This is a trumpet retrofitted to produce MIDI signals. The instrument is still playable as a trumpet. The trumpet sound is captured by a pickup, amplified, rectified and then sent as a control voltage to a converter and a microcomputer which uses it as Key Velocity data for MIDI Note On signals. Switches are mounted at the bottom of the three trumpet valves and 5 more are mounted on the trumpet. Two slide pots and a pedal provide MIDI Controller data.
The Horn is connected by cord to a single board microcomputer. The micro is programmed in Forth language.
A PDF file describes the circuitry and programming of the horn.