This schematic diagram show a single chip Theremin circuit. Theremin is
an electronic music instrument which sense hand movement to control the
tones/frequency. This Theremin circuit uses two separate Colpitts LC
oscillators to produce a beat frequency.
The frequencies of two
Colpitts LC oscillators are mixed and then rectified. This
rectification demodulate the mixed signal to get the beat frequency
which is in audible range. This beat frequency or difference is the
real Theremin’s output. The oscillator is operated at high frequency
(inaudible) to get wide audible frequency range of beat frequency when
two oscillator output is mixed. This circuit uses a 4011 quad gate to
construct the high frequency oscillator operating at 250kHz. Here is
the schematic diagram of the circuit.
Single Chip Theremin Circuit Diagram
The metal probe that is used to sense your hand produces only small
frequency shift in term of percentage of original frequency, that’s why
we need to derive the beat frequency to get wide audible frequency
range as the result of high frequency shifting. The IC2, an LM741 is
used to amplify the mixed signal before rectification.
The D1 will
rectify the mixed signal to detect the audio (the beat frequency). This
audio signal is then filtered by an adjustable bandpass filter IC3. The
further audio amplification before power amplifier IC5 is done by IC4.
The metal toilet-tank float is used for the hand probe since is has
better sensitivity than a simple wire antenna, but any conductive
material will work.
