I made this keyboard from a $1 toy that I bought at Savers. I made some changes to the electronics including pitch control, a 555 timer circuit that adds extra resistance in secret places, a speed control for the timer, 1/4″ output jack, and a touch-contact for good measure. I fabricated the case from cold-rolled steel and acrylic.
Just a quick experiment to show that the NESpad library I wrote for the Arduino microcontroller actually works. An NES Advantage joystick acts as a mini MIDI drum pad.