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karoshi posted:I'm not an engineer and I need a safety/sanity check. I have some stuff This seems like a very long-winded way of asking "can I plug two or more of my laptop's USB ports into a breadboard and connect their grounds together" and the answer is yes, if they are normal USB-A ports. You should also be able to share the power lines with each other, as the laptop will probably be powering all the ports from a common 5v rail anyway. USB-C may be fine too, but that spec allows several different voltage levels and there's some negotiation with the device involved so I don't know what would happen. The regulators in your devices should not matter. The grounds are almost certainly not isolated from one another. In the case that you do something bad, e.g. short the power and ground lines together, your laptop has a polyfuse on every USB port that should instantly shut it down in an overcurrent condition. You might have to restart to get it to reset. The only way you're likely to cause serious damage is if you accidentally pump 12v into the 5v rail or something -- but maybe not even then. I once did that to a laptop by accident and it immediately shut the system down like pulling the plug on a desktop, but it came right back up afterwards and kept working.
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May 11, 2020 22:14
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Sagebrush posted:This seems like a very long-winded way of asking "can I plug two or more of my laptop's USB ports into a breadboard and connect their grounds together" and the answer is yes, if they are normal USB-A ports. You should also be able to share the power lines with each other, as the laptop will probably be powering all the ports from a common 5v rail anyway. Thanks for the quick answer. I got a sacrificial USB hub to protect the laptop. I'll just go ahead.
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May 11, 2020 22:25
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Got myself one of those beginner’s Elenco project kits, specifically the resistor substitution unit: https://www.elenco.com/product/resistor-substitution-box/ it’s a very simple project and not really geared to my experience level, but i would actually make real use of it in the future + the kit is actually p good value for what you get. it’ll make for a fun lil afternoon build. also i love the super retro styling, i coulda put together my own version for $10 but without that slick housing
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May 11, 2020 23:10
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shovelbum posted:Is that a diode or a resistor? I meant resistor, but said diode - this is the danger of falling back on componentry/electrical theory from science lessons in school 15+ years ago. Sagebrush posted:That looks to me like a bog-standard 5mm LED in a custom threaded housing. Looks like a resistor inside soldered to one of the legs, not a diode. You might be able to pry it apart and read the color code; I'd guess it's about 100-300 ohms if you're getting 4v on the circuit to illuminate it. Thanks! That's really helpful. I think my next step is going to be to desolder the broken lamp unit from its wires and see if I can prise the LED and its holder out of the translucent housing. That will let me get a read on the resistor colour bands if needed, but (and this might be a fool's errand) but if it's possible to get the original LED+resistor, which is still functional, out of the casing, it should be possible to buy a new casing of a suitable type and swap the innards over. If that doesn't work then I'll try and get the individual components and make something up - a nice little lockdown project! I've just read one of clredwolf's early posts in the this thread about LEDs, which combined with this tangible example, has finally made me understand something which baffled me in school. So result there!
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May 11, 2020 23:44
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If you have some resistors handy, you can just try some out. An LED will emit light with very little current. Something like a 10k resistor which would limit current to 10mA at 100V (safe for almost all LEDs that aren't tiny) will still light up a red led at 4V with something like 200uA. That will be visible in darkness for sure and probably still a little visible in office lighting, though not in daylight. You can be very conservative if you are worried. taqueso fucked around with this message at 00:00 on May 12, 2020 |
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May 11, 2020 23:56
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100 V * 10mA = 1 watt power dissipation in the resistor, which will burn up a normal size one. If you are actually going to use this circuit at 100V, please use a 5W ceramic resistor.
