#garfield Logs

Jan 24 2023

01:41 AM rue_mohr: huh
01:52 AM rue_mohr: looks like asking apt to take a system from 8 to 11 in one step was a bad idea
05:49 PM aandrew: wow
05:49 PM aandrew: y'all aren't gonna believe this
05:49 PM ruenahcmohr: your in a movie?
05:50 PM aandrew: so I took that usb connector and scratched it (the contacts) up a bit, dissolved as much salt as I could into lemon juice and put that into the connector, mated it a bunch of times just to make sure the solution was everywhere, ran 2A though it for a while
05:50 PM ruenahcmohr: k...
05:50 PM aandrew: before: 15ish mOhm. After: 1.8 Ohm, did it again, got it up to 15ish Ohms
05:50 PM aandrew: so a good high resistance
05:50 PM ruenahcmohr: yep
05:51 PM aandrew: ran 2A through it, calibrated fingertip said it was above 50C, thermal camera corroborated the finger testimony
05:51 PM aandrew: in fact it was up to about 90C after 30m or so
05:51 PM aandrew: so hot
05:51 PM aandrew: let it sit and stew and corrode overnight
05:51 PM aandrew: measured again, it could barely keep a connection but it was still like 15-18 ohms
05:51 PM ruenahcmohr: yes, but, would that happen under normal conditions
05:51 PM aandrew: threw the connector and its mate into the ultrasonic for 15m
05:52 PM ruenahcmohr: k...
05:52 PM aandrew: took them out, dried them off, measured again... 15.6mOhms
05:52 PM ruenahcmohr: nice
05:52 PM ruenahcmohr: but
05:52 PM aandrew: bullshit, I said out loud and re-measured a few times, readings are consistent
05:52 PM ruenahcmohr: how many connections, how much air till it blows up on its own?
05:52 PM aandrew: it's been running 2A through it for the last 20m or so, cold as a cucumber (my alligator clips are hotter)
05:52 PM ruenahcmohr: mmm
05:54 PM aandrew: measured the voltage drop with my meter: 76mV, current is 1.82A (power supply says 1.99, load says 1.91)... .076/1.82 is 42mOhm for the sum of V+ and GND which is plausible
05:54 PM aandrew: I was not expecting that given how shitty those connectors looked
05:55 PM aandrew: https://ibb.co/pPwf8B4
05:55 PM aandrew: https://ibb.co/VtcY3Lm
05:55 PM aandrew: https://ibb.co/r5ZPD57
05:55 PM aandrew: https://ibb.co/wJGMhY0
05:55 PM ruenahcmohr: hah
05:55 PM ruenahcmohr: wow
05:55 PM aandrew: and yes, I do realize this is not indicative of "normal wear", I was trying to figure out a way to intentionally create high resistance and I would be willing to bet that normal wear would NOT be as bad as this
05:55 PM ruenahcmohr: +1 for ultrasonic cleaner
05:56 PM aandrew: I guess that gold plating did a damn good job, even with my attempt to breach it
05:56 PM aandrew: I also spent some time looking at the plug and receptacle design just out of curiousity
05:57 PM aandrew: I can see how they tried to make the plug wear more than the receptacle
05:57 PM ruenahcmohr: the max232 works great as a 1-component clock source btw
05:57 PM aandrew: the receptacle is really quite simple, the metal fingers are just flat/flush with the plastic, there's no spring, nothing that could catch or scratch really
05:57 PM aandrew: the jack though has springy pins and such
05:58 PM aandrew: I saw that on twitter, pretty funny
05:58 PM aandrew: did you manage to make a 7805 oscillate?
06:00 PM ruenahcmohr: well, as its got nothing to control its frequency, I'm not tooooo into that one
06:35 PM aandrew: hmph.
06:35 PM aandrew: graphite lubricant is not (very) conductive
06:35 PM aandrew: 5k in one direction, 1.6k in the other
06:36 PM aandrew: (ther's a TVS on the board)
09:25 PM ruenahcmohr: http://ruemohr.org/~ircjunk/distractions/synchro/slide.htm
09:28 PM Tom_L: that's cool
09:32 PM ruenahcmohr: http://ruemohr.org/~ircjunk/projects/gearCounter/slide.htm
09:32 PM ruenahcmohr: assembling these things on not-twitter...
10:00 PM aandrew: haha I have one of those led&key PCBs too! http://ruemohr.org/~ircjunk/distractions/synchro/p1260889.jpg
10:00 PM aandrew: and yes that is cool
10:14 PM ruenahcmohr: :) quick
10:56 PM rue_shop2: I meant my pocket calculator...