Clap Sensitive On-Off Relay

This circuit was intended to activate a relay by means of a hand clap. Further claps will turn-off the relay. An interesting and unusual feature of this project is the 3V battery operation. The circuit's sensitivity was deliberately reduced, in order to avoid unpredictable operation. Therefore, a loud hand clap will be required to allow unfailing on-off switching. Q1 acts as an audio amplifier. IC1 timer, wired as a monostable, provides a clean output signal and a reasonable time delay in order to allow proper switching of the following bistable circuit. A discrete-components circuit formed by Q2, Q3 and related parts was used for this purpose, in order to drive the Relay directly and to allow 3V supply operation.

Parts:

R1 = 12K

R2 = 1M

R3 = 6.8K

R4 = 220K

R5 = 2.2M

R7 = 100K

R8 = 22K

R9 = 6.8K

R10 = 100K

Q1 = BC550C

Q2 = BC328

Q3 = BC328

C1 = 220nF-63V

C2 = 22nF-63V

C3 = 220nF-63V

C4 = 22nF-63V

C5 = 22nF-63V

C6 = 47uF-25V

D1 = 1N4148

D2 = 1N4148

B1 = 3V Battery

IC1 = 7555 CMos IC

RL1 = DIL Reed-Relay SPDT

SW1 = SPST Switch

MIC1 = Electret Mic

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Notes:

A small DIL 5V reed-relay was used in spite of the 3V supply. Several devices of this type were tested and it was found that all of them were able to switch-on with a coil voltage value comprised in the 1.9 - 2.1V range. Coil resistance values varied from 140 to 250 Ohm. Stand-by current consumption of the circuit is less than 1mA. When the Relay is energized, current drain rises to about 20mA.