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Splode posted:You shouldn't use tantalum caps if you can avoid it anyway, they're a conflict resource. Yeah I know, I'd never buy them but I find taking apart old dumpster junk or stuff I got for $5 at a thrift store and carefully desoldering / heat-pencilling off all the useful-looking components very zen and therapeutic so I have pounds of random parts. It's the big reason I was practicing surface mount stuff in the first place, so I can actually use half the stuff  e: While I'm thinking about it are there any other weird things with SMD components I should know? I even looked up tantalums and the site I landed on said the stripe was negative even though (after burning the cap out) I went back and looked and everyone else (including the footprint itself) said positive. The only other weird thing I've discovered so far is that some things that look like diodes are also actually just sneaky capacitors. Shame Boy fucked around with this message at 14:27 on Apr 19, 2017 |
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Apr 19, 2017 14:23
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Platystemon posted:At least it doesn’t have a fake ground pin. Speaking of grounds, I was getting some weird ground loop noise on a project and I tried to hook it up to the oscilloscope and it went nuts. Looking more deeply into it, AC current was flowing from my board's GND to earth through the oscilloscope's ground clip. Taking everything out of the equation I could, I get 65uA of current running at 50VAC RMS (60Hz) between my 12VDC adapter's negative output and any earth connection. This happens with any 12V power adapter I have and at any outlet I try. I would think that the negative terminal would referenced to the AC neutral line, which would essentially be mains earth. Is this normal? 
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Apr 19, 2017 14:54
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Foxfire_ posted:Anyone know a bunch about audio circuits? What's your experience with this sort of thing, because you might want to just start with a kit at first if this is a first project. Audio stuff is notoriously fickle to little weird design things introducing noise. e: Oh wait you've posted in this thread a few times before and clearly this isn't your first goat gently caress nevermind!
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Apr 19, 2017 14:56
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Splode posted:You shouldn't use tantalum caps if you can avoid it anyway, they're a conflict resource. They also have a tendency to fail short with not very much overvoltage.
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Apr 19, 2017 16:10
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taqueso posted:They also have a tendency to fail short with not very much overvoltage. Ah I'll keep an eye out for this. The thing i'm working on now has a 1.5A fuse already though (because I salvaged a bunch of SMD ones!) and as far as I can tell the caps are rated 16V vs. the 12V my circuit runs at so I think it'll be okay. Also I had no idea tiny ceramic SMD capacitors could have such huge values, I put in a few SMD spaces to solder in ceramic caps thinking they'd be in the nF to pF range and I measure some tiny ones and they're 10-100uF somehow  e: Well tiny by my standards, they're pretty big as far as SMD caps go I guess Shame Boy fucked around with this message at 16:15 on Apr 19, 2017 |
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Apr 19, 2017 16:12
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CapnBry posted:I had a good laugh about those tiny wires in the OP's photos, but I was moving some things around on my workbench and my eyes settled on a 12V 5A power supply I have there which has a very light and flexible 3-pin power cord. ha HA! The ground tests out as not connected through the wire so I cut it open and it is just like the OP's. 2 wire, 0.75mm diameter. Capacitive coupling? I don't know at all, because I'm lousy with this kind of thing, but I spitball because nobody else said anything yet. Also that clipping on the waveform looks like a clue. Edit: How big are these adapters? Have you taken them apart to see what kind of topology is involved?
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Apr 19, 2017 23:56
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ate all the Oreos posted:Ah I'll keep an eye out for this. The thing i'm working on now has a 1.5A fuse already though (because I salvaged a bunch of SMD ones!) and as far as I can tell the caps are rated 16V vs. the 12V my circuit runs at so I think it'll be okay. 1uF is about as big as I go for ceramic SMD capacitors (in the 0805 size anyway). You can get values above that, as you've seen, but they tend to have really lovely other properties or are just expensive. What are you pulling these high value ceramics out of?
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Apr 20, 2017 03:32
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Splode posted:You shouldn't use tantalum caps if you can avoid it anyway, they're a conflict resource. tbf if he's pulling them out of old junk electronics the conflict already happened and he's not funding it in any way.
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Apr 20, 2017 06:12
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Oh for sure, but I had no idea until someone told me fairly recently, so I figured I'd point it out for anyone else who didn't realise.
