How to input the buzzer into this circuit

Do i need a capacitor in this circuit to store the charges to keep the buzzer on?

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Thread Starter


Joined Sep 18, 2015
I'm trying to create this circuit for motion detector using a heat sensor.
first off, there is no PIR sensor on Proteus library. instead i used a 2 pole switch to portray the common working/ idea of the circuit.
the circuit is working fine, the RED LED should turn on when there is movement/ heat detection, but there also should be a sound factor incase the user is sleeping or is blind.
hence, my second challenge. I put the buzzer in series with the LED but the voltage across it isnt enough to power it. this is just what i need to complete this circuit.
please i need a solution or at least ideas on how to fix that.



Joined Jun 22, 2012
Your led needs a series resistor of 330ohms, and put the buzzer from the positive supply and collector of the transistor.

Also remove the green led and R7, as these are lowering your op amp supply.


Joined Aug 1, 2013
when the circuit is running, the current rating 0.82A.
You have 470 ohms in series with a 12 V battery. This limits the max current to 25 mA even if everything else is a dead short. Are you saying that 820 mA is the rating on the buzzer's label or datasheet? If so, that is one big buzzer.