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ante posted:No, my statement stands. With your scope, it's not the voltage that you have to worry about (although you do). It's the grounding situation that will arc through your scope, even on the low voltage side. Good to know. 4.5V (3xAA) radio it is, then, for the learning process.
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Nov 21, 2018 06:03
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Bad Angus! Bad!
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Shame Boy posted:Yeah, all plants have to sync up to the grid so they're not at risk of interference cancelling each other out (and until they sync up they dump their power output into what is basically a massive building-sized resistor which is real cool imo) but the grid as a whole could slowly drift if everyone's just using the grid itself as the reference they're sync'd to. I think America's grid is still very very accurate but I know Europe's grid has been having weird issues with frequency drift lately that may or may not be Russia intentionally loving with it... Amusingly, it was because of the Kosovo / Serbia "history". All of EU would much rather have slow clocks than try to intervene there.
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Nov 21, 2018 19:18
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Posted this in the general house stuff thread, but maybe this is more suited.. I'm a hipster artist weirdo, so I'm looking at wiring up some LED tube lights to hang in my workspace for some artsy lighting. Any idea on how difficult it would be to direct-wire 3 or 4 of them to a plug? Or is there a product that already does this? I googled around but Google just wants to give me listicles about the top 10 ways fluorescent tube lighting is making you sick.
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Nov 21, 2018 20:44
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Shame Boy posted:Yeah, this old EEVBlog goes into why if you're interested: Finally watched the video (I somehow missed that post earlier). So if it doesn't have a ground pin on the plug it's safe to poke at with the 'scope? Everything I was planning on poking at has a 2-prong plug. I don't recall ever seeing a TV with a ground pin, now that I think about it. If that's not the case, it should be fairly easy to tell (by looking at the wiring or prodding with the demonic multimeter) that the transformer between mains* and whatever I'm poking at is or isn't isolated, right? (*I'm in the US, if it matters, I just occasionally use Commonwealth terminology.) (Edit: ... I can't actually think of the American word for "mains." Probably because all the "messing with electronics" youtube people I watch have the Queen on their money.) Edit again:  Huh, so that's what the modem and TVs are working with. Neat. (I unscrewed the coax from the TV and clipped the 'scope leads onto the respective parts of the connector.) Chillbro Baggins fucked around with this message at 22:11 on Nov 25, 2018 |
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Nov 25, 2018 20:02
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I mean I know it's called universal serial bus but I don't think this is what they had in mind... 
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Nov 28, 2018 16:24
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Chillbro Baggins posted:Finally watched the video (I somehow missed that post earlier). I didn't notice nobody had replied to you, sorry. Lemme give it a shot since it's important safety stuff we're talking about Chillbro Baggins posted:So if it doesn't have a ground pin on the plug it's safe to poke at with the 'scope? Everything I was planning on poking at has a 2-prong plug. I don't recall ever seeing a TV with a ground pin, now that I think about it. A 2-prong plug simply means it's insulated in such a way that the chassis doesn't need to be grounded for safety. This is not the same thing as isolated, and you can still explode your scope. It just means that even if there's a fault inside you won't get a whammy off touching the outside of the device. An important thing to keep in mind is that the neutral prong of the plug and the ground prong go to the same place - they're literally connected together at your distribution box. You can absolutely cause a short to flow through the ground prong of your scope, out to the distribution box, and back over the neutral line of the thing you're probing. You can tell using the multimeter if the thing is isolated, yeah. When it's not plugged in and the capacitors have drained put the multimeter into continuity or diode-detection mode, hold one probe on one of the prongs and poke the other probe around the output of the power supply, anything that looks like a grounding screw or wire, etc. Make sure you do this for both prongs, and in both directions - there's almost always a diode between the outlet power and the regulated power, which will show up as an open circuit in one direction but as a diode in the other direction. Generally you can tell something's a "diode" if you put your meter across it in continuity / diode detection mode and it shows something like '0.6'. Note that it will not beep, so you have to actually pay attention to what it's saying. If the thing is using an isolated power supply, your meter won't show anything no matter what you poke. However if you're going to be poking around stuff connected to mains, isolated or not, you really should buy an isolation transformer. They're a little on the expensive side (this one's $120) but cost less than blowing up your scope and hand. Chillbro Baggins posted:(*I'm in the US, if it matters, I just occasionally use Commonwealth terminology.) Yeah I call it mains too, for the same reason  The American term is "line power", "wall power" or just "line", which I've never really liked the sound of.Chillbro Baggins posted:Edit again: That's the lower end of it, yeah. It extends way up into the gigahertz so you can't really see much with the scope, but if you want to poke around exploring signals like that you should pick up an RTL-SDR - you can get them pretty cheap, complete with antenna kit and they're very fun to play around with and see what signals you can pick up.
