Midi mixer

 It has two independent midi inputs and six midi outputs that can be configured in many ways. Two input streams can be mixed into one. The sliders can change many values in the input or output streams: channel volume control, note velocities, pitch bend etc. There is a 25 pin RS232C interface for simultaneous monitor access. The 68701 runs in expanded mode with its internal EPROM enabled at 0xf800 to 0xffff There is a loader there which can load programmes into the two battery backed 32k RAMs. The eight sliders are connected to a ZN437 A-D converter. The following pictures include a hand drawn circuit diagram. In this project, I colour coded the wiring to make tracing the signal paths easier.

circuit front back enclosed