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Anybody have a simple trick or device for CC/CV at 500ma/3v as a discharge? I want to pop arbitrarily-charged lipos into a holder and have them discharge at 500ma until 3v, then reducing current to keep terminal voltage at 3v until I get around to noticing that it's at 3v and ready to be removed.
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Dec 21, 2020 03:13
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insta posted:Anybody have a simple trick or device for CC/CV at 500ma/3v as a discharge? I want to pop arbitrarily-charged lipos into a holder and have them discharge at 500ma until 3v, then reducing current to keep terminal voltage at 3v until I get around to noticing that it's at 3v and ready to be removed. Making your own constant current electronic load is a lot more annoying than you'd think. If you want to spent a little money (<$100) you can get one of two things that will do this: 1. Some hobby li-ion/lipo/life chargers have a discharge or storage mode, allowing you to drain batteries at a set current until they hit the cutoff voltage. 2. You can get a chinese digital load module that does this, if you're willing to spend a while finding one that does what you want. For instance, this appears to support a CC load as well as a configurable undervoltage cutoff (had to go to their website to find out the details, but they're there). Just stay well under the advertised power rating and I suspect it should work just fine. https://www.amazon.com/Icstation-Constant-Electronic-Adjustable-Detector/dp/B07NVDL27X/ There are other sellers selling this same item (or nearly the same) domestically as well, if you don't want to wait for overseas shipping edit: after writing this I just ordered this one lol, it seems handy https://www.amazon.com/Constant-Current-Electronic-Adjustable-Detector/dp/B08GKX2LWM/ref=psdc_14244481_t1_B07NVDL27X
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Dec 21, 2020 03:39
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insta posted:Anybody have a simple trick or device for CC/CV at 500ma/3v as a discharge? I want to pop arbitrarily-charged lipos into a holder and have them discharge at 500ma until 3v, then reducing current to keep terminal voltage at 3v until I get around to noticing that it's at 3v and ready to be removed. Opus BT-C3100 will do this, but to 2.8V if that's acceptable. BT-C3100 Manual posted:Discharge Mode: It is used to reduce the memory effect. The rechargeable battery is discharged to a preset battery voltage (0.9vfor Ni-Cd & Ni-Mh, 2.8v for Li-ion batteries). Once discharge is finished,total accumulated discharging capacity is displayed at mAH display mode, showinghow much energy is discharged from the battery, whichis always referring to the accumulated discharging capacity. Trickle charge current will be applied after discharge cycle is finished, preventing the batteries from discharging any further. Edit: A basic constant current circuit can be made with a BJT as well but you'll need a microcontroller or something to handle switching between CC and CV. https://www.youtube.com/watch?v=h1RwqxZEhKc CV can of course be achieved with a voltage regulator. Forseti fucked around with this message at 04:34 on Dec 21, 2020 |
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Dec 21, 2020 04:30
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If you need something within a few months probably don't try to roll your own, since the devil is always in the details. (edit: I realize I say later in this post you can knock this together quickly from parts on hand. There's a difference between works once OK and works always perfectly and it takes a long time to close that gap) That said, you could do something like this with an op-amp, a power FET, a resistor, and a 3V Zener diode: You would need an external power supply for the op-amp. 7V would be plenty but you would definitely want significantly more than 3V. That 3V+IR thing is meant to be a voltage 3 volts more than the resistor drop at your required current. So if you wanted 500mA you would do a 1-ohm resistor, 3.5V on the non-inverting op-amp input. The commercial solutions will have features this doesn't. This will continue to leak tiny currents below 3V. That said, if you just need to expediently throw together something that mostly works on the bench and you have the parts handy, this is a place to start. Stack Machine fucked around with this message at 04:59 on Dec 21, 2020 |
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Dec 21, 2020 04:41
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Also, that Zener has to be pretty buff. 1.5W 3V zeners are probably not somthing you'd have on hand. One thing you could do is swap it for a P-channel power FET, connected just like the top, source toward the resistor, drain to ground, op-amp inverting input to the source and non-inverting input on 3V. You could make the 3V and 3.5V with dividers from whatever powers your op-amps.
