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GnarlyCharlie4u posted:RE: revolver chat Different resistance would only change the brightness, unless you're suggesting different combinations of R,G, and B, i.e. Chamber 1: 20mA R Chamber 2: 10mA R, 10mA G Chamber 3: 20mA G Chamber 4: 10mA G, 10mA B Chamber 5: 20mA B Chamber 6: 10mA B, 10mA R Which is a cool idea, but triples the contact alignment problem.
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Dec 7, 2020 20:49
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You could use a single resistor of a different value in each chamber and run it into a voltage divider and analog input to figure out which one it is. The other end of the resistor could be grounded, so you'd only need a single point of sliding contact. Non-contact, single-point option that might work: analog hall effect sensor and a stack of 1-6 small magnets in each chamber. Comedy option: get one of these $5 RGB color sensors, paint a colored dot on each chamber, read the color as it goes by and set the LED to the same value.
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Dec 7, 2020 21:26
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You would need sliding contacts everywhere because otherwise you can't load one bullet, spin the chamber, then ask if someone feels lucky
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Dec 7, 2020 22:02
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Is there a
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Dec 9, 2020 02:30
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Honestly I like the old fashioned style but there are two key things that make a good one: 1) Has to be a vintage one with a real big heavy base and chunky arms. The cheap ones on Amazon and eBay these days are like the minimum possible metal to keep it from tipping over under its own weight. 2) Take the magnifying glass off and replace it with a third alligator clip.
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Dec 9, 2020 02:35
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Howdy goons. The following figure shows the power spectral density of a system noise measurement (sensor -> amplifier -> ADC). You will notice it is not flat. https://postimg.cc/nXP4KYm4/de0921b2 This figure shows the same data, now plotted in units of V/sqrt(Hz) and log of frequency - https://postimg.cc/yJ3FLghw/ec38b2af The linear roll-off is certainly indicative of 1/f noise, but it is dropping off at ~1dB/decade, unlike the typically quoted rule of -3dB/decade (though, I have read articles that generalize it to other proportionalities, eg., c x 1/fa, with c and a obtained through fitting). Anyway, has anyone seen this sort of thing before? I'm rather puzzled about what's causing it.
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Dec 10, 2020 07:32
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Is there a guide for what AWG to use for just very short DC electronics runs? Like I'm looking for the most appropriate gauge for 12vdc at 50 amps going into an XT60 connector, etc.
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Dec 11, 2020 00:48
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Current capacity is a function of wire gauge, voltage capacity is a function of insulation. 12v doesn't require any special insulation so you just need to worry about the gauge. Take your maximum current, add 50% for safety, and look it up in this table: https://www.powerstream.com/Wire_Size.htm So you want about 8-gauge for that, 3mm diameter, which feels right to me. 50A is a LOT of current
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Dec 11, 2020 00:55
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Can any of you PCB-smart guys do a quick sanity check of this for me? I'm trying to make a PCB that uses 10 WS2812-2020 Neopixels to make a sort of bar graph that sits within a very particularly sized footprint (.24" x 1") Board: https://www.altium.com/viewer?token=Emo5m7LkzU22ojLi8cO3460k Schematic:https://www.altium.com/viewer?token=Jx%2FcajhfgkOBmMaKw3c%2BH6wk ERC looks clean in EAGLE, and DRC using OSHPark's settings only gives me a warning that my GND/DI/VIN pads are a hair close to the edge of the board, which I think should still be fine?  Planning on solder paste/flux pen/hot air assembling these given how tiny those LEDs are.
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Dec 11, 2020 00:58
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Sagebrush posted:Current capacity is a function of wire gauge, voltage capacity is a function of insulation. Thanks, that looks about right. What do they mean by "chassis wiring" vs "power transmission"? edit: also when I'm googling there's a lot of people complaining that 8AWG is too thick for XT60 connectors even though they are specifically rated for 60 amps. Maybe I can get away with 10awg if I'm only peaking at the 50 amps? https://www.youtube.com/watch?v=8nC00j7QnZ8 Zero VGS fucked around with this message at 01:51 on Dec 11, 2020 |
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Dec 11, 2020 01:47
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Chassis wiring = wiring entirely inside you washing machine/fridge/whatever Power transmission = wiring inside building walls Current through wires will make heat. It will also make voltage drop. Eventually there is too much voltage drop or insulation melts/catches fire or someone touches the wire and burns themselves. Actual thickness of wires will depend on how well your wires are cooled (e.g. a single wire in box with vents and a fan will dissipate heat faster than one in a sealed box bundled with a bunch of other high current ones) and how much voltage drop you can tolerate. If the voltage drop is okay and it's not running long enough to get hot, you can use smaller wire. If you're wrong, it may catch on fire though.
