics, and my love of herding electrons goes back to when I was a kid. I read IEEE publications and understand them far better than anything coming out of the software development or computer science world. </p> <p>Unfortunately I have no formal degree in EE, only in Physics, a fine subject but apparently not sufficient to land an EE job, so I've found over the past several years.</p> <p>The question is whether it's best to somehow get into a full time job first, with my existing experience, enthusiasm and education, and then perhaps earn a Master's to further my career, or to go full blast studying for a Master's in EE while continuing work in software, and only then try to land a job.</p> <p>I'm currently employed, live next to a reputable tech school, and my employer depends heavily on electronics although there aren't any opening right now. </p>

Shifting into an EE Career - with or without Master's first?

2010-11-02T05:19:11.073

6043

|kirchhoffs-laws|

<p>It doesn't particularly matter which direction you assign to each loop, it's just your best guess, so long as once you pick it, you keep it. </p> <p>For instance, on Node A, you have blue arrows i1 + i2 - i3 - i4 = 0. That's fine. If you keep that, then when you solve for what the currents actually are, you may find that i2 comes out negative. Which is okay, it just means that the current is flowing in the opposite direction of what you guessed. </p>

<p>I know applying kcl but I dont know how to consider the directions of the current.What I do is I make a general current direction for the whole loop,then with the help of that I see the currents entrying the node or leaving it but I usually go wrong with this logic..Here's an example which includes my try an the real directions<br> <img src="https://i.stack.imgur.com/zNhEd.gif" alt="alt text"> <img src="https://i.stack.imgur.com/OLB0R.gif" alt="alt text"></p>

How to suppose the current directions for KCL?

2010-11-02T10:40:59.140

6047

|serial|wireless|xbee|zigbee|

<p>You can [reduce to zero the dropped packages][1] by assigning the correct destination address before starting transmission. </p>

<p>I am transmitting continuously at 9600 bps using the default configurations for both my XBees XB24-B. The communication is one way only, the transmitter is connected to the ATMega328 UART and the receiver is connected to the PC via USB (FTDI). Here is the actual data rate for a given program:</p> <ul> <li>Wired connection (no XBee) : 7694 bps</li> <li>from the ZNET 2.5 Router/End Device AT to ZNET 2.5 Coordinator AT: 6800 bps (some lost packets)</li> <li>from the ZNET 2.5 Coordinator AT to ZNET 2.5 Router/End Device AT: 0356 bps (many lost packets)</li> <li>from the Zigbee Router/End Device AT to Zigbee Coordinator AT : 0000 bps (doesn't work)</li> <li>from the Zigbee Coordinator AT to Zigbee Router/End Device AT : 0328 bps (many lost packets)</li> </ul> <p>Why is that? Is there anything I can do to improve these rates?</p> <p><strong>Edit</strong> For higher baud rates (115200) I get even worse packet drop rates:</p> <ul> <li>Wired connection (no XBee) : 94200 bps</li> <li>using XBee XB24-B ZNet 2.5 : 27900 bps</li> </ul> <p><strong>Edit</strong> If I make the Coordinator address the End device, then the packet drop rate falls to the normal levels (6800 bps), which is not ideal but better than the previous scenario</p>

XBee dropping packets and actual data rate lower than expected

2010-11-02T12:44:48.783

6050

|thevenin|

<p>For Rth，first short the power supply of 10V, then calculate resistance.<br /> R1 is in series with R5, 3k+3k=6k, the result is in parallel with R2 =&gt; 6k || 4k = (6k x 4k )/(6k+4K)=2k4, then that is in series with R3 and R4.<br /> 2k4+3k+3k=8k4.</p>

<p>How do I find the Thévenin voltage in this diagram? </p> <p>In parallel the voltage remains the same, so should it be 10 volts across AB?</p> <p>I am given that since \$R_3\$ and \$R_4\$ are not connected on one end, they do not carry current. Therefore, they cannot have a voltage drop. The voltage present between points A and B is the voltage drop across \$R_2\$.</p> <p><img src="https://i.stack.imgur.com/V9aWS.png" alt="enter image description here"></p>

How to find the Thévenin voltage?

2010-11-02T14:50:23.403

6053

|adc|

<p>Okay, from your response to my comment I think I can be more help with a full answer.</p> <h2> Build it!</h2> <p>Build your simple Resistive divider. This has many advantages, for one size, another is cost.</p> <h2> Characterize it!</h2> <p>Now, you are going to use a microcontroller also, this is where you need to characterize your error. use a voltage generator that is very accurate, now check voltages and see what error the uC actually measures.</p> <h2> Analyze it!</h2> <p>Now is when it gets fun. There are a number of things you could measure. </p> <p><a href="http://en.wikipedia.org/wiki/Accuracy_and_precision"><h3> Accuracy and Precision </h3></a> The biggest thing to measure here is if the error at the points is repeatable. IF every time you sweep you get a different error, or if your sweep following a different path gives a different error at the same point, this is not an option. This often happens with leakage currents. The important part here is that <strong>you do not need high accuracy, just a high degree of precision.</strong> If you can characterize your error, your uC can correct for it. If you have a large variance you need to change your solution.</p> <h2> What is an X point calibration?</h2> <p>Now, if you have a high precision, as discussed before, you can move on to correcting the accuracy. Now, if when you graph your input voltage versus your output voltage you are going to have to decide the number of "reference points" you need. Nice devices allow a 1 point(or zero point, no need for calibration). Many temperature probes.</p> <h3> One point calibration </h3> <p>Both lines have the same slope, but an offset, so you just need to find the value you must add to a data-point to correct it. This is an ideal situation, as any new calibration only needs a single data-point to calibrate again.</p> <h3> Two Point calibration </h3> <p>both linear curves, possibly an offset and there is a slop difference, you only need two reference points and linear interpolation to extract your offset. This is still relatively easy, you just take any point, multiply it by a scalar and add an offset.</p> <p>As you can see, it gets messier the more points you need. At some point it is easier to just take every datapoint and correlate it to the actual value. For example, finding that 0000 is 1V, 0001 is 2V, 0002 is 1.5V. This is messy, and this still only works if the offsets are repeatable. This can happen though.</p> <h2> Summing it up</h2> <p>I hope this helps, tell me if you need more clarity. If you end up with a varying leakage current that is not dependable, it is time to just deal with needing a buffer, or something of the like.</p> <p>I can see a possibility of high error from leakage, but I would bet that the error is relatively small over most of the range, and when it is there can be easily corrected.</p>

<p>I want to read a voltage from 0-30V with an MCU ADC which has a maximum input of 3V. </p> <p>Initially I thought of using a 100k-10k divider (so 33V translates to 3V) but according to the answers to <a href="https://electronics.stackexchange.com/questions/5404/adc-input-impedance-on-mcus">ADC input impedance on MCUs</a>, this will add a 3% error due to the input leakage current; I'm looking for 0.5% error maximum. However, at lower values for the divider, I risk damaging the MCU's inputs because of overvoltage (the resistors act in tandem with the clamping diodes on the input.) I also increase power dissipation in my resistors, which are tiny 0603 devices, rated for 0.063W maximum. How can I avoid this? n.b. input impedence is not critical.</p> <p>I'm not worried about sampling speed, it will be monitoring a battery voltage at a maximum of 100 samples per second.</p>

Voltage dividers and ADC's

2010-11-02T15:56:30.607

6055

|voltage|current|

<blockquote> <p><em>"I guess they also enjoy the same current."</em> </p> </blockquote> <p>No, that's wrong. Your understanding of the current through the resistor with switch open and closed is correct. With nothing connected to the output the current only goes through resistor and switch. So the switch sees the same 20mA the resistor sees. When you place another 600\$\Omega\$ in series with the switch that will be 10mA. Let's keep that resistor there.</p> <p>This circuit in itself is useless, you always want to connect something to the output. Let's assume that's a circuit which can represented by a 1200\$\Omega\$ resistor to ground. Then, with the switch open the output will be 8V, and there will flow 6.67mA into it. Zero through the switch. When you close the switch the 1200\$\Omega\$ becomes parallel to the switch's 600\$\Omega\$ giving an equivalent resistance of 400\$\Omega\$. The total current through the top resistance will then be 12V/(600\$\Omega\$ + 400\$\Omega\$) = 12mA, causing a 7.2V drop across the top resistor, so that the output level is 12V - 7.2V = 4.8V. </p> <p>Now you're right that all components on that horizontal line to the output will see that same voltage, but <em>they don't share the same current</em>. Part of the 12mA will go through the switch with its resistor, part will go in the output's 1200\$\Omega\$. The distribution of the current is inversely proportional to the resistance of the different paths. The switch will draw 4.8V/600\$\Omega\$ = 8mA, the load will draw 4.8V/1200\$\Omega\$ = 4mA.</p>

<p>I'd like to understand this simple schematic to see if I get things clearly</p> <p><img src="https://i.stack.imgur.com/vGqHl.jpg" alt="alt text"></p> <p>If I understand things correctly:</p> <ul> <li>when the switch is open, the current at the right black point is zero, the voltage is 12V.</li> <li>when the switch is closed, the current at the right black point is 20 mA, the voltage is 0V</li> </ul> <p>If this is correct, suppose now a similar schema with the following difference: between the switch and ground I have another 600 ohm resistor.</p> <ul> <li>the potential at the black dot with the closed switch is now 6 V ?</li> <li>any point along the horizontal connection between the T junction and the black dot are at the same potential. I guess they also enjoy the same current. If two points in a circuit experience the same potential and they are directly connected, do they always experience the same current as well ?</li> </ul>

Voltage and current in this schematic

2010-11-02T16:19:03.090

6066

|power-supply|voltage|switches|low-battery|undervoltage|

<p>Maybe its a bit strange to answer my own question, but after a few months, I found an excellent detailed description with schematics how to make one here: <a href="http://www.gorum.ca/lvdisc.html" rel="noreferrer">http://www.gorum.ca/lvdisc.html</a></p> <p>Scroll down to about 50% of the page, and there starts a description of a version built using Solid State High Side Switches instead of mechanical relay, because one with a mechanical relay, can drain even about 100 mA from the battery, which would be unacceptable in my situation, that would be a loss of 20 Ah per week!</p>

<p>How can I make a device that will make the power connected as long as the voltage of the power-supply keeps over 12.4 V (adjustable) and disconnect it if it falls below?</p> <p>It also must connect the power back, but only if it rises above 13.5 V.</p> <p>This has to sustain at least 70 A.</p> <p>Is there a simple way to build such device?</p>

how to build a low-voltage disconnect switch for DC 12.4V 70A?

