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something like a simple green-type gentle degreaser work as a substitute? I've had a nose out for IPA at the grocery store/pharmacy for weeks and havent been able to snag a single bottle
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May 1, 2020 02:51
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I dunno mang, that's kind of a hard one to answer. I've never used anything else (other than, say, MG Chemicals Flux Remover) because alcohol has never been a scarce commodity before. As with paints / adhesives / metal treatments, try it on a corner of the board first to make sure it won't gently caress up your solder mask?
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May 1, 2020 03:00
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Dunno about Simple Green's flux cleaning capability but if it has citric acid in it probably isn't great for copper. Maybe try to find HEET in an auto parts store or gas station? That's methanol I believe, people use it to power those little beer can alcohol stoves for backpacking. If your state sells it I'd bet that Everclear works really well, although that'll be relatively expensive.
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May 1, 2020 03:45
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Forseti posted:Dunno about Simple Green's flux cleaning capability but if it has citric acid in it probably isn't great for copper. That poo poo will seriously gently caress up aluminum if you don't get it off quickly. I used to put it in my ultrasonic cleaner and drop in old 70's Japanese motorcycle carbs that looked too far gone and it would absolutely MELT all the oxidation off in just a couple mins. But If I forgot and left them in too long, the passages would get completely fuckered and either clog with all the destroyed aluminum, or be enlarged to the point that the carb performed completely differently, or had air leaks all over and was useless.
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May 1, 2020 03:49
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Yellow is methanol (not iso-heet, red) [and I have zero idea if it is a good idea other than it runs a little camping stove good]
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May 1, 2020 03:49
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Ambrose Burnside posted:something like a simple green-type gentle degreaser work as a substitute? I've had a nose out for IPA at the grocery store/pharmacy for weeks and havent been able to snag a single bottle No. You should use IPA to clean electronics, specifically the 99.9% stuff. CarForumPoster fucked around with this message at 03:56 on May 1, 2020 |
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May 1, 2020 03:53
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CarForumPoster posted:No. You should use IPA to clean electronics, specifically the 99.9% stuff. There's a massive global supply chain disruption tho?
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May 1, 2020 04:05
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They still have it at the hardware store here, I imagine because it's not medical grade or maybe people just dont know about it yet. e: comedy, perhaps a still is in order, use sugar and bread yeast and it'll be ready real quick
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May 1, 2020 04:07
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yeah i can source an alternate high-purity alcohol like methanol or denatured alcohol, or maybe diluted 70% iso w a lot of water in it, but high-purity iso is just. flat-out not available where i am, full stop, and hasn't been for over a month at this point. i've already been looking for it for other purposes and have tried to show up early to catch new shipments and all that jazz, no dice. i accept that a substitute will probably not be the pareto-optimal product for this purpose, because the alternative appears to be "just don't clean anything you assemble, indefinitely", and im fine with sth Not-Best-Practices if it's not horrendously-deleterious towards typical components unrelated: i wanna limit/regulate the output current of a lm2596 buck converter-based adj power supply down to at least, like, ~50ma or lower, so I can use it for some v crude small-scale electroplating experiments (not an ideal plating rectifier, but i'm workin with what's on hand). i've got some lm317/338 voltage regulators, so is there any reason i can't stick a basic-rear end current regulator circuit like this one from the TI lm338 datasheet onto the supply output, with R1's value changed to adjust the current? any cautionary notes on implementation? 
Ambrose Burnside fucked around with this message at 06:20 on May 1, 2020 |
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May 1, 2020 06:17
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Ambrose Burnside posted:unrelated: i wanna limit/regulate the output current of a lm2596 buck converter-based adj power supply down to at least, like, ~50ma or lower, so I can use it for some v crude small-scale electroplating experiments (not an ideal plating rectifier, but i'm workin with what's on hand). i've got some lm317/338 voltage regulators, so is there any reason i can't stick a basic-rear end current regulator circuit like this one from the TI lm338 datasheet onto the supply output, with R1's value changed to adjust the current? any cautionary notes on implementation? I don't see any reason why it won't work. That device does have a minimum load of 3.5-5mA though, but I don't think that will matter when using it as a current-regulator.
