Micro Arcade Machine

Adafruit’s cupcade and retro-pi gaming consoles are great fun! In my version I didn’t use their kit but built one from scratch, using the template drawings supplied by adafruit (for customising the look of your cupcade) and instead of the clever PI interface board, I used the electronics of an old HP USB keyboard which was gathering dust and missing some keys.

The fun bit here is that you -CAN- use an analog joystick as switch – if you’re willing to experiment a little with resistance values and diodes to make it work..

Mapping of the keyboard traces for the keys you will need in your games (typically Q, R, Z, X, arrows and Escape) is a simple exercise (using a multimeter. The resistance is quite high so the beep might not work)

Then find yourself a numbering strategy and solder wires to the points on the keyboard PCB you need for the designated switch actions.

The resistance of the potentiometer was not high enough (10k, so 5k for one switch) to be detected as ‘open’. Another 1k resistor was necessary in series (found experimentally). The diodes have been used to make sure two switch contacts can be combined on one potentiometer.. (in this case switch down is apparently B1 and B3 on the board, switch up OB1 and OA4)

All in all the USB keyboard electronics is pretty responsive, even with the joystick-as-switch option. My first guess was using an Arduino Leonardo as keyboard emulator, but this option is probably cheaper and has better performance.