2010-11-02T19:25:25.343

6069

|pcb|mechanical|drawing|

<p>Consider this approach: <a href="http://www.penguin.cz/~utx/pstoedit-pcb" rel="nofollow">http://www.penguin.cz/~utx/pstoedit-pcb</a></p>

<p>I'm trying to understand <a href="http://www.farnell.com/datasheets/359827.pdf" rel="nofollow">this mechanical drawing</a> so I can create a layout for it in gEDA PCB. </p> <p>Specifically on page 4. I've already managed to place GND 1 and GND 2; those were fairly simple to work out. But GND 3 confuses me, because it's apparent from close inspection of the drawing that it doesn't quite line up with GND 1 and the offset doesn't appear to be given. The same is true for GND 4 which doesn't quite line up.</p> <p>Also on a semi-related note it is unclear whether the pins are in the order as they are on the SD card or if they are numbered arbitrarily - that is, does pin 1 correspond to pin 1 on the SD card?</p> <p>While this isn't strictly electronics, I think it passes as an appropriate question because it is an electronic connector and it requires a PCB layout.</p>

Help me decode this mechanical drawing of an SD card PCB layout

2010-11-02T20:12:59.357

6074

|reference|

<p>I think the LM4040 is the way to go. I don't know of any "pre-biased" shunt diodes, and if there were they would likely cost more and you would have to weigh that against the scant space savings.</p> <p>If you can ease up on the 0.1% to 0.2 (B-grade) or 0.5 (C), the prices seem to drop quite dramatically.</p>

<p>I've been looking for a 3V ±0.1% reference in a SOT-23 package to replace my current ±0.5% solution of a TL431 and about 5 passive 0603 components. </p> <p>At the moment I've found LM4040A30 which is $1 at 1ku, and comes in a SOT-23 package. It also requires a 0603 resistor, but is stable without a capacitor.</p> <p>I'm wondering if anyone has any better solutions. Even more awesome would be something like an ultra stable precise zener diode in 0603 or 0805 size. </p>

3V ±0.1% reference

2010-11-02T21:34:22.687

6076

|coin-cell|lithium|rtc|

<p>If size is an issue I would go for a tabbed <strong>rechargeable lithium</strong> cell. Since it's rechargeable it doesn't have to be user-replaceable so it can be soldered to the PCB. Since it doesn't require a holder it can be kept compact; a holder may otherwise add up to 200% to the volume).<br> You don't specify how low the battery should last, but the Panasonic <a href="http://www.panasonic.com/industrial/includes/pdf/Panasonic_Lithium_ML414_ML421.pdf" rel="nofollow">ML-414</a> is only <strong>4.8mm diameter</strong> and <strong>1.5mm thin</strong> yet at a capacity of <strong>1.2mAh</strong> it should last 50 days if you draw only 1\$\mu\$A.<br> <a href="http://industrial.panasonic.com/www-data/pdf2/AAA4000/AAA4000DE127.pdf" rel="nofollow">This</a> is a drawing of the tabbed version.</p>

<p>I'm considering putting a small lithium battery on my Super OSD Pro boards. The battery would provide power to the RTC. I am wondering how small can you get a battery? I don't really care about capacity, I expect current draw to be less than 1µA, so it's really only size I'm looking for. </p> <p>Best solution would be one that is removable, because I'd like people to be able to replace the battery when it does go flat.</p> <p>And I'm open to suggestions on how to control the power to the main bus which has some heavier current draw devices which would overwhelm the 1µA for the RTC (the RTC is provided by a PIC24F in deep sleep mode.) I'm thinking of a power monitor, but it needs to be able to switch at least 100mA for the MCU when it's running full speed.</p>

Smallest lithium battery backup?

2010-11-02T21:40:18.097

6077

|audio|synthesizer|

<p>In addition to the excellent reading sources already suggested - in particular Terence Thomas's Sound Synthesis: Analog and Digital Techniques - I would like to add the following two books:</p> <ul> <li><p>The late Ray Wilson's <a href="https://docs.google.com/file/d/0B3wD73e_RyWdbFlUbEpqeExRa0U/edit" rel="nofollow noreferrer"><em>Make: Analogue Synthesisers</em></a>, May 2013.</p> <p>Ray is the brains behind Music From Outer space (MFOS) as described in <a href="https://electronics.stackexchange.com/questions/6077/building-a-synthesizer-with-no-prior-experience#answer-6085">Rob Kam's answer</a>. It describes the basics of synthesisers and providing the essential electronic theory behind sound generating circuits as well as explaining VCO, VCF and VCA.</p> <p>In addition, it also details the construction of the <a href="http://musicfromouterspace.com/analogsynth_new/NOISETOASTER/NOISETOASTER.php" rel="nofollow noreferrer">Noise Toaster</a>, which is a nice synth starter project.</p></li> <li><p>Barry Klein's <a href="http://issuu-download.tiny-tools.com/pages.php?doc_id=170805010116-a8df628185757cb73dc7a05240e7e986" rel="nofollow noreferrer"><em>Electronic Music Circuits</em></a>, 1982</p> <p>It is this book that I would recommend to someone starting out to build modular synths, if they wanted just one book.</p> <p>As Barry notes himself, the original publication contained a number of errors, </p> <blockquote> <p><strong>Electronic Music Circuits</strong></p> <p>This is a complete copy of the original book (published by Sams in 1982). It contains circuits for most every type of module you would want to make for a modular analog synthesizer. Some circuits are my own, some slightly modified from the Digisound series, many Electronotes circuits. There were a few errors in the original printing and I have made the corrections in this copy. Also, this copy is enlarged up to 8 1/2" x 11" - lots easier to read! I include a 32 page update booklet that suggests alternative approaches, parts substitutions, an updated source list, etc. There are no new circuits (in case you have the original book already). Many of the circuits use CEM/SSM chips that are no longer available, but these circuits may serve as examples for repairing analog synths using these IC's. There are discrete examples of VCO's, VCF's, envelope generators, etc. many of which you have seen discussed on this list. Page count is around 335 pages.</p> </blockquote> <p>He is selling a corrected version, if you contact him directly. See <a href="http://www.abacom.com/~ivanohe/synth/books.txt" rel="nofollow noreferrer">http://www.abacom.com/~ivanohe/synth/books.txt</a></p> <p>There is also a sister publication:</p> <blockquote> <p><strong>Electronic Music IC Databook</strong></p> <p>This is a collection of all SSM and Curtis Electromusic (CEM) IC datasheets as well as volume 1 and 2 of the Curtis Synthesource shortlived newsletter/ applications bulletin. As the majority of these IC's are no longer manufactured, this manual serves as a one source reference databook for all of them. The written material in these datasheets is surprisingly detailed as to how the IC's work internally, and how they should be applied. The Synthesource material is especially cool. I also include some material from Linear Integrated Systems, a source for matched transistor pairs.<br> Page count is around 300 pages (8 1/2" x 11"). </p> </blockquote> <p>If you want to get hold of the book, it might be worth reading this thread (which does <strong>not</strong> provide the PDF), <a href="http://electro-music.com/forum/topic-49865.html" rel="nofollow noreferrer">Barry Klein Book. Link to PDF</a>.</p></li> </ul> <hr> <p>Note that I am not affiliated in <em>any way</em> with either of these authors, but I just think that their books are great.</p>

<p>I've got an extensive music background and have been infatuated with synthesizers since I was young. I had dreamed of going into an EE program to make my dream a reality, but I couldn't afford school (long story).</p> <p>Basically, I'd like to build a 3 oscillator analog synthesizer, but I have zero experience building boards. I know basic signal flow and process and have a strong design sense, but I really lack the knowledge otherwise to get started. </p> <p>I think starting simple with a 1 oscillator and building upwards would be an awesome learning experience, and I would love to get to the level that some of you are at and actually make a fully usable synthesizer.</p> <p>My question is, for audio-oriented electronics, where can I get started for this full analog synthesizer? Am I reaching too far? What will I need to make this happen?</p>

Building a synthesizer with no prior experience

2010-11-02T21:41:36.660

6078

|pcb|

<p>I am also inexperienced and a learner on this. However, here are my thoughts:</p> <ul> <li>I would re-layout the "Buck Power Supply" part. I am hopeful that you can lessen its EMI radiation by reading a little on SMPS PCB design and current loops etc. Especially, see the application notes and sources below that were really helpful to me.</li> <li>For the "Buck Power Supply" part again, the tracks could be wider, I think you have space for that, for example the connection from D2 to L1.</li> <li>Your designators could face the same direction so that one can easily read them without turning his/her head.</li> </ul> <p>Here are some of the sources I remember and benefited much from:</p> <ul> <li><a href="http://www.national.com/an/AN/AN-1229.pdf" rel="nofollow">National Semiconductor - Application Note 1229</a></li> <li><a href="http://www.maxim-ic.com/app-notes/index.mvp/id/2997" rel="nofollow">Maxim - TUTORIAL 2997</a></li> <li><a href="http://www.analog.com/library/analogDialogue/cd/vol41n2.pdf" rel="nofollow">Analog Devices - An article from Analog Dialogue</a></li> <li><a href="http://www.edn.com/contents/images/336862.pdf" rel="nofollow">EDN designfeature article by Jay Scolio</a></li> </ul>

<p>Here's the current design for Super OSD Lite, an open hardware project to bring a low cost on screen display to the masses. The price target is $71 to $90.</p> <p><img src="https://i.stack.imgur.com/x7ZIB.png" alt="alt text"></p> <p><a href="https://i.stack.imgur.com/x7ZIB.png" rel="nofollow noreferrer">bigger image</a></p> <p>There are components on the bottom, but most components are on the top.</p> <p>It's one of my first PCB designs involving such a complex circuit, so I expect I've made a few mistakes. Constructive criticism appreciated!</p>

Have a look at my PCB design and tell me how I can improve

2010-11-02T21:43:42.943

6088

|temperature|

<p>The 0.1% means that the voltage can be 0.1% off at the rated temperature, which is usually 20°C. Since the temperature coefficient (TC) is positive and you're talking about higher temperatures you should count on +0.1%, not -0.1%, for worst case calculations. (For worst case calculations always make sure that errors add instead of cancel each other out.) So at 20°C your reference will be 3.003V worst case.<br> At 85°C the voltage may increase by 100 ppm/°C \$\times\$ (85°C - 20°C) = 6500 ppm, or 0.65%. So the voltage will be 3.003V \$\times\$ 100.65% = 3.023V. </p> <p>Yes, it also applies to resistors. Temperature coefficients range from a low 5 ppm to 250 ppm, depending on the materials used. <strong>Thick film</strong> resistors are the least temperature stable with a TC of 200 to <a href="http://www.vishay.com/docs/68036/rchr.pdf" rel="nofollow">500 ppm</a>. The widest variation can be found in <strong>metal film</strong> and <strong>thin film</strong> resistors, with some precision types having a TC as low as <a href="http://www.vishay.com/docs/60082/pltt.pdf" rel="nofollow">5 ppm</a>, while others have a TC of <a href="http://www.vishay.com/docs/31013/ccf07.pdf" rel="nofollow">200 ppm</a>.<br> If you would use a resistor divider to scale down your reference voltage, choose the same type for both resistors, then you don't have to account for TCs.</p>

<p>I have a 0.1% 3V reference with a temperature coefficient of 100ppm/°C.</p> <p>Does this mean it will be off by 8500ppm (0.085%) on top of my 0.1% when operating in an environment at 85°C?</p> <p>Does something similar apply to resistors?</p>

How does temperature affect voltage references, resistors etc.?

2010-11-03T00:28:14.840

6090

|sd|

<p>I think that T-flash and TransFlash are just the name of the microSD spec before it was adopted by the Secure Digital standards body.</p>

<p>Something interesting I've noticed with cheap devices from China (such as iPhone clones and digital cameras and the like) is that the manuals always specify they are "T-flash" (TransFlash) compatible, instead of "microSD" or "SD" compatible. Is this to get around paying the $3k/yr license fee, or is it something else entirely? The devices seem compatible with microSD as well as TransFlash cards.</p>

Micro SD cards & T-flash?

