|
Could someone explain impedance to me? I have a kind of fuzzy understanding of it -- I can kind of see how if you're trying to run a high frequency signal through a long wire, stray capacitance and inductance and the natural resistivity of the wire can degrade signal quality (I guess I kind of think of impedance as a special type of resistance that affects AC circuits). I know that for some reason, it's a good idea to buffer analog output from a microcontroller with an opamp before driving a speaker, but I've never really understood what a high impedance or low impedance load are, or what I'd have to do if, say, I wanted to alter an audio circuit designed for headphones to drive a larger speaker.
|
#
¿
Feb 7, 2008 08:05
|
|
|
|
| # ¿ May 3, 2024 23:26 |
|
|
I'm interested in building a high voltage, low current power supply so I can make my own ozone generator like this guy did with a cold cathode driver: http://www.bigclive.com/oz.htm I've already made one with a cold cathode driver from a dead flatbed scanner, but what's the fun in using something pre assembled? I'd like to put one of these power supplies together on my own so I can tinker with it. I built the 555-based inverter described on this page http://joshua.raleigh.nc.us/LM555-inverter/ and while it does a nice job lighting up electroluminescent wire, I don't get the nifty corona discharge and ozone like the scavenged cold cathode driver produces. I assume this is because it does not produce as high a voltage as the cold cathode driver. Is there any way I can modify this circuit to output higher voltage, like by modifying the frequency at which it runs, or is the winding ratio of my transformer the limiting factor? I noticed on the cold cathode driver, the transformer has 5 taps on the input side (feedback windings?). I've always been rather bewildered by transformers with multiple windings and taps.
|
|
#
¿
Dec 7, 2009 06:58
|
|
|
Could someone help me understand a little transistor theory? I'm trying to multiplex some nixie tubes. As you can see in my schematic, the transistors at the top are hooked up to the tubes' anodes and are used to enable/disable each tube. The transistors on the bottom allow me to control which digit in the tube lights up (I've drawn tubes with only 3 elements because I'm lazy; the actual tubes have 10). I use a microcontroller to rapidly switch the tube enable transistors and digit transistors to get a 2-digit readout. In practice, the bottom half of my design works - if I hook my tube anodes directly to power, I can switch the individual digits of the tube with transistors hooked up to the cathodes. The transistors at top, however, don't seem to work. In other words, the transistors seem to be able to sink current but not source it (right?). Would my design work if I replaced the NPN transistors at the top with PNP transistors and controlled them with negative logic? Transistors are MPSA42 and resistors are 10K.
|
|
#
¿
Feb 7, 2010 19:21
|
|
|
Oh yeah, and the schematic, dumbass!
|
|
#
¿
Feb 7, 2010 19:21
|
|
|
Ok, thank you guys so much! I was originally thinking about using an optocoupler for the high side, but I wasn't sure what specs I should look for other than a really high collector-emitter voltage. Are there any inherent drawbacks with using the MPSA42 - MPSA92 switching method as opposed to an optocoupler, other than the higher risk of accidentally frying the entire circuit?
|
|
#
¿
Feb 7, 2010 20:15
|
|
|
Couple questions: 1. Does anyone know of a decent supplier of surplus servos/gearboxes? None of my usual surplus suppliers (bgmicro, goldmine electronics, surplus shed, etc) have anything, and I'd like to avoid paying $15+ for an overpriced Parallax servo. 2. What's a good book that goes over basic electronics? I'm talking transistors and op-amps, mostly. I've had the standard Physics II classes in college that cover Kirchhoff's laws and basic RC circuits, but I'd really like to have a better understanding of analog electronics. I can kind of put together a circuit that does what I want if I treat it as a bunch of functional black boxes that I can assemble together into a working whole, but there are still massive gaps in my knowledge when it comes to the actual operation of semiconductor devices, and often times, I find that components don't necessarily behave as I thought they would. Are there any books out there that, while explaining theoretical concepts, also show practical applications of this theory?
|
|
#
¿
Jun 26, 2010 05:07
|
|
|
babyeatingpsychopath posted:"Timers, Op-amps and Optoelectronic Circuits and Projects" By Forest M. Mims III. Get it from Radio Shack. It's a fabulous book. Yeah, I have most of Mims' books already, and most of what I know about electronics I learned from them. I'm looking for something that's a little more advanced, but that doesn't require a PhD in physics or electronics to understand.
