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Anybody have recommendations for highly-accessible standalone circuits / small projects I could tackle, in this time of COVID foreverjail? by accessible i mean "low-part-count circuits making use of commonly-available discreet components, or which can otherwise be DIYed from mundane objects"- a joule thief is a good example of the first, a basic RF project making use of hand-wound inductor coils an example of the mundane-objects angle. i've got an ok spread of must-have discrete components as well as microcontrollers/sensors/inputs/displays etc, i can make little arduino gizmos until the cows come home but those'll be more programming-centric which isn't what i'm feeling right now, i'd really like to attempt some shoestring 'conventional' electronics projects with just what i've got on hand
Ambrose Burnside fucked around with this message at 01:42 on Mar 23, 2020 |
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Mar 23, 2020 01:38
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Hah, I was going to suggest joule thief. Make a capacitor voltage doubler, and create some cool arcs and/or kill yourslef
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Mar 23, 2020 01:41
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Got another one: What's the best way to convert AC to multiple DC voltages? I'm interested in having a single AC wall plug that takes 120-240 50-60hz, and outputs lines at 24v, 12v, and 5v. Are there OTS products you can buy, or do you need to do the circuit/wiring yourself? Looking to make a device that has 24v lights (high current draw), 12v pumps and other accessories (med draw), and 5v for powering the electronics. Prototype has a sep AC adapter for each, but this isn't great for production. Dominoes fucked around with this message at 05:00 on Mar 23, 2020 |
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Mar 23, 2020 04:56
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Dominoes posted:Got another one: What's the best way to convert AC to multiple DC voltages? I'm interested in having a single AC wall plug that takes 120-240 50-60hz, and outputs lines at 24v, 12v, and 5v. Are there OTS products you can buy, or do you need to do the circuit/wiring yourself? Looking to make a device that has 24v lights (high current draw), 12v pumps and other accessories (med draw), and 5v for powering the electronics. Prototype has a sep AC adapter for each, but this isn't great for production. Stagger your converters. Some sort of OTS AC->24V adapter, feeding a 12V and 5V adapter. For your 5V electronics, I'd suggest some sort of switch-mode linear replacement. For the 12V, some sort of medium-duty switcher to buck the voltage down would work. We'd need more info to recommend specific parts. You could also just buy 3x AC->DC Adapters, with corresponding power outputs and run all of them off the incoming AC rail.
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Mar 23, 2020 05:04
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Dominoes posted:Got another one: What's the best way to convert AC to multiple DC voltages? I'm interested in having a single AC wall plug that takes 120-240 50-60hz, and outputs lines at 24v, 12v, and 5v. Are there OTS products you can buy, or do you need to do the circuit/wiring yourself? Looking to make a device that has 24v lights (high current draw), 12v pumps and other accessories (med draw), and 5v for powering the electronics. Prototype has a sep AC adapter for each, but this isn't great for production. Depends on how much current you need, but yeah this is why so many lab power supplies have two 30 V channels and a 3rd channel that can be 3.3 V, 5 V or 12 V As for how to do this, depends how much current you want.
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Mar 23, 2020 07:24
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Also you should be able to buy a triple output AC/DC supply, but it might be cheaper to get a dual or single output and do the conversion yourself. Per murphys law the amount of power on each rail will usually be all wrong for whatever application you're thinking about. "What do you mean no one needs a 20A 5V rail?!" If you have  ++ you can absolutely get a custom/configured power supply with the right balance of power.See e.g. Vicor FlatPACs.
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Mar 23, 2020 08:09
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Depending on your current needs you may be able to get there with a dual-rail PC supply.
