The micro-TS is a key fob sized DIY synthesizer (61x41mm) with actually useable knobs like an analog synthesizer. The ball pen is for size reference.
It has a one octave touch keyboard, 6 knobs and a stereo headphone output.
Running on a CR2032 button cell battery it is the smallest playable and programmable synthesizer in the world.
The key fob battery box is for hooking it to a keychain or neck band.
This is what it sounds like:
The synthesizer parameter knobs includes:
DCO: Coarse pitch and Double. The CV out follows the keyboard and coarse pitch.
DCF: Filter peak and ENVmod.
ENV: Attack and Release affecting amplitude.
Here it is built as the euro-TS, a 14HP eurorack synth/keyboard module:
The synth is built on the ATmega328 MCU and is very easy to build as a kit.
The full circuit diagram is as below.
Code for the micro-TS: