MIDI Volume Pedal Based on Arduino

This Arduino based MIDI volume pedal is capable of reading the position of an analog pedal, translating the A/D value into the proper numerical range, and sending MIDI signals to a synthesizer.

A current loop is used by MIDI to connect devices where a certain amount of current makes it work. The current-limited power that goes through the cable to the receiver is supplied by the sender on the output side while the current is limited and fed through the LED side of the optocoupler on the input side.

A serial output running at 31250baud is needed to transmit MIDI with the output driving an NPN transistor and being open-collector. Two transistor stages are need to get the serial signal positive-going again since the transistor being used as a logic buffer inverts the signal coming through it and a high signal on the base pulls the collector low. The signal can be restored using a hex inverter or using a second transistor.

The volume pedal is wired to an analog input where it enters on the black cable and exits on the white cable that came from an old AT computer keyboard.

Rest of the project