|
|
#
¿
Jul 1, 2010 18:24
|
|
|
Quick question: why would a schematic call for tantalum capacitors as opposed to metal film or electrolytic? I know higher capacitances can be achieved in relatively small tantalum caps as opposed to electrolytics, but board density is not an issue here and I don't know any other reason to go with tantalum. The circuit I'm looking at is a stepper motor driver, if that helps.
|
|
#
¿
Feb 8, 2011 01:37
|
|
|
taqueso posted:http://www.illinoiscapacitor.com/pdf/Papers/comparison_surface_mount_aluminum.pdf From what I can tell from the schematic, one is a decoupling cap between the +5v and ground pins on a microcontroller, and the other caps look like they filter a resistor-based DAC network that controls the base current on a Darlington transistor. Here's the schematic: http://www.piclist.com/images/member/RB-ezy-Q33/LiniV2_sch.gif C3, C5, and C6 are listed as tantalum capacitors in the bill of materials. I know I can get away with an electrolytic cap on the microcontroller pins (or get rid of it entirely, since I'm using a pretty stable power supply for my circuit), but I don't know about those filter caps. nobody- fucked around with this message at 03:28 on Feb 8, 2011 |
|
#
¿
Feb 8, 2011 03:22
|
|
|
Can someone recommend me a decent autoranging multimeter with capacitance measurement? I'm too poor for a Fluke meter, so is there anything reasonably decent for under $100?
|
|
#
¿
Jul 17, 2011 18:38
|
|
|
taqueso posted:http://www.eevblog.com/2010/06/04/eevblog-91-50-multimeter-shootout/ Thanks for the link! In one of the comments on that site, someone mentions the Fluke 17B and 18B multimeters. Anyone used one of these? A $100 Fluke meter just sounds too good to be true.
|
|
#
¿
Jul 17, 2011 21:04
|
|
|
Speaking of op amps, is there a rail to rail single supply amp that'll run off of 5V? I'm looking for something to use as an input buffer for an ADC on a PIC chip.
|
|
#
¿
Sep 16, 2011 02:35
|
|
|
I'm going to be looking at mostly DC and low frequency stuff -- 15 kHz max. The goal of this project is to implement an IIR filter in a PIC, and I just want something that will give me the full 0-5 volt range on my ADC pins. Since this is just something I'm playing around with, the original signal will come from a function generator or potentiometer voltage divider.
|
|
#
¿
Sep 16, 2011 04:42
|
|
|
I picked up one of these GSM modems because they're cheap and you can desolder the USB-serial chip inside them and get a raw serial interface that's easy to interface with a microcontroller. I've gotten this work, and I've sent and received SMS messages with success, but my problem is that signal strength is abysmal and it's basically only useable from the top floor of my home near a window. The built-in antenna is a joke -- just a chunk of metal that screws into a threaded ring. I imagine most of the reception problems are likely due to cheap, poorly engineered electronics with poor noise rejection, but is there any sort of external antenna I could build for this thing that would improve reception at all? I'm using T-mobile as my service provider, by the way, so I'm interested in the GSM-1900 band specifically. I know basically nothing about RF electronics and antenna design, so feel free to treat me like a complete idiot.
|
|
#
¿
Oct 30, 2011 21:06
|
|
|
Stupid question time: should the 50k potentiometer in the feedback path of the op-amp in this (PDF) schematic be a linear taper or audio taper pot?
|
|
#
¿
Dec 23, 2011 01:39
|
|
|
Is there such a thing as non-polarized electrolytic capacitors? I got a bunch of cheap ones from an electronics surplus shop online, and all their leads are the same length and there are no markings on their cases that would indicate polarity.
|
|
#
¿
Dec 26, 2011 23:17
|
|
|
I'm trying to add a LCD readout to one of my PIC projects, but I'm having trouble getting the LCD module to initialize reliably when I power the circuit on. Normally, when I switch it on, the LCD will stay blank or print a bunch of gibberish instead of the text string I'm sending it. Once I pulse the MCLR pin on my PIC low to reset the microcontroller, the LCD works perfectly, so the problem only seems to occur from a cold start. I've tried adding a 1 sec delay in my firmware so voltages have a chance to stabilize before I initialize the LCD, but this doesn't seem to have any effect. Anyone have any suggestions? This is just a standard HD44780 2 line text LCD module, by the way.
|
|
#
¿
Jan 30, 2012 00:32
|
|
|
I'm looking at getting into FPGAs, and this caught my eye: http://www.linkspritedirect.com/product_info.php?products_id=75&osCsid=8a9c713f08ee534f7773342c0557dcf0 Do you guys think this is a decent "babby's first FPGA" board?
