Since the ATtiny2313 is merely translating MIDI into touchpad signals, the input could be anything. The first thing that comes to mind is a dance floor that changes the music based on how many ...

A bunch of pads connected to a MIDI out port is as old an idea as the ... on an Arduino Mega with 16 clock and data points for each touchpad eating up 32 of the 54 available pins on the ‘duino.