The IO board is using a MCP23017 16 bit port expander to control a matrix of pushbuttons and LEDS. The Raspberry Pi Pico has enough GPIO pins to handle a small keypad like this but I wanted to try out the MCP23017 to see what kind of performance I can get out of a I2C interface. The Yamaha Reface DX is connected via MIDI and as you can see in the video, I can load a midi file from the SD card and play it back on the Reface.
Now that the initial H/W prototype is complete, most of the remaining effort will be firmware development.