Circuit diagram:
Parts:
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.
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.
