A very simple theremin.
The pitch control is the TXL230R at the bottom of this photo.
The volume control is the four CDS photocells at the top.
The leads at the bottom go to a 5 volt power supply.
The leads at the top go to a speaker.
Ultra-simple optical theremin consisting of a TSL230R chip, a 100 uf electrolytic capacitor, 4 AA batteries (connected to the leads at the right), and a speaker (connected to the leads at the left).
TSL230R with black foam surround to block light from the side.
Ultra-simple optical theremin with cardboard tube to block excess light.