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Dec 11, 2020 02:10
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Harvey Baldman posted:Can any of you PCB-smart guys do a quick sanity check of this for me? I'm trying to make a PCB that uses 10 WS2812-2020 Neopixels to make a sort of bar graph that sits within a very particularly sized footprint (.24" x 1") Things I would do: - Put footprints for some caps on it even if you're not going to populate them - Run the DO pin on the last LED out to a test point unless you're absolutely positive you're never gonna daisy chain more off it - Print it out on paper on actual size and make sure the LEDs and the connector don't bump each other and you will be able to physically place them without it sucking too much - I would probably flood VCC on the top and put GND on the bottom, but that's just habit, it ought to work as is. It's too small to warp from uneven copper or have a lot of voltage drop, and the extra etching being done is mostly the fab's problem, not yours. You can violate the design rules a little bit probably/maybe, but you lose your ability to complain if they refuse to try to make it or it cracks from drilling. I didn't look at any of the pinouts or footprint sizes. Also, what are you planning on controlling them with? They are picky about timing since they don't have a separate clock and you can't simultaneously update them all. May or may not matter depending on what exactly your doing. e: APA102 / SK9822 are the ones that work with normal SPI. APA102 is the original one, but has a stupid part of the protocol that SK9822 fixed either on purpose or accidentally, so they're not interchangeable. Foxfire_ fucked around with this message at 02:48 on Dec 11, 2020 |
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Dec 11, 2020 02:36
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Yeah, the power transmission values on that chart are deliberately conservative because they're meant for wires being bundled up and shoved into a wall with no cooling airflow. If the wire is hanging out on its own in the air, with room for heat to dissipate (as you might see in e.g. an RC car battery pack) then you can run more current before you melt the insulation or start a fire. If you actively cool the cable, you can go even further past what that chart specifies. Duty cycle is also worth considering. You might be able to run 50 amps through a smaller wire than the chart suggests as long as it's only for a short time and you give plenty of time for the wire to cool down afterwards. This is the situation with car starter motors, for example; the motor and its wiring are way undersized for the current if it were to run continuously, but since you only energize it for a few seconds at the beginning of the drive it doesn't have time to overheat and it's fine, and the smaller motor saves space and weight and money. But if your car has trouble starting and you keep cranking at it for a minute straight, instead of cranking a few times then pausing to let it cool down as the manual says, there's a very good chance you'll burn out the motor. Maybe that's your situation too; if 50 amps is only the peak load and it's only occasional, a smaller wire might be suitable. So yes, 10 gauge is probably just fine, as long as you think about your specific situation and the demands it's placing on the wire.
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Dec 11, 2020 02:39
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I've been asked to turn a lashed-together setup for a LED light strip Ambilight running via a Nano into a PCB version. I've made what I think is the first revision of the board, but I haven't done the +5V trace yet from the jack to the left and right LED strip plugs. The ground is a single plane on the back (USB powering the Nano but apparently the grounds can be tied together). I am trying to figure out how to do this in KiCad. Apparently with a 6A current my track on a 2 layer board needs to be about 3.5mm wide, maybe 4mm for a good buffer. How do you actually connect a trace of that width to a small, circular pad? Is it just with the automatic thermal relief connections? Are those wide enough to actually take the current over the 3 or 4 little legs it makes to join the pad? Never worked with this amount of current before. Edit:  Have to get over to the right somehow too. Should I just make the entire top layer a +5V pour? Apparently that's a bad idea. Edit 2: Also very tempted to just have my buddy solder some thick wires to the pins instead of laying tracks out. Just be on the safe side. thehustler fucked around with this message at 14:07 on Dec 11, 2020 |
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Dec 11, 2020 13:50
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I can’t comment on your actual questions but I do want to say that if the footprint for the Nano module is the KiCad built-in footprint, double check the hole drills and spacing. The first time I tried to use it without checking the drills were too small and when I fixed that the spacing around the 1 pin was jacked up.