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Apr 20, 2017 06:33
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Lifehack: use leaded solder to minimise your consumption of the conflict metal tin.
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Apr 20, 2017 09:46
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Splode posted:1uF is about as big as I go for ceramic SMD capacitors (in the 0805 size anyway). You can get values above that, as you've seen, but they tend to have really lovely other properties or are just expensive. What are you pulling these high value ceramics out of? I'm not sure what these came out of specifically since they all go into the same bin, most of them are bigger than 0805 though, at least 1206/1210 and up since those are the smallest ones I can reliably solder manually so far. Some came from some old TV's with busted screens that I took the power supplies and processor boards out of, some old printers, an old 80's video camera, the broken motherboard of a junked laptop... Most of the TV's were ones people left sitting next to the apartment complex dumpster (and christ do people ever throw away a lot of really nice flat screen TV's) and the rest is from occasional trips to thrift stores where I just buy up a bunch of $5-$10 electronics items that seem like they'd have cool poo poo inside them Also if the TV's don't have visible cracks on the screen i'll generally go in and repair the busted capacitor (and it is always a busted capacitor) and then have a nice spare TV, but that's only happened twice so far e: Oh I just remembered that some of the smaller, nicer high value caps came from an old server motherboard from a junked server my last company was throwing out, along with a lot of very cool-looking inductors
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Apr 20, 2017 15:38
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Platystemon posted:Lifehack: use leaded solder to minimise your consumption of the conflict metal tin. I use lead solder because it's actually great.
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Apr 20, 2017 15:53
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I use lead solder because I grew up using it as a kid since my dad used it so I figure it's already done me some brain damage that i'll never be able to fix so why stop now. I actually have an air filter these days though, but that's mostly to keep my apartment fire alarm from going off or the apartment smelling like smoke. I wonder how much lead actually volatilizes in solder smoke, I'm sure some evaporates into the smoke but I'm guessing it's a tiny amount and probably insignificant compared to the amount of carcinogens the burning flux is probably emitting
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Apr 20, 2017 16:04
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I use leaded solder because eutectic lead/tin alloys melt real good and everything I make is a personal project or a one-off piece of research equipment.
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Apr 20, 2017 16:27
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ate all the Oreos posted:I use lead solder because I grew up using it as a kid since my dad used it so I figure it's already done me some brain damage that i'll never be able to fix so why stop now. I actually have an air filter these days though, but that's mostly to keep my apartment fire alarm from going off or the apartment smelling like smoke. From what I've read, lead solder does not evaporate at all since it's boiling point is way way higher. The smoke is 100% flux, still not good for you but not lead at least.
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Apr 20, 2017 16:50
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Zero VGS posted:From what I've read, lead solder does not evaporate at all since it's boiling point is way way higher. The smoke is 100% flux, still not good for you but not lead at least. Well liquids evaporate well below their boiling points, otherwise we'd have no clouds or rain or anything. I did some quick reading though and the amount of lead that actually evaporates below ~450C is negligibly small, however solder tends to make tiny dust particles where tiny bits of it were bubbled off or aerosolized and those can get on your hands or you can inhale them. Just washing your hands and using a filter and wiping down your work area occasionally seems to be good at managing it though. Meanwhile the flux vapor is actually pretty terrible and is apparently the number one cause of occupationally-acquired asthma in some countries and has a bunch of nasty other poo poo in it
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Apr 20, 2017 16:57
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That's like, assembly line occupational illness, though. For noodling around on your workbench, a little fan should be totally fine, forever.
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Apr 20, 2017 18:55
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 Tin–lead eutectic will always flow the best.  But lead‐free solder isn’t hard to work with at all.
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Apr 20, 2017 19:19
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ate all the Oreos posted:I use lead solder because I grew up using it as a kid since my dad used it so I figure it's already done me some brain damage that i'll never be able to fix so why stop now. I actually have an air filter these days though, but that's mostly to keep my apartment fire alarm from going off or the apartment smelling like smoke. Yeah the flux is the bad bit tbh The lead is problematic for lovely recyclers 63 37 EUTECTIC for life
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Apr 20, 2017 19:46
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Effective-Disorder posted:Capacitive coupling? I don't know at all, because I'm lousy with this kind of thing, but I spitball because nobody else said anything yet. Also that clipping on the waveform looks like a clue.
