“This is a simple MIDI keyboard designed for use with standard PC soundcard with MIDI/Game connector. Keyboard is powered directly from Game port an there is no need of power supply unit, and no high voltage risk. If you need to use it as standard MIDI device, you should build (or buy) a proper power supply and opto-isolated MIDI output buffer. You could find more information about such buffer module on MIDI Technical Fanatic’s Brainwashing Center under Hardware projects topic.
The schematic design is based on most popular PIC16F84 (or PIC16C84) single-chip controller by Microchip. It supports up to 64 keys without velocity sensing. I used keyboard from an old analog instrument, just adding a swich under every key and wiring swiches to connect them as shown on schematic below.”