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Room Noise Detector
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This schema 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 schema gain for sounds picked-up by a miniature electret microphone to drive a LED. With SW1 in the first position the schema is off. Second, third and fourth positions power the schema and set the input sensitivity threshold to 85, 70 & 50 dB respectively.Current drawing is <1ma>
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
Use:
* Place the small box containing the schema 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
Room Noise Detector
This schema 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 schema gain for sounds picked-up by a miniature electret microphone to drive a LED. With SW1 in the first position the schema is off. Second, third and fourth positions power the schema and set the input sensitivity threshold to 85, 70 & 50 dB respectively.Current drawing is <1ma>
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
Use:
* Place the small box containing the schema 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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