The Optigan and Orchestron were a pair of electronic organs built by Mattel in the 1970s which used swappable optical discs to store instrument information. The discs can still be found today, but the organs are extremely scarce, much to [Gan’s] dismay. After researching the organs for a bit, he decided he could probably build his own MIDI-compatible interface for the audio discs.
The discs have audio waveform data printed on them, which can be read using an LED on one side of the disc and an optical transistor on another. After successfully prototyping a reader that could interpret one of the disc’s audio tracks, he constructed a device to read all of the tracks simultaneously, just like the original organs.
His makeshift turntable was constructed on top of an old record player using acrylic discs and toy car wheels to keep things steady. Once the disc is placed on the turntable, he sets his reader in place, and via some custom circuitry, he is able to play the discs using his much more modern keyboard. It sounds pretty decent as you can see in the video below, though he does admit he would like to tweak a few things to make it sound even better.