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May 1, 2020 15:34
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GnarlyCharlie4u posted:weird request, but this is probably the best place for it, so here goes: For potentiometers, I'd look through Digikey. The circuit is simple enough you could do it on protoboard with a simple microcontroller (ATtiny85 would work) and transistor (IRLB8721 would work). That said, LED dimmers are common, and if the only issue is the knob feel, I wonder if you could get a cheap off the shelf LED controller and replace the potentiometer on it?
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May 1, 2020 16:56
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Bourns PDA24 HRT (high torque) pots are pretty cheap and have a pretty ok feel, like they're filled with heavy grease but very little stiction. https://www.digikey.no/product-detail/no/bourns-inc/PDA241-HRT02-502B0/PDA241-HRT02-502B0-ND/3781538 No switch on those though, and it's an open carbon track so they're not super high end (but probably easier to clean than sealed types when they do go bad).
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May 1, 2020 17:00
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Adafruit has a switched potentiometer. https://www.adafruit.com/product/3393
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May 1, 2020 17:04
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I'd try to take one off a vintage receiver, I guess something that was good but not so desirable even broken ones are worth money. Like Sony instead of Marantz.
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May 1, 2020 17:22
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The really really nice-feeling knobs tend to be custom jobs that have big flywheels on the back to add inertia, so unless you want to make something up yourself or harvest one from some nice stereo equipment you're probably out of luck. They do sell fancy potentiometers for stuff like guitars specifically spec'd to be "smooth" though, here's one on ebay: https://www.ebay.com/itm/Seymour-Duncan-SMOOTH-TURNING-500K-Short-Split-Shaft-Pot/140571176138 It's not switched, but you can probably find a switched one. Keep in mind that anything meant to control volume is probably a logarithmic pot rather than a linear one, so you might have to adjust the dimmer circuit accordingly unless you want it to go from "off" to "full brightness" over like 1/5th of a turn.
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May 1, 2020 17:45
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Ambrose Burnside posted:because the alternative appears to be "just don't clean anything you assemble, indefinitely", and im fine with sth Not-Best-Practices if it's not horrendously-deleterious towards typical components If you're using no-clean flux, not cleaning the assembly would be what would happen in mass production. Cleaning that is for aesthetics/stickiness only. If you're using more aggressive flux, not cleaning will lead to corrosion, but on 6month+ timescales usually. If it's water-soluble flux, DI is fine.
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May 1, 2020 18:05
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Cojawfee posted:Adafruit has a switched potentiometer. longview posted:Bourns PDA24 HRT (high torque) pots are pretty cheap and have a pretty ok feel, like they're filled with heavy grease but very little stiction. Stabby McDamage posted:For potentiometers, I'd look through Digikey. The circuit is simple enough you could do it on protoboard with a simple microcontroller (ATtiny85 would work) and transistor (IRLB8721 would work). That said, LED dimmers are common, and if the only issue is the knob feel, I wonder if you could get a cheap off the shelf LED controller and replace the potentiometer on it? I could look through DigiKey but it's not going to give me any input on how they 'feel' which is important for this project. Shame Boy posted:The really really nice-feeling knobs tend to be custom jobs that have big flywheels on the back to add inertia, so unless you want to make something up yourself or harvest one from some nice stereo equipment you're probably out of luck. Yeah that's the problem I'm having. All the pots I have are log from stereos and such and I can't seem to find a "nice" one that's linear. I mean I SUPPOSE I could deal without an integrated 'off' function, but knobfeel is going to be very important for this project. I'm making a luxurious desk lamp so it needs to look and feel like a million bucks. e: oh poo poo I forgot servo mount potentiometers are a thing! I could even attach it to a remote controlled servo motor for that extra  feeling...I'm gonna wind up spending like $1000 on a knob aren't I? GnarlyCharlie4u fucked around with this message at 19:02 on May 1, 2020 |
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May 1, 2020 18:53
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If you find a pot that you like and you're willing to do custom stuff, you could hack together your own "switch" feel. Make your own knob with a 3D printer or whatever that's hollow between the outer edge and the inner part that attaches to the potentiometer. Put a little notch or a bump on the inner part and then use some spring steel that latches onto it to make it feel like a switch. And then just treat that value as "off".