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Apr 20, 2017 20:16
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ante posted:That's like, assembly line occupational illness, though. For noodling around on your workbench, a little fan should be totally fine, forever. I've operated soldering machines as a full time job, and yeah, the lead exposure from soldering at home is insignificant. Don't smoke a cigarette while soldering. Don't smoke a cigarette after soldering until you've washed your hands. Don't eat cheetos while soldering. Don't eat cheetos after soldering until you've washed your hands. Don't pick your nose while soldering etc Inhaling lead off of your fingers is the primary thing you need to avoid when working with solder. Wash your hands before sticking your fingers up near your face.
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Apr 20, 2017 22:18
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Dumb question but it's not actually possible to solder with a low enough heat that the rosin doesn't smoke, right?
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Apr 20, 2017 22:29
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Doubtful. Tin-lead eutectic might theoretically be able to melt at a lower temperature than rosin's smoke point, but you need to raise it well above its basic melting point to solder anything successfully.
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Apr 20, 2017 23:29
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CapnBry posted:They're just standard no-name 12V power wall warts, I have a variety of them in all sorts of shapes. Interestingly, on my Samsung 5V USB power cube I get 4.7VAC from GND to Earth. On a Netgear router (an ethernet router, not an internet gateway) 12V DC supply I get 18VAC between GND and Earth. All the no-name stuff is around 50VAC though so they must share the same topology. On my bench power supply there is 0.1VAC between GND and Earth. So maybe it has something to with the quality of the transformer inside? Well, the obvious cheap stuff is basically just a big transformer with a cheap bridge and passive filter hooked up to a linear regulator. Given that you're seeing something at the same frequency as mains, I'd suppose that's what you're looking at. This document gets into common mode interference in switch-mode supplies, obviously the Netgear, Samsung, and anything else that isn't obviously a very heavy block of iron combined with some cheap passive/linear components. The bench supply has to be better shielded from parasitic impedances simply by virtue of its purpose. http://slpower.com/reference/SLPower_CommonModeNoiseArticle.pdf
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Apr 21, 2017 00:14
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CapnBry posted:I had a good laugh about those tiny wires in the OP's photos, but I was moving some things around on my workbench and my eyes settled on a 12V 5A power supply I have there which has a very light and flexible 3-pin power cord. ha HA! The ground tests out as not connected through the wire so I cut it open and it is just like the OP's. 2 wire, 0.75mm diameter. Yes, capacitive coupling as said. 65uA is pretty reasonably. The negative output is very purposely not connected to earth because outlets aren't reliably grounded and line/neutral are frequently reversed. By far the safest thing is an isolated output which, as you measured, can only supply 65uA of current to ground (and you). ate all the Oreos posted:Yeah I knew it's there to limit the current, though I didn't realize that zeners were okay with high voltages as long as the current is low. Or are you saying that the resistor and the zener will make a weird version of a voltage divider, with the zener dropping its zener voltage and the resistor dropping... everything else? Because I thought you'd need a higher Vbe than the output voltage to actually make current flow and turn the transistor on, meaning I'd need like a 400V zener (do they even make those?) I disagree with the satement about the zener. Zeners are zeners and they're reasonably ideal at regulating voltage. It takes orders of magnitude of current variations to get significant (more than a few percent) of voltage variation. Ff you want voltage variation with current you use a resistor. Zeners do come in hundreds of volts but can also easily be put in series. ate all the Oreos posted:My first design used a transformer driven by a fixed oscillator that was turned on or off by a comparator. The secondary of the transformer was connected to a Cockcroft-Walton like that, but multiplying the output meant the manageable ripple coming from the transformer turned into something like 100-200V of ripple, and that was only a few multiplication stages. Admittedly if I actually used a micro to drive it instead of a fixed oscillator I could probably get it more stable but I have a bunch of extra CCFL drivers that output very nice clean stable voltages already... This circuit is going to be problematic because with two mosfets following the op-amp you have two large gain multipliers. This is a circuit that very well may simulate but might oscillate randomly in real life. You can see, increasing C3 may help or adding resistor dividers on the gates to limit their swing. Also there is only a Vgs drop between the gate of M1 and the output. If you put the feedback there, on the gate of M1 it cuts a transistor from the loop with limited impact on output precision (this essentially returns to your shunt regulator idea but adds a final transistor stage). asdf32 fucked around with this message at 02:04 on Apr 21, 2017 |
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Apr 21, 2017 01:49
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Lead free solder isn't to protect you from it when you're soldering it (the flux fumes from lead free solder are worse for you than the ones in leaded solder), it's a lifecycle thing for when the part is in the dump and the lead leaches down into the groundwater
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Apr 21, 2017 04:07
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taqueso posted:They also have a tendency to fail short with not very much overvoltage. The good news is that failed tantalums aren't hard to diagnose, open the case and there will literally be a giant blackened crater on the board.
