An Outline For An 88 Key Design Using An Arduino

This design is for two digital switches per key.

2 Arduino outputs -> 4 bit Binary Counter -> 4 to 16 Decoder (really a couple 3 by 8's ) -> 16 x 11 diode matrix -> 11 Arduino inputs. Leaving one pin for serial transmission.

This design uses every DIO pin on the Arduino and accounts for the 176 keyswitches required for a velocity sensitive 88 key keyboard. There are still 6 ADC inputs available to be used for pedals, pitch bend, etc. (Note I'm banking on still being able to use the TX pin while using the RX pin as a DIO)

Update: I think there are better designs using mux chips. Paying an extra buck or so for another chip would greatly simplify the PCB layout.