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Wednesday, November 11, 2009

Room Noise Detector Circuit

This circuit is called the Room Noise Detector, which is intended to signal, through a flashing LED, which exceeds the threshold specified in the room noise, chosen from three fixed levels, namely 50, 70 & 85 dB.

This circuit diagram using two Op-amps, which provides the circuits required to obtain a voice-picked by a miniature electric microphone to drive a LED. SW1 to the first position in the circuit is not active. Second, third and fourth position in the power circuit and set the input sensitivity threshold to 85, 70 & 50 dB respectively.

Part :
R1 = 10K
R2,R3 = 22K
R4 = 100K
R5,R9,R10 = 56K
R6 = 5K6
R7 = 560R
R8 = 2K2
R11 = 1K
R12 = 33K
R13 = 330R
C1 = 100nF
C2 = 10µF 25V
C3 = 470µF 25V
C4 = 47µF 25V
D1 = Red LED
IC1 = LM358
Q1 = BC327
MIC1 = Miniature electret microphone
B1 = 9V Battery


  1. punda tell me the hw the switch sw2 works? fucker.

  2. The sw2 switch it's used to turn off the circuit, as you can see, there are two cases, one: the battery is connected, the other, the battery is not connected.!

  3. But I also have a question:
    How is the Op-amp V- pin connected? As I see is floating; where should I connect that pin?

    Best regards!

  4. Done, this project is working;) look for more details on