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May 12, 2020 04:44
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ryanrs posted:100 V * 10mA = 1 watt power dissipation in the resistor, which will burn up a normal size one. If you are actually going to use this circuit at 100V, please use a 5W ceramic resistor. I think he said that the LED circuit runs at about 3-4v. Certainly that little 1/4 watt resistor inside the housing isn't having to handle 100v
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May 12, 2020 05:47
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It's a good point, I was saying it would be conservative but a normal 1/4 or 1/8W will smoke after a bit
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May 12, 2020 06:00
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taqueso posted:If you have some resistors handy, you can just try some out. An LED will emit light with very little current. Something like a 10k resistor which would limit current to 10mA at 100V (safe for almost all LEDs that aren't tiny) will still light up a red led at 4V with something like 200uA. That will be visible in darkness for sure and probably still a little visible in office lighting, though not in daylight. Further to this, you've got a multimeter, so you can measure the current into the LED and pick a resistor until you get 1-10 mA depending on how bright you want it.
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May 12, 2020 10:11
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Can any of you recommend an inexpensive Pulse Generator, 1Hz to 1kHz, 5Vpp, adjustable offset (or fixed at 2.5 for 0-5v signal), adjustable duty cycle (fixed 50% would be ok for now), including the ability to selectively limit output to a fixed number of pulses? I can make something using an Arduino, but on short notice I'd like to buy something and I need several.
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May 12, 2020 17:20
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 I ordered a box of 24V LED pilot lights (impossible to find 3-4V ones of the right sort, and cheaper to buy a box of 14 than just one, so I at least have plenty to experiment on). I desoldered the original lamp unit from the wiring and tried to get the innards out. Unfortunately I think a combination of my previous attempts to superglue the lamp back together, the heat from the soldering iron and the twisting needed to get the base out of the unit broke the tail of the resistor or one of the contacts in the base because after putting the original LED unit into the new body and soldering it back into place it doesn't work. I'm going to swap the resistor from the 24V lamp to something suitable. With the old lamp apart I was able to read the colours, and it's a 120-ohm resistor, which tallies nicely with Sagebrush's estimate and confirms that my voltage reading was in the right area. Predictably (now I understand how LEDs work...) the 24V one has a 1.2k-ohm resistor in it.
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May 13, 2020 14:50
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The temperature sensor in my off-brand circuit board heater is dead, and I never liked the way the thing worked anyway, so I figured I'd open it up and see if I could redo the control board. I love when you open something up and can just tell that it's someone's ripped-off hobby project: ATMega processor, 74HC595 to drive the LED display on the front, nicely socketed LM358 op-amps everywhere, whole thing is powered by a 7805, classic  They also did that cheap crap move of putting in isolation slots, then completely defeating them by having a trace snake right up next to a point where there's a gap in the slot 
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May 14, 2020 04:27
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I don't have any means to add fuses to my circuits and I wanna change that; is there any reason I can't use automotive blade fuses + an inline fuse holder vs the glass cartridge fuses you tend to see in electronics, assuming the amps are the same? ATM or ATC fuses seem a lot easier to get a hold of, and are cheaper to boot.
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May 14, 2020 04:55
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Ambrose Burnside posted:I don't have any means to add fuses to my circuits and I wanna change that; is there any reason I can't use automotive blade fuses + an inline fuse holder vs the glass cartridge fuses you tend to see in electronics, assuming the amps are the same? ATM or ATC fuses seem a lot easier to get a hold of, and are cheaper to boot. As long as the voltages and current type also match then you should be fine.