2010-11-03T00:31:00.797

6091

|oscilloscope|

<p>We have 2 and 4 channel scopes round the lab, and sometimes 4 channel is a lifesaver... however, these days we are just as likely to break out the BusPirate or Open Logic Analyser from Dangerous Prototypes when debugging digital stuff, especially comms protocols. There's some good scripting and capture capabilities that even a $1000+ (or $5000+) scope won't have.</p> <p>Total cost for both devices plus some nice colourful hookup leads will be a lot less than the extra you'd pay for your 4-channel scope, and between them they extend your capabilities further than an extra 2 channels.</p>

<p>I already have a 4 channel oscilloscope but it's quite old and I might have some money soon to upgrade with. The price for a 4 channel is almost 2-3x that of a 2 channel, but is the cost justified by the increased utility? I find I mostly use 2 channels on my scope currently, occasionally using a third but so far no use for all four. I'm dealing with serial protocols and video signals most of the time.</p>

4 channel scope vs 2 channel scope

2010-11-03T00:36:55.673

6093

|microcontroller|led|transistors|

<p>You might be better off with a pchannel mosfet (inverted logic out) or low side n-channel mosfet as they will perform will as switches for this type of application, and reduce the voltage drop across the device to be directly proportional to the LED current. With the bipolar transistor the LED current will be proportional to the PIC output current, and you will always lose 0.7 V across the emitter. A mosfet will have a low Rdson which can result in much less losses across the switching device.</p> <p>For selection purposes you need to know your maximum bus voltage, then double it, to give you margin of error, next look a device with the smallest Rdson for a given voltage and package and cost.</p>

<p>I'm going to be driving a bank of 20-25 LEDs from a single output of a PIC micro. Obviously, I need a transistor, because that's going to be somewhere in the vicinity of 400 mA (the LEDs are speced at 20 mA with 3.2V of drop, which I'll get close to by using a 100 ohm resistor and a 5V power supply). </p> <p>I get into trouble when I try to figure out what sort of transistor I should use for this, because I don't understand how transistors are rated. In discussions of general transistors, the 2N3904G &amp; 2N3906G come up as good, all-around NPN &amp; PNP transistors. How do I look at the transistor data sheet and understand that these transistors will work? What parameters do I need to pay attention to? I want to be sure the transistor can handle the load, and I want to be sure that my PIC's output can force the transistor all the way on.</p> <p>I've got some familiarity with digital electronics, but when we get into the analog world I just don't have enough of a frame of reference yet.</p>

How to pick a switching transistor to drive LEDs? Or, how to read a transistor data sheet?

2010-11-03T00:46:23.180

6099

|atmel|rs485|

<p>Try the MAX485 or MAX483 from Maxim IC: <a href="http://www.maxim-ic.com/datasheet/index.mvp/id/1111" rel="nofollow">http://www.maxim-ic.com/datasheet/index.mvp/id/1111</a> Very cheap and easy to use. Plus they can send data up to 4000 feet.</p> <p>Here's someone's tutorial on using them with Arduino: <a href="http://pskillenrules.blogspot.com/2009/08/arduino-and-rs485.html" rel="nofollow">http://pskillenrules.blogspot.com/2009/08/arduino-and-rs485.html</a></p>

<p>I am attempting to connect and control a device which only accepts RS-485 input. I wish to communicate to this device via my existing UC3A1512. Does anyone have any existing source code or examples that may help me to create this interface?</p> <p>I need a method of outputting date via RS-485 format.</p> <p>I do not need to establish round trip communication, I simply need the ability to send commands to the device.</p> <p>I have looked at Atmel's website and also on AVRFreaks and I see nothing of value to my project.</p> <p>Any help is welcomed and appreciated!</p> <p>I originally posted this question on <a href="https://stackoverflow.com/questions/4033256/does-anyone-have-any-sample-code-or-suggestions-to-help-me-to-interface-my-100-pi">StackOverflow</a> before I knew of <a href="http://electronics.stackexchange.com">electronics.stackexchange.com</a></p>

Does anyone have any sample code or suggestions to help me to interface my 100 pin uc3a1512to a device via RS-485?

2010-11-03T03:23:04.630

6108

|components|surface-mount|markings|

<p>A bit late reaction, so I guess you've found out by now, but for completeness: </p> <p><strong>WR5</strong> in SOT23 = <strong>BZX84-B6V2</strong>, 6.2V zener, by Philips </p> <p><strong>A7W</strong> in SOT23 = <strong>BAV99</strong>, dual diode, by Philips </p> <p><strong>1E</strong> in SOT23 = probably <strong>BC847A</strong>, NPN transistor, by Philips, but may also be either:<br> CM9NB847A, NPN transistor, by Canaan Microelectronics<br> FMMTA43, NPN transistor, by Zetex<br> KST43, NPN transistor, by Samsung<br> MMBTA43, NPN transistor, by ITT<br> R3131N29EC3, Vdet-IC 2.9V, by Ricoh<br> SMBTA43, NPN transistor, by Infineon<br> TMPTA43, NPN transistor, by Allegro </p> <p>All found in the <a href="http://turuta.md/smd2011.html" rel="noreferrer">SMD databook 2011</a>, 2500 comprehensive pages. Recommended.</p>

<p>I've got a SOT-23 transistor (I think, but it could also be an IC) marked with 1E. Another one is marked with A7W. Then I can also see WR5. How are you supposed to decode these?</p>

Small SOT-23 transistor markings

2010-11-03T07:40:06.913

6123

|power|wall-wart|

<p>Not enough to worry about. If you want to save the earth, you're better off washing your clothes in cold water, line-drying them, and using the microwave instead of the oven.</p> <p>Some actual tests of wall wart power consumption:</p> <ul> <li><a href="http://blog.lastinfirstout.net/2008/09/unplug-your-wall-warts-and-save-planet.html" rel="nofollow noreferrer">Unplug Your Wall Warts and Save the Planet?</a> <ul> <li>measured 0.5 to 2 W (= 0.4 to 1.5 kWh/month). </li> </ul></li> <li><a href="http://www.electronicsweekly.com/blogs/electro-ramblings/weird-wireless/weird-wireless-does-unplugging-all-your-wall-warts-really-matter-2009-08/" rel="nofollow noreferrer">Weird &amp; Wireless: Does unplugging all your wall-warts really matter?</a> <ul> <li>measured 0.4 W on average (= 0.3 kWh/month)</li> </ul></li> <li><a href="http://www.embedded.com/electronics-blogs/break-points/4230391/Vampire-Power" rel="nofollow noreferrer">Vampire power, Jack Ganssle, November 07, 2011</a> <ul> <li>4× &lt;0.1 W (= 0.07 kWh/month)</li> <li>1× 0.6 W (= 0.4 kWh/month)</li> <li>1× 8.1 W (= 6 kWh/month)</li> </ul></li> </ul> <p>By comparison:</p> <ul> <li>A single hour of running an electric oven uses <a href="http://energyusecalculator.com/electricity_oven.htm" rel="nofollow noreferrer">2.4 kWh</a></li> <li>A single load of laundry in a hot clothes washer uses <a href="http://michaelbluejay.com/electricity/laundry.html" rel="nofollow noreferrer">4.5 kWh</a></li> <li>A single load in an electric dryer uses <a href="http://michaelbluejay.com/electricity/dryers.html" rel="nofollow noreferrer">3.3 kWh</a></li> </ul> <p>If the wall wart is warm to the touch when unloaded, it's wasting a little energy and you could try to unplug it when not in use. If it's cool to the touch, then it's wasting very little energy. Don't worry about it.</p> <p>SMPS supplies and AC supplies shouldn't draw too much (an unloaded transformer is just an inductor, and only the residual resistance is wasting energy). DC supplies with linear regulators inside would be the worst.</p> <p>And in winter, definitely don't worry about it. The "wasted" energy is heating your home and making your heater work less. All household appliances magically become 100% efficient in the winter.</p>

<p>The title pretty much sums it up... Hyperbole aside, how much actual power is consumed by a typical wall wart when the device it's attached to isn't powered on? And are there designs for wall warts that minimize or eliminate this sort of parasitic load?</p>

How much power is really wasted by a wall wart?

2010-11-03T14:07:45.230

6134

|high-voltage|interference|

<p>Most likely partial HV discharges (corona) - these have an extremely fast risetime (sub nS) and therefore have a very wide spectral content. The high voltage also means the instantaneous current can be extremely high, so it gets everywhere.</p>

<p>In class today our physics teacher was demonstrating how ionic fluids move when a high voltage exists between them. A USB microscope was placed above the test rig, and the image was projected onto the virtual board. He used a 500V-5kV supply, limited to 60µA. The demonstration was interesting, but more interesting was what happened when he turned the supply voltage up: the image on the board began to flicker, then broke up completely and eventually "no signal" popped up. It also caused the USB microscope to reset.</p> <p>I'm thinking it was interference, but how could a high voltage but low current supply cause such problems for the projector? </p> <p>I think it might be related to my digital clock having difficulties (resetting, alarm going off randomly, time skipping several seconds at a time) when it is within about 10 cm of my plasma ball, because both use high voltages.</p> <p>Any ideas?</p>

Interference from high voltage power supply (EHT power supply)

2010-11-03T18:23:35.610

6140

|power-supply|batteries|

<p>Instead of measuring the output of your 3.3V regulator to find out when it's crashing due to low battery input, you should probably be measuring the battery voltage so that your battery doesn't get overdischarged. Done properly you can switch from one battery to another as the input to your 3.3V regulator without its output fluctuating below spec. If switching to a smaller battery you'd probably want to reduce the load at the same time.</p> <p>This question is basically the same: <a href="https://electronics.stackexchange.com/questions/4012/how-do-i-design-a-device-to-automatically-switch-to-the-backup-battery">How do I design a device to automatically switch to the backup battery?</a></p>

<p>I'm looking for a device which monitors a 3.3V line. When the line drops below, say, 2.7V, I would like it to switch power over to a battery backup (3V lithium coin cell.) It would also be good if it provided a logic signal to alert of the supply failure so the MCU in my project can switch over to a low power mode. It needs to be able to switch up to 120mA when the supply is high. What is the name of this device? I have a feeling it's quite common in applications like laptop computers. </p> <p>Ideally it would have 5 pins: Vin main, Vin backup, GND, Vout, Logic out.</p>

What's the name of the device I'm looking for

2010-11-03T19:39:07.590

6145

|microcontroller|netduino|

<p>The 100mA current requirement is easily met. On page 2 of the <a href="http://www.datasheetcatalog.org/datasheets/90/366828_DS.pdf" rel="nofollow">datasheet</a>, you can see that 3V will provide for up to 300mA sink current.</p>

<p>I want to be able to switch on a device that requires 5v and 100mA from a Netduino. From looking on the web, I believe I need to use a Darlington array in order to meet the current requirements (since the Netduino pins are only at 8mA max). Is a ULN2803 the right component to use? Can it generate what I need with the 3.3v of the Netduino?</p>

Using an ULN2803 with Netduino

2010-11-03T20:23:56.673

6148

|distributors|cable-assemblies|ribbon-cable|glcd|

<p>I ended up buying these and some pin headers from ebay. Not the prettiest solution but probably the handiest.</p> <p><img src="https://i.stack.imgur.com/qAEM7.jpg" alt="alt text"></p>