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Mar 23, 2020 12:21
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good lord did you guys know there's a Teensy 4.0 now? it's got a 600mhz superscalar processor and a megabyte of RAM and like a million different peripherals and high-speed USB and a crypto accelerator and a hardware RNG and it still costs $20 and is the size of the end of your thumb  what a world
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Mar 23, 2020 22:58
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TacoHavoc posted:Depending on your current needs you may be able to get there with a dual-rail PC supply. The 24V (or well, +-12V) of a computer PSU is definitely not enough to run the high loads of anything, in modern PSU's the -12V rail is barely even there since pretty much nothing has a serial port these days. The "rail" terminology is actually marketing lies, it's all the same 12V backend with the same common ground, putting them in series will just short it out. You could use a 12V PSU and a reasonably beefy DC-DC boost converter though, but at that point you might want to just get a 24V power supply (they're easy enough to find) and do the DC-DC step-down idea.
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Mar 23, 2020 23:46
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Shame Boy posted:The "rail" terminology is actually marketing lies, it's all the same 12V backend with the same common ground, putting them in series will just short it out. Welp there's some poo poo I didn't know. That makes the thought of putting them in series for 24V not feasible so forget I suggested it.
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Mar 24, 2020 00:34
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Sagebrush posted:good lord did you guys know there's a Teensy 4.0 now? it has CAN bus support
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Mar 24, 2020 04:30
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Dominoes posted:Got another one: What's the best way to convert AC to multiple DC voltages? I'm interested in having a single AC wall plug that takes 120-240 50-60hz, and outputs lines at 24v, 12v, and 5v. Are there OTS products you can buy, or do you need to do the circuit/wiring yourself? Looking to make a device that has 24v lights (high current draw), 12v pumps and other accessories (med draw), and 5v for powering the electronics. Prototype has a sep AC adapter for each, but this isn't great for production. Like others have said, off-the-shelf AC -> 24V, then a 24V -> 12V regulator, then a 12V -> 5V regulator. You can get all the active parts for a switching regulator in a single IC that just needs caps, resistors, and inductors to work. Datasheets will have example circuits and part sizing calculations. Throw on some output filters or make the 5V have a linear regulator in it if you need it to be less noisy. Example from a random 5V converter:  The category for this stuff on digikey is Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Regulators.
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Mar 24, 2020 05:06
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Sagebrush posted:good lord did you guys know there's a Teensy 4.0 now? There are older hardware engineers at my work who still think it's important to group gpio signals by port for the software guys, meanwhile the micro is doing https cryptography in software and it takes milliseconds. A lot has changed pretty quickly
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Mar 24, 2020 08:23
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Much appreciate the wisdom re multiple DC voltages! Going to attempt the double-step-down regulator approach / Foxfire's circuit. Dominoes fucked around with this message at 06:58 on Mar 25, 2020 |
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Mar 25, 2020 06:53
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Question about non-integer sampling rates! A board I'm working with uses a 16 MHz clock with a clock divider of 1536, resulting in an ADC sampling rate of 10416.666666..... For DSP purposes, can I just round this to 10417? Or maybe, just keep some number of decimal places, say, 10416.667? How do I go about assessing possible error accumulation from doing this? Thanks! (FWIW, its part of a low-fi audio system)
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Mar 25, 2020 17:53
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What does the DSP expect to see? My quick answer is it's probably fine, especially for 'low-fi'
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Mar 25, 2020 18:33
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taqueso posted:What does the DSP expect to see? "I" am the DSP :P The analog signal is digitized at 10416.6666....the digitized samples then pass through my fully-software digital chain (there is no hardware DSP happening, to be clear).
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Mar 25, 2020 18:41
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I'm guessing you can't change the divider, or you would have already done that. I can't see any reason to not use as much precision as you can; if you are operating in floating point that shouldn't be a problem. If you are working with integers, I guess just do whatever you can to keep precision up.
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Mar 25, 2020 18:51
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How do you recommend connecting 10 or so devices (sensors, actuators) to a PCB? Screw terminals? Some type of jack? Given there'll be around 25 connections, the terminal block section at digikey looks kind of expensive, at $3/8 terminals on the bigger blocks. I'm not sure if a screw terminal is the answer. Shouldn't ever have to be removed, but it's possible, ie adding functionality later.
