The MIDI Trigger Box has 16 inputs for connecting to simple switch devices and one MIDI output. The inputs accept 1/4 inch phone plugs. When the plug's tip makes a connection with the sleeve, a Midi Note On is sent out on one of 16 Note values. When the connection is broken, a Midi Note Off signal is sent for that note.
The application most used here at Oberlin Conservatory is a sound installation using foot pads as the switches. The audience members walk around the installation area causing Midi Note On and Off signals to be generated depending on where they are stepping. These Midi signals are sent to a computer running Max programming language which controls what the participants see and hear.
The circuitry employs a PIC single chip microcomputer. The software watches for changes on the 16 inputs and sends out Midi signals when it sees a change. Timing for the Midi signals is controlled by carefully controlled software loops.