<p>Is it possible to buy Pre-Made cables &amp; headers to suit GLCD's, the model Im using has a 20-Pin interface like the model in the image below.</p> <p>If as I fear such a convience does not exist what do you use/have you found to be the neatest way to connect these?</p> <p><img src="https://i.stack.imgur.com/aPurB.jpg" alt="alt text"></p>

Pre-Made Cables & Headers for (Parallel Interface) GLCD's

2010-11-03T21:29:31.840

6151

|diodes|parallel|

<p>One thing I don't see discussed is the peak to average current. The parallel rectifiers have a capacitor on the DC side that is charged up somewhat close to the peak voltage. Therefore the rectifiers conduct only when the peak AC voltage exceeds the capacitor's voltage plus 1 diode drop. If the average load on the DC side is say 1 amp, then the rectifiers are going to conduct peak currents several times that much.</p> <p>So the rectifiers see high peak currents, and these make the low internal resistance of the diode junctions look to be equalizing the current between the paralleled rectifiers, just as someone else's suggestion to add external resistors to balance the current. I've seen this happen with LEDs.</p> <p>So it seems to me that besides (or instead of) matching diodes for forward voltage, they should be matched for forward voltage at their peak current.</p> <p>Here's a .PDF from ST with the nitty gritty. After I perused it I took away that if forward voltage difference is less than 40 mV it's ok to parallel diodes.</p> <p><a href="https://www.google.com/url?sa=t&amp;source=web&amp;rct=j&amp;url=http://www.st.com/resource/en/application_note/dm00098381.pdf" rel="nofollow noreferrer">https://www.google.com/url?sa=t&amp;source=web&amp;rct=j&amp;url=http://www.st.com/resource/en/application_note/dm00098381.pdf</a></p>

<p>I'm trying to repair an 800W power supply (see my previous question on this.) One thing that gets me is that the design has two schottky diode packages (in TO-220) in parallel. I was always told this was A Bad Idea, but since they are thermally coupled to the same heatsink, does it present a problem in this instance? I've also noticed the same for the input bridge rectifier, two are used in parallel.</p>

Is paralleling diodes a bad idea?

2010-11-03T23:43:28.923

6160

|ethernet|stepper-motor|tcp-ip|

<p>It looks like the <a href="http://ultimachine.com/ramps" rel="nofollow">Arduino Mega RepRap Pololu Carrier</a> (RAMPS) is compatible with the <a href="http://www.arduino.cc/en/Main/ArduinoEthernetShield" rel="nofollow">Arduino Ethernet shield</a>. The RAMPS board doesn't seem to use mega pins 50, 51, 52 and 10, which is what the shield page says it uses. I've never actually tried this myself though. The Pololu drivers can do about 1A and up to 35V. </p>

<p>For small batch production I am looking for small low cost product. Need it to be network controlled (Ethernet TCP/IP) with open documentation. The current is about 1..2..3 Ampere, voltage 24..48V. Also nice to have just 1..4 axes and DIN rail mount. </p> <p>Problem is, that everything I can find is serial port controlled or modular blocks with 2-3 accessories with proprietary software and lot of unnecessary features, making software part complicated and requiring for host PC to be equipped with extra $100 I/O ports.</p>

Sourcing for low power stepper motor driver assembly. Which is best cost and host software wise?

2010-11-04T01:52:42.313

6163

|microcontroller|netduino|pwm|

<p>Assuming your PWM output can supply enough current for both LED's then put a FET between the cathode and ground for each LED. Control each FET's gate with an I/O line from the microcontroller. This way you can turn either on, both off, or both on by controlling the I/O lines.</p> <p>Just make sure the PWM pins on the uC can actually provide enough current to drive the LED and that the current is properly limited.</p>

<p>I'm building a project where I will be lighting up 2 RGB LEDs using PWM. Since the Netduino only has 4 PWM pins (of which I will only use 3 - one pin each for the R, G, and B values respectively), I need a way to be able send the signal to either LED or both. Something like the following: <img src="https://i.stack.imgur.com/CcP8L.png" alt="Netduino PWM"></p> <p>What component(s) do I need for that black box? I considered something like a <a href="http://www.sparkfun.com/commerce/product_info.php?products_id=10136" rel="nofollow noreferrer">TLC 5940 PWM Driver</a>, but I want to be able to power this off of the Netduino itself (i.e. no external power source). Do I just use a bunch of AND gates?</p>

How to switch control between 2 RGB LEDs with PWM from a Netduino

2010-11-04T02:36:05.407

6168

|rf|antenna|

<p>cksa361, I am confused by your bounty because I am not sure what else you need answered except for the comment you left me, so I will answer that.</p> <p>When you pick between different chip antennas you will normally not find one that is significantly better than another in every way unless a new process was developed. In most cases you will have to pick the one that better fits your application, and to you this will seem significantly better.</p> <h3>Radiation Strength</h3> <p>The larger one, <a href="http://antenova.com/?id=408" rel="nofollow noreferrer">Mica</a>, has better radiation characteristics(more power out for the same power in). This means that for two transmitters radiating the same power, this antenna will get greater range. This also means the Mica antenna will receive from a source at a great distance much better.</p> <h3>Size</h3> <p>The <a href="http://www.taoglas.com/images/product_images/original_images/PA.15%20FR4%20SMT%202.4GHz%20Antenna%20090810.pdf" rel="nofollow noreferrer">Taoglas</a> is smaller. This is self explanatory, if space is an issue, or if the odd size of the mica causes problems, the Taoglas wins.</p> <h3>Tuning</h3> <p><strike> You will need to tune the matching circuit for the Mica one. For the Taoglas it seems they have a set matching circuit. This problem is approached in the question about <a href="https://electronics.stackexchange.com/questions/6917/measuring-output-impedance">measuring output impedance</a>. This can be challenging if you do not have the right equipment. A mistuned antenna will severely hurt your range, if you cannot tune you may find the Taoglas will be easier to use.</strike> </p> <p>Edit: I misread the datasheets, they both have reference designs. If you are going to vary your layout from the reference design (ie. You do not have room to do the exact say layout) on either antenna you will need to re-tune the circuit, as was linked in the paragraph with the strike-though.</p> <p>I hope this helps.</p>

<p>In my application, the device is going to be placed on top of a metal disc, less than a centimeter away from the pcb!</p> <p>Now I have prototyped up the device using a nRF24L01+ breakout board with only a chip antenna, and I can communicate with the device from a few meters away (obviously from a receiver with line of sight to the PCB, not from underneath the disc). However, if I want to enhance my design and enhance the reliability of the wireless link what kind of antenna should I use?</p> <p>Should I switch to a lower RF frequency band?</p> <p>From what I have read around the internet, a patch antenna with a ground plane underneath might be a good antenna to use, because the effects of the metal disc underneath the whole pcb will be reduced since our design involves a ground plane underneath the antenna anyway. This seems to take up a lot of space as opposed to a IFA antenna etched directly on a pcb.</p> <p>However, being quite new to all this RF theory, I basically don't really have a clue. Any ideas?</p>

Which antenna to use if close proximity to metal objects is unavoidable?

2010-11-04T03:51:30.757

6171

|prototyping|pcb-fabrication|etching|

<p><a href="http://www.pabr.org/pcbprt/pcbprt.en.html" rel="nofollow">"pcbprt - Experiments in inkjet PCB printing"</a> by pascal. Some inkjet printers can print directly CD and DVD. They can print on copper-clad FR4 to make reasonably good etch resist. The main trick seems to be baking the freshly-printed boards to dry out the ink and get the dyes/pigments to stick to the copper -- otherwise the water-based ink immediately washes off as soon as you drop the board in the etch tank.</p>

<p>Just what is special about the resist pens used to draw directly on PCBs before etching? Would a permanent marker work as well, or some other kind pen or marker? Naturally I have in mind something cheaper but good enough. This is for one-off handmade projects, single or double sided boards only.</p>

What's Special about Resist Pens?

2010-11-04T05:34:07.220

6172

|safety|workbench|

<p>Any good chemistry lab only has stools, rather than chairs. If you spill something and need to step away from it quickly (before it runs off the counter and into your lap), you don't want a chair with a back. </p>

<p>What was your worst electronics workbench accident involving equipment, voltage, soldering irons, chemicals, or whatever else, and what changes have you made to prevent that type of accident from happening again?</p>

What Workbench Safety Improvements Have You Made?

2010-11-04T05:46:43.433

6173

|resistors|colour-coding|

<p>The basic principle is simple enough.</p> <p>Each color represents a number. Black: 0, Brown: 1, Red: 2, Orange: 3: Yellow: 4, Green: 5, Blue: 6, Violet: 7, Grey: 8, White: 9.</p> <p>The normal pattern is.</p> <ul> <li>2-3 bands for significant digits of the value (interpreed as an integer, e.g. brown-black-black is 100).</li> <li>1 band for multiplier (10ⁿ for normal colors 0.1 for gold, 0.01 for silver)</li> <li>wider gap</li> <li>1 band for tolerance (this uses it's own meanings for the colors, the most common on modern resistors are probablly 5%: gold 1%: brown and 0.1% violet)</li> <li>Some resistors have an extra band for temperature coefficient, but this is rare.</li> </ul> <p>The reality though is that reliablly reading color codes on modern 1% resistors* in the "¼W" or worse "⅛W" body sizes** is very difficult. The bands are often very thin and perception of the colors can easilly be shifted by lighting and the background color, so it's really easy to misread a color band. Further the wider gap is at best only marginally wider and sometimes there doesn't seem to be any distinguishable difference at all in the gaps, so it's easy to end up reading the code backwards.</p> <p>You can mitigate misreads to some extent by knowing or having a table of likely resistor values. If the value you read isn't in a table of standard resistor values ( <a href="http://www.logwell.com/tech/components/resistor_values.html" rel="nofollow noreferrer">http://www.logwell.com/tech/components/resistor_values.html</a> ), then you almost certainly misread it. This doesn't help you with misreading the multiplier though.</p> <p>* 5% resistors are easier for several reasons, first they usually have the 4-band code giving more space per band. Secondly the last band is gold which basically eliminates the chance of reading the code backwards. Thirdly the background is usually a relatively neutral tan color rather than the blue/green backgrounds typical on metal film resistors.</p> <p>** Note, body size and power rating are not nessacerally the same, it's common to see 0.6W resistors in the "¼W" body size and 0.4W resistors in the "⅛W" body size</p>

<p>The title says it.</p>

How to find the resistor value using the color codes?

2010-11-04T06:35:40.660

6174

|led|infrared|components|

<p>Funnily enough, I've solved the problem myself assuming the question didn't come up, and only then searched for it :). Although I think the camera phone approach is usually the most practical, here's the solution I applied, in case someone finds it useful:</p> <p>If you have a photoresistor that's sensitive to IR, you can just connect it to a multimeter and place it in front of the LED. Obviously, if there's a change of resistance as you turn the LED on and off (without affecting ambient light sources), this means the LED is working.</p> <p><em>Caveat: you have to have to at least have the datasheet for your photoresistor somewhere handy (and one good enough to show you wavelength sensitivity), and at least remember the highest operational wavelength of the IR LEDs you have stocked.</em></p>

<p>For all the other stupid things I often do, I've found ways to boobytrap myself. For example keeping my wallet on the floor where the door opens - I can't help but stumble on it when I leave the house. But here's an electronics parts problem that has me stumped.</p> <p>I sometimes accidently throw out IR LEDs as "nonworking" since they don't visibly glow when tested. How can I prevent myself from doing that, at least to force myself to reconsider and remember there's such a thing as IR?</p>

Keeping those IR LEDs

2010-11-04T06:36:56.007

6191

|pcb|tqfp|

<p>L is for Low-profile (1.4 mm) and T is for thin(er, 1.0 mm), so I think the only definitive difference between them is height. The pitch and package size can vary within each.</p>

<p>In my PCB editor, both LQFP and TQFP have the same footprints, except the TQFP has shorter leads than the LQFP. Is that the only difference?</p>

LQFP package vs. TQFP package?

