Steam Whistle

This circuit consists of
six square wave oscillators. Square waves are made up of a large number
of harmonics. If six square waves with different frequencies are added
together, the result will be a signal with a very large number of
frequencies. When you listen to the result you’ll find that it is very
similar to a steam whistle. The circuit should be useful in modelling or
even in a sound studio. This circuit uses only two ICs. The first IC, a
40106, contains six Schmitt triggers, which are all configured as
oscillators. Different frequencies are generated by the use of different
feedback resistors.

Circuit diagram:

Steam Whistle Circuit

Steam Whistle Circuit Diagram

The output signals from the Schmitt triggers are mixed via
resistors. The resulting signal is amplified by IC2, an LM386. This IC
can deliver about 1 W of audio power, which should be sufficient for
most applications. If you leave out R13 and all components after P1, the
output can then be connected to a more powerful amplifier. In this way a
truly deafening steam whistle can be created. The ‘frequency’ of the
signal can be adjusted with P2, and P1 controls the volume.

Author: Gert Baars – Copyright: Elektor Electronics 2004

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