Open Theremin V3 - Schematics
The Open.Theremin V3 is designed on KiCad, the open source PCB design software. The schematics includes different clearly separated functional blocks.
Open.Theremin V3 Schematic - click on the schematics to get a PDF version.
PITCH: Variable and fixed frequency pitch oscillators. LC and quartz resonators operating at 500kHz output frequency.
VOLUME: Identical variable and fixed frequency oscillators for volume. Different centre frequency of 460kHz to avoid interference.
AUTOTUNING: Auto-tuning circuit based on a BB914 variable capacitance diode. Software controlled through voltage generated by 2x 12bit DAC (MCP4922).
Frequencies of the two variable oscillators as well as the Arduino quartz frequencies are measured to characterize the antennas and tune the oscillators automatically.
MIXER: Digital mixer based on a D-Flip-Flop 74HC74
AUDIO DAC: 12bit audio converter (MCP4921) with rail-to-rail operational amplifier
ARDUINO AND INTERFACE: Arduino UNO, distance of hand to antenna is converted to a digital value and audio signal generated through a look up table