2010-11-04T13:47:40.407

6206

|oscilloscope|ratings|

<p>AC signals sometimes ride on a DC voltage level. On the scope you may see a sin wave of +60 to - 40 VDC. This is 100 V Ac signal riding on a 10 V DC voltage. </p> <p>I once worked with a 10 V peak to peak sin and cos signal from a resolver. The reference signal had a 0 V, 400 mV or 800 mV DC level applied to it. A multiplexer would switch between 3 different resolvers based on DC level.</p> <p>Your scope could handle anything from 250 V peak AC signal to a peak 125 VAC on top of 125 V DC to a pure 250 V DC or any mix as long as the AC Peak signal + the DC level is less then 250 V</p> <p>For dealing with High voltage signals, use high voltage probes. These typically reduce the signal by a factor of 10 or more. So a 250 VAC signal become a 25 V signal.</p>

<p>My oscilloscope's inputs are rated "250V DC + AC peak (10 KHz)." Does this mean it would withstand mains voltage (325V peak) or only 250V DC? I have <strong>no</strong> plans on doing this any time soon, I am only curious.</p>

What does 250V DC + AC peak mean?

2010-11-04T15:45:37.543

6211

|operational-amplifier|

<p><img src="https://i.stack.imgur.com/eFrK1.jpg" alt="enter image description here"></p> <p>I will try to answer to answer in a simple way. When we cascade to systems its gain will be multiplied in frequency domain. Assume that the maximum gain of the system is 1. So its 3db frequency is '.707'. Let's call this frequency F' which is the cutoff frequency of the system. </p> <p>Let's check the value of gain at F' for the cascaded system. This is were it gets interesting. For the cascaded system the gain at F' will be .707×.707=0.499. So F' is not the cutoff frequency of the cascaded system. Thus the new cutoff frequencies shifted from the old value and the new bandwidth will be lower than previous one. I have tried to illustrate this in the above drawing. Hope you will get my point. </p>

<p>I've had this question for a while.</p> <p>Assume you have an otherwise perfect op-amp with a gain-bandwidth product of 5 MHz. You input a signal of 50mVp-p and amplify it by 10x. This limits your bandwidth to 500 kHz. Now, say you stack another op-amp on the output and configure that as a 10x amplifier. Your overall bandwidth is 500 kHz but you have amplified by 100x, so your GBWP is 50 MHz. Where is the flaw in this logic?</p>

Op-amp gain bandwidth product

2010-11-04T16:05:23.160

6212

|reliability|

<p>People already named ceramic SMD as alternative. But there are even better things. Look at stacked film SMD caps which are even more reliable, can stand mechanical stress, self heal and acoustically immune.</p>

<p>I'm trying to design my project, Super OSD, to be as reliable as possible. I want it to work good as new when 5 years old. I hate unreliable products, environmentally it's a waste, and economically it's expensive.</p> <p>To that end, I'm avoiding electrolytic capacitors, and I've spec'd everything at least 1.5x, most 2x where size/cost permits. However, I am still having to use tantalum bead caps for the on-board regulators of the microcontrollers.</p> <p>Are there any other things I should be aware of?</p>

Component reliability

2010-11-04T16:11:08.413

6220

|microcontroller|

<p>It's not just possible, it's darn useful.</p> <p>All pins are inputs on power up.</p> <p>Commonly used by embedded software guys like me to give a interrupt from a GPIO.</p> <p>Who says there's no software interrupt instruction ?</p>

<p>My dsPIC33F does not seem to support routing the comparator to the input capture module. Would it be okay to run a wire from the comparator output to the input capture input?</p> <p>I'm using a <a href="http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en532298" rel="nofollow">dsPIC33FJ128GP802</a>.</p>

Is it okay to wire an MCU output to an MCU input on the same chip?

2010-11-04T18:52:08.100

6227

|sensor|

<p>LOL 75 Gauss means never having to say your circuit failed; the electrons in there aren't going in any loop the magnet didn't pick first! Pick an optical sensor (e.g. a mineral anvil or mirror, or more easily a simple F/O loop) and remotely detect changes in light transmission and polarization to confirm the field characteristics. Are you making bets with <a href="http://www.magnet.fsu.edu/" rel="nofollow">http://www.magnet.fsu.edu/</a> , installing your first maglev train, or just in charge of field cleaning COTS naval artillery? I knew One Piece was popular, but not maglev trains....</p>

<p>I'm looking for a sensor that can detect large magnetic fields. Basically, I want a 1 when the field is greater than 75 Gauss, and a 0 when it's less than 75 Gauss.</p> <p>I believed (EDIT: Wrongly!) Hall Effect sensors rely on moving through a magnetic field. <s>Unfortunately, my application does not permit me to move through the field, and the field is not changing.</s> It's since been pointed out that the Hall Effect does not rely on a change in the magnetic field. However, I still do not have any control over the orientation of the field.</p> <p>Does anyone have any suggestions on how to detect such a magnetic field?</p>

Magnetic Field Sensor?

2010-11-04T22:05:02.537

6228

|programmable-logic|

<p>A simple GAL programmer: <a href="http://elm-chan.org/works/pgal/report_e.html" rel="nofollow">http://elm-chan.org/works/pgal/report_e.html</a></p> <p>And if you want to know how to program: <a href="http://www.rexfisher.com/Downloads/CUPL%20Tutorial.htm" rel="nofollow">http://www.rexfisher.com/Downloads/CUPL%20Tutorial.htm</a></p>

<p>GAL chips seem expensive to get started with, since programmers cost hundreds of dollars and even ISP cables aren't cheap.</p> <p>Is there a cheaper way?</p>

Is there an inexpensive way to get started with GAL (Generic Array Logic) chips?

2010-11-04T22:05:38.717

6229

|sensor|amplifier|sampling|

<p>Your DAQ probably looks pretty similar to an opamp from the sensors perspective. I can't imagine your DAQ having anything overly special about its input impedance. Even if it did, you would need to be concerned about the input impedance of a new DAQ.</p> <p>What I would be concerned about is the noise floor associated with your sensors and circuitry. You are needing to look at voltage ranges that most oscopes can't even see. You will need to put time into every aspect of your signal acquisition including board layout and shielding from noise.</p> <p>You may be able to to use just a simple op-amp to provide your gain, but be cautious of the noise as opamps can be very noisy if you aren't careful on what you buy. There are other methods of providing a gain, but I suspect that will all have issues with noise.</p>

<p>For my senior design project, we have various sensors (Thermocouples, Heat flux sensors, load cell) plugged into our DAQ. We are using LabView and some National Instruments devices (ugh) and discovering that our loaned equipment doesn't have the resolution necessary to read accurate values from our heat flux and load cell sensors. The DAQ can read around a 100 mV range effectively. The heat flux sensor provides values in the microvolt range (0-100uV IIRC) and the load cell is in the milivolt range (0-5mV). We're looking into getting a better DAQ, but I was wondering if there is a way to easily amplify these signals into the volt range? Our grad student we have working for us is very concerned about impedance and other factors that can throw off our readings and is very against any sort of amplification circuits. Is amplification a viable route, and how would we go about amplifying the signal?</p>

What should I be using to amplify a heat flux and load cell signal?

2010-11-04T22:07:57.083

6230

|radio|data|hd|

<p>First of all compress the data to get the bandwidth down to less than 20 Mb/s, then get long range 5GHz 802.11n radios with directional antennae like these:</p> <p><a href="http://ubnt.com/" rel="nofollow">http://ubnt.com/</a></p> <p>If one end is mobile, then you will need to steer the antennas to keep them pointing in the right direction.</p> <p>I'd find some low-bandwith + long-range radios that can be used to transmit the GPS position of the rover back to the base to allow the base-antenna to be aimed.</p> <p>An alternative solution would be to have two radios at either end and scan the second radio around to optimize the aim of the main radio, but mechanically that's quite complicated and heavy.</p> <p>You might get away with an omnidirectional antenna on the rover and only use a directional antenna on the station, but range will suffer a lot.</p>

<p>I'm considering a future product. A high definition (720p) video transmitter. Ideally a compressed MPEG link would be used but this would still require at least 80 Mbit/s. I'm not looking at a simple solution, and I don't even think it's possible without high cost and big transmitting gear, but what is everyone's opinions? What about sending component video over long distances? I'm talking about 10km or so and the link must be wireless. The nodes may move, one would likely be an RC plane.</p>

What kind of options are there for very high bandwidth long distance data links?

2010-11-04T22:19:10.530

6248

|connector|pins|

<p>As well as potential shorting issues, you should consider physical robustness, and which end is more likely to sustain damage by handling etc.</p>

<p>I think I've found a solution for <a href="https://electronics.stackexchange.com/questions/5620/mechanical-connectors-for-flexible-pcbs">my previous question</a> and I'm now going to order some <a href="http://portal.fciconnect.com/res/en/pdffiles/datasheets/950500-025_FPC-Clincher2.pdf" rel="nofollow noreferrer">FCI "Clincher"</a> connectors from a local supplier to try them out.</p> <p>My question is, should I terminate the ends of the <a href="https://electronics.stackexchange.com/questions/5620/mechanical-connectors-for-flexible-pcbs">flexible LED strips</a> with <a href="http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&amp;name=609-2160-ND" rel="nofollow noreferrer">sockets</a> or <a href="http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&amp;name=609-2178-ND" rel="nofollow noreferrer">pins</a>? And why?</p> <p>(In practice I'm going to be using sockets for this prototype because that's what <a href="http://sg.element14.com/" rel="nofollow noreferrer">Element14</a> have in stock, but if there's a strong reason to do it the other way 'round its worth me waiting for the stock to come in for the "real" (much bigger, more expensive) project.)</p>

Sockets or pins, and why?

2010-11-05T06:24:19.230

6259

|measurement|energy|current-measurement|

<p>Energy consumed by the electrical loads or appliances can be measured by the Induction type energy meter. The basic principle governing the working of the energy meter is same as that of wattmeter (power measuring instruments) except that in an energy meter a counting or registering mechanism is used which accounts for time interval over which the meter is being used, i. e, power integrated over a<br> time which gives the energy consumed. In energy meter we have a rotating Aluminum disc which rotates due to the torque exerted on it (the torque is produced due to the interaction between the flux and the eddy current induced in the disc) .The rotating torque is proportional to the power consumed, To have a constant speed of rotation a braking magnet is installed which enables the disc to rotate with a constant speed which is directly proportional to the power consumed. Since a recording mechanism is used(consisting of gears and racks and pinions arranement), which gives integral of Pdt, i. e the energy consumed which is equal to the total number of revolutions(integral of No. Of revolutions × dt). Hence by knowing the number of revolutions and the meter energy constant we can calculate the energy consumed.</p>

<p>How do devices which measure energy consumed work? For example the ones in solar regulators/chargers which display how many Ah went into the battery and how many went out?</p> <p>Do they just measure the current for example every second and a microprocessor constantly adds up the measurements, assuming that the current 0.5s before and after each measurement is the same as while they take the current measurement, or do they have a way of really measuring how much energy went through, without referring to such, possibly inaccurate approximation?</p>

how do energy consumption (Ah, kWh) meters work?