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May 14, 2020 05:34
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Ambrose Burnside posted:I don't have any means to add fuses to my circuits and I wanna change that; is there any reason I can't use automotive blade fuses + an inline fuse holder vs the glass cartridge fuses you tend to see in electronics, assuming the amps are the same? ATM or ATC fuses seem a lot easier to get a hold of, and are cheaper to boot. As with everything fuse-related, it depends on what you're doing. If you never need it to break more than 12V at low current you're fine, but they're not rated for high-rupture-capacity or anything so if you dump wall power into them accidentally they'll probably explode on you. BigClive did a good video on fuses that covers a lot: https://www.youtube.com/watch?v=kx35WN3uLis
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May 14, 2020 05:38
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So I bought a very cheap battery to try out a couple things for that chicken coop. I wanted to have a solar powered setup that at minimum would run a pi zero W with a temperature sensor and be able to extend and retract a linear actuator on command, or on a timed schedule to open and close the coop door. This isn't the final battery I'll likely use but it's good enough for now. I verified that the battery is at full charge via an automotive trickle charger that indicates it's at 100%. Step 1 is to step down the 12v battery to 5v and get it to power the Pi Zero W. Battery: https://smile.amazon.com/gp/product/B003S1RQ2S/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 Buck converter: https://smile.amazon.com/gp/product/B071FJVRCT/ref=ppx_yo_dt_b_asin_title_o00_s02?ie=UTF8&psc=1 I did my 1st soldering in probably 25 years connecting to the Buck. I set up the following rig to test everything out. Positive has an in-line fuse of 5A. I used bullet connectors to connect 12g wire to 21g to solder to the Buck. The USB cable plugged into the converter was sacrificed and I crimped butt connectors to the + and - leads to make it easier to use my volt meter probes on since I'll probably be testing a few other USB sources for this and other projects later on.  Battery: 12.87 V, 0.226 A Converter 1: 5.00 V, 0.060 A Converter 2: 4.99 V, 0.060 A So my question is, are these converters just poo poo, or is the way I have wired it up caused a problem, or is this the expected amount of current I should see? I was under the impression that the output current for each converter should be very similar to that from the battery, just at a lower voltage. I am completely new to all of this and may have misunderstood. If it's how it's wired, please let me know? If it's a poo poo converter does anyone have a rec for a better one?
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May 14, 2020 13:05
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Cheap USB cables, especially if they're intended for data and not charging, tend to have really small wires, though it's short enough I wouldn't think it'd make a huge difference in this case. Also at that low of an output the blue LED could probably take a good chunk of it. Did you have it hooked up to a dummy load when you tested?
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May 14, 2020 14:39
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Forseti posted:Cheap USB cables, especially if they're intended for data and not charging, tend to have really small wires, though it's short enough I wouldn't think it'd make a huge difference in this case. Also at that low of an output the blue LED could probably take a good chunk of it. Did you have it hooked up to a dummy load when you tested? No I just had the probes from my voltmeter shoved into the other ends of those open butt splice connectors. How can I hook it up to / create a dummy load?
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May 14, 2020 14:51
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Oh, in that case that should've been a dead short and a big current lol. Multimeter in current mode is equivalent to a piece of wire (ideally). I'm guessing you tripped a short circuit protection mode of the converter. You can use a resistor though you probably only have 1/4W ones if you have any on hand I'm guessing which wouldn't really be easy to create a significant load with. An incandescent lightbulb is pretty good if you have a small one. Personally, if you have voltage, I'd probably just assume it was working as advertised and hook up the rest of the circuit and then maybe test it with the real circuit attached.
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May 14, 2020 15:01
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You can't measure amps on an open circuit. The battery is giving you the voltage it's supposed to, and so are your buck converters.
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May 14, 2020 15:02
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That Works posted:No I just had the probes from my voltmeter shoved into the other ends of those open butt splice connectors. Without a load on it, all you're measuring is the current the DC-DC converter itself is using. Think about the water analogy - voltage is pressure, current is, well, current, the amount of water flowing. In this case, the only "water" flowing is the amount needed to keep the DC-DC converter and its little LED running. I don't actually think you need a dummy load in this case unless you want to stress test the converter, but generally they're just a big fat resistor that can dissipate all the energy as heat. Just try plugging in some USB doodad and measure the current while that's running, like a USB light or a power bank or something that will draw some current. e: Oh wait you were measuring current across the end wires? Yeah that just shorted it out and the converter was probably entering some kind of shutdown mode 
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May 14, 2020 15:02
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That Works posted:So I bought a very cheap battery to try out a couple things for that chicken coop. I wanted to have a solar powered setup that at minimum would run a pi zero W with a temperature sensor and be able to extend and retract a linear actuator on command, or on a timed schedule to open and close the coop door. How are you measuring current? I don't see a load in your picture. Did you put your multimeter in current mode and then put it across the buck? Because that would be a dead short and might: - if you're lucky, trip a protection circuit - if you're unlucky, damage the board How did you measure current for the battery? In-line? Did you have a load connected, or is that 226mA what the buck takes to run?
