This a prototype board for a Casio SK1 midi adapter. I chose the ATMEL atmega 328 because it has enough pins and I am familiar with it. I may have a go at creating an SMD version in the future, so it can be done on a tiny board that will fit in the SK1 without removing the speaker. The diode array is there so I can trigger an interrupt on state change of any of the sense pins. Obviously if the state changes have no delay between them, this strategy will fail. It is probably unnecessary. At the moment, I am including it as an experiment.