Sound-Activated Switch

This circuit provides either latched switching or timed switching. U1A and UlB provide audio amplification from the

microphone. U2 is a retriggerable monostable multivibrator. SI A and SIB select either U3, a flip-flop, or U2. R13 and R14 allow a 6- to 60-second timer delay after the sound ceases, in the timed mode. BR1, U5, and associated components form a power supply. Ql drives optocoupler U4 and triggers triac TRl. -If desired, four silicon diode rectifiers connected as a bridge can be substituted for BR1. Just make certain the diodes are rated at least 50V, 1A.

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