Michael Una brings us the Beep-It optically controlled squarewave generator in a petri dish enclosure –

This minimalist electronic musical instrument eschews esoteric interface in favor of intuitive, expressive control. One button turns the device on or off, which can produce a continuous tone or a rhythmic sequence. One sensor varies pitch of the output waveform in response to ambient light. The resulting system encourages playfulness and body movement.

In addition to selling these, Michael has kindly posted the hand-drawn schematic to his blog – Beep-it for Sale

[via Create Digital Music]