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Mar 26, 2020 03:24
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Dominoes posted:How do you recommend connecting 10 or so devices (sensors, actuators) to a PCB? Screw terminals? Some type of jack? Given there'll be around 25 connections, the terminal block section at digikey looks kind of expensive, at $3/8 terminals on the bigger blocks. I'm not sure if a screw terminal is the answer. Shouldn't ever have to be removed, but it's possible, ie adding functionality later. How much current do the actuators draw? How often do you need to disconnect/reconnect things?
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Mar 26, 2020 03:41
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Screw terminals tend to be enormous, support high currents, are expensive, and less reliable than other connectors. The best way to do things is: - crimp male pins onto the sensor/actuator leadwires a couple inches off of it - have a male pin connector header on the PCB - have a cable with female sockets crimped to both ends It lets you disconnect from either end. For choosing a connector, pick something common where you can get precrimped leads if you don't have proper tooling. Try to design your pinouts so that you can use off-the-shelf cable assemblies (either pin 1 <-> pin 1 or the mirror image of that). On the sensor/actuator end, you can either use generic crimping pliers (very finicky) or solder on a precrimped lead extension (fragile). Micro-fit 3 is a very common connector series. It's ~8A rated and medium sized. Tooling is also very cheap (~$140). Digikey stocks cable assemblies and precrimped leads (if you ask you can also get different lead lengths for ~$15 setup fee if they don't stock a length you want)
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Mar 26, 2020 03:50
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I think they'll all be low current, and all on 5v or 3v. (relays, variable resistors etc). Sounds like screw terminals aren't the answer. That pin idea already sounds better. Are Micro-fit3 (from googling) the Molex connectors used in desktop computer PSUs? Ie a genericized trademark. Looks dramatically cheaper, and easier to connect/disconnect.
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Mar 26, 2020 04:03
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Look into the Molex KK series, had to redo a bunch of these at work that got melted and they seemed pretty useful. https://www.molex.com/molex/products/group/kk_interconnect_solutions
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Mar 26, 2020 06:29
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quote:Ideal for... wire-to-board low-power and signal applications
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Mar 26, 2020 06:32
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Microfit isn't computer psu molex. PSU 'molex' is actually a TE connector that Molex also makes a knockoff of. https://www.molex.com/molex/products/family/microfit_30 e: terminology: boart-to-board: there are pcb parts that mate to pcb parts wire-to-board: there are pcb parts that mate with parts that attach to wires wire-to-wire: there are equivalents of pcb parts that attach to wires Not all series will have wire-to-wire connectors. Molex KK for example does not. So you can't have a disconnect on the sensor/actuator side, which may or may not work depending on how long their leads are and whether you want to be able to swap a device without pulling out the cabling. Foxfire_ fucked around with this message at 06:41 on Mar 26, 2020 |
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Mar 26, 2020 06:37
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Anyway be sure to look into crimping tools for these, we had to do the KKs without the proper $400 tool and they were a bear
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Mar 26, 2020 06:41
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http://tech.mattmillman.com/info/crimpconnectors/ My choice would be Molex SL. I use the KK 0.1 and 0.156, Sherlock, JST-PH and PHD, MiniFit, but really like the SL.
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Mar 26, 2020 14:04
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KK is my standard "I don't want to have to think about this" connector for projects since it's easy to get cheap brand-name high quality gold-plated ones, it's big enough to solder real easy, it comes with a friction latch (or well, can be ordered with one), and its 2.54mm pin spacing means if I need to I can jam DuPont connectors on it or use it as a pin header or stuff like that. While it can be a pain to crimp without the $400 tool, I've gotten good consistent results with that Engineer brand crimp tool this thread recommended me a while ago, it's just a bit more tedious.
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Mar 26, 2020 15:31
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Also since I just fixed a very annoying problem, note to future self: don't put the mounting holes on the corners of the board, then put connectors in the middle of the board and expect all the solder joints to be happy about it.