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Nov 28, 2018 16:41
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Can anyone recommend any books or resources to learn more about motor control? I took a class in college about motors but that was a long time ago and I've forgotten everything.
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Nov 29, 2018 04:33
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Here's an interesting problem I found last night: I have an audio processor board I designed, and it was producing horrible distorted sound on the speaker outputs (not random noise. The line outputs are built with the same amplifier, hookups etc. and were fine. The speaker outputs are powered using a LM4871 BTL speaker driver, and the line outputs are generated using a LM4861 which is the same part but lower power. On the outputs I put 600 ohm ferrites (2A DC rated) + 10 nF decoupling (cap on the external side). Basically looked like this:  (Equivalent circuit) The outputs of the amplifier were perfectly fine on the scope when running a sine wave test signal, but measuring the voltage after the ferrites there was horrible crossover-like distortion clearly visble on the scope. Bypassing the ferrites resolved the problem entirely (I also removed the caps first, they had no significant impact). Best guess: The ferrites are operating in their inductive frequency range, and were saturating because they're not really meant for that. When the current reverses, they discharge their stored energy which is absorbed by the speaker. Any thoughts?
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Nov 29, 2018 09:58
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qsvui posted:Can anyone recommend any books or resources to learn more about motor control? I took a class in college about motors but that was a long time ago and I've forgotten everything. If you can narrow down your application range a little bit that'd really help I think, there's a lot of good stuff out there but it's hard to generalize entirely.
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Nov 29, 2018 18:25
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shovelbum posted:If you can narrow down your application range a little bit that'd really help I think, there's a lot of good stuff out there but it's hard to generalize entirely. Looks like my application involves a 3-phase BLDC motor with FOC commutation. I hope this makes sense to someone.
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Nov 29, 2018 19:35
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I can't recommend any books, but how deeply do you want to get into it? The quad copter market is blowing up the available support for BLDCs right now, so there are probably a million articles talking about how to drive them and the math behind them. And you can get drivers (called ESCs) for less than ten bucks from China, which can be reflashed with open source firmware
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Nov 29, 2018 19:52
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Hi guys! My wife has a project for physics due in a few days and I cannot figure out how to do it. I have a beginner hobbyist amount of knowledge about electronics which is uniquely not useful for this problem, and she and her partner are hopeless. So the problem is this: make a circuit with 2 alternating flashing lights (like at a train stop). Simple right? Well, here is the problem: You are only allowed to use A battery, 2 lights, capacitors, inductors, and resistors. It would be easy if we could use transistors but I have no idea how to do it with just these components. We did a bunch of searching on youtube and trial and error in the falstad simulator but couldn't figure out the right set up. If someone could even just post a screenshot of something like this set up on the falstad simulator I would be extremely grateful. Thanks for reading 
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Nov 29, 2018 20:22
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LEDs? Or lamps?
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Nov 29, 2018 20:27
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Are the lights LEDs?
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Nov 29, 2018 20:28
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I -think- they are supposed to be lamps. But at this point I will take anything.
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Nov 29, 2018 20:30
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Can you even get a circuit to oscillate without active components? (or moving parts like the vibrators in old radios?)
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Nov 29, 2018 20:42
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I was thinking there might be a way to use the LEDs as a switch in an LC oscillator but I haven't been able to make it happen.
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Nov 29, 2018 20:44
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I was thinking LC oscillator as well, but I don't know how you get it to do anything useful without amplification.
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Nov 29, 2018 20:46
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BattleMaster posted:Can you even get a circuit to oscillate without active components? (or moving parts like the vibrators in old radios?) This is a neat puzzle. I suspect you use the diodes in reverse bias and have an lc/Rc oscillator to create an alternating current
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Nov 29, 2018 21:31
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Can you just put a lamp and inductor in parallel with the other lamp and a capacitor, in parallel with the battery? I’m not sure that works, but it’s where I would start. You have to somehow create an oscillation so that you don’t just light them up continuously, so I feel like there needs to be a loop that contains both the cap. and the inductor, without the battery. You’ll also need to pick component values such that the resonant frequency is something you can actually see, so around 10 Hz or less, ideally. That’s a really interesting challenge, I’ve never thought about doing something like that without ICs. Edit: some new posts appeared, I’ll leave this here in case it’s useful still though.
