The Therething is an open source MIDI controller based on an Arduino. OK, so it’s not a true analog Theremin, but it sounds pretty good, and it’s enclosure is awesome! Check out the link for more information, including the source code and more videos.
Ultrasonic sensors are used to return a distance value, from the sensor to the player’s hand. This value is converted by an Arduino or other microcontroller into a MIDI key value and is output at the correct baud rate (31,250 bps) onto a serial pin. Since MIDI needs a signal to turn off a key pitch as well as a signal to turn it on, it is recommended that when the note changes, two MIDI signals are sent – one to turn off the previous note and one to activate the required note. It may be possible to program some sort of delay/sustain effect in here, so that the off signal is delayed. This would mean that note changes are not too abrupt as there could be a slight overlap between notes.
Give the gift of Arduino this holiday season!