2010-11-05T11:02:20.647

6288

|mosfet|

<p>just get some solder paste, apply to the board (not too much), drop on the fet, and bake it... easy</p>

<p>I'm looking for a replacement MOSFET for the SI7460DP. It's a 60V 11A 0.0096 ohm MOSFET.</p> <p>I don't think I can solder the PPAK, but a design I am using requires this fet. So I'd be okay with SOT-89, SOT-223, DPAK, SOIC-8 - anything with exposed leads - if it fits the requirements I'd be happy with it.</p> <p>Any suggestions?</p>

Replacement MOSFET (in a different package)

2010-11-05T19:16:24.210

6295

|pic|filter|iir|fir|

<p>Best way is to design and simulate your filters and algorithms in matlab and then implement the functions by writing your own C code. By using matlab you can tune your filters on real data for optimum results and then write your c code based on the initial values.</p> <p>At some point you will need to consider rounding and errors (for example real filter coefficents are floats in matlab) and you will probably want to implement them as integers on the pic to reduce the overhead of floating point arithmetic.</p> <p>Once you have written your code and tested it, transfer it back to matlab to see the effects of the rounding errors, and optimise your filter coefficients there.</p> <p>This may sounds difficult, but in the long term it will give you a few things. Better understanding of the filters, better understanding of the dsPIC architecture and built in hardware (integer multiplier), understanding of rounding errors on the filter coefficents, and most importantly highly optimised code! </p> <p>It is the optimised code that you really want running on your dsPIC. You will only be able to acheieve this by iterating between matlab and your c code (perhaps even assembly if you want to getter maximum performance out of the pic).</p>

<p>I have to make a filter with DSPIC33 and I want a program that design the filter (there are a lot), yet export code to DSPIC (in c, any compiler or assembly).</p>

Does somebody know about a tool to design filters for DSPIC?

2010-11-05T22:08:57.870

6301

|capacitor|ceramic|

<p>Ceramic capacitors close to their maximum voltage rating lose capacitance. A 6.3V cap may have up to 60% lost in capacitance at the full rated voltage and over the full temperature and tolerance range. Depending on your application, this could cause a lot of intermittent problems.</p>

<p>What is the difference between a ceramic capacitor of the same dielectric, but different voltage rating?</p> <p>Would the lower voltage one have lower ESR or ESL?</p> <p>For example,</p> <p>X7R 10uF 4V </p> <p>as compared to a</p> <p>X7R 10uF 10V</p>

What is the difference between a ceramic capacitor of the same dielectric, but different voltage rating?

2010-11-05T23:28:35.297

6303

|batteries|

<p>No, it is definitely not safe.</p> <p>The Li batteries and compatible chargers usually mate with more than just 2 wires. The battery must include termoswitch or thermometer circuit which is servo feedback to charger controller. The constant parameter of control loop is not a voltage or current, but top temperature over time figure to avoid fire damage.</p>

<p>I have 9V Li-ion battery. If I apply regulated 9V to it, will it recharge? What about other kinds of rechargeable batteries?</p>

Is it safe to recharge a battery without a specific device?

2010-11-05T23:45:08.083

6305

|current-measurement|

<p>Allegro is often a first choice for high side current monitors, but it appears they don't have anything smaller than SOIC, like the <a href="http://www.allegromicro.com/en/Products/Part_Numbers/0712/0712.pdf" rel="nofollow">ACS712</a>, CMIIW. This has the current sensor itself integrated, so it may compete with a SOT-23 solution. </p> <p>For a SOT-23 you have for instance the Zetex <a href="http://www.diodes.com/zetex/_pdfs/3.0/pdf/ZXCT1009.pdf" rel="nofollow">ZXCT1009</a>. This has a transconductance of 10mA/V; a short PCB trace could serve as current sensor. A 1cm zigzag trace 0.2mm wide then gives you 250\$\mu\$A/A, so a 1k\$\Omega\$ load resistor will result in 750mV full scale.</p>

<p>I'm looking for a high side current monitor which can measure 0-3A on a 12V rail with either a built in sense resistor or with a hall effect current sensor. I'm also space constrained, to SOT-23 or so in size. Does anyone have any suggestions?</p>

Measuring current drawn on a 12V rail

2010-11-06T00:36:20.097

6312

|voltage|basic|

<p>­The­ three most basic units in electricity are voltage (V), current (I, uppercase "i") and resistance (r). Voltage is measured in volts, current is measured in amps and resistance is measured in ohms.</p> <p>A neat analogy to help understand these terms is a system of plumbing pipes. The voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the resistance is like the pipe size.</p> <p><a href="http://science.howstuffworks.com/environmental/energy/question501.htm" rel="nofollow noreferrer">Courtesy</a></p> <p><img src="https://i.stack.imgur.com/Ub2NK.jpg" alt="enter image description here"></p>

<p>I understand that this is a really basic question, but, I've been unable to really understand electrical terminology for some reason. What exactly is an amp? How does it correspond to a watt?</p> <p>And: How does a watt correspond to a volt? What does the frequency of electricity refer to? (Hz, 50/60)</p> <p>Please be as specific, and laymeny as possible :).</p> <p>Thank you!</p> <p>Edit: Since I didn't get anyone yelling at me for talking about adding a few more questions, here goes:</p> <p>What is a volt? My understanding of it is the difference between the neutral and phase, but, this doesn't make it any clearer. If anyone can help out with more information, with an analogy or two, plus some technical information, I'd appreciate it very much!</p> <p>What does the "earth"/ground portion of the circuit do? How does it help safety? If it helps safety, why aren't all plugs 3-pin instead of 2-pin?</p> <p>Hypothetical:</p> <p>If I plugged in two wires to a socket, and put the other end into something conductive (for instance, a bucket of water), assuming the breaker doesn't go off (if it would, why would it?) after I remove said wires(or turn off the socket), does the water "hold" the charge? Is it in any way unsafe?</p> <p>For what it's worth, I'm assuming no. The current flows from phase-neutral, the water simply facilitates this. Right? If I'm right, I assume this means that I am in some way "using" the electricity? How does this differ if I for instance put the wires up against a block of wood? How does it differ if I stick the wires on myself?</p> <p>I apologize if some of these questions show a fundamental mis-understanding of electricity. If they do, smack me across the head and point me to a resource that will educate me and help me answer such questions myself. These questions have plagued the back of my mind for a while, but I've never found the right place to ask.</p> <p>I have more such questions, both hypothetical, and real (how does a stabilizer work, why is it required? Why do motors require 2x as much electricity to start up vs to run? Why can't this be optimized/why hasn't it been fixed yet?). I'm hoping I'll be able to answer the hypothetical ones myself once I gain more of an understanding, with your help.</p> <p>I hope questions at these level (and their answers) are useful to at least one other person!</p> <p>Again, Thanks to whoever helps me out!</p>

What is an amp (and other such basic questions) in the simplest possible terms?

2010-11-06T04:38:21.930

6315

|vhdl|verilog|hdl|

<p>Coincidence or not, I just came across to this today: <a href="http://www.nandland.com" rel="nofollow">http://www.nandland.com</a></p> <p>[moderator note: This answer had arrived here as a result of a merge.]</p>

<p>I was planning on learn an HDL (preferably verilog as I have to take a course in it in subsequent semesters). My initial plan was to first learn the syntax and then implement all the digital systems I studied in my digital electronics course using HDL. But just out of curiosity, is there a book which would combine teaching computer architecture with HDL implementation? I think that would be much more fun.</p>

Exercise based book to learn Verilog/vhdl?

2010-11-06T09:02:06.530

6316

|inductor|sepic|

<p>I think coupled inductor is marketing techno-term. I fail to see difference between 100% coupled inductors and perfect transformer. and.. Look, you can buy whole 2 inductors for price of one transformer.</p>

<p>What is the difference between a coupled inductor and an actual transformer? The LT3757 datasheet mentions that I need a coupled inductor for the SEPIC to work</p>

Coupled inductor vs an actual transformer?

2010-11-06T09:13:18.467

6321

|transformer|inductor|

<p>Most off-the-shelf inductors are "shielded" specifically to <em>prevent</em> one inductor from coupling with another inductor (or anything else).</p> <p>If you use "unshielded" inductors, or wind your own coils without shielding, or break the shielding off some inductors, all too often you <em>do</em> get unwanted coupling between inductors -- enough to be annoying, but usually not enough to do anything useful.</p> <p>To get good coupling between coils, you pretty much have to wind them both on the same bobbin -- producing a transformer.</p> <p>Some examples of coupled inductors made from 2 coils that are different from standard wire-wound transformers (and therefore have worse coupling than a standard transformer):</p> <ul> <li><a href="http://en.wikipedia.org/wiki/Transformer_types#Planar_transformer" rel="nofollow">planar transformer</a></li> <li><a href="http://www.afrotechmods.com/cheap/arnoldpad/arnold.htm" rel="nofollow">Arnold fixed my mousepad charger</a></li> <li><a href="http://web.mit.edu/newsoffice/2007/wireless-0607.html" rel="nofollow">WiTricity</a></li> </ul>

<p>Is it possible to create a coupled inductor (with high coupling coefficient) by just placing two inductors very close to each other on the PCB? (Even as far as placing them on top of each other.)</p>

Creating a coupled inductor with two discrete inductors

2010-11-06T12:25:50.533

6323

|power|resistors|reliability|

<p>Be careful of film resistors, where the film can be easily vaporized during power surges, EVEN IF the temperature of the entire package remains within safe limits.</p> <p>Wire wound and resistive pellet resistors have much more thermal inertia than film resistors.</p>

<p>I am dealing with a 0.01R 500mW resistor. It is a current sense resistor and measures the current flowing through a MOSFET and inductor. According to simulations, when the supply starts up, the RMS current is very high (~3A) for about 1 millisecond, and the resistor will be exposed to pulses of ~1.2W. The pulses then drop down to 200mW, and the RMS is around 125mW. Is it okay to briefly exceed the ratings of any resistor? </p> <p>If I have to pick a 2W resistor it will be much bigger, so I'd like to use a smaller resistor, but reliability is a high priority for this product.</p>

Is it okay to briefly exceed a resistor's power rating in a high-reliability product?

2010-11-06T12:48:57.980

6331

|buck|ldo|

<p>Buck converters usually perform poorly at 'standby' currents of just a few microAmps.</p> <p>I've actually used battery powered designs combining both an ldo and a buck converter together, where the uC runs of an ldo, and switches on a buck converter powered circuit which consumed ~300mA for a few minutes at a time.</p>

<p>I want to step down 5V to 3.3V at around 250mA. </p> <p>As far as I see it, there are two options to consider:</p> <ul> <li>Buck: more space, higher cost</li> <li>LDO: less space, lower cost, more difficult to remove heat(?), less efficient(?)</li> </ul> <p>What I am wondering is will the LDO be more efficient and better at doing this job? I've heard things like 6V to 5V solutions usually use LDO's instead of buck regulators because they are more efficient, but I'm wondering if this works for 5V to 3.3V?</p>

For a small Vin-Vout difference, is it worth using an LDO vs a buck regulator?