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Mar 26, 2020 16:50
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Sagebrush posted:good lord did you guys know there's a Teensy 4.0 now? I have a pretty big project based on the 4.0 that is in stealth mode right now... I'm waiting for 1 more feature to get support before I make the first demo and unleash it. It's definitely the biggest embedded thing I've ever made, I've been developing it since June of last year.
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Mar 26, 2020 17:08
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Awesome. Re the KKs, where do you recommend getting them? Could go off-brand? Ie googling KK on Amazon shows this 560-piece offbrand kit for $10, which seems cheaper than what I can find on Digikey. Compared to SL, KK seems more popular, so maybe easier to get an off-brand crimping tool? Should I set up the board for 2-3 10-pin headers like this from Digikey? ($2 each) I think one of the lines could pull up to 25A on 24V. Would screw terminals be a good bet for that? It'll still be connected to the board due to connecting to a relay. Is that OK? Even if this proj fails miserably, it's evidently worth it for the learning. Dominoes fucked around with this message at 17:32 on Mar 26, 2020 |
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Mar 26, 2020 17:26
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Dominoes posted:Awesome. Re the KKs, where do you recommend getting them? Could go off-brand? Ie googling KK on Amazon shows this 560-piece offbrand kit for $10, which seems cheaper than what I can find on Digikey. Compared to SL, KK seems more popular, so maybe easier to get an off-brand crimping tool? I have some of the lovely Amazon boxes of generic KK connectors and they really suck, like they "work" but tend to be a pain to crimp and I wouldn't trust them to work for long. Definitely want to go for something beefier for a 25A circuit though, geez. Screw terminals with crimped lugs on the wires or something like that is probably your best bet.
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Mar 26, 2020 17:48
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Awesome. The majority of the devices are 3 × 10⁻⁴A, one will be 1A. Seems like those will be fine on the pin connectors, and the high-current one I mentioned will need something diff. Can I just keep it away from the other items on the board, and make sure the relay can handle it? I imagine a short here could be disastrous. Or maybe an off-board relay for it so that current doesn't get near the rest of the stuff?
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Mar 26, 2020 17:54
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At 25A, you need to stop and think about what you're doing. If those cables are leaving an enclosure, they're supposed to be 8awg. And you'll need heavy fat traced to not burn your pcb.
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Mar 26, 2020 22:09
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25A shouldn't even be on the PCB if you can help it lmao
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Mar 26, 2020 23:22
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Hmm. It's a series of daily-chained grow lights. Ie 65-100W each @ 24v, × 1 - ~8 or so. Idea is it's modular, so 4A per unit. Nothing else in the setup is anywhere near that current. So sounds like I should just buy a separate relay unit that doesn't get near the other stuff, other than for the signal/pwr/fround for the relay. The proto's using a single 4A light on a standalone relay board.
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Mar 26, 2020 23:32
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Dominoes posted:Hmm. It's a series of daily-chained grow lights. Ie 65-100W each @ 24v, × 1 - ~8 or so. Idea is it's modular, so 4A per unit. Nothing else in the setup is anywhere near that current. So sounds like I should just buy a separate relay unit that doesn't get near the other stuff, other than for the signal/pwr/fround for the relay. The proto's using a single 4A light on a standalone relay board. This is getting a little scary to give advice on because 25A is a lot and can go wrong quickly, but the term you probably want to google is "lighting contactor".
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Mar 27, 2020 00:20
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Might be worth while to limit the num of units connected until resolved.
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Mar 27, 2020 00:25
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Dominoes posted:Hmm. It's a series of daily-chained grow lights. Ie 65-100W each @ 24v, × 1 - ~8 or so. Idea is it's modular, so 4A per unit. Nothing else in the setup is anywhere near that current. So sounds like I should just buy a separate relay unit that doesn't get near the other stuff, other than for the signal/pwr/fround for the relay. The proto's using a single 4A light on a standalone relay board. Grow lights huh?
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Mar 27, 2020 00:26
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it's not weed.
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Mar 27, 2020 00:29
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