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Dec 21, 2020 05:40
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Little late to the last page discussion, but what does an SMD workflow look like? And what kind of decision making or tradeoffs should I consider before using or switching to SMD components?Cojawfee posted:If you're using breadboards to test, then through hole stuff is what you'll want. I need to buy an SMD kit to see if I'm any good at it, then I'll use SMD components for a project I'm working on. Also curious to know what an SMD kit entails. I'm seeing these kits that let you practice soldering. Is that the same thing?
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Dec 21, 2020 22:56
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Cory Parsnipson posted:And what kind of decision making or tradeoffs should I consider before using or switching to SMD components? quote:Also curious to know what an SMD kit entails. I'm seeing these kits that let you practice soldering. Is that the same thing? Dominoes fucked around with this message at 23:04 on Dec 21, 2020 |
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Dec 21, 2020 23:01
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Cory Parsnipson posted:Little late to the last page discussion, but what does an SMD workflow look like? And what kind of decision making or tradeoffs should I consider before using or switching to SMD components? "SMD" is just 'a device that uses surface-mounted components, instead of thru hole or similar'. You can solder SMD components by hand if you want (I wouldn't), but you generally use a specific workflow to populate those boards. A basic SMT workflow is: 1) Stencil printing -- apply solder paste to a substrate, either with a stencil or a solder paste head on a pick and place 2) Populate board -- place components on the solder paste, either by hand or with a pick and place 3) Reflow -- bake the board to melt all the solder at once, either with a hand heater or a reflow oven If you want to 'practice soldering' you want through-hole kits, not SMT. The only hand soldering you should do during SMT is for rework or fixing gently caress-ups. Or crusty old nerds who try to flex on each other by hand soldering 0402's with a microscope e: there's a lot more to 'real' SMT lines, like optical imaging, x-ray inspection, component test and traceability, visual inspection, bake and outgas, etc, but that's the core of it PRADA SLUT fucked around with this message at 23:29 on Dec 21, 2020 |
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Dec 21, 2020 23:24
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Sweet, thanks! This is good stuff
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Dec 21, 2020 23:50
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I'll just throw in that hand soldering isn't too bad with a little practice. Mainly it's tedious if you had to do a large board, but I do it all the time with a normal soldering iron with a 2.4mm chisel tip and a regular spool of solder. You'll want solder braid for cleanup occasionally if you don't already have some. I try to get 0805 package resistors but a lot of my capacitors are 0603 which is about as small as I'd want to deal with by hand. I use a toothpick sometimes to hold it to the board after soldering because they're so small sometimes they like to stick to the soldering iron tip from surface tension.
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Dec 22, 2020 00:16
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I would consider a hot air gun mandatory
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Dec 22, 2020 01:27
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A note on SMT packages: Resistors and capacitors come in several common sizes. Think of 0603 as a default, 0805 as larger, ie if you plan to hand solder, and 0402 or smaller if you're making something small or weight-critical. There are a range of standard packages most parts are avail in. Some common ones: -SOIC: Relatively large and easy to work with pins on 2 sides -MSOP and TSOP: Smaller pins on 2 sides -QFP: Roughly MSOP-like pin spacing, on 4 sides. Common for MCUs -QFN: Flat pins underneath at the edges, and a center ground pad to conduct heat.These offer practical improvements like heat management and clean routing, but make it tough to visually check for shorts. Common on newer parts. -BGA: Balls under the package. I haven't tried these. Likely tough to work with, as you can't see most of the pins. Allows clean routing of a high number of pins. Common on high-pin specialty parts, and some MCUs. Dominoes fucked around with this message at 02:03 on Dec 22, 2020 |
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Dec 22, 2020 01:39
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Hot air gun for sure if you need to do BGA or something with a big center heat dissipation pad under it. Probably QFN as well. Also if you're getting PCBs made, a fab that can put solder mask between the leads makes things much easier.
