SOUND OPARETED SWITCH CIRCUIT
DESCRIPTION -
This circuit is built around the versatile 741 operational amplifier. Through it looks straightforward, the circuit can be utilized for varies applications.
Sound hitting the microphone creates an electrical signal that is developed across R1, which provides control of the operating level. This signal is then amplified by 741 IC & fed to the base of T1. When T1 conducts, a voltage appears on the gate of the thyristor, causing it to fire, and thus operates the relay.
Resistor R7 holds the gates at or near earth Potential until the trigger pulse arrives show preventing the thyristor drifting into a random firing condition. Normally closed (NC) pushbutton switch S1 is introduced in series with the relay to facilitate the resetting of circuit in its non-triggered condition.
Preset potentiometer R2 can be set to give an output from 741 IC of about +600 mV under no signal condition so that Q1 is one the point of conduction. Two small 9V batteries provide adequate power to test the wired unit.
PART LIST –
1. R1 – 1M
2. R2 – 10K
3. R3,R4 – 1K
4. R5 – 1M
5. R6 – 470 Ω
6. R7 – 1M
7. Q1 – BC147
8. SCR – SN101
9. Relay – 9V/120 Ω
10. 741 IC One pic
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