2010-11-06T14:01:11.663

6334

|soldering|surface-mount|

<p>I have no expirience in manual dispense, but I know the automatic and semiautomatic paste printing. Talking of how much manual effort is involved, consider this. When you are using oven for reflow step, then there are no hands involved. So the limit is defined only by 2 factors. Proper amount and type of solder and thermal profile.</p> <p>Component placement is not critical, because reflow is automatically aligning components with wet forces. The geometry of footprints and solder masks is not manual either, just follow the specified footprint for each component. Thermal profile is easy to achieve with measurement, timing etc. For simple components (not a bga or 100 pin) the geometry of paste is not critical.</p> <p>So limit is in accuracy of amount of paste dispensed on a pad. For manual dispense, I'd recommend create a syringe with some screw pusher and calibrate the amount of paste per angle of screw rotation. This must work for any sizes.</p>

<p>0402 packages - absolutely tiny. I'm wondering if it's possible to reflow solder them using a hotplate/skillet or toaster oven. Does anyone have any experience with doing this?</p>

Boundary of DIY soldering: is it possible to reflow 0402?

2010-11-06T15:18:40.600

6339

|wireless|infrared|

<p>Like the others said, use a modulated signal. It will give you a much more reliable transmission. For the receiver I often use <a href="http://www.vishay.com/ir-receiver-modules/" rel="nofollow">Vishay</a>, which has a wide offering in carrier frequencies, packages and protocols. </p> <p>In its most basic form the transmitter is just an astable multivibrator driving the IR LED. But the <a href="http://www.vishay.com/ir-receiver-modules/agc-list/" rel="nofollow">AGC</a> (Automatic Gain Control) in the receiver is not designed to receive a continuous carrier. So it's better to simulate some RC protocol and choose a receiver for that protocol. </p> <p>For the transmitter you can use a small microcontroller like the AVR <a href="http://www.atmel.com/Images/doc8127.pdf" rel="nofollow">ATTiny4</a> or Microchip <a href="http://ww1.microchip.com/downloads/en/DeviceDoc/41239D.pdf" rel="nofollow">PIC10F200</a>. Both have an internal oscillator and work without any external components, then all you need is a resistor, a transistor and the IR LED. </p> <p>While the AVR is more performant than the PIC, this is not required here, and overmore: the accuracy of the "calibrated" internal oscillator for the AVR is a disappointing 10%, while the PIC is 1% accurate. So the PIC may be the better choice.</p>

<p>What I need is: when I turn on a IR led, a receiver circuit in the other side would have 5V or 0V depending on the state of the transmitter. Simple.</p> <p>I have a IR transmitter and a photo-diode for receive, those used on every IR control and receiver. I don't know how the photo-diode works so how should the circuit be? Should I use a transistor configured in saturation / cut-off working with the receiver?</p> <p>Feel free to recommend me. Thanks</p>

Simplest remote IR?

2010-11-06T15:57:00.070

6344

|serial|uart|tv|

<p>If you just need to shift the voltage levels, use a <a href="http://en.wikipedia.org/wiki/MAX232" rel="nofollow">max232</a>.</p> <p>These chips are very dependable and resilient. I would suggest against building a logic shifting circuit.</p>

<p>I have a <a href="http://www.newegg.com/Product/Product.aspx?Item=N82E16889259013" rel="nofollow">Magnavox 42MF438B/27 42" LCD TV</a>. The IR sensor (or something related) quit working after awhile, so we have been unable to use the remote. Today, I was digging around behind the TV and noticed a "Serv U." port on the back with what looks to be a standard 1/8" jack. I figured this was a serial port for firmware upgrades and what not. Some quick googling revealed this assumption was correct... the manual calls it "Service UART". So I am assuming it is a standard 1/8" TRS plug, one ground, one send, one receive.</p> <p>My hope is that I can send it commands... volume up/down, power on/off, etc. over this port. Trouble is, I can't find any specs.</p> <p>Does anyone know what the voltage this serial port runs at? I'd rather not fry it with RS232 levels if it is just 3.3V. Then, any thoughts on what the pinout might be? Or, any safe way to find out?</p> <p>Finally, any thoughts on where I can find protocol spec? I certainly have no problems poking around, but I'm hoping perhaps a Philips tech can help me out here a bit.</p> <p>Thanks a ton!</p> <p><strong>Edit:</strong> I found <a href="http://answers.yahoo.com/question/index?qid=20080127142336AA3gAmN" rel="nofollow">another message board post</a> where someone's manual says, "For use by authorized service personnel, for installers, integrators, do not connect RS232 without level shifter", so I think I am on the right track. 3.3V then I am guessing? I think I have an old USB->cell phone cable around with the appropriate adapter.</p> <p><strong>Edit #2:</strong> <a href="http://www.scribd.com/doc/26366292/Philips-q528e-Service-Training-Manual-Part2" rel="nofollow">I found a service manual</a>! It says their techs can connect with HyperTerminal... 38400 bps, 8/N/1. It also says I can access "Customer Service Mode (CSM)" by keying in the code <code>123654</code>. For "Service Default Mode (SDM)", <code>062596menu</code> or for DVB-T Service Mode, <code>062593menu</code>. For "Service Alignment Mode (SAM)", <code>0625961+</code> (osd/status). That last character may be an "i", not sure. Program display option code, <code>062598menu</code>. No specs on the port itself though, or what is in those modes. Still digging...</p> <p><strong>Edit #3:</strong> Seems the service cable adapter kit is called ComPair, or possibly ComPair II.</p>

Philips/Magnavox LCD TV Service UART / ComPair

2010-11-06T20:49:25.740

6370

|antenna|

<p>Here's the "Dropout's guide to antenna design"</p> <p><a href="http://colinkarpfinger.com/blog/2010/the-dropouts-guide-to-antenna-design/" rel="nofollow">http://colinkarpfinger.com/blog/2010/the-dropouts-guide-to-antenna-design/</a></p>

<p>I know that getting a perfect tuning network for an antenna and transceiver requires some rather expensive equipment plus human knowledge to operate the equipment. I have never done any antenna tuning, but I would like to know if there is any way a DIYer can perform at least a semi-decently good match.</p> <p>Is there any way I can use an oscope to do this? Is there any difference between tuning a PCB antenna versus a wire antenna?</p>

DIY Antenna Tuning

2010-11-07T18:04:36.943

6372

|pcb|soldering|heatsink|heat|

<p>Like others have said: use a clamping vice. I use a Bernstein <a href="http://www.bernstein-werkzeuge.de/Kataloge/WSPGB.pdf" rel="nofollow noreferrer">Spannfix</a>: </p> <p><img src="https://i.stack.imgur.com/5CEgV.jpg" alt="Bernstein Spannfix"> </p> <p>It won't help to keep the PCB cool, but at least you won't burn your fingers.<br> The seemingly hot PCB is not really a problem. A PCB which is at 60°C may be too hot to touch, but during reflow soldering the whole PCB is exposed to temperatures close to and above 200°C <em>for minutes</em>. This way much more thermal energy is applied than you can with a hand soldering iron.</p>

<p>I've noticed that when soldering small PCBs can get very hot. Since I haven't yet been able to find a good vise in which to hold PCBs, I mostly hold them in my hand and after several minutes of soldering, they tend to get uncomfortably hot.</p> <p>I haven't seen many information on Internet about this, so I'm asking for tips here.</p>

How do I keep PCBs cool when soldering?

2010-11-07T20:15:03.667

6379

|cooling|fan|

<p>All the air that gets in will get out and the air resistance is the same in both direction so it is more or less the same thing. There are however some scenarios where it does make a difference. For example, if you have:</p> <blockquote> <p>| Low power sensible components | High power components | Fan ---> |</p> </blockquote> <p>Then you definitely want the fan to take the air out because otherwise, the high power component would heat the sensible component.</p> <p>Another aspect to keep in consideration is that air speed is faster and more directional at the output of fan and slower and more distributed at the input. If you have a single very high power component that is difficult to cool down, you may want to point airflow directly to it, even if it will cause the rest of the unit to be hotter.</p> <blockquote> <p>| Heat resistant components | Single very hot component | Fan &lt;--- |</p> </blockquote>

<p>For a fan, should air be sucked in, or should it blow air out?</p> <p>I'm talking about an enclosure mounted fan.</p>

Fans: suck or blow?

2010-11-07T22:11:08.353

6381

|breadboard|

<p>The spikes you are seeing are just an effect of your breadboard allowing coupling. This is expected with any breadboard.</p>

<p>I'm using a breadboard to prototype my projects. On one pin of an MCU, which is an output, I'm getting a 0-3.3V signal, as expected. However, another pin has a 20mVp-p signal almost matching the other one, but lower in amplitude. Where is this coming from? Has my board got a weak short or something like that?</p>

Is my breadboard faulty?

2010-11-07T22:35:02.630

6388

|power-supply|

<p>The voltage regulator compares the output voltage against a reference voltage (often built into the regulator itself), so <strong>if</strong> there were no any imperfections, the output voltage would be totally independent from the input voltage, output current, temperature etc.</p> <p>A switching regulator may not necessarily be a bad idea, if you can make sure the switching noise is always out of frequency band of your signal of interest (here 20Hz~20kHz) - then it is just as good as a linear voltage regulator. In practice that might not be so easy to verify (the noise is modulated by the loop response etc.)</p>

<p>I'm building a small audio amp (<a href="http://diyaudioprojects.com/Solid/IRF610-Class-A-Headphone-Amp/">a current controlled varient of the szekeres design</a>) and it apparently needs a very clean, regulated power source. Due to minimum parts order requirements, i'm going to end up with, amongst other things, a spare lm317 and others. As i understand, both the standard transformer-> <s>wheatstone bridge</s> bridge rectifier and switching power supplies are relatively noisy, so since i have parts spare, i'm wondering if following the reference design to build a voltage regulator would make a difference, or if i should just use a switching power supply to power it - i should be able to find a 15-20 v one which i'm planning on using anyway, and not using the voltage regulator at all for power supply</p> <p>For that matter <em>does</em> using a voltage regulator reduce rippling and noise, or is it just a complicated voltage divider?</p>

Regulated power supplies - how do they work?

2010-11-08T01:44:11.770

6392

|embedded|

<p>A few (perhaps obvious) tricks I've used successfully in compressing some customer's code:</p> <ol> <li><p>Compact flags into bit fields or bit masks. This may be beneficial as usually booleans are stored as integers thus wasting memory. This will save both RAM and ROM and isn't usually done by the compiler.</p></li> <li><p>Look for redundancy in the code, and use loops or functions to execute repeated statements.</p></li> <li><p>I've also saved some ROM by replacing many <code>if(x==enum_entry) &lt;assignment&gt;</code> statements from constants with an indexed array, by taking care that the enum entries could be used as the array index</p></li> </ol>

<p>I have worked on developing a feature on a particular product of ours. There has been a request to port the same feature to another product. This product is based on a M16C microcontroller, which traditionally has 64K Flash and 2k of RAM.</p> <p>It is a mature product, and therefore, only has 132 Bytes of Flash and 2 Bytes of RAM left.</p> <p>To port the feature requested (the feature itself has been optimised), I need 1400 bytes of Flash and ~200 Bytes of RAM.</p> <p>Does anyone have any suggestions on how to retrieve these Bytes by code compaction? What specific things do I look for when I am trying to compact already existing working code?</p> <p>Any ideas will really be appreciated. </p> <p>Thanks.</p>

How to squeeze code for more Flash and RAM?

