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# Room Noise Detector Circuit (LM358)

2017-08-11 15:04
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This article describes the Room Noise Detector Circuit (LM358). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: LM358.

OneLEDmonitors three levels: 50, 70 & 85 dB, Useful to detect too noisy environments

This circuit is intended to signal, through a flashingLED, 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 aLED. 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 withLEDoff and 12-15mA when theLEDis steady on.

#### Figure 1 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. RedLED
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 theLEDis 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.

dB Example of sound sources

20 Quiet garden, electric-clock ticking, drizzling rain30 Blast of wind, whisper at 1m40 Countryside areas, quiet apartment, wrinkling paper at 1m50 Residential areas, quiet streets, fridges, conversation at 1m55 Offices, air-conditioners60 Alarm-clocks, radio & TV sets at normal volume64 Washing machines, quiet typewriters67 Hair-dryers, crowded restaurants69 Dish-washers, floor-polishers70 Loud conversation, noisy street, radio & TV sets at high volume72 Vacuum cleaners78 Telephone ring, mechanical workshop80 Passing trucks, noisy hall or plant, shuffling at 1m90 Passing train, pneumatic hammer, car hooter at 1m95 Mega “disco”, circular saw100 Motorcycle without silencer