Signal and Tone Activated Relay Switch

  
In the Fig.1, exist a circuit, which is a sensitive switch that corresponds in AC signals of input, for signals above 5mV. Corresponds in all the signals from 50 HZ until 3KHZ, region in which found the human voice. The RV1 is regulated so much what RL1 it?s in situation OFF, when the input is it has null signal. In the Fig.2, exist a band - pass filter, coordinated in the 1KHZ, which can be placed in line in the bronchus of negative feedback, in points A, B, C, making sensitive the circuit only in this frequency.
Signal and Tone Activated Relay Switch - schematic

Part List R1-2-6=10Kohm C1-2-3=100nF D2=1N4001 R3=1Mohm C4=47uF 16V Q1=BC214L R4=33Kohm C5-7=10nF IC1=LM741 R5=1Kohm C6=20nF [10nF//10nF] RL1=12V Relay >120ohm R7-8=15Kohm RV1=10Kohm TRIMMER R9=7.5Kohm [15K//15K] D1=1N4148



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