Mini Operated Voice Relay SchematicComponent Parts list:
R1, R7 1K
R2, R4, R8 10K
R3 2K2
R5 1M
R6 200K
R9 39K
D1, D4 1N4004
D2, D3 1N4148
C2, C5 2.2uF/16V mini ecap
C1 10uF/16V mini ecap
C4 100pF
C3 100nF
Q1 BC548
IC1 LM358 (of Hitachi HA17358)
8 pin IC socket
Relay AX-SH-112L
LED 3mm
Electret microphone
This mini-VOX – voice operated relay – is based on a circuit published in Silicon Chip, 9/1994, p31. The off delay time may be adjusted by varying R3 and R4. Reducing R3 will result in a longer release time. You could change the release time constant (C2 & R5) to say 30 seconds and use the VOX as a light switch with this delay time before turning off. Increase C2 to say 10uF and R3 to 3M3.
To make the easy adjustment, you may use potensiometer or trimpot to varying the value of resistor. You will need additional place on the PCB but it will easier for you to make some adjustment The kit of this circuit available at kitsrus.com anf electronickits.com, you may buy the circuit there.
HERE the manual instruction of this Mini Voice Operated Relay circuit