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Nov 29, 2018 22:31
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The obvious solution is trick LEDs: https://www.youtube.com/watch?v=YRSYQGNftLg (it's a trick, but not a fake)
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Nov 29, 2018 22:47
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I don't have the real answer, but I have a smark-alek nonsense one. Did they specify what kind of diodes? Apparently if you make them Gunn diodes, you can make an oscillator out of them. https://en.wikipedia.org/wiki/Negative_resistance Scroll to "Gunn diode oscillator".
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Nov 29, 2018 23:19
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LC oscillator tank circuit with an LED in each direction? Charge it up and let it go? http://www.circuitstoday.com/lc-oscillators-and-types Idk I'm a fake engineer I'd probably try to bash the parts together into crude relays honestly
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Nov 30, 2018 00:12
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I'm ~95% sure it's impossible with just passives. I think you can prove that for any arrangement of resistors, capacitors, inductors, and ideal voltage sources, every point in the circuit has a constant voltage in the limit as t->infinity. Passives can't add AC energy and you need something to compensate for heating losses. I don't think LEDs can add AC energy either.
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Nov 30, 2018 06:39
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longview posted:Here's an interesting problem I found last night: What are you using the ferrites for? Reducing EMI? If it's a hobby project, just cut them. Or replace with a real RL low-pass. Ferrites do some interesting nonlinear stuff from hysteresis in the magnetic bits.
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Nov 30, 2018 06:46
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BattleMaster posted:Can you even get a circuit to oscillate without active components? (or moving parts like the vibrators in old radios?) Depends on your definition of active. You can get most gas discharge lamps to oscillate with a capacitor and a voltage source, since the resistance drops when the gas ionizes and there’s a gap between the strike, maintain, and extinguish voltages. https://en.m.wikipedia.org/wiki/Pearson%E2%80%93Anson_effect
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Nov 30, 2018 07:12
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ullerrm posted:Depends on your definition of active. You can get most gas discharge lamps to oscillate with a capacitor and a voltage source, since the resistance drops when the gas ionizes and there’s a gap between the strike, maintain, and extinguish voltages.
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Nov 30, 2018 07:18
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Foxfire_ posted:What are you using the ferrites for? Reducing EMI? If it's a hobby project, just cut them. Or replace with a real RL low-pass. Of course, hysteresis! Totally forgot that ferrite beads are ferrite. It perfectly explains the behaviour. Yeah this is a hobby board with no EMI requirements, but it's going inside a short wave radio receiver that covers 15 kHz to 30 MHz and avoiding massive interference from conducted emissions is a priority. It's probably fine to not have a series element on a class AB amplifier output, in any case this and several other signals will go through feed-through caps before leaving the backplane. Common mode chokes would be optimal here since it's a fully balanced signal going to a speaker, but those are expensive so I put in ferrite LC filters which are fine for everything else on the board. E: I ran a LTSpice simulation with an inductor with hysteresis and the output waveform is a perfect match! longview fucked around with this message at 07:38 on Nov 30, 2018 |
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Nov 30, 2018 07:22
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Wires are allowed, right? Use one of the inductors and a bunch of extra wire and build an oscillating electromagnetic switch like in an old doorbell.  I agree with the posters above in that I don't think it's possible to make a self-sustaining oscillation with only the components you're given and no moving parts. A temporary one like shovelbum's LC tank sure, but that doesn't continue indefinitely. Maybe there's some bizarre electrical phenomenon that no one here has remembered, but I think it would be pretty dumb for a basic physics class assignment to rely on the students knowing about obscure behaviors that aren't part of the devices' normal function. Please come back and post the professor's solution, whenever you find it out. Sagebrush fucked around with this message at 07:53 on Nov 30, 2018 |
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Nov 30, 2018 07:51
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Can you post the actual like, assignment wording? Maybe y'all missed something obvious, because I can't imagine giving this as actual homework (instead of like, idk, a bonus points problem)
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Nov 30, 2018 15:55
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Or wait, maybe it doesn't have to oscillate continuously but only a few times? In which case when you complete the circuit by putting the battery in or whatever the voltage going from zero to Vbat could get an oscillation going (that would damp out eventually) that you might be able to do something with...
