Build Your Own Theremin That Is Played with Infrared Strings

The theremin is an unusual musical instrument that is and always has been purely electronic. Unlike most other electronic instruments, such as the keyboard which evolved from the piano, the theremin had no acoustic counterpart. Since it was invented by Leon Theremin and patented in 1928, its eerie, otherworldly sound has come to be associated with science fiction. That is, in large part, a result of the way a theremin is played. Theremins don’t have conventional keys or buttons, and are instead played by waving your hands around special antennas, which results in a unique sound. Voja Antonic reimagined the way a theremin is played by building this special version with infrared “strings” in place of the traditional antennas.

A standard theremin will have two antennas: one controls the pitch of the note being played and the other controls volume. Those antennas are essentially very sensitive capacitive touch sensors — so sensitive that you don’t actually need to touch them. Simply placing your hand nearby is enough to tweak the capacitance, which affects the oscillator creating the pitch or the volume. That arrangement made a lot of sense for most of the 20thcentury, because it is purely analog. But we have digital electronics today and Antonic figured he could use them to redesign the theremin. His design omits the antennas entirely and replaces them with infrared light emitters paired with photodiodes.

Antonic’s Infrared Theremin has two infrared emitters and two photodiodes. One IR emitter and photodiode is used to control the volume, while the other pair is used to control the frequency (pitch). Instead of relying on capacitance, this setup relies on the intensity of the infrared light being picked up by the photodiodes. IR light from the emitters bounces off your hands and back to the photodiodes, but the amount of light changes depending on how far away your hands are. The instrument is controlled by a Microchip PIC16F18426 microcontroller. There is a USB port, but that is only used to provide power. The audio signal is output through a standard 3.5mm jack, so headphones or speakers can be connected. All of those components, including those for filters and amplification, are soldered onto a pair of custom PCBs. Unfortunately, Antonic doesn’t have a video for us to hear what this Infrared Theremin sounds like, but it should sound nearly identical to a conventional theremin.