Clap Relay

Clap sensitive on-off Relay

3V Battery operated, small portable unit

Circuit diagram:

Clap Relay


R1,R6___________12K  1/4W Resistors
R2_______________1M  1/4W Resistor
R3,R9____________6K8 1/4W Resistors
R4_____________220K  1/4W Resistor
R5_______________2M2 1/4W Resistor
R7,R10_________100K  1/4W Resistors
R8______________22K  1/4W Resistor

C1,C3__________220nF  63V Polyester Capacitors
C2,C4,C5________22nF  63V Polyester Capacitors
C6______________47µF  25V Electrolytic Capacitor

D1,D2_________1N4148  75V 150mA Diodes

IC1_____________7555 or TS555CN CMos Timer IC

Q1_____________BC550C 45V 100mA Low noise High gain NPN Transistor
Q2,Q3__________BC328  30V 800mA PNP Transistors

MIC1___________Miniature electret microphone

SW1_____________SPST  Switch

RL1_______________5V  DIL Reed-Relay SPDT (See Notes)

B1________________3V  Battery (2 x 1.5V AA, AAA Cells in series etc.)

Device purpose:

This circuit was intended to activate a relay by means of a hand clap. A further clap 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.

Circuit operation:

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.