Not really retro computing but cool. Using a C64 as an actual Theremin.
The Theremin is one of the earliest electronic instruments. It’s played by moving one’s hands in front of two antennas: One controls pitch and the other controls volume.
Electronically, the instrument works by monitoring the capacitance between its antennas and Earth and detecting the small increase that occurs when a human moves closer. The amount of extra capacitance is inversely proportional to the distance.
I used a C64, two 555s, four resistors, a spoon, and a clamp to build a working Theremin. In the video I try to explain how it works in layman’s terms. What follows below is a more thorough description for those who want to dig deeper.
Video on YouTube