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# Strange voltage variation in circuit

#### rahulb

Mar 14, 2018
45
Hi,

I made a circuit which turns on according to sounds. actually it toggles. One loud sound, it turns on and in the next, it turns off.

When I measure voltage across the electret. it is around 6 v. I am using 9 volt battery for power which is producing around 8.5 volts.

Now the problem is, in case of a loud sound, the voltage is increased to 6.3 to 6.4 v and it remains there. then, on next sound in comes back to 6 v. The voltage doesn't change until it receives next sound.

I am not getting it what is going wrong? I am measuring voltage across the electret.

thanks

the circuit is below:

#### duke37

Jan 9, 2011
5,364
I made a circuit which turns on according to sounds. actually it toggles. One loud sound, it turns on and in the next, it turns off.
Is this how it operates as you say or how it should work?

Sound is a collection of AC signals, I think you will need a diode detector to give a voltage envelope when sound is detected.These envelopes can then be amplified by the 741 to trigger the 4027.

#### aurelZ

Jun 10, 2019
98
This circuit should be so called sound switch..right?
So when sound comes then amplified signal from 741 trigg flipflop IC wihich must stay open to hold
relay connected then next sound deactivati IC and relay is off,
if your battery is old and cannot hold constant voltage then you have drops
so try use new battery .

#### Audioguru

Sep 24, 2016
3,650
If you have an old 741 opamp that works when its power supply is only 9V (its datasheet shows only a 30V power supply) then almost any sound will cause it to have an AC output which will trigger the flipflop thousands of times.

You need a "peak detector" circuit that produces a DC output corresponding to the peak or average amplitude of the sound and it can hold its voltage for a time that you decide. The peak detector can feed a comparator for you to select the loudness of the sounds that activate this circuit.

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