Clap Sensitive On-Off Relay
Description
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.
Circuit Diagram:
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
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.