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Dec 22, 2020 02:25
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Yeah, hand soldering SMT components is perfectly doable for if you don't go overboard. At work technicians sometimes have to hand-solder entire protoypes if they aren't meant for production (like if someone spins a board specifically for testing out various motor driver chips). It takes a bit of practice, maybe some additional tools (like a lighted magnifier to save yourself from eye strain, and having access to a stereo microsope is always handy if you need to inspect stuff, especially when solder paste is involved). Some basic tips: 1. Learn how to use flux both to solder small components and small pin packages, and also to adhere small components to the board. 2. Make sure to clean that flux off at the end (this applies to through hole soldering too) 3. When doing your design, try to minimize the number of unique passive components, especially capacitors (since nonpolarized SMT capacitors are typically not labelled with their value). It's usually easier to just put multiple capacitors in parallel (or multiple resistors in series) to minimize the number of component values. 4. If you want to make more than a few boards at a time, look into solder paste. You can order laser cut solder stencils online and squeegee paste onto a board with an old credit card, and then hand place components. It's easier than it seems, because if the solder reflows properly then slightly misaligned leaded packages will "snap" into place as surface tension pulls their leads towards the pads. For single sided boards you can even do reflow on a hotplate (if you dont mind cooking the FR4 a bit...), but you can also use a toaster oven or a temperature controlled hot air gun with multiple nozzles (although I've never tried this with a whole board at a time).
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Dec 22, 2020 02:44
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insta posted:Anybody have a simple trick or device for CC/CV at 500ma/3v as a discharge? I want to pop arbitrarily-charged lipos into a holder and have them discharge at 500ma until 3v, then reducing current to keep terminal voltage at 3v until I get around to noticing that it's at 3v and ready to be removed. Stack Machine posted:Also, that Zener has to be pretty buff. 1.5W 3V zeners are probably not something you'd have on hand. One thing you could do is swap it for a P-channel power FET, connected just like the top, source toward the resistor, drain to ground, op-amp inverting input to the source and non-inverting input on 3V. You could make the 3V and 3.5V with dividers from whatever powers your op-amps. A little follow-up on this, since I hate to kramer into the thread and drop a sketch of a circuit down without some description of its function: I simulated a variant on the design I described, with two N-channel power MOSFETs.  The bottom op-amp/FET is just a 3V shunt regulator. The top tries to maintain 3.05V so the current through the resistor is 500mA but once the battery voltage drops below 3.05V that is no longer possible since the top FET can't get any more conductive and the op-amp output can't go any higher. So below that voltage the top FET is more-or-less a wire and the battery discharges through the resistor to 3V. Note the +/- terminals are swapped on the bottom op-amp because the N-channel FET there adds an extra inversion. In the sim I used ideal op-amps with a gain of 10k and a 5V supply and a capacitor charged up to 5V as a substitute for the Li-Po cell. Seems to have a nice constant-current drain until it stops abruptly at 3V. The delay before it starts is just a bit of overshoot:  Zooming in you can see why I went with 0.1 instead of 1.0Ω. The transition from constant current to constant voltage starts at the top reference voltage, so the closer that is to the constant voltage the more "ideal" the behavior, at the cost of needing tighter tolerances on the top voltage.  I'm kind of surprised I didn't have to do anything else in this sim for stability, but in a real circuit with real op-amps it would probably need a little compensation.
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Dec 22, 2020 04:37
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Dominoes posted:If you're doing something subject to high accelerations or rough conditions, or something safety critical, use THT. Ie airplanes, spacecraft, military vehicles etc. Or large parts that don't make sense for SMD. Otherwise, use SMD IMO this isn't practical advice. Stress in lead wires will be proportional to the relative displacement, this paper does a good job covering the factors that go into estimating that displacement including component types. The paper is based on Steinberg's Vibration Analysis for Electronic Equipment, which is the industry standard for vibration design for electronics. It's also highly "real world" focused and available with filez if you do some googling. CarForumPoster fucked around with this message at 13:47 on Dec 22, 2020 |
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Dec 22, 2020 13:45
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Thank you guys for the discharge circuits 
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Dec 22, 2020 15:19
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CarForumPoster posted:IMO this isn't practical advice. Stress in lead wires will be proportional to the relative displacement, this paper does a good job covering the factors that go into estimating that displacement including component types. The paper is based on Steinberg's Vibration Analysis for Electronic Equipment, which is the industry standard for vibration design for electronics. It's also highly "real world" focused and available with filez if you do some googling. Yeah like, I've seen teardowns of somewhat modern aircraft black boxes (things I'd assume would need to endure the most g-loads of anything) and they're all using surface-mount poo poo now.
