Two light-coupled 555s · One of a kind
Duet
My Opto Duet with two knobs added. Two 555 theremins on one board that only talk to each other through light: a slow one flashes an LED sealed against a photocell, which sets the pitch of a fast one. This box adds a tempo knob to the slow one and a tone knob to the fast one, and leaves two photocells out in the open for your hands.
- TypeTwo 555 oscillators coupled by light, on stripboard
- BoardMy own layout, the free Opto Duet guide, plus two pots that are not in the file
- ControlsTempo knob, tone knob, two exposed photocells, a power toggle on the top edge
- OutputQuarter-inch jack on the top edge. No speaker inside
- Enclosure125B lying flat, purple hammertone, the labels in pastel lettering
- Power9V DC, barrel jack on the top edge
- BuiltSeptember 2026
- StatusOne of a kind. When it is gone it is gone
What it is
Two 555 timers on one stripboard, coupled by nothing but light. The first runs slow and flashes an LED that is sealed against a photocell; that cell is the timing resistor of the second, so the second chirps at whatever rate the first is ticking. The two photocells on the face are the ones you play: one is the slow oscillator's eye, the other the fast one's, and covering either changes what it does.
The guide's layout has no pots. This box has two: tempo on the slow engine, so you can set how fast it ticks without finding the right light, and tone on the voice, so the pitch has a home position before the cells move it. The clear dome in the middle of the face is the coupling LED, out where you can see it work.
The controls
Tempo on the left, tone on the right, each with a photocell above it. The toggle on the top edge is power. Wave at the cells, cup them, shine a phone torch on them; everything you do to the light does something to the sound.
The box
A 125B lying flat, purple hammertone, with the jack, the DC socket and the power toggle along the top edge and the labels in pastel lettering on the face. This is the box from the Opto Duet guide's boxing photos, now with a DC jack and the two knobs.
Demo
Demo video coming soon - it's on the bench being filmed.
Or build it yourself
The board inside is the free Opto Duet guide: the stripboard drawing, the parts list, the netlist, the file for Copper Bottom, and the drill template for this very box. The two knobs are the only thing here the guide does not draw.