Simple Oscillator / Pipe Locator

Sometimes the need
arises to construct a really simple oscillator. This could hardly be
simpler than the circuit shown here, which uses just three components,
and offers five separate octaves, beginning around Middle C (Stage 14).
Octave # 5 is missing, due to the famous (or infamous) missing Stage 11
of the 4060B IC. We might call this a Colpitts ‘L’ oscillator, without
the ‘C’. Due to the reactance of the 100-µH inductor and the propagation
delay of the internal oscillator, oscillation is set up around 5 MHz.
When this is divided down, Stage 14 approaches the frequency of Middle C
(Middle C = 261.626 Hz).


Circuit diagram

Stages 13, 12, 10, and 9 provide higher octaves, with Stages 8 to 4
being in the region of ultrasound. If the oscillator’s output is taken
to the aerial of a Medium Wave Radio, L1 may serve as the search coil of
a Pipe Locator, with a range of about 50 mm. This is tuned by finding a
suitable heterodyne (beat note) on the medium wave band. In that case,
piezo sounder Bz1 is omitted. The Simple Oscillator / Pipe Locator draws
around 7mA from a 9-12 V DC source.

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