Bed Room Noise Detector Circuit Schematic

This circuit is intended to signal, through a flashing LED, the exceeding of a fixed threshold in room noise, chosen from three fixed levels, namely 50, 70 & 85 dB. Two Op-amps provide the necessary circuit gain for sounds picked-up by a miniature electret microphone to drive a LED. With SW1 in the first position the circuit is off. Second, third and fourth positions power the circuit and set the input sensitivity threshold to 85, 70 & 50 dB respectively. Current drawing is 1mA with LED off and 12-15mA when the LED is steady on.

Bed Room Noise Detector Circuit Schematic 

Room Noise Detector Circuit Diagram

Parts:

R1 = 10K

R2 = 22K

R3 = 22K

R4 = 100K

R5 = 56K

R6 = 5.6K

R7 = 560R

R8 = 2.2K

R9 = 56K

R10 = 56K

R11 = 1K

R12 = 33K

R13 = 330R

C1 = 100nF-63V

C2 = 10µF-25V

C3 = 470µF-25V

C4 = 47µF-25V

D1 = 5mm. Red LED

Q1 = BC327

B1 = 9V PP3 Battery

SW1 = 2 poles 4 ways rotary switch

IC1 = LM358 Low Power Dual Op-amp

MIC1 = Miniature electret microphone

Use:

• Place the small box containing the circuit in the room where you intend to measure ambient noise.
• The 50 dB setting is provided to monitor the noise in the bedroom at night. If the LED is steady on, or flashes bright often, then your bedroom is inadequate and too noisy for sleep.
• The 70 dB setting is for living-rooms. If this level is often exceeded during the day, your apartment is rather uncomfortable.
• If noise level is constantly over 85 dB, 8 hours a day, then you are living in a dangerous environment.

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