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I'm trying to remember a best practice from two decades back when I was doing digital systems stuff in college. It had to do with powering LEDs from TTL chips. If I remember right, we were discouraged from trying to power our LEDs from TTL outputs directly and instead use an inverter. We would tie a resistor in series with the LED from Vcc into the output. When the inverter was low, it would suck in the current to drive the LED. I believe the idea was buffers and inverters both were more robust with the current they could pull but this could damage the regular logic chips. Furthermore, inverters were preferred because they'd drive the LED as you'd expect from the original digital output; A high signal coming into the inverter would become a low signal, but that would sink current and cause the light to turn on). I kind of suspect that I could get LEDs these days that have very low current requirements so this practice is less important, but when I was trying to search for it, I was seeing a lot of transistors driving an LED instead.
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Jan 7, 2024 15:26
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Yeah, TTL gates will sink a lot more current than they'll source, so if you're running, say, an indicator LED (maybe 1mA for bright but not blinding indoors) off of a 74LS00 (only sources 0.4mA) you'd want to use it active-low with a pull-up to VCC (the same part will sink 1mA just fine). That's TTL though, and TTL is largely obsolete. The 74HCT00 you should consider using instead can both source and sink 4mA so you choose the most convenient polarity for the LED. Microcontrollers and FPGAs are CMOS too, so if they can drive enough current for your LED, they can usually do it in either direction.
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Jan 7, 2024 16:02
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Rocko Bonaparte posted:I'm trying to remember a best practice from two decades back when I was doing digital systems stuff in college. It had to do with powering LEDs from TTL chips. If I remember right, we were discouraged from trying to power our LEDs from TTL outputs directly and instead use an inverter. We would tie a resistor in series with the LED from Vcc into the output. When the inverter was low, it would suck in the current to drive the LED. I believe the idea was buffers and inverters both were more robust with the current they could pull but this could damage the regular logic chips. Furthermore, inverters were preferred because they'd drive the LED as you'd expect from the original digital output; A high signal coming into the inverter would become a low signal, but that would sink current and cause the light to turn on). To amplify the above post, look at the "fanout" and the sinking/sourcing current available. Inverters and buffers were designed to have CRAZY HIGH fanout, specifically to do this kind of thing. The logic chips were designed with the intent that if you had to drive more than a small number of other logic chips, you'd send the signal through a buffer or inverter first. For a random chip, I picked the 7411 (3-input AND gate). It can drive up to 10 other 74-series, 12.5 74H-series, 25 74HC-series, or 5 74LC-series. There are adifferent drive ratings depending on if the chip is driving with a HIGH or LOW signal. The 7411, 74H11, and 74HC11 can source and sink roughly 4mA per output, with a total of roughly 20mA for the whole chip. The 74LS11 can sink 15mA but only source 2mA. So yeah, two decades ago, it was very specific to which actual logic chips you're using, and (in general) a bad idea to try to drive LEDs with them. Now? Tiny microcontrollers are rating their pins at 10 or 20mA per pin with a max current for the whole chip at 200mA.
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Jan 7, 2024 17:45
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If a microcontroller pin can't drive a LED directly, I'll use a little n-ch mosfet instead of an inverter gate. Usually though, 1mA through a high efficiency LED is bright enough, sometime too bright.
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Jan 8, 2024 03:26
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Okay, I can see why my Google searching on trying to shove a resistor in series with an LED into an inverter isn't coming up with much. That time's gone on. I don't know about 74xx generational changes and it'll be pretty wild what I see when a sack of them show up for me late in the week. I'm just starting to stock myself up on stuff in any capacity that I could consider for a hobby.
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Jan 8, 2024 04:35
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FYI, LEDs are one of the only things I will prototype/breadboard before committing to a PCB. You just have to see them for real to understand what an LED will look like. Same thing for switches, buttons, and beepers. Compare this to something like digital logic, which I do not bother breadboarding.
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Jan 8, 2024 06:00
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ryanrs posted:FYI, LEDs are one of the only things I will prototype/breadboard before committing to a PCB. You just have to see them for real to understand what an LED will look like. What, you don't like blinding customers? 