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May 14, 2020 15:08
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In case you need a visual reference to what everyone is saying, this page explains it.
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May 14, 2020 15:23
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 Thanks everyone. One Legged Ninja posted:In case you need a visual reference to what everyone is saying, this page explains it. Yup seeing that made total sense. I plugged the buck output into a cheap bluetooth speaker via a USB cable and that charged / acted as normal. I then plugged in a really old raspberry pi I had and that booted right up and seems to run fine. I'll set up a proper test circuit and measure amps across that once some more parts get in (I have a pack of resistors, LEDs and other parts + a breadboard that hasn't shown up yet). Seems like the converters weren't damaged at least not to the point of total failure as they both put power out to the little speaker. Lesson learned. KnifeWrench posted:How are you measuring current? I don't see a load in your picture. Did you put your multimeter in current mode and then put it across the buck? Because that would be a dead short and might: It was a dead short  but seems like nothing was damaged (at least to complete failure). Battery current measure was also dead short connected both probes to each battery lead and read voltage then spun the multimeter dial over to amps and took the reading.
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May 14, 2020 15:33
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I'm going to end up destroying so much hardware aren't I?
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May 14, 2020 15:41
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That Works posted:I'm going to end up destroying so much hardware aren't I? Ideally! One of my favorite quotes: Niels Bohr posted:An expert is a man who has made all the mistakes which can be made, in a narrow field.
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May 14, 2020 15:47
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You can get a usb charging tester like this for a few bucks. I'll show you the voltage and current. Generally a pretty useful thing to have around. But tbh I'd just hook up a phone and see how quickly it's charging (or if it blows up)
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May 14, 2020 16:24
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Blowing up your first multimeter by trying to measure current with it the same way you would voltage is an ancient and time-honored tradition
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May 14, 2020 16:39
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Extra credit if you vaporize a puny clip lead in the process
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May 14, 2020 16:45
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We received multiple echo dots over the past few years from the same uncle of mine who just forgot. I managed to get rid of two, but now I've got a third. I was cleaning the other day and found it, so it's either going in the bin or I'm re-purposing it. The boards don't seem very useful, and I couldn't find anything about wiping them anyway, so I was thinking about just using the case for something as a novelty. Does anyone have any ideas or help? Looking at the dimensions it's a little small for even the smaller raspberry pi's but I'm not very familiar with microcontrollers in general so maybe there's something that works in a similar vein. Is this even the right thread?
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May 14, 2020 16:51
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That Works posted:Battery current measure was also dead short You should look around your probes/meter for charring and also measure something known to see if the meter still works. A dead short across a lead acid battery will surge tens to hundreds of amps. High power output is one of the things they excel at. As far as what you should expect to see from the circuit when everything's working, the current leaving the battery should be smaller than the current leaving the converter. The power (voltage * current) should be similar, depending on the efficiency of the converter. i.e if it were 100% efficient, 1A@12V (12W) would turn into 2.4A@5V (also 12W)
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May 14, 2020 17:22
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Forseti posted:Extra credit if you vaporize a puny clip lead in the process It's basic arc welding, no more, no less. Practicing multiple skills at once for added efficiency: electronics and metalworking.