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Nov 30, 2018 15:58
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$5 says the next classes lecture starts with "Did anybody find a way? No? Well it turns out that those are all passive components which is a grouping of the parts that can't do that. Next, let's talk about active components, which can"
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Nov 30, 2018 16:58
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Shame Boy posted:I didn't notice nobody had replied to you, sorry. Lemme give it a shot since it's important safety stuff we're talking about This is why I need to dig out that "How to oscilliscope" book I mentioned. Thanks for the tips. The AM/FM clock radio I was eyeing does seem to be isolated per your testing regime, but probably not worth the risk. I'll find something battery-powered, and buy that SDR kit because I've been wanting to play with SDR anyway. In related news, the 'scope shows a 60hz sine wave when I connect it to an 18" alligator lead, or touch it to my own body. When I have one thumb on the probe, the amplitude goes up and down depending on how close I put my other hand to the fluorescent desk lamp. I'm an antenna! ... I think I just independently invented the theremin*. Neat! *I've played with one, and know how it works in theory, but seeing the waveform on the 'scope made me actually understand it. Chillbro Baggins fucked around with this message at 21:19 on Nov 30, 2018 |
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Nov 30, 2018 21:07
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Anyone know of any project-based from-first-principles educational electronics resources? Screwing around with Arduino crap and/or discrete active components is fun but I'd like a better grasp on the fundamentals, and reading textbooks and academic resources definitely isn't the same thing as actually Doing Stuff. Simultaneously, It'd be nice to expand my limited electronics resources with stuff like a simple adjustable power supply, a signal generator etc. I've run into electronics kits for those that are clearly geared towards beginners, and I could just buy a whack of them off AliExpress and go nuts in 2-3 months' time and if I gently caress up the kit cost $4.51 so no biggie... but if there's a structured version of this, particularly something that actually builds theoretical understanding by tying it into the projects instead of just building kits as per instructions, I'd be very much into that. A while back I ran into something like this for DC power supplies- starting with an AC waveform and working through each component and explaining how and why it tweaks the output like it does. This isn't what I'm talking about specifically, but it's in a similar vein- https://www.teamwavelength.com/power-supply-basics/ Something like that but for additional + more advanced projects would be swank.
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Dec 1, 2018 05:53
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edit: I missed Stabby McDamage's post. I basically spent most of my post, which is now deleted, describing a type of device, the 'tunnel diode', which is very similar to the 'Gunn Diode' he or she identified. It is arguable about whether these kinds of oddball devices are active or passive though. Here is a snippet from what many call the first integrated circuit patent, where Jack Kilby explains that according to a certain definition, these kinds of diode devices are not passive devices, but are active devices. 
silence_kit fucked around with this message at 15:27 on Dec 1, 2018 |
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Dec 1, 2018 14:36
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silence_kit posted:False, this can be done with certain kinds of oddball two-terminal semiconductor devices that people got really excited about in the 50's. I'm technically correct, the best kind of correct. So I am even more technically correct, an even better kind of correct. But, yes. There is a actually much larger group of semiconductor devices, and similar tube based devices, that amplify and filter some kind of quantum noise into usable RF. Even most LEDs are part of that group. Though all that I know of generate high frequency oscillations which is not exactly useful for flickering a lamp. I actually thought of another joke solution. Get a really strong lamp and some lenses and use the heat to bring some part of your circuit outside of it's heat tolerance, whereupon the lamp switches off. It won't blink too many times, but it might technically count.
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Dec 1, 2018 15:29
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Oh I missed the post where the original problem was stated. Oops.tonberrytoby posted:A negative resistance setup is not really converting DC to AC, it is amplifying some kind of background noise to an useful level. Isn't that kind of what an amplifier is? A device which converts DC electricity to AC electricity? Isn't this the principle of many oscillators? The oscillation starts as noise. tonberrytoby posted:But, yes. There is a actually much larger group of semiconductor devices, and similar tube based devices, that amplify and filter some kind of quantum noise into usable RF. Even most LEDs are part of that group. In principle, you could combine the oddball device with monster inductors & capacitors and generate a low frequency oscillation that way. I think it would probably be pretty weak though, since the negative resistance regions of these devices is not so big. silence_kit fucked around with this message at 15:40 on Dec 1, 2018 |
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Dec 1, 2018 15:34
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silence_kit posted:Oh I missed the post where the original problem was stated. Oops.
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Dec 1, 2018 15:39
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My instinct is to replace the resistor in an LRC circuit with a lamp, but I spent two hours trying on Falstad circuit simulator and I can't manage to get enough power to the bulb without damping the oscillation. I tried a bunch of combinations including reluctance of electrolytic capacitors to make a pseudo-diode, but nothing actually works for more than half a second or so. A question of my own, what's the best solution for simultaneously reading analog voltage off of a large number of sensors (one hundred, ideally scaleable to several hundred)? Just stack multiplexers and ADCs?
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Dec 1, 2018 23:13
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I think the only way to do it would be to use 2 neon lamps, or at least one. Sure, it's kinda cheating, but you said "lamps" which doesn't prevent using neon bulbs.
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Dec 1, 2018 23:56
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