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Jan 8, 2024 07:32
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I once gave an intern the task of designing a front panel PCB with just some LEDs, current limiting resistors, and a connector figuring that it would be a good project since it was so simple she could just focus on learning the CAD tools. I suggested that the LEDs could run at 3-5mA and went through the calculations for that, somewhere along the line she decided 20mA would be better. Luckily it's easy to swap out resistor values. Speaking of stupid LED tricks, just today I was designing a microcontroller that will run an RGB LED pointed into a light pipe so we will have an electrically isolated way to indicate that some high voltage equipment is idle/running/faulty. I noticed that the micro had three unused PWM generators on board and their output pins weren't being used so I connected the LEDs to them so I can make it do super  smooth color transitions because that is definitely the best use of my time.
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Jan 9, 2024 01:26
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PDP-1 posted:I once gave an intern the task of designing a front panel PCB with just some LEDs, current limiting resistors, and a connector figuring that it would be a good project since it was so simple she could just focus on learning the CAD tools. I suggested that the LEDs could run at 3-5mA and went through the calculations for that, somewhere along the line she decided 20mA would be better. Luckily it's easy to swap out resistor values. Awww yeah - equipment status: GAMER
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Jan 9, 2024 03:02
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Stack Machine posted:Capacitors are a good first step. A 22pF ceramic capacitor across the video signal at the head unit end might be enough. If not, maybe 10uF across the camera's power and, for good measure, a 10-ohm resistor between the reverse light wire and your camera/capacitor for a little extra filtering and short-circuit protection. LimaBiker posted:A 100nF/100 ohm snubber network connected parallel to the brake light switch might help against any bursts of RF caused by the tiny spark that switch contacts can produce. If the brake lights are powered via a relay, put one over the relay switch contacts too. These are great suggestions, thank you! I wasn't able to tackle it for a bit thanks to crappy weather, but I was also told that trucks of the type I own are rather notorious for poor grounding, so I'm going to go out there and see if I can ground the camera power to the chassis and see if that helps before I pull out the prototyping boards.
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Jan 11, 2024 17:24
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funeral home DJ posted:These are great suggestions, thank you! I wasn't able to tackle it for a bit thanks to crappy weather, but I was also told that trucks of the type I own are rather notorious for poor grounding, so I'm going to go out there and see if I can ground the camera power to the chassis and see if that helps before I pull out the prototyping boards. You know, I said capacitors were a good first step, but a separate ground is a much, much better first step.
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Jan 11, 2024 18:28
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Yeah I was thinking initially "well if the ground is bad then when the brake light first comes on there's gonna be a brief but huge surge of current while the bulb is cold and that could be trying to find its way back via the camera circuitry" but then discarded that thinking everything in a vehicle is referenced solidly to the chassis. If that assumption's not true, well
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Jan 11, 2024 18:34
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Shame Boy posted:Yeah I was thinking initially "well if the ground is bad then when the brake light first comes on there's gonna be a brief but huge surge of current while the bulb is cold and that could be trying to find its way back via the camera circuitry" but then discarded that thinking everything in a vehicle is referenced solidly to the chassis. If that assumption's not true, well Yeah, I don't know how on earth I managed to not think of the ground immediately after I found that the bed and cab were ungrounded from the factory.  Not my smartest moment, I'll admit.
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Jan 11, 2024 18:50
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My piles of poo poo (along with an esp32 and a display) from Jameco showed up: (I already had a pile of resistors, capacitors, wires, and some cables, so I didn't order a bunch of those) The programmable IC's:  I was kind of figuring there'd be an obvious z80 but I don't think there was one at all. I got a few BIOS chips for 486s though! I'm a bit surprised by the FPGAs. The LED display bag came with some goofy rear end display board that they've apparently been dumping on people for a decade now. It's some proprietary fan board controller but people who are particularly motivated can yank it off the control board get themselves a tactile display. Now I still won't have anything I actually need, but a lot of stuff that's close enough to just hack and stab my way through half of it.
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Jan 12, 2024 08:33
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Bear Radar gets its first two kills! We've been having a problem with mail thieves in my apartment complex, so I reprogrammed my Bear Radar for the most dangerous game. I took a chainsaw to the frequency hopping code, and totally excised GPS from the firmware. This was a huge change, but it was necessary since I needed the devices to operate without GPS inside an aluminum mailbox bank. I got the power down to 7 mA, which translated to something like a week of runtime off an Anker 10k power bank. I used an accelerometer to detect when the mail bank was tipped open using the USPS master key. Then, depending on the time of day, the tilt would either trigger a polite chime (mail's here!), or an angry alarm (thieves!). Tonight at 2 AM, the angry alarm went off. [details omitted] And the two thieves are in jail right now!