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Dec 22, 2020 15:48
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The flat pack, the OG surface mount package, was used preferentially to DIP in military applications for years, but I don't know if that was for mechanical or thermal reasons. Makes for some really interesting looking boards though.
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Dec 22, 2020 16:22
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Flat packs are primarily used for space electronics now, but even there there's a lot of standard-ish gull-wing stuff usually in special ceramic QFP packages with gold plated everything. TI still has a lot of old school mil-spec components in their catalogs, the classic 54 logic was mostly made in ceramic DIP packages. I've seen teardowns of various 90s and newer military hardware and it's usually rigid-flex assemblies using mostly off the shelf stuff presumably assembled to IPC Class 3 and fitted with a solid conformal coating. Expensive, but not cold-war military budget expensive.
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Dec 22, 2020 21:02
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The military plane PCBAs I've worked with have been normal SMT stuff under conformal coat for the modernized ones and DIPs on the PCBAs in the same box that haven't been changed since the 80s
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Dec 22, 2020 21:27
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Shame Boy posted:Yeah like, I've seen teardowns of somewhat modern aircraft black boxes (things I'd assume would need to endure the most g-loads of anything) and they're all using surface-mount poo poo now. In 1972 airplanes and the MIC drove electronics... ...now its all gently caress YOU DEFENSE CONTRACTOR RoHS compliance will make us more profitable and I'm all NO BUT MY TIN WISKERING AND THIS NEED TO FLY FOR 30 YEARS AND MIGHT GET REWORKED PLEASE DONT TAEK MY LEAD What I'm saying is I've been drinking. Happy holidays. EDIT: Also yea I've qualified plenty of two sided all surface mount cards at 13+ GRMS PSDs, 40G crash shock and -55°C to 57°C. (gently caress >1" long BGAs tho) Conformal coating is the absolute bees knees except when you need to mask it for various reasons or need to rework cards. It makes passing basically every test easier INCLUDING vibration. The viscoelastic attenuation of a good thick conformal coat is actually a big deal. CarForumPoster fucked around with this message at 22:03 on Dec 22, 2020 |
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Dec 22, 2020 21:44
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CarForumPoster posted:EDIT: Also yea I've qualified plenty of two sided all surface mount cards at 13+ GRMS PSDs, 40G crash shock and -55°C to 57°C. (gently caress >1" long BGAs tho] do you have any insight into how they make electronics that can survive the 10,000g of being fired out of an artillery piece, e.g. for the https://en.wikipedia.org/wiki/M982_Excalibur
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Dec 22, 2020 21:49
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Sagebrush posted:do you have any insight into how they make electronics that can survive the 10,000g of being fired out of an artillery piece, e.g. for the https://en.wikipedia.org/wiki/M982_Excalibur Kinda, I powerpoint designed a 40mm version in ~2016. I really really like electronics and circuit card vibration/dynamics but I left that industry in 2018 to start a business and write software for said business now. The great thing about it versus aircraft dynamics is its a really practical field that balances cost, reliability and capability requirements all the time. Generally the answer is potting and isolation to decrease peak stress but happy to talk about it far more than anyone cares about. EDIT: For example at the sort of input's we're talking about here, the lead wires in the ICs themselves start to become really important and it becomes worthwhile during a tradestudy of contenders to cross section the actual ICs and make sure they pot or otherwise mitigate the deflection the inside the ICs if you're using COTS. Since the whole MIC has moved to favoring COTS for many many good reasons you will often trade things like..."ideal power supply design in the eyes of the EEs" for "can be shot out of a cannon" CarForumPoster fucked around with this message at 22:01 on Dec 22, 2020 |
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Dec 22, 2020 21:57
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CarForumPoster posted:IMO this isn't practical advice. Stress in lead wires will be proportional to the relative displacement, this paper does a good job covering the factors that go into estimating that displacement including component types. The paper is based on Steinberg's Vibration Analysis for Electronic Equipment, which is the industry standard for vibration design for electronics. It's also highly "real world" focused and available with filez if you do some googling.
