whistle responder

Posted on Feb 7, 2014

The first two inverters contained in IC1 are used as audio amplifiers. IC1A amplifies consistently the signal picked-up by the small electret-microphone and IC1B acts as a band-pass filter, its frequency being centered at about 1. 8KHz. The filter is required in order to select a specific frequency, the whistles one, stopping other frequencies that

whistle responder
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would cause undesired beepers operation. IC1C is wired as a Schmitt trigger, squaring the incoming audio signal. IC1D is a 2 second (approx. ) monostable driving the astable formed by IC1E & IC1F. This oscillator generates a 3 to 5Hz square wave feeding Q1 and BZ1, thus providing intermittent beepers operation.

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