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Jan 12, 2024 13:51
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Rocko Bonaparte posted:(I already had a pile of resistors, capacitors, wires, and some cables, so I didn't order a bunch of those) There's no such thing as too many of those.
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Jan 12, 2024 15:41
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ryanrs posted:Bear Radar gets its first two kills! Cool! That was more or less an idea I had back when our complex was getting a bunch of stuff stolen from unlocked cars. I noticed my car would have the little sunglasses box drop down thing open in the morning occasionally if I forgot to lock it (and we never ever open that thing). Nothing would be stolen cuz I don't keep anything valuable in my car but I could tell someone had been in there. I was going to build a thing that detected if that opened and fire a light in their face, take their picture and beep real loud, and got as far as designing parts of it before we got a message that the cops were now taking proactive measures to ensure people were locking their cars, such as opening cars if they're unlocked, looking for valuables and leaving little notes (the gently caress, can they even do that) and I figured my idea would most likely just result in a cop panic-shooting my car or something. Glad yours actually worked
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Jan 12, 2024 15:47
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I think I need to ask how I should start storing all that random stuff I got. It's all mostly still just bagged up. I need to get some stuff to cushion all those pins on the ICs and just bins and bins and bins. It'll all probably just live in a giant box at least until I move across the country some day kid sinister posted:There's no such thing as too many of those. True, but comparatively, I had zero of everything else so they were really pulling ahead.
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Jan 12, 2024 21:21
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Akro-Mils 10164 64 Drawer Plastic Parts Storage Hardware and Craft Cabinet, 20" x 15.75", Black https://a.co/d/eTvaxSE Akro-Mils 10144, 44 Drawer Plastic Parts Storage Hardware and Craft Cabinet, 20-Inch W x 6.37-Inch D x 15.81-Inch H, Black https://a.co/d/9qD9GY7 And then just keep buying more as needed, forever.
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Jan 12, 2024 21:24
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I like index card cabinets. You can get ESD bags that are the same size as a 3x5 card and fit well in drawers meant for that, then stick dividers in to split up different general categories of parts and sizes ("0805 caps", "0603 resistors", ...)
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Jan 12, 2024 21:27
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Foxfire_ posted:I like index card cabinets. You can get ESD bags that are the same size as a 3x5 card and fit well in drawers meant for that, then stick dividers in to split up different general categories of parts and sizes ("0805 caps", "0603 resistors", ...) Ooh I really like this idea, thanks! Those little plastic organisers are great for through hole but for SMD you really need a way of keeping everything in their ESD bags so you can work out what it is from the bag label
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Jan 12, 2024 21:52
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Bad Munki posted:Akro-Mils 10164 64 Drawer Plastic Parts Storage Hardware and Craft Cabinet, 20" x 15.75", Black https://a.co/d/eTvaxSE Seconding this, at least for thru-hole stuff. SMD stuff gets put in different variations of these guys: https://www.amazon.com/AideTek-BOXALL96AS-Anti-static-Enclosure-Transistor/dp/B0787166LX/ https://www.amazon.com/AideTek-BOXALL96-Enclosure-Organizer-Surface/dp/B078RFCQSG/
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Jan 12, 2024 22:36
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SMD's good to bring up because I did get a baggy of random-rear end SMD crap. I figured a pound of that or whatever would go a loooooong way. ...then I found a lot of it was in a bunch of strips and containers that probably heavily bump their weight.
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Jan 12, 2024 23:42
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Jan 12, 2024 23:48
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PRADA SLUT posted:
EEVBlog Dave sold binder sheets made of antistatic material specifically designed for strips of SMD stuff which were pretty good and I used them a lot before I switched to the little bin thing I posted, though he was chronically out of stock of them and probably still is. Pokemon card binder sleeves are great for storing the other 4 copies of the PCB you got made with a minimum quantity of 5 though, I got a binder that's just like a catalogue of my old designs that I can flip through if I ever need to make another of something.
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Jan 13, 2024 05:47
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I just keep stacks of the little plastic baggies you get from Mouser and Digikey. It's... not ideal.
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Jan 13, 2024 07:48
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ryanrs posted:Tonight at 2 AM, the angry alarm went off.