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Dec 22, 2020 22:32
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Slanderer posted:a lighted magnifier to save yourself from eye strain, and having access to a stereo microsope is always handy if you need to inspect stuff, I don’t do much soldering so ymmv: but a very cheap worked in a pinch solution for me is using clip on lenses for a phone. These can be had on eBay for $10 and work pretty great.
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Dec 23, 2020 11:04
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Buy a nice 10x loupe imo, that's come in super handy. You can get very solid high quality BelOMO ones for not that much. Like I even have a full stereo microscope setup and I still prefer the loupe most of the time unless I need to get in real close cuz it's just easier, since I have it hanging from my little fume extractor fan so it's always right in front of me if I need to spot-check something. e: Here's the one I got, it's only $32, made of metal and glass rather than plastic and feels like I could swing it around by the lanyard and throw it through a brick wall and it would still be completely fine: https://www.amazon.com/BelOMO-Triplet-Folding-Magnifier-Anti-Reflection/dp/B00EXPWU8S/ Shame Boy fucked around with this message at 15:42 on Dec 23, 2020 |
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Dec 23, 2020 15:39
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Haven't done any electronics in a while but I just got the replacement LED for my Tizio lamp to replace the halogen bulb It's... a bit inappropraite. I should probably read the descriptio and specs more carefully.  I then remembered that i had some COB LEDs I got for my car's dome light. I also had 5 random diodes and exactly the right capaciotr (as far as I could figure out). Ta-da!  It's sketchier than any of my aliexpress pruchases but it works, even kind of dimmable if you don't mind the 50hz PWM lol.  Well that's my big project, thanks for following like and subsribe.
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Dec 23, 2020 16:07
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Is... that a capacitive dropper with mains wires just chilling out in midair?  God drat dude, you are brave! As for magnifiers, I'll second the good 10x loupe. I have some made in japan one that I got from a knife sharpening place at some point that works really well for inspection. If you want magnification while you're actually soldering or otherwise need free hands, I'll continue to espouse my love of headband magnifiers. Very good value for the money, I have the glass lenses but the plastic probably works fine, just more prone to scratches. VVV True, that is a bit of an issue. I pretty much only use I think the 2x lens. So much less money to try out than a more serious stereo magnifier though that I think it's worth it to try and see if it works for what you're doing. Forseti fucked around with this message at 18:33 on Dec 23, 2020 |
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Dec 23, 2020 18:08
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One thing I don't like about head mounted magnifiers is that you have to be so close to the object at the higher magnifications. You can get maybe 1.5x or 2x magnification at a decent viewing distance. But if you want 3 or higher, you have to be on top of the thing you're looking at, which isn't great for soldering.
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Dec 23, 2020 18:29
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Forseti posted:Is... that a capacitive dropper with mains wires just chilling out in midair? It's just a recitfier, I didn't realize it initially (or bother to check) but the lamp outputs around 12V AC and not DC, so when I plugged in the LED directly, I got awesome seizure-inducing flickering. I don't have a scope to check it but it seems to be stabilizing reasonably well. I cleaned up and insulated the circuit and it fits pretty neatly into the lamp housing now.
mobby_6kl fucked around with this message at 14:09 on Dec 24, 2020 |
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Dec 23, 2020 19:17
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mobby_6kl posted:Nah I'm pretty stupid but not that suicidal Wow that's really resourceful. Awesome! Do you have pics of the final result?
