He reckons it cost him about $5 to build each of his cheap USB MIDI adapters which receive notes and pedal data from the keyboard’s MIDI OUT and transmit ... his simple circuit on a bread ...

[Furrtek] sniffed out how the touchpad ... an ATtiny2313 as the core of a circuit that spoofs those signals. The microcontroller now listens for incoming MIDI data, looks up the proper signal ...