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May 14, 2020 18:23
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You just need to learn some basic electricity stuff and learn how a multimeter does what it does. When measuring voltage, you have to put the meter in parallel with the component because every component in parallel has the same voltage. The meter runs the current through a really high resistor like a megaohm so it doesn't siphon much current off of what you're trying measure. When measuring current, you have to be in series because the meter acts like a wire and will take all the current it can, so it needs some component in series with it to slow the current down. Hopefully your meter wasn't too expensive and now you know. Hopefully it just blew the fuse and you just have to replace that and maybe you might need to replace the probes. But the fuse should be there to protect the probes.
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May 14, 2020 18:31
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Cojawfee posted:You just need to learn some basic electricity stuff and learn how a multimeter does what it does. When measuring voltage, you have to put the meter in parallel with the component because every component in parallel has the same voltage. The meter runs the current through a really high resistor like a megaohm so it doesn't siphon much current off of what you're trying measure. When measuring current, you have to be in series because the meter acts like a wire and will take all the current it can, so it needs some component in series with it to slow the current down. Hopefully your meter wasn't too expensive and now you know. Hopefully it just blew the fuse and you just have to replace that and maybe you might need to replace the probes. But the fuse should be there to protect the probes. This should be clear, but DON'T LEARN ON MAINS VOLTAGE. Learn on low-voltage DC. And buy a decent meter if you're ever touching mains power: https://www.youtube.com/watch?v=OEoazQ1zuUM&t=326s
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May 14, 2020 18:36
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I bought a "cathode rejuvenator tester" diagnostic tool at an estate sale for $2.50 a few years ago for the retro look + maybe to salvage the wooden case + hardware from it. then i promptly forgot about it. today i remembered and immediately peeled it open, this time interested in the circuitry  extremely cool faceplate, every button and knob is an absolute delight to fiddle with  i am... in uncharted territory here. the vacuum tube and the total reliance on incandescents for indicators and the point-to-point wiring place this as from, what, the 60s at the latest? at least i can still read the resistor codes  side view, w a better view of the tube + switches n hardware. is that ceramic tube-lookin thing up top a coil winding of some sort? i recognize most of the other parts from their descendants but i can't get a better look at that bit without tearing stuff out anyways: idk what to do with this, my hoarder side says "leave it be, ITS AN ANTIQUE, some gormless fool with an all-original arcade cabinet might need his CRT rejuvenated some day", my more practical side says "all the capacitors will have gone to poo poo, theres no way this thing will work again without a total rebuild, just strip it for the timeless components- transformer, switches/knobs, funky indicator lense covers, etc- and leave the faceplate as the conversation piece". in particular im curious about : - the analog gauge on the front seems to measure from 0-1000 microamps, if im reading it correctly- is there any reason i couldnt directly reuse it for that specific indicating purpose, assuming it still reads true? - i'm assuming all the electrolytic caps are kaput, but are there likely to be more durable or useful capacitors in the design, given that it seems to have operated at fairly high volts and most of the caps are rated to at least 1000VDC? for all i know silver mica caps or some poo poo coulda been opted for back in the plentiful days of yore - the transformer looks fairly gnarly irt whatdver it's been laquered with, but is there any reason i couldnt make use of it post... cleaning, or whatever? or should i just pull the ferrite and wrap it fresh? Ambrose Burnside fucked around with this message at 19:54 on May 14, 2020 |
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May 14, 2020 19:27
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Cojawfee posted:You just need to learn some basic electricity stuff and learn how a multimeter does what it does. When measuring voltage, you have to put the meter in parallel with the component because every component in parallel has the same voltage. The meter runs the current through a really high resistor like a megaohm so it doesn't siphon much current off of what you're trying measure. When measuring current, you have to be in series because the meter acts like a wire and will take all the current it can, so it needs some component in series with it to slow the current down. Hopefully your meter wasn't too expensive and now you know. Hopefully it just blew the fuse and you just have to replace that and maybe you might need to replace the probes. But the fuse should be there to protect the probes. just wanna correct this: you need to be in series because the only way