The theremin (originally known as the ?therphone/etherphone, thereminophone or termenvox/thereminvox) is an electronic musical instrument controlled without physical contact by the thereminist (performer). It is named after its inventor, Leon Theremin, who patented the device in 1928.

The instrument's controlling section usually consists of two metal antennas that sense the relative position of the thereminist's hands and control oscillators for frequency with one hand, and amplitude (volume) with the other. The electric signals from the theremin are amplified and sent to a loudspeaker.

Wiki: https://en.wikipedia.org/wiki/Theremin

I'm working on open source open hardware digital theremin project.

This PCB is Oscillator for Digital Theremin project based on Teensy 4.1 MCU board.

Two oscillators are needed for theremin - one for pitch antenna and one for volume antenna.

Low noise stable dual colpitts LC oscillator with 3.3V square wave output (500KHz..2MHz, depending on inductor L).

Power supply: DC +3.6..+6V 50mA

Connect air core single layer inductor 1..3mH and 10mm copper tube as antenna.

Can be used in digital theremin project.

Teensy MCU is measuring frequency on input pin by capturing of timer counter every raising and falling edge of signal.

Additional filtering is used to collect enough bits of frequency.

Teensy 4 arduino library for theremin sensor:

https://github.com/fpga-theremin/theremin/tree/master/teensy4theremin/firmware/sketches/src/FreqMeasureDMA

Project topic on Thereminworld site:

http://thereminworld.com/Forums/T/32640/teensy-40-600mhz-arm-cortex-m-7-mcu---ideal-for-digital-mcu-based-theremin?Page=0

LTSpice model of oscillator:

https://github.com/fpga-theremin/theremin/blob/master/teensy4theremin/ltspice/2020_npn_pnp_osc_v15.asc