|
|
#
¿
Apr 1, 2012 00:57
|
|
|
I don't have any specific application in mind. Just thought I'd get one to play around with because FPGAs sound really interesting based on what I've read about them.
|
|
#
¿
Apr 2, 2012 00:03
|
|
|
I have a 12V lead-acid battery and a photovoltaic panel that I hope to use to charge the battery to run some LEDs to light my back porch. Is there anything special I need to do in order to trickle charge the battery with the PV panel, or do I just connect it to the battery terminals? I know that overcharging Li-ion batteries is bad, bad news, but I know nothing about lead-acid batteries. If I do need some sort of circuit to cut off the PV panel when the battery reaches 12V, could someone give me some tips as to how to accomplish it? The only method I can think of right would be to use a resistor divider to get the battery voltage down to a max of 5V so it can be input to a microcontroller's ADC.
|
|
#
¿
Jul 1, 2012 03:03
|
|
|
I picked up one of those USB TV tuner dongles that you can get hacked drivers for, allowing you to basically tune into any radio frequency from 64MHz to 1.7GHz with SDR software. I've had fun listening to people talking on walkie-talkies, CB radios, and aircraft/control tower conversations, but I want to be able to listen to shorwave. I found this project where a guy built a heterodyne mixer with filters so he could do exactly what I'm talking about : http://george-smart.co.uk/wiki/FunCube_Upconverter Do I just plug an appropriate antenna into the input of this thing, or do I need some sort of preamplifer for it?
|
|
#
¿
Jul 26, 2012 22:32
|
|
|
Pretty much any DVB-T tuner dongle with a Realtek 2832 chip will work; someone figured out that that chip can send raw I and Q signals over USB with the proper drivers. Dongles with the Elonics E4000 tuner are preferred, as it has the widest frequency range. I bought mine off an Ebay seller in the US because I didn't feel like waiting a month for DealExtreme to ship it. Right now I'm using SDR# because it's really simple to use. I'm going to play with GNURadio when I get some free time, as it seems to be more powerful. I was amazed at what I could pick up with just this cheap little $25 thing and a crappy old set of TV bunny ear antennas. I was asking about a preamp for the mixer because my understanding of RF stuff is a little shaky. I know that when you mix two sine waves, you get a sum and difference frequency out, but I don't know if they have to be of roughly equal amplitudes. It seems to me the weak signal coming off an antenna would get completely swamped by the 5V peak sinewave coming from the oscillator crystal. nobody- fucked around with this message at 03:05 on Jul 27, 2012 |
|
#
¿
Jul 27, 2012 02:58
|
|
|
If I drive a canned crystal oscillator at 5V when it's specced to run at 3.3V, how likely am I to completely destroy it?
|
|
#
¿
Aug 3, 2012 01:12
|
|
|
But does TI provide a good, non-crippled toolchain for it?
|
|
#
¿
Sep 3, 2012 15:56
|
|
|
Corn Nuts posted:Warning: I am really new to electronics. Piezo elements are capacitive in nature, not resistive. Commercial ultrasonic foggers utilize this capacitance along with an inductor to form an LC resonant circuit that's tuned to 1.5 or 1.7 MHz or whatever frequency is needed. This produces a clean sinusoidal wave form, rather than the square wave you'll get by switching a MOSFET with a microcontroller. This guy has a pretty good overview of the inner workings of some ultrasonic humidifiers as well as schematics.
|
|
#
¿
Sep 10, 2012 03:45
|
|
|
From what I understand, in the US, at least, with 220VAC power, each leg carries a 110V AC waveform that's 90 degrees out of phase with the other so you end up with 220V total. This means that even if you interrupt one leg of the heater and no longer have a complete circuit, the other leg is STILL at 110V potential with respect to ground and you could still shock yourself or start a fire. Even if you're using a 120V wall outlet where there's a hot leg and a neutral leg, you need to be drat sure you're actually interrupting the hot side of the circuit, because you can have a device that's switched off but still at line potential. That's why polarized plugs exits.
|
|
#
¿
Oct 7, 2012 17:55
|
|
|
ante posted:Question. I had the same problem trying to program certain PIC 16f88 chips within MPLAB X. I downloaded the standalone PicKit 3 programmer app thing here: http://www.microchip.com/Microchip....ocName=en538340 and had much better success with it. You can set it to watch a directory and automatically flash new firmware on your chips when you recompile it. I've personally found it easier to use than the ridiculous MPLAB X hidden sub-sub menu buried inside another dialogue that you have to use to get at PicKit settings, even though it is crash prone.
