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04-05-2010

Room Noise Detector

One LED monitors three levels: 50, 70 & 85 dB
Useful to detect too noisy environments

Circuit diagram:

Room Noise Detector

Parts:

R1

10K   1/4W Resistor

R2, R3

22K   1/4W Resistors

R4

100K   1/4W Resistor

R5, R9, R10

56K   1/4W Resistors

R6

5K6 1/4W Resistor

R7

560R   1/4W Resistor

R8

2K2 1/4W Resistor

R11

1K   1/4W Resistor

R12

33K   1/4W Resistor

R13

330R   1/4W Resistor

   

C1

100nF 63V Polyester Capacitor

C2

10µF 25V Electrolytic Capacitor

C3

470µF 25V Electrolytic Capacitor

C4

47µF 25V Electrolytic Capacitor

   

D1

5mm. Red LED

   

IC1

LM358 Low Power Dual Op-amp

   

Q1

BC327 45V 800mA PNP Transistor

   

MIC1

Miniature electret microphone

   

SW1

2 poles 4 ways rotary switch

   

B1

9V PP3 Battery

   

Clip for PP3 Battery

 

Device purpose:

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.

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.

dB

Example of sound sources

20

Quiet garden, electric-clock ticking, drizzling rain

30

Blast of wind, whisper @ 1 m.

40

Countryside areas, quiet apartment, wrinkling paper @ 1 m.

50

Residential areas, quiet streets, fridges, conversation @ 1 m.

55

Offices, air-conditioners

60

Alarm-clocks, radio & TV sets at normal volume

64

Washing machines, quiet typewriters

67

Hair-dryers, crowded restaurants

69

Dish-washers, floor-polishers

70

Loud conversation, noisy street, radio & TV sets at high volume

72

Vacuum cleaners

78

Telephone ring, mechanical workshop

80

Passing trucks, noisy hall or plant, shuffling @ 1 m.

90

Passing train, pneumatic hammer, car hooter @ 1 m.

95

Mega "disco", circular saw

100

Motorcycle without silencer

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