OpenTheremin V4 - Schematic
The Open.Theremin V4 is designed on KiCad, the open source PCB design software. The theremin signal is generated through a variable digital Coil-Capacitor (LC) oscillator that is compared to a fixed frequency oscillator stabilized with a quartz crystal. The two signals are then compared in a Flip-Flop based mixer. An Arduino compatible Atmega328P design is used to calibrate and linearize the signals and generate look-up table based audio signals. The audio signals are played back through on board digital to analogue converters (DAC).
Of see the open source files on GitHub here.