How To Make Clap sensitive on-off Relay

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.

Parts: 

1. R1,R6     12K  1/4W Resistors

2. R2        1M  1/4W Resistor

3. R3,R9     6K8 1/4W Resistors

4. R4        220K  1/4W Resistor

5. R5        2M2 1/4W Resistor

6. R7,R10    100K  1/4W Resistors

7. R8        22K  1/4W Resistor

8. C1,C3     220nF  63V Polyester Capacitors

9. C2,C4,C5  22nF  63V Polyester Capacitors

10. C6        47µF  25V Electrolytic Capacitor

11. D1,D2     1N4148  75V 150mA Diodes

12. IC1       7555 or TS555CN CMos Timer IC

13. Q1        BC550C 45V 100mA Low noise High gain NPN Transistor

14. Q2,Q3     BC328  30V 800mA PNP Transistors

15. MIC1      Miniature electret microphone

16. SW1      SPST  Switch

17. RL1      5V  DIL Reed-Relay SPDT (See Notes)

18. B1       3V  Battery (2 x 1.5V AA, AAA Cells in series etc.)

Circuit Diagram:

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.