|
|
#
¿
Jan 5, 2013 05:21
|
|
|
Inductor/DC-DC converter question here, for you analog experts: I got a LT1302 boost converter sample that I'm planning to build an iPhone charger around. Problem is, I don't have any 10uH inductors and can't really justify putting an order in to Digikey or Mouser for a single $0.50 part. I do have some ferrite toroids in my junk box. Is there any compelling reason I shouldn't wind 3-4 turns of wire on a toroid and use that as the inductor? The datasheet for this IC says the inductance value isn't critial, you just want low DC resistance and a core that won't saturate easily.
|
|
#
¿
Jan 12, 2013 23:33
|
|
|
ANIME AKBAR posted:Sure a handmade inductor can work, but pieces of ferrite/powdered iron can vary enormously in their permeability and frequency capabilities. So you should have at least a rough idea what the core's properties are. Ok, thanks! I used this guy's trick: http://dos4ever.com/inductor/inductor.html to get a rough measurement, and it looks like I can get about 15uH with four turns. I just got curious as most power supply inductors I've seen involve 10s to 100s of turns of thin copper wire around a cylindrical core, when it seems to me you'd get lower series resistance by using just a few turns of thick wire around a toroidal core.
|
|
#
¿
Jan 13, 2013 18:10
|
|
|
Is there such a thing as a small (8-pin) microcontroller with 16kB or more flash? It seems with Microchip's and Atmel's offerings, flash size scales with pin count and peripheral features, and I don't need a monster IC with tons of features and pins. I'm trying to build a character display driver for an an e-ink panel and just need a few GPIO pins and a lot flash to store character bit patterns. I could store the characters on an external EEPROM, but I'm trying to keep the parts count and price as low as possible.
|
|
#
¿
May 16, 2013 04:52
|
|
|
I've had good luck so far with Sparkfun's Eagle library. Most common parts are already in it, and the descriptions are actually useful when you're browsing through it. I just rip off their footprints whenever I need to create a new part, and it's worked well for me.
|
|
#
¿
Jul 2, 2013 03:09
|
|
|
Parallel Paraplegic posted:This thread introduced me to the EEVBlog, which is a great source of both practical knowledge about electronics and theory behind things. Plus he takes apart old poo poo a lot and looks at it's sexy DIPs In a similar vein, Alan Wolke AKA W2AEW's channel on Youtube has some of the most engaging and well presented electronics tutorials I've ever seen. I've learned a ton by watching his videos, as they're essentially pure distilled knowledge in video form. I also like listening to the Amp Hour podcasts while I work. Dave from the EEVBlog and this electronics nerd from Ohio discuss happenings in the electronics industry, and they often have really interesting guests on the show. nobody- fucked around with this message at 06:01 on Nov 23, 2013 |
|
#
¿
Nov 23, 2013 05:59
|
|
|
Or you can get a handful of ESP8266 wifi modules for $3-4 off some skeevy Chinese seller on Aliexpress. I finally got a few in about a month after ordering them, and they work amazingly well. This guy: https://scargill.wordpress.com/ talks about some experiments he's done running something called MQTT on the modules so he can set a PC broker or wifi router with modded firmware to receive and broadcast periodic small bits of data to/from the modules for, say, home automation and monitoring.
|
|
#
¿
Jan 4, 2015 21:49
|
|
|
asdf32 posted:With the addition of a mosfet this circuit has a number of advantages and is also better suited for PWM control. I have a few stupid questions about this circuit: 1. The output current is determined by the value of the current sense resistor (in conjunction with the reference voltage of the TL431), so I could use a lower value resistor and use this circuit to control a high power LED, assuming I spec a FET with low Rds and sense resistor that can dissipate the heat? 2. I won't release the magic smoke from the TL431 by cranking up the current, as long as I stay within the part's 36V cathode voltage max, correct? All the thermal dissipation is done through the transistor and resistor? 3. The efficiency of this circuit will be better than a linear regulator (power is switched, rather than being burned off as heat), but not as good as with a carefully designed smps (since this circuit still burns off some power in the current sense resistor and FET)? Basically, what I'm looking for is a way to do constant current regulation for high power LEDs without wasting poo poo-tons of power using linear regulators or having to spec out inductors and deal with the layout requirements most switch mode regulator ICs need. This sounds too good to be true.
