In the Adafruit Arduino Lesson 10, Pseudo-Theramin, an Arduino Uno is combined with a light-sensitive cadmium sulfide (CdS) photocell to make a light responsive music machine. This project allows you do do the same with an Adafruit Trinket or Gemma mini-microcontroller. This project costs less and works in smaller circuits or wearable projects.
Changes in light intensity on the photocell will change the pitch of a note on the piezo speaker as you wave your hand in front of the cell. While not a true theramin (which uses changes in a circuit’s reactance), this project is much simpler to build.