An Arduino board, Spectra Symbol linear potentiometer, and USB/MIDI adapter are used to create a MIDI controller with continuous pitch (as opposed to discrete notes as played on a piano).
The resulting instrument works with Windows, Mac OS, and Linux. It has been tested successfully with Acoustica Mixcraft and GarageBand.
Additional features have been added such as buttons to temporarily switch octaves, and a knob which adjusts how quickly the pitch is tuned.