Mini Voice Operated Relay

This is the circuit diagram of a voice operated relay. It similar with sound activation switch circuit which will turn on and turn off (connect and disconnect) the switch depending on the sound input. The output switch of this circuit is act by a relay.

voice operated relay

Components 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 and, you may buy the circuit there.
Below document is the manual instruction of this mini voice operated relay circuit (download) :

One thought on “Mini Voice Operated Relay

  1. manal

    which sound will activate this circuit,is it any sound?

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