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May 1, 2020 19:01
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Cojawfee posted:If you find a pot that you like and you're willing to do custom stuff, you could hack together your own "switch" feel. Make your own knob with a 3D printer or whatever that's hollow between the outer edge and the inner part that attaches to the potentiometer. Put a little notch or a bump on the inner part and then use some spring steel that latches onto it to make it feel like a switch. And then just treat that value as "off". That's actually really clever and I might go this route, especially if I wind up with a servo controlled knob. I can just hide a simple SPST switch with a nice click underneath (for the lamp circuit) and have a V machined into the inner edge of the knob so it flips the switch when the servo rotates the knob to that point. GnarlyCharlie4u fucked around with this message at 19:05 on May 1, 2020 |
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May 1, 2020 19:03
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Oh yeah, I forgot that roller switches exist. Put one of these guys next to the potentiometer so that it runs along the rim of a circle with a notch cut in it for when it needs to turn off. Run the potentiometer through the normally open pin so it turns off when the switch opens.
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May 1, 2020 19:16
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You can even belt/gear a knob to the pot itself, right? Give yourself sturdier/smoother mounting and options for switches and buttons without having to worry about using the pot itself as a bearing?
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May 1, 2020 19:19
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Attach wings to the rotatey bits and immerse the whole thing in mineral oil
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May 1, 2020 19:23
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Fill the entire box with dielectric grease
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May 1, 2020 19:25
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Shame Boy posted:I don't see any reason why it won't work. That device does have a minimum load of 3.5-5mA though, but I don't think that will matter when using it as a current-regulator. ofc i forgot to mention my actual point of concern, the generic wallwart 12v1a switching supply that powers the linear regulator i want to limit the output current of. i’ve read that current limiting can get “weird” with switching supplies and the simple current limiting circuits used w linear regulators don’t necessarily play nice with more sophisticated regulator types. my thinking and/or hope is that having the linear voltage regulator between the switching supply and the current regulating circuit will buffer the switching supply from any potential weirdness
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May 1, 2020 19:45
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I found an old potentiometer in my parts bin and was gonna use it for a thing but it turned out to be...well, it wasn't audio taper or linear taper. It had two distinct tapers that each were mostly linear but changed suddenly from one rate to another in the middle of the range. I graphed it out on a scope and it looked like this: What is the purpose of that? I suppose it could be a really crappy audio taper but there was such a clear step between the two different slopes that it had to be intentional. Why would you use something like that?
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May 1, 2020 19:50
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I am an idiot. I just remembered that the old-style wall mount dimmer switches with big gently caress-off knobs still exist and I can just use one of those. I can probably fine a sealed one that's full of grease and has enough resistance to make it feel reasonably nice. My mom even has one for the attic fan that has a very satisfying CLUNK when it turns off. ...I still really like where this servo controlled knob idea is going though. Cojawfee posted:Fill the entire box with dielectric grease If I go that route I feel like I need to take it all the way and put a crank on a dynamo (submerged in the grease) that's attached to a relay that actuates only when you've provided enough power by hand cranking the generator fast enough. Sagebrush posted:I found an old potentiometer in my parts bin and was gonna use it for a thing but it turned out to be...well, it wasn't audio taper or linear taper. It had two distinct tapers that each were mostly linear but changed suddenly from one rate to another in the middle of the range. I graphed it out on a scope and it looked like this: So... that attic fan switch I just mentioned... I'm willing to bet that's what the taper on that thing looks like (or maybe the inverse). You have to turn it all the way right and it will only barely get the fan going, but when you turn it back to the left it takes off like a rocket until you eventually turn it back to the off position and it kills the circuit. GnarlyCharlie4u fucked around with this message at 19:56 on May 1, 2020 |
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May 1, 2020 19:53
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Ambrose, it should be fine.