2010-11-08T03:32:44.240

6395

|radio|frequency|

<p>The question sounds like it's asking: What if a radio "lets through" high frequency (RF) signals into the audio spectrum - will it hurt people to hear audio signals way above (or below) the normal audio spectrum of human hearing? It's not asking about the effects of radio waves on a human.</p> <p>From an engineering perspective you might translate this as: does the audio amplifier in a radio even try to amplify signals outside the range of human hearing, roughly 20Hz-20kHz? It would be bad if it did, as such behavior can cause components in the radio to run hotter than they would otherwise (wasting battery life and shortening the operating lifespan of the radio) without producing any effect in the audio output that human ears could hear. So a well-designed radio would probably have a lowpass filter before the audio amp to get rid of high-frequency noise, wherever it may come from (not necessarily a broken part upstream in the radio). Whether a very cheap radio would bother with this is questionable.</p> <p>The next question would be, suppose you tried to drive a speaker with a signal way above the normal audio frequency range - what would happen? Speakers can't respond quickly enough to the signal to generate sounds all that far above audio range. They might be able to reproduce the signal accurately up to 22kHz or maybe 30kHz but much above that and the signal won't be getting made into vibrating air, it'll just dissipate as heat somewhere in the system. You won't get 1MHz audio from a consumer product because the speakers can't reproduce it.</p> <p>Which is not to say that sound outside the range of human hearing doesn't exist or can't hurt you, just that generally speaking, a consumer radio won't reproduce such sound.</p> <p><a href="http://en.wikipedia.org/wiki/Sonic_weaponry" rel="nofollow">http://en.wikipedia.org/wiki/Sonic_weaponry</a></p>

<p>I hope many people might feel little awkward to see this question. But I feel this is important. Because in my place where I am living I can get a radio (Audio Receiver) very cheaply. I don't know till what extent they allow the audio frequency ranges. I guess they use ICs for Frequency Demodulators, Frequency Clippers, etc. If the Frequency demodulator doesn't work properly and allows all the frequencies that comes through air then its going to be a big problem to the humans. Can somebody answer which are all the frequency ranges that are available and which causes human hazards?</p>

Frequency ranges that causes a hazard to humans

2010-11-08T05:49:30.813

6403

|integrated-circuit|

<p>Short answer: The geeks at TI said so, and everyone else followed suit by making compatible or competing products.</p> <p>5 Volts was chosen for <a href="http://en.wikipedia.org/wiki/Transistor%E2%80%93transistor_logic#Interfacing_considerations" rel="noreferrer">noise immunity</a>. Early chips were power hogs, causing ripple in the power supply every time something switched that designers would try to overcome by putting a capacitor on the supply pins of every chip. Even so, an extra 2.4 volts of headroom gave them a cushion against going into the forbidden area between 0.8V and 2.2V. Also, the transistors caused ~0.4 V voltage drop just by their operation.</p> <p>The supply voltages have been dropping to extend battery life, and because the chip dies have been shrinking to make your portable devices smaller and lighter. The closer spacing of the components on the chip demands lower voltages to prevent excessive heating and because the higher voltage could cross through the thinner insulation.</p>

<p>Integrated circuits seem to have standard voltages of 5 V, 3.3 V, 2.5 V, 1.8 V, etc.</p> <ul> <li>Who decides these voltages?</li> <li>Why do smaller devices require lower voltages?</li> </ul>

What's up with the operating voltages 5 V, 3.3 V, 2.5 V, 1.8 V, etc.?

2010-11-08T09:38:38.480

6409

|voltage-regulator|

<p>Please be aware, on the 79xx regulator, the center pin (2) is common to the heat sink. The 79Mxx is isolated tab. If you ignore this you can get bad problems. Use the insulator, and screw bushing...</p>

<p>I have an old computer, an <a href="http://en.wikipedia.org/wiki/ABC_80" rel="nofollow noreferrer">ABC80</a> from the late seventies or early eighties, in which I have reason to believe one or more of the voltage regulators are broken.</p> <p><img src="https://i.stack.imgur.com/BkUd2.jpg" alt="alt text"></p> <p><img src="https://i.stack.imgur.com/ub1e2.jpg" alt="alt text"></p> <p>Now I wonder, what may be suitable replacement parts? I know that similarly named parts are still produced, but I am not sure about the details.</p> <p>What about <a href="http://shop.conrad.se/websale7/?shopid=conrad%2dswe&amp;act=product&amp;prod_index=179205&amp;cat_index=SHOP%5fAREA%5f17336%5f0204453&amp;Ctx=%7Bver%2F7%2Fver%7D%7Bst%2F3ec%2Fst%7D%7Bcmd%2F0%2Fcmd%7D%7Bm%2Fwebsale%2Fm%7D%7Bs%2Fconrad-swe%2Fs%7D%7Bl%2F01-aa%2Fl%7D%7Bsf%2F%3Cs1%3E7805%3C%2Fs1%3E%3Cs5%3E2%3C%2Fs5%3E%2Fsf%7D%7Bp1%2Fb1288725c4222b966991d7bc317fb8ae%2Fp1%7D%7Bmd5%2F78386f0c816881a98a1d5c0a5270a784%2Fmd5%7D" rel="nofollow noreferrer">this for a 7805 replacement</a>?</p>

Replace broken 79M12 and 7805 voltage regulators?

2010-11-08T12:19:39.717

6421

|output|inverter|

<p>Logic gates either have open drain outputs or push-pull. If it's open drain you need a pull-up to get a defined level when the output MOSFET is off. If it's on it will pull the output level low.<br> The <a href="http://www.fairchildsemi.com/ds/74/74AC04.pdf" rel="nofollow">74AC04</a> has push-pull outputs. This isn't mentioned explicitely, but you can tell from the driving capabilities: "Outputs source/sink 24 mA". Push-pull outputs always have a defined output level, either 0V or \$V_{DD}\$, so you can leave them open.</p>

<p>For a project, I am connecting the output ports of a 74AC04E hex inverter to bnc ports.</p> <p>Something could be (but not necessarily) be plugged in at one or more ports at a given time.</p> <p>Should the ports have pull-up:s / pull-down:s or could they be left floating?</p> <p><img src="https://i.stack.imgur.com/YLnwU.gif" alt="alt text"></p>

Hex inverter floating outputs

2010-11-08T14:37:05.467

6436

|manufacturing|dfm|

<p>I am a newbie myself, so take this with grains of salt, but I have researched this a lot over the last month, and so I hope to bring a good newbie-needs perspective to it. Here's what I've found out:</p> <p>NOTE: I am using a couple of acronyms (PCB, SMD, etc.). I have not written what these mean on purpose, since you will definitely also need to know these concepts intimately.</p> <ol> <li>You need to go from prototype (Arduino?) to PCB version. First of all, see these two videos by EEVBlog: <a href="https://www.youtube.com/watch?v=VXE_dh38HjU" rel="nofollow">Video 1</a>, <a href="https://www.youtube.com/watch?v=Uemr8xaxcw0" rel="nofollow">Video 2</a></li> <li>Going from prototype to PCB version means switching from through-hole components to SMT components, and from a full-fledged Arduino to a barebones chip solution. The good news is that you can still program it like an Arduino. <a href="https://hwstartup.wordpress.com/2013/03/06/how-to-build-a-5-arduino-clone/" rel="nofollow">See this blog post for how to do so.</a> If your project is simple enough, use an ATTINY (45 or 85) instead of the ATMEGA328p. See <a href="http://highlowtech.org/?p=1695" rel="nofollow">this post from MIT Lab</a> for how.</li> <li>Build your no-arduino prototype using a breadboard or other prototyping tool as normally. You can find the parts you need using <a href="http://octopart.com/" rel="nofollow">Octopart</a>. A very good thing to use is their BOM feature.</li> <li>Now find out how much your components will cost by making a BOM (Bill Of Materials). Use <a href="http://octopart.com/" rel="nofollow">Octopart</a> to find the price and best place to buy your parts.</li> <li>Once your prototype is done in this way, it is time to convert it to a PCB version. You can use <a href="http://fritzing.org/home/" rel="nofollow">Fritzing</a> for the PCB schematics and Gerber files for PCB manufacture if your board is simple enough. Otherwise, use a program like <a href="http://www.cadsoftusa.com/" rel="nofollow">EAGLE</a> or <a href="http://www.kicad-pcb.org/display/KICAD/KiCad+EDA+Software+Suite" rel="nofollow">kiCAD</a>.</li> <li>Get your PCB made and solder on the components by hand. <a href="http://www.youtube.com/watch?v=wUyetZ5RtPs" rel="nofollow">Here is a video with a good technique for SMD parts</a>. For even more info (I needed all of it) <a href="http://store.curiousinventor.com/guides/Surface_Mount_Soldering" rel="nofollow">here you go</a>.</li> <li>After soldering, TEST IT OBSESSIVELY. You do not want to buy 500 manufactured only to find out you have made a mistake and none of them work. Fritzing will produce one-off boards made with their program. They will cost about 40-50$. Not cheap, but this is a prototype, after all. You can also make the PCB yourself using the press-n-peel process. <a href="https://www.youtube.com/watch?v=mv7Y0A9YeUc" rel="nofollow">There is a good video on it here</a>.</li> <li>HUGE gotcha! You may need to get your board CERTIFIED. This is a lengthy and expensive process.</li> <li>Once you are confident in your PCB, Seeed studio will manufacture (not just PCB, the whole board) for small quantities (100-1000) at reasonable prices, through their <a href="http://www.seeedstudio.com/propagate/" rel="nofollow">Propagate</a> program.</li> </ol>

<p>I'm a software guy who wants to get into the hardware side of things so I can enjoy the same creativity from software design in the physical world. </p> <p>I've found plenty of posts here regarding how to get "up and running" in the electronics world, but I would like to know if there are any gotchas when embarking on this journey if your goal is to potentially have a device manufactured in the future. (probably robotics-centric solutions, boards that would control servos, sensors, etc).</p> <p>I would like to make sure that wherever I aim my focus, I won't be "learning myself into a corner", so to speak.</p> <p>I have read good things about the flexibility and easy to learn nature of Arduino devices, but have trouble finding anything about getting them manufactured. Are there manufacturers that can produce an arduino-based solution? What kind of production volume is available for something using Arduino?</p> <p>What realms/devices of programmable electronics are best for having manufactured? </p> <p>Any tips or info regarding learning and designing with manufacturing in mind? Any general tips for a newbie?</p>

How to go from newbie to manufactured?

2010-11-08T19:04:48.203

6442

|pic|interrupts|

<p>You can find the names of interrupts in linker file of MCU, as an examples if you use dspic33ep512MU810, linker file is p33ep512mu810.gld and it is located in compiler folder. If you edit the file you can see all interrupts vector names which are defined.</p>

<p>I'm asking for the ISR name for the comparator interrupt for a dsPIC33F. I've tried _CompInterrupt, _CMInterrupt and _CMPInterrupt. All three bring up warnings about non-existent ISR names. I can't find it anywhere in the datasheets.</p>

What is the ISR for the comparator change interrupt on a dsPIC33F?

2010-11-08T20:35:08.227