Opto Duet Optical Theremin

My Opto Duet exactly as the free guide draws it: two 555 theremins that only talk to each other through light. The slow one flashes an LED sealed against a photocell, the cell sets the pitch of the fast one, and two more photocells sit out on the face for your hands. No knobs at all. The light in the room is the controls.

The box is painted glow-in-the-dark and the LED in the middle of the face is ultraviolet, which the glow paint drinks. A few minutes of playing leaves the whole box lit for a while after you switch it off. Play it in the dark by its own light.

Upright 125B with everything on the face: 3.5 mm output top left, photocell top center, power toggle top right, the UV LED in the middle, a second photocell bottom left and the 9V DC jack bottom right. No speaker inside.

The layout, the parts list and the vertical drill template that made this box are a free guide on messopedals.com. Built September 2026, one of a kind. Free shipping.