Kernel Bob Aug 13, 2025

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

Show threadLovesThašŸ„§Aug 13, 2025
@kbob Sorry, what!
Show threadKernel Bob Aug 13, 2025

@LovesTha What?

The dishwasher has a green LED on the steel front panel. The tech put a magnetic device onto it that covered the LED and had a cable running to his computer. He said it was a photo sensor and was reading diagnostic data from the LED. He didn't do anything to start data transmission. I extrapolated that the dishwasher must always be transmitting diagnostic info by modulating the LED output. At least that's what I think was happening.

Show threadLovesThašŸ„§Aug 13, 2025

@kbob oh, I communicated badly.

How and technical things were immediately obvious.

That it was 2025 and I'm 42 before I learned that such a thing was real is my in credulousness.

This has amazed me with child like wonder

Show threadKernel Bob 
@LovesTha Same here. When I saw it, I had a moment of disbelief, then a moment of "where has this been all my life?"
Aug 13, 2025 at 4:27amWeb
Show threadLovesThašŸ„§Aug 13, 2025
@kbob I do have questions, like can a phone camera go fast enough to plausibly decode it....
Show threadraweAug 13, 2025

@LovesTha @kbob if you diffuse the image and use rolling shutter artifacts, it should be possible to cature a few bytes per image - probably enough to extract some data

Edit:

https://hal.science/hal-03235346/document

Show threadSamuel āœ… moved to raphus.sociaAug 14, 2025
@stereo4x4 @LovesTha @kbob I vaguely recall an older device at work - this was years ago - that used that principle but in reverse. I think it was a stamp machine. You'd pay for stamps on an app, then show the phone's screen (which flickered rapidly) to a glass window on the stamp machine, which would load it with the monetary value of the stamps.
It usually took a few tries, but it worked.