you can measure current through a device is by having the same current go through your multimeter. electrons don't get lost, so the current through any device in a series loop is equal to the current in the whole loop. if you put the multimeter in parallel with the device, some current will go through the meter and some through the device and you won't measure anything useful. and just putting another another component with little resistance (say, an LED) in series with a beefy power supply and a multimeter is not enough; in current mode, you will still blow something up, because it's the same as just putting the low-resistance device across the power supply. you need a resistive device that will reduce the current in the circuit to an appropriate level for the device and your meter. also resistors don't slow the current down; it always travels at the speed of light (+/-). resistors change how many electrons go through per time interval. the water analogy is okay for the most basic explanations of electricity but you really can't make any deeper assumptions based on how water works in pipes because electricity is not water in a pipe  e: well probably not +/- the speed of light. only -. current travels at the speed of light or a bit less depending on the type of conductor and its inductance. Sagebrush fucked around with this message at 19:49 on May 14, 2020 |
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May 14, 2020 19:43
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Cojawfee posted:You just need to learn some basic electricity stuff and learn how a multimeter does what it does. When measuring voltage, you have to put the meter in parallel with the component because every component in parallel has the same voltage. The meter runs the current through a really high resistor like a megaohm so it doesn't siphon much current off of what you're trying measure. When measuring current, you have to be in series because the meter acts like a wire and will take all the current it can, so it needs some component in series with it to slow the current down. Hopefully your meter wasn't too expensive and now you know. Hopefully it just blew the fuse and you just have to replace that and maybe you might need to replace the probes. But the fuse should be there to protect the probes. Got it. Thankfully no buzz, no spark no smoke and no error codes or beeping on the multimeter. Spent a little more time reading instructions again and watching a couple of vids. I tried again just now with the USB output connected to a wireless phone charger (that had a chargeable phone on it) I was able to read current of 0.6A between the + battery connection and connecting the circuit from there to the + wire I soldered onto the Buck. So, at least the multimeter seems ok but I wasn't expecting that low of a current. While the ammeter was connected the phone did begin to charge. sharkytm posted:This should be clear, but DON'T LEARN ON MAINS VOLTAGE. Learn on low-voltage DC. Warning noted! I have no interest in working on mains electrical stuff, at least not tinkering around like this. I'm staying far away from anything like that for a good long while.
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May 14, 2020 19:49
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That sounds completely correct. Under usual circumstances, USB is rated for about 500mA, but everything breaks the spec, so that's a ballpark that I would be comfortable with. Household products completely break peoples' brains for their intuitive feel for how much current they think stuff should take. Car stuff, too. If you're messing around with Raspberry Pi stuff, I don't ever expect you to see anything about maaaybe 1.5A or so, and often closer to 300-400mA.
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May 14, 2020 20:15
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ante posted:That sounds completely correct. Under usual circumstances, USB is rated for about 500mA, but everything breaks the spec, so that's a ballpark that I would be comfortable with. Awesome thanks! I went ahead and plugged in the Pi and it booted right up and is broadcasting so step 1 is good at least for the moment and it seems that I didn't break my multimeter. This is a good time to note that one Buck converter offered itself up to the gods when my probe touching the soldering point slipped and touched an IC as well. The little blue LED promptly died and nothing ever happened with it again. Note to self to make some little alligator clamp leads or something. The other one worked on the phone charger and the Pi. Now that the weather outside is nice, time to unbox this solar panel and charge controller and wire that up to the battery (and then the panel).
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May 14, 2020 20:23
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I know this is all Electrical Devices 101, but as someone who thinks he doesn't understand electricity I'm very pleased that I've managed to replace my generator's oil light   Resistor removed from the 24V LED, replacement 120-ohm one trimmed to suit.  Quick and dirty test on a 3V 'supply'. I was inordinately happy when it lit up!  Fitted and successfully tested! Thanks for your guidance, thread!
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May 14, 2020 20:33
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