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Dec 11, 2020 15:52
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Thanks for the tip, I'll look into that! Edit: using the 3.x footprint
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Dec 11, 2020 15:57
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Yeah I was using the 3.x footprint too. Given the disparate nature of Arduino Nano clones, it's entirely possible that I got a clone with oddly fat pins or that the footprint was designed around a clone with oddly thin pins. Either way I just copied the footprint into a local library and upped the drill diameter to 0.95 and the modules I had fit a lot better.
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Dec 11, 2020 16:35
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thehustler posted:I've been asked to turn a lashed-together setup for a LED light strip Ambilight running via a Nano into a PCB version. I've made what I think is the first revision of the board, but I haven't done the +5V trace yet from the jack to the left and right LED strip plugs. The ground is a single plane on the back (USB powering the Nano but apparently the grounds can be tied together). 6A is a lot of current to run through a PCB. Generally I would consider 3A to be the limit of male header pins for example. I'm not sure what connector you're using, but double check that it's rated for what you're trying to do with it. Keep your trace as short as possible, and don't cross the microcontroller. So like, right next to your power input if you can.
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Dec 11, 2020 18:39
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Header pins are a placeholder for now, but fair enough, perhaps him soldering wires is better. Are you sure though? I’ve seen people say more is okay. This would be 1oz copper though, so...
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Dec 11, 2020 18:42
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You can look up the datasheet for header pins
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Dec 11, 2020 18:48
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thehustler posted:Apparently with a 6A current my track on a 2 layer board needs to be about 3.5mm wide, maybe 4mm for a good buffer. thehustler posted:Are you sure though? I've seen people say more is okay. This would be 1oz copper though, so... Presumably you got that number from a calculator like this one: https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-pcb-trace-width Note that that 3.5mm number is assuming it's fine that it heats up 10C above ambient. Also plugging in 40mm for the needed length, a 3.5mm track would be dissipating nearly a quarter of a watt which is quite a lot for something that small. If you increase it to 14mm you can get the heat rise down to 1C and the power dissipation down to 50mW but with corresponding difficulty in routing such a big fill. You can also do something like put the fill on both sides of the board and via stitch them together, that's usually what I do whenever I need to move currents of more than about an amp around a board. Also I'd think the little thermal reliefs on the pads there are prolly gonna be problematic hot spots too since they're so small.
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Dec 11, 2020 19:17
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You can draw ordinary tracks over the thermal relief spokes if you want a wider connection to your pin, too. As long as they're the same net as the zone they'll merge with the fill.thehustler posted:Should I just make the entire top layer a +5V pour? Apparently that's a bad idea. That sounds like a fine idea to me and would be my default for approaching this problem. The awesome thing about it is even though copper far from the current path won't conduct much current, it'll all act as a heat sink for the current path.
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Dec 11, 2020 19:50
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Yeah I don't see any reason not to make an entire layer +5V, unless you can't easily connect it and you wind up with islands or something, but I don't think this board is complex enough for that to matter.
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Dec 11, 2020 19:53
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To remove the thermal relief, point at the pins, push e (edit), pick the pad if there's a disambiguation popup, go to the local clearances tab, and set the thermal relief width/gap to 0. That will change that pin on that instance of the footprint only, not it globally. You could edit the footprint template itself and then update footprints if you wanted to do it everywhere. (This will make it much harder to solder, since by design you are increasing how fast heat transfers from the pin to the other copper) thehustler posted:Should I just make the entire top layer a +5V pour? Apparently that's a bad idea. Foxfire_ fucked around with this message at 20:30 on Dec 11, 2020 |
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Dec 11, 2020 20:20
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Random internet search suggested that it may not be as safe if you nick some of the mask off accidentally and somehow cause a short, but that does sound very unlikely to happen. Okay, pour it is. Thanks for the pad tips. Best to do that with the ground connections too, I guess. thehustler fucked around with this message at 20:31 on Dec 11, 2020 |
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Dec 11, 2020 20:28
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Every tutorial I've seen for PCBs has had the person filling the top with VCC and the bottom with GND.
