Single Chip Theremin Circuit
This is a design circuit for 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 is the
figure of the circuit;
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. 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 band pass 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. [Circuit diagram
source: seekic.com]
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