Tone-actuated relay

  
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 - schematic

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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