|
|
#
¿
Jan 21, 2015 02:59
|
|
|
I'm trying to get a handle on switching power supplies, so as an exercise, I came up with this super minimal circuit to power a 1W high intensity LED. Note: this is all theoretical; I haven't actually built anything, I'm just putting this thing out there so you guys can tell me why it won't work the way I expect. My idea is to use the microcontroller's PWM peripheral to toggle a FET. When the transistor turns on, current flows to the LED, and the capacitor absorbs large inrush currents and smooths things out. The voltage going to the LED is monitored by the microcontroller's ADC, and firmware on the controller increases or decreases the PWM duty cycle to maintain a constant voltage of 3.4V or whatever the forward drop for the LED is supposed to be at its optimal operating point. Now, I know a "real" buck converter utilizes inductors and diodes and several other components, and that if I really want super efficiency and low output ripple, etc, etc, the layout of the parts is critical. I also know that I can get a pre-built converter off a Chinese ebay seller for a little more than a dollar. What I really want to know is, is my thinking correct? Will this thing I've devised have any chance of working at all? I really don't care if the output voltage has a poo poo ton of ripple, since it'll just be used to light an LED at PWM frequencies that are too fast for the human eye to detect.
|
|
#
¿
Jan 27, 2015 06:26
|
|
|
I'm interested in learning FPGAs, but I'm having trouble deciding on a development board and ecosystem. Really, all I want is something that can do LVDS communications, say with an old laptop display panel or an imaging sensor, and that has a little bit of RAM on board for framebuffer, etc. Does anyone know of such a thing at a < $100 price point? Would it be possible to do basic digital imaging projects using the freely available tools from Altera/Xilinx/Lattice, or would I be stuck shelling out more money for advanced dev tools and IP blocks?
|
|
#
¿
Oct 6, 2017 16:37
|
|
|
I want to switch a 36 VDC, 750 mA load with 3.3 V logic. It seems to me that this thing http://www.mouser.com/ds/2/205/LCB710-22935.pdf is absolutely perfect for my needs. Datasheet claims it can switch up to 60 V at 1 A, only needs 1.2 V at 1 mA to power its LED, and it'll only dissipate 1/3W at the load I'm putting through it. I don't particularly care about switching speed. Is there some drawback to this thing that I'm missing? Being able to switch a 60V circuit using only 1.2V with an on resistance of 0.6 ohms seems too good to be true.
|
|
#
¿
Dec 16, 2017 18:47
|
|
|
Aurium posted:It's much more expensive than a mosfet that would do the job just as well if you didn't need the isolation. Thanks. I was under the impression that there aren't really any FETs that could switch 36V with a gate voltage of just 3.3V.
|
|
#
¿
Dec 16, 2017 22:26
|
|
|
Idiot filtering/sampling question for you guys: I want to sample audio into a microcontroller and do an FFT on it so I can display its frequency spectrum on some Nixie bargraph tubes I got off Ebay. I was planning on sampling the audio at 32kHz, which would give me a theoretical maximum identifiable frequency of 16kHz, which should cover most of the frequency components you'll hear in music. I'm having trouble coming up with an antialiasing filter, though. The filter design tools I've been using keep coming up with ridiculous 8+ order filter topologies since my passband is so close to my sample rate. Am I overthinking things, and should I just do a cheapass RC low pass on it with a cutoff frequency around 16kHz? Or could I get away with not pre-filtering it and just do an FIR or IIR on it in the chip after sampling it in? The little bit of DSP I know, I picked up along the way from various sources, so I'm not entirely sure what the "proper" way is to go about something like this. I assume there is some way to do what I'm trying to do, since most digital audio stuff samples at 44.1 kHz, and picks up frequencies of (I assume) up to 22 kHz. nobody- fucked around with this message at 16:27 on Jun 8, 2018 |
|
#
¿
Jun 8, 2018 16:24
|
|
|
|
| # ¿ May 3, 2024 23:26 |
|
|
Thanks for the tip! I got one of these things, since it takes care of the mic input, filtering, ADC, and decimation all together. I would've just bought the mic module without the breakout board, but Mouser and Digikey were both out of stock  Anyways, it works much better than the crappy electret mic/preamp setup I was feeding into my microcontroller's ADC.
|
|
#
¿
Jun 11, 2018 00:54
|
|