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May 1, 2020 20:24
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I'm not sure you don't want a logarithmic taper actually. Light isn't a linear thing either, at least its relation to duty cycle. Your eyes/brain mess with that perception just like audio. Does the LED controller expect a linear taper and compensate for you? I've never really messed with an LED controller before, just PWM from a microcontroller. RGB LEDs: How To Master Gamma And Hue For Perfect Brightness
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May 1, 2020 20:45
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The controllers I've used were linear in output power. The LED power/efficiency curve and vision are both sublinear so you might be on to something
taqueso fucked around with this message at 20:51 on May 1, 2020 |
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May 1, 2020 20:46
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taqueso posted:Ambrose, it should be fine. thanks. normally i'd just wing it and keep an eye on things in case of Problems, but i'm being neurotic about everything now b/c if i Summon The Magic Smoke i wont be able to replace the afflicted components for a couple of weeks at minimum. covid lockdown continues to be cool and good
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May 1, 2020 21:06
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Older linear regulators can have trouble with too much capacitance or capacitance that has too low ESR, they might start oscillating. But I can only recall seeing the issues being on the output side. Read the datasheet and it will tell you if there are restrictions. You have a nice current limiting resistor in there, it should be hard to blow stuff up if you don't short around that. anyways, putting a linear regulator after a switcher is pretty standard stuff, I'd be interested to hear what topology can be problematic if you can find the source taqueso fucked around with this message at 21:18 on May 1, 2020 |
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May 1, 2020 21:09
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Forseti posted:I'm not sure you don't want a logarithmic taper actually. Light isn't a linear thing either, at least its relation to duty cycle. Your eyes/brain mess with that perception just like audio. Does the LED controller expect a linear taper and compensate for you? I've never really messed with an LED controller before, just PWM from a microcontroller. I've had trouble using log pots with dimmer circuits before, where it would be unstable or off for most of the turn, then suddenly ramp up to 100% in a small window. You can probably work around it but yeah they're not great imo.
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May 1, 2020 21:14
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Yeah just in general logarithmic pots are a pain in the rear end to work with. Unless you're doing purely analog audio stuff, it's much better these days to just use a linear pot and a nice high-res ADC and remap the output in software to whatever curve you want.
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May 1, 2020 23:47
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Yeah, that makes sense. I actually tend to use rotary encoders and a microcontroller for human-machine interfaces myself.
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May 2, 2020 00:33
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I will say though that one of my favorite teaching moments was when I was helping a student with some sort of water flow/level sensor he had built, and it was giving a pseudo-logarithmic output that he wanted to convert to a volume of water, and I pulled out my graphing calculator and showed him how to collect some values and do various regressions until we found one that fit the data and plugged that into his program, and he was like "oh my god I remember doing this in high school and I had no idea what it was about but I get it now, this is amazing" and he went and showed a bunch of his friends 
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May 2, 2020 00:38
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I'm much the same way... and I suspect most people (everyone?) is. Things are much easier to learn when applied to a problem, then when presented without immediate context.
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May 2, 2020 01:26
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That's the hugest problem in engineering
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May 2, 2020 02:33
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ante posted:That's the hugest problem in engineering I thought that was space elevators 
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May 2, 2020 03:23
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KnifeWrench posted:I thought that was space elevators The hugest problem in engineering is actually preventing engineers from experting outside their narrow field.
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May 2, 2020 04:04
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TotalLossBrain posted:The hugest problem in engineering is actually preventing engineers from experting outside their narrow field. Yeah it's this
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May 2, 2020 05:11
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