555 optical theremin in a toy shell · One of a kind
Screaming Creep
A 555 optical theremin living inside a gutted toy monster, with photocells for pupils. Light is the instrument: a shadow across its face, a hand cupped over one eye, a flashlight swept past it. The creep sees all of it and complains loudly.
- Type555 optical theremin in a toy shell
- ShellGrumblies rage-monster, the fire-colored one - gutted
- EyesTwo photocells in series, one per pupil - the timing resistor
- ControlsOn/off toggle and a volume pot, both through the back
- OutputIts own speaker. No amp needed
- Power9V battery in the gutted AA bay
- BuiltAugust 2026
- StatusOne of a kind
What it is
Grumblies are little interactive rage-monsters: provoke one and it rumbles, growls and eventually blows its top. This one does not need provoking any more. The stock electronics came all the way out, and a 555 oscillator went in where the toy's brain used to be.
Two photocells in series are its timing resistor, one in each pupil, so how much light reaches its face is the pitch. Cup a hand over one eye and it swoops. Cover both and it drops to a growl. Carry it past a lamp and it shrieks about it.
A ball-top toggle through the back switches it on, so it no longer has to be shaken awake, and a bare-shaft volume pot sits beside it buried in the fur. It plays through its own speaker - no amp, no jack, no cable. The AA compartment was stripped out for a 9V snap connector, and the battery door still closes over it.
Hear it scream
Demo filmed by Onion Madder on the actual unit.
How it was built
The circuit is the same one as my free 555 Optical Theremin guide, so you can read exactly what is inside it, or build your own on a breadboard for the price of the parts. The full build log for this one is on the project page.