A Pure Data very simple 3 operator FM synth that works well with MIDI Theremin (version 2.6 and above) https://github.com/MrDham/OpenTheremin_V3_with_MIDI
This synth is developed in Pure Data language. for more information go to : www.puredata.info/.
It consist in 3 serialised FM operators (Modulator 2 --> Modulator 1 --> Generator), a filter, a VCA and a vibrato (mod wheel).
yml file gives configuration options to use it in Zynthian project https://zynthian.org/.
Control is very simple: CC 07 or CC11 control the volume in 7 bit resolution, CC16 (MSB) and CC48 (LSB) are combined together to control the pitch in 14 bits resolution. (CC16 (MSB) 1st , Send CC48 (LSB) 2nd as per MIDI 1.0 standard). No need to send Note On/Off messages or Pitch Bend messages.