As part of my Big Trak refurbishment (not going as well as I wanted it to), I decided to use theAdafruit Prototyping Pi Plate to mount the additional electronics on.. The keypad was originally going to be the Big Traks own keypad, but I substituted one I’d made earlier (some 25 years ago!) – it’s a simple 4×4 matrix and you can see 4 resistors on the protoboard. There is a 5th next to them which acts as a limiter for the LED that’s on one of the switches.
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