Post Ax8C75z5q8YprLhJJ2 by kbob@chaos.social
 (DIR) More posts by kbob@chaos.social
 (DIR) Post #Ax8C74RNZzzz4Uus7M by kbob@chaos.social
       2025-08-13T04:00:46Z
       
       3 likes, 0 repeats
       
       Today we got our dishwasher fixed under warranty.  To diagnose it, the tech stuck a photosensor+magnet onto the front panel over the green status LED and started reading diagnostics.  It turns out the status LED is actually a serial port*, and it's continually transmitting status.I can think of so many gadgets that could and should use this trick...*It's probably something other than regular serial -- a UART's TX would flicker.  I don't know any details.#HidingInPlainSight
       
 (DIR) Post #Ax8C75z5q8YprLhJJ2 by kbob@chaos.social
       2025-08-13T12:12:18Z
       
       0 likes, 0 repeats
       
       Effectively, this is an opto-isolator.  Except it's not all in one device.  Wikipedia has a good article on them, and notes that they can manage 10s of KHz.  (See MIDI.)The nice thing is that there's zero extra hardware -- every gadget already has an LED or seven, and if your MCU has a spare DMA channel, you can stream a bitstream to it (however it's encoded) with low overhead.  If it's a short status message, you can just let the DMA loop over it and there's no MCU overhead.
       
 (DIR) Post #Ax8C776veUQHLwN59s by tomjennings@tldr.nettime.org
       2025-08-13T15:30:04Z
       
       0 likes, 0 repeats
       
       @kbob OMFG why did I never think of this!
       
 (DIR) Post #Ax934p1HErW8EfWIj2 by shironeko@fedi.tesaguri.club
       2025-08-14T01:23:35.546143Z
       
       0 likes, 0 repeats
       
       @cliffle @kbob hmm, I wonder if phone video typically uses a open shutter or not, but if so with a magnifier it can probably sample the led at super high speed.
       
 (DIR) Post #Ax96A90idjGPXyULiK by shironeko@fedi.tesaguri.club
       2025-08-14T01:58:08.868095Z
       
       0 likes, 0 repeats
       
       @cliffle @kbob yeah a trick with rolling shutter is to use each row as a sample, but it would be a problem if the shutter angle is 180 for example cus the sampling is stopped half the time every frame.
       
 (DIR) Post #Ax99mRHBTd8V3z8r0y by shironeko@fedi.tesaguri.club
       2025-08-14T02:38:41.938305Z
       
       0 likes, 0 repeats
       
       @cliffle @kbob I think with those 4K high frame rate modes probably camera can sample at MHz range. so just need to send the data way slower than that I guess
       
 (DIR) Post #Ax9h2s1t4cbv9qQhcG by shironeko@fedi.tesaguri.club
       2025-08-14T08:51:25.892474Z
       
       0 likes, 0 repeats
       
       @cliffle @kbob I just found this https://github.com/horshack-dpreview/RollingShutter/tree/main?tab=readme-ov-file#effect-of-shutter-speed-on-banding