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Jan 13, 2024 14:55
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I have a really frustrating cable/connector design issue I can't find the right connector for, maybe someone can help. The basic specs: 1. The connector has to support at least three 22awg stranded wires. 2. It's a free-hanging connection, not wire-to-board. 3. Either the plug or receptacle has to be small enough to pass through a 8mm circular hole. 4. Need to mate and un-mate it by hand, but should also have some basic retention (a basic latch) Basically I want something like a micro-fit 3.0, but small enough to fit through an 8mm round hole. So far it looks like no such thing exists. I can find receptacles with 1.5mm pitch which satisfy the size limitation, but they only mate with board-mount headers, no free-hanging plugs available. Even considered a 2x2 connectors, but then the latch always pushes it over the 8mm limit.
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Jan 13, 2024 17:17
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ANIME AKBAR posted:I have a really frustrating cable/connector design issue I can't find the right connector for, maybe someone can help. The basic specs: Something like this? https://www.molex.com/en-us/products/part-detail/2145252031 Receptacle https://www.molex.com/en-us/products/part-detail/5055650301 Plug edit: missed the 22awg part. That's gonna be tricky. babyeatingpsychopath fucked around with this message at 19:09 on Jan 13, 2024 |
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Jan 13, 2024 19:06
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https://www.ultimateconnector.com/products/nano-circular/ilbps I have used these, they don't 'latch' but they do mate with a nice little clipping force and they're very little. Could you double up smaller wires? I think these are 24 or 26 or something. Edit: never mind looks like 30AWG is the largest. Giganticon fucked around with this message at 10:50 on Jan 14, 2024 |
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Jan 14, 2024 10:45
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1/8" headphone connector?
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Jan 14, 2024 12:26
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roomforthetuna posted:That's awesome that your thing worked, but now I'm really curious how you managed to transform an alarm going off to people actually getting arrested. I find it hard to imagine police being available quickly enough to be of any use, unless you know of some police who live in the apartment complex? Did you just prepare a mob to capture them while you wait for police to show up? Was there also a Home Alone style series of traps in addition to the alarm? These thefts are happening 2-4 AM mid-week, so police response time in my neighborhood is well under 5 minutes. The complex has 2 buildings with 50 mailboxes each, so the thieves took 5+ minutes to do their thing. And while they were busy cleaning out the mailboxes, I locked them inside the apartment complex. Due to the peculiar geography of the parcel and our below-grade parking lot, the fences are effectively 20 ft tall. This lets me trap the thieves inside the building/grounds, while I'm out on the street directing the cops. Then while the police were searching for them with a dog, I walked up and down the street feeling car hoods, and found their car. Car interior was clean, but the trunk was full of mail. tl;dr: I am actively hunting them
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Jan 14, 2024 13:04
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ryanrs posted:These thefts are happening 2-4 AM mid-week, so police response time in my neighborhood is well under 5 minutes. The complex has 2 buildings with 50 mailboxes each, so the thieves took 5+ minutes to do their thing. drat, nice! They didn't stand a chance.
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Jan 14, 2024 13:13
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They are very stupid and predictable. There's another group I'm hoping to get on the 29th.
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Jan 14, 2024 13:24
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ryanrs posted:I'm out on the street directing the cops.
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Jan 14, 2024 15:03
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ryanrs posted:1/8" headphone connector? I was going to say "don't bother with a 3 pin connector and just use bullet connectors" but a stereo headphone jack is brilliant.
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Jan 15, 2024 00:37
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ryanrs posted:1/8" headphone connector? I wasn't able to find a 1/8" stereo connector with an overall barrel diameter below 8mm. The locking ones have M6 threads on them, and even with the barrel nut that should be below 8mm, but even the thinnest ones ended up being 9mm or larger in diameter. There's probably something out there, but I couldn't find it easily.
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Jan 15, 2024 01:16
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They definitely make audio cables with housings less than 8mm in diameter. Can you just buy one of those and clip one end to bare wires?
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Jan 15, 2024 02:32
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Yeah, pre-terminated headphone cables are available down to something like 6mm dia, but most have 28 awg wires.
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Jan 15, 2024 02:39
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WTF digikey, you've been sitting on my order for new switches to fix my mouse for a week! I get that the weather is bad but they haven't even tried to ship it yet...
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Jan 15, 2024 19:03
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