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Apr 21, 2017 04:34
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Effective-Disorder posted:Well, the obvious cheap stuff is basically just a big transformer with a cheap bridge and passive filter hooked up to a linear regulator. Given that you're seeing something at the same frequency as mains, I'd suppose that's what you're looking at.
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Apr 21, 2017 13:14
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asdf32 posted:This circuit is going to be problematic because with two mosfets following the op-amp you have two large gain multipliers. This is a circuit that very well may simulate but might oscillate randomly in real life. You can see, increasing C3 may help or adding resistor dividers on the gates to limit their swing. Also there is only a Vgs drop between the gate of M1 and the output. If you put the feedback there, on the gate of M1 it cuts a transistor from the loop with limited impact on output precision (this essentially returns to your shunt regulator idea but adds a final transistor stage). You posted this the day after i finished etching and assembling the board only to discover that the settings to get the thing to actually regulate had to be so precise that breathing on the potentiometers would throw it into a crazy oscillation Luckily the way I had laid it out I could replace one of the transistors with a zero-ohm link and the 1M resistor with a piece of wire and turn it into the original shunt regulator and that seems to work just fine. I was gonna make a post about it since I actually got a project working for once but I'm having some weird clipping problems that I wanted to try and diagnose first. Basically if you look at the input waveform, it should be a sine wave, but the tops and bottoms of each sine wave are getting clipped off. this is even with the regulator set way below the point where the transistor turns on at all (and I measured it, and even tried shorting the transistor gate to ground just to make sure it wasn't turning on at all). The only thing I can think of is the diodes are undergoing breakdown at a significantly lower voltage than I thought a 1N4007 was rated for, but whatever it is it's causing my regulator to abruptly stop increasing in voltage at almost exactly 400 volts, even though the CCFL transformer itself was capable of outputting much higher than that (and is still trying to if you look at the waveform, it's just getting clipped)
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Apr 21, 2017 14:25
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asdf32 posted:I disagree with the satement about the zener. Since you mentioned them another thing I changed about my circuit was the Vref that was feeding into the op-amp was originally a zener except I didn't have one in the voltage I needed and I got the resistor size wrong anyway so it wound up regulating to a volt below what it should have and being really unstable. I replaced it with a TL431 so thanks for whoever in this thread recommended that I get some since it's working great 
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Apr 21, 2017 15:04
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ate all the Oreos posted:Since you mentioned them another thing I changed about my circuit was the Vref that was feeding into the op-amp was originally a zener except I didn't have one in the voltage I needed and I got the resistor size wrong anyway so it wound up regulating to a volt below what it should have and being really unstable. I replaced it with a TL431 so thanks for whoever in this thread recommended that I get some since it's working great Ok I meant to add that the exception to my "zeners are good" statement are zeners below about 4.7V. They start to turn into resistors down there. That was probably me and I'm glad to have a new convert to the under appreciated TL431.
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Apr 21, 2017 17:30
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ate all the Oreos posted:You posted this the day after i finished etching and assembling the board only to discover that the settings to get the thing to actually regulate had to be so precise that breathing on the potentiometers would throw it into a crazy oscillation Double check your measurement set-up, the scope might clip if you over-range it or anything else in the measurement path (I've thrown myself off many times with high v diff probes clipping) Also if something is really clamping your source then its drawing current. You could track the current directly or look for heat. Even 1ma at these voltages in these parts should be detectable as heat.