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Dec 23, 2020 21:47
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Ahh that makes sense, glad you're not living it up Victorian style 
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Dec 23, 2020 21:58
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Cory Parsnipson posted:Wow that's really resourceful. Awesome! Do you have pics of the final result? Honestly I'm pretty impressed myself that it works since I usually mostly just glue arduino parts together. The final circuit is what you see above, I just cut off the legs and wrapped everything in tape. It fits like this in the housing, with all the crap stuffed behind it:  The actual COB could've been larger but it looks fine in use. One small detail is that it doesn't fully turn off. That's as low as it goes, I guess the normal halogen bulb just stops working when you turn the dimmer enough.  I ordered another LED from aliexpress that should fit properly, since I'd like to have a usable dimmer, but in the meantime this is pretty nice. One other benefit is that the lamp, as cool as it is, has some electrical issues since it has to conduct like 5 amps through the three joints, and this takes just a few hundred milliamps.
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Dec 24, 2020 14:20
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PRADA SLUT posted:Anyone have a take on a desktop pick-and-place? Looking to spend less than $5-6k. Was looking at the CHMT36VA. IMO the only way owning your own pnp is worthwhile (regardless of cost) is if you are either doing circuit assembly as a side business, or your business has you doing frequent low-volume runs of small and simple boards (basically what sparkfun was doing 15 years ago). An individual owning one for personal reasons just makes no sense.
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Dec 24, 2020 15:21
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ANIME AKBAR posted:IMO the only way owning your own pnp is worthwhile (regardless of cost) is if you are either doing circuit assembly as a side business, or your business has you doing frequent low-volume runs of small and simple boards (basically what sparkfun was doing 15 years ago). I've got some parts for one I started putting together as part of the hobby coin project mentioned in my red text. Was originally going to be for sorting but then I realized there was a much much better/easier way to do this sorting.
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Dec 24, 2020 15:27
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Well to make up for this, I think I broke my drone lol. The gimbal has been damaged and glued in place before (not by me), it works fine but would occasionally get stuck tilted. So I got a new used one to swap it.  The drat cable was also glued the gimbal case, great job previous DIY repair rear end in a top hat. I thought I managed to pry it off carefully but I guess not, because neither the camera nor the gimbal itself works now. And because it's loving DJI I have to wait a month until the parts arrive from aliexpress 
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Dec 25, 2020 13:17
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I use one of these things for most solder work. Nice big lens with a light so you can work in a normal sitting position instead of hunched over a microscope or bent in so close that you're huffing flux smoke like with the head magnifiers. One of my co-workers recently got a digital camera setup with an HDMI output and loves it for soldering and small part work. Apparently these are coming down into the 100ish dollar range which makes them pretty tempting. 
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Dec 25, 2020 15:44
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Update on the water monitor project - A short-notice tasking at work will put it on hold for a while. It's almost ready otherwise.   There are some cleanup items re the assembly. Thoughts on how to handle the USB and JNC port in the last photo? Using rubber washers on the outside for the BNC ports. For the bottom of the screen, I think I can cover it with a rubber strip etc. Also need to figure out how to use a sticker to label where to drill without leaving residue all over. Using a CNC machine for the top, but the other edges are too tall.The switch mounting is still undetermined too, but leaning towards having it on its own board (pictured), on standoffs that screw into the main board, with a hole on top it sticks out through (pictured, but too small). Dominoes fucked around with this message at 16:15 on Dec 25, 2020 |
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Dec 25, 2020 15:51
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Dominoes posted:Update on the water monitor project - A short-notice tasking at work will put it on hold for a while. It's almost ready otherwise. Short answer I though of after type the below parts: Take apart a rainbird sprinkler controller and see how they do it. Longer more detailed answer: Assuming the enclosure is likely to be in low and high temp, very high humidity environments with condensation like greenhouses, aquariums, near docks, gardens with sprinklers, I’d likely case mount my connectors with plastic screws, silicone or HMA. I would also be sure I let the box breathe/drain (ie don’t try to 100% seal it, but do 99% seal it with a drain hole in each axis) and make sure my board/connectors/case are good against corrosion or humidity. What exactly you do for this is likely driven by cost and rework constraints but conformal coat is your friend.
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Dec 25, 2020 22:55
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