Tone-actuated relay

Posted on Jan 24, 2013

The circuit is built around the LM567 tone decoder IC that requires about 100 millivolts at its operating frequency. The frequency is set by a 10 K variable resistor and can be between 700 and 1500 He

Tone-actuated relay
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When a tone at the set frequency is present, the 567"s output goes low to energize a relay through a 2N3906 PNP transistor.

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