Greg’s Harp Is a Robotic Polyphonic MIDI Instrument

Hacking and electronic music are inextricably linked, from the invention of the Theremin, to Queen’s experimentation for novel sounds, to a huge number of devices seen here. Few, however, combine a unique sound, “MIDI-fication,” and an extremely clever mechanical design, like this instrument by Frank Piesik.

This project, known as “Greg’s Harp,” (as Piesik's friend Gregor commissioned the design) features three strings that are activated by a "KickUp” assembly, which taps the strings from below using a solenoid coil setup. This is combined with a coil to allow the note produced to infinitely sustain — i.e. not ever fade out.

Additionally, the strings can be plucked with a trio of motor driven “tape-propellers” that give the harp a unique droning sound, reminiscent of a sitar. Finally, frets are pulled (not pressed) down by a series of micro servo motors. This enables it to play a variety of notes, and would seem to take care of the positioning hassles of pressing down on each string. The video of it in action below, is definitely worth watching with the sound on.

The strings are picked up by piezo elements connected to a little preamp circuit, both embedded in the bridge. Controls-wise, Greg’s Harp uses a Teensy 3.2 as the audio DSP unit and MIDI interface, and sends commands on to a pair of Arduino Nanos. These directly trigger the fret servos, as well as a half dozen MOSFETs for the motors and KickUps. A seventh MOSFET switches power to all the servos off when not actuated to avoid unnecessary motor noise.