Schematics > Security and other sensors and detectors > Room Noise Detector
Room Noise DetectorOne LED monitors three levels: 50, 70 & 85 dB
Useful to detect too noisy environments
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 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 live 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 |
Title: Room Noise Detector
Source: www.redcircuits.com
Published on: 2005-02-10
Reads: 781
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