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Apr 22, 2017 01:47
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Foxfire_ posted:Anyone know a bunch about audio circuits? I put together a little tube amp I found a while ago, as a sort of "get into soldering and electronics" project. After some stupid mistakes (yes, that is a ground plane despite looking like disconnected solder pads) it worked ok, though the 12V wall wart I used added a lot of noise. Some playing with capacitors helped a little bit, but what I ended up doing was to take an old 20V laptop supply and put it through an LM317(with a chunky heatsink) set to output 12.6V. That made it dead quiet when playing from the old android phone I used as my test audio source ... but brought out a whole different set of ground loop-ish noise from the computer. It seems a gaming tower is a noisy electrical environment; who'd have thought. Cleaning up the grounding layout to a star ground centered on the line in ground helped a fair bit, but it was still a bit annoying. After playing around with it for a bit I basically gave up and bought a tiny TOSLINK DAC as my line-level audio source ; at least optical fibre is an electrical insulator. Anyway. Doing your own USB audio means you don't have to worry about audio ground being notably different from power ground, which is nice. The USB data pins are differential, and the cable shield is separate from the power ground, so all in all it seems like it should be possible to make it perfectly quiet? The tube amp above is basically line-level audio in through coupling caps into the triode tube (as voltage amp), into an IRF510 (as a current amp), into the output capacitors. I do volume control on the line in and that seems fine, so if the output from the DAC you plan to use isn't too feeble, I think it should be fine to just route it through a volume pot on the way to the amplifier? Computer viking fucked around with this message at 21:30 on Apr 25, 2017 |
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Apr 25, 2017 21:01
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This is the current plan: Signal Path - USB goes into a PCM2707C and the audio data comes out as I2S. There's not a lot of options for parts here since I don't feel like doing the USB part on a microcontroller and dealing with clock recovery. Annoyingly, it doesn't look like there's a good way to do volume control from the computer with this. - The I2S goes into a DAC with differential outputs. There's lots of these - Audio goes into a differential in-single sided out amplifier, which spits out to the headphones. Decent selection of parts for this too Volume control is a pot adjusting the amplifier gain. There's also the comedy option of using a differential in-differential out amplifier since each earcup on my headphones has its own connector (the normal cable is a Y from the headphone out) Power - 5V USB power comes in and immediately goes through a ferrite + capacitor filter to filter incoming noise and limit what noise my circuit will emit back - That 5V goes into the PCM2707C, which runs it through an internal linear regulator to power itself - It also goes into an external linear regulator to drop it to 3.3V and clean noise - 3.3V powers the DAC and the amp. - The amp either has to have an internal charge pump (these exist), or need an external charge pump + linear regulator to make a negative rail for it Layout - I'm going to try to squeak by with a 2 layer board unless routing gets hairy. I think I can probably route all the signals and power on one layer and have an unbroken ground plane except for vias. - The design separates out pretty naturally into digital and analog parts, so it should be pretty easy to keep digital return currents away from the analog stuff.
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Apr 26, 2017 08:07
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Anyone try subscribing to Adafruit's AdaBox? Seems pretty cool.
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Apr 26, 2017 18:50
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In theory it could be cool, but if a chunk of every months cost is ribbon cables and breadboards and LEDs, then it likely makes more sense to buy the one useful component you don't have ala carte Unless you're buying it for a teenager then it's probably worth it to have easily digestible projects self-contained
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Apr 26, 2017 19:03
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I never really "got" those subscription box junk services, they just seem like a way for companies to get rid of stuff they wouldn't be able to sell otherwise at a markup. I guess if you only dabble in electronics as a hobby every now and then and just want a fun little toy to build every 3 months or whatever it's fine but I'm not really sure most people here would fall into that market niche 
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Apr 26, 2017 19:25
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I love a good junk box -- it's a fun way to get random stuff to inspire a new idea every now and then -- but I can't imagine subscribing to a monthly junk box service.
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Apr 26, 2017 19:45
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I watched the video and without commenting on the quality of the box - who eats a slice of watermelon over their electronics bench? I can barely be trusted with a glass of water on a separate table 
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Apr 26, 2017 22:08
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There is a high probability that the boxes consist of whatever kits were overstocked at that time.
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Apr 26, 2017 23:43
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