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Dec 11, 2020 20:42
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It lowers DC resistance and voltage drop + more copper provides heatsinking. There's also a not-particularly-sound argument for it adding distributed capacitance from the VCC copper-FR4-GND copper structure. In bigger manufacturing, having equal amounts of copper on top and bottom reduces board warping and delaminating (FR-4 and copper have close but not equal thermal expansion). Layers also start as fully covered with copper foil. If you remove most/all of that, that copper goes into the etching fluid and you have to change it more frequently
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Dec 11, 2020 21:01
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There was mention of capacitance on the sources I saw too, but it sounds like over-worrying.
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Dec 11, 2020 21:11
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thehustler posted:There was mention of capacitance on the sources I saw too, but it sounds like over-worrying. I mean capacitance between VCC and GND is usually a good thing, it's basically acting as one large distributed board-wide decoupling cap. It's just not a very big one so it probably doesn't actually matter.
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Dec 11, 2020 21:13
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In fact, there's already a big electrolytic capacitor between +5 and ground, so using a fill will not noticably increase the capacitance there.
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Dec 11, 2020 22:40
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Foxfire_ posted:To remove the thermal relief, point at the pins, push e (edit), pick the pad if there's a disambiguation popup, go to the local clearances tab, and set the thermal relief width/gap to 0. That will change that pin on that instance of the footprint only, not it globally. You could edit the footprint template itself and then update footprints if you wanted to do it everywhere. So I changed it to "solid" and then it made just a straight connection around the entire pad. Presumably this may need a higher soldering temp then to keep the temperature up if all it's going to want to do is transfer it to the pour?
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Dec 12, 2020 14:23
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I want to project text about 3 or 4 ft. Think 'laser pointer, but a clock.' I figured there might be something like that with the pico projector\augmented reality craze. Any recommendations or search terms?
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Dec 12, 2020 17:45
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Do you mean the use case is carrying it around like a laser pointer? Aside from one of those laser projectors that uses a moving mirror to project something, I don't think you will be able to have it be in focus unless you take a few seconds to adjust it every time.
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Dec 12, 2020 18:01
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thehustler posted:Presumably this may need a higher soldering temp then to keep the temperature up if all it's going to want to do is transfer it to the pour? A hotter iron setting probably won't actually matter, if its control loop is any good. Heat will be moving out of the tip fast enough that the iron's heater should be running at 100% to try to get back to its setpoint either way. A higher starting temperature will have a bigger starting reserve of heat so it'll help a bit. Preheating the board or a more powerful iron are the best solutions but more equipment obviously.
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Dec 12, 2020 20:07
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bobua posted:I want to project text about 3 or 4 ft. Think 'laser pointer, but a clock.' I figured there might be something like that with the pico projector\augmented reality craze. Any recommendations or search terms? I don't really understand your question. Something like this? https://www.aliexpress.com/item/32858279783.html
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Dec 12, 2020 20:11
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ante posted:I don't really understand your question. Something like this? Just like that. Was hoping someone sold a projector like that as a product to integrate into your own project
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Dec 13, 2020 00:58
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Take it apart and hack it. You're not going to find anything cheaper than that
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Dec 13, 2020 01:29
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That's probably just a reversed* clock LCD in front of a red LED, maybe with a lens. *dark bg, light fg: 
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Dec 13, 2020 01:35
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Mmmmm, yeah I need a solid 3 to 4 ft and real bright, that won't work.
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Dec 13, 2020 01:38
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Do you need to make a bunch of these? If it's just one, I would suggest buying that alarm clock and seeing what's in it. The projector part is in its own part of the clock on a hinge or something. I would bet that everything to make it work is in that separate bit and it just runs data lines to the rest of the clock to control it. I'll bet you can figure out how it works with a logic analyzer or something. Or maybe if they didn't epoxy the chips, you can look up a datasheet.
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Dec 13, 2020 01:47
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