Though the old Tesla keybaord I described here and here and described by @Benchoff in #Metal Dome Keyboard is still in my drawer in amount higher than small, I'm looking for alternatives for my MiniBSD.
I found one in here, for the case the listing is unavailable, here is screenshot
I dissected the thing on arrival and didn't bother whether it works or notThere is nothing but 20x8 cm keyboard matrix with 28-pin 1mm pitch FPC connector and tiny PCB containing USB controllerWith the testing pads it looks like perfect breakout board for testing, after cutting the epoxy blob. The keyboard itself looks quite usable and has nice feelthere are rubber domes under each key and mechanical supportThere are 25 pins used on the 28-pin flex cable, checking all the combinations manually with multimeter would be quite annoying, so I decided to build a test rig.
Not the cleanest example of engineering work, but for quick testing it is adequate. There is PIC16F1519 on board, testing all combinations of wires for conductivity few times per second and pushing results via serial port. Not exactly interesting thing, but quick and ugly test sources will be available for download in the "files" section.After a few minutes of poking the keys and noting the results, I got this nice table
where line 11 is unused, being apparent on pictures above - or translated into keyboard layout
For example, pressing key Q connects lines 20 and 7.