Here’s the Theremin circuit shown that uses digital component, so we can call it a digital Theremin. This circuit employs logic inverter 74C04 or CD4069 hex inverter and CD4046 phase-locked-loop (PLL) IC. The CD4069 logic inverter is operated as a fixed-frequency oscillator with frequency around 100kHz. The CD4046 is operated as a variable frequency oscillator which is adjustable around 100kHz. The exact center frequency of the on-chip oscillator is determined by R4, C2 and R3.
This is the
figure of the circuit;
The frequency of variable oscillator frequency circuit can be
shifted several kilohertz by moving your hand approaching the antenna since the
C2 and the antenna form an equivalent parallel capacitance. The frequency of
the variable oscillator should be set to the same frequency of fixed oscillator
when there is no hand or human body close to the antenna. This calibration is
done by adjusting the zero control R4 pot with this simple rule: If both
oscillators (the fixed and the variable) are set to the same frequency then the
Theremin will produce no output (silent).
This Theremin circuit will start producing audible tone if
you move your hand approaching the antenna since it will shift the frequency of
the variable oscillator. You can play this Theremin circuit by moving your
right hand around the antenna and at the same time turning the volume knob R5
with your left hand. [Circuit’s schematic diagram source: seekic.com]
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