Noise Meter

Noise pollution is tends to many non-communicable diseases and. Safe level of noise is considered up to 30 dB. Here is a interesting circuit by dreamlover technology, "Noise Meter" used to measure the level of noise indicting by LED and in addition it give warning when noise crosses the safe level of 30 dB by beeping sound.

Circuit description of Noise meter

The entire circuit of noise meter has been designed and fabricated using sound intensity sensor and display unit. Here condenser microphone is used as sensor  of noise meter with operational amplifier (IC2) and corresponding passive components. The inverting and non-inverting input is given to operational amplifier IC (IC2) from pin 2 and pin 3 respectively. Where output from pin 6 of IC2 is connected to the inverting input for negative feedback through resistor R5. The controlling sound ac signal from potentiometer VR1 is first rectified by diode (D1 and D2) and maintains it at the output level of IC2.

The display unit is designed around monolithic IC LM3914 (IC3). It drives ten LEDs by sensing analog voltage. Each LED is connected to output of IC3 represents the sound level of 3 dB in descending order from 18 to 10. The glowing all ten LEDs indicate sound intensity is 30dB.

The PNP transistor get base bias when output at pin 10 of IC3 goes low to drive the piezo buzzer in order to give sound. This indicates noise crosses the safe level of 30 dB.


Resistors (all ¼-watt, ± 5% Carbon)

R1, R3, R4, R7 = 10 KΩ

R2 = 12 KΩ

R5 = 10 MΩ

R6 = 27 KΩ

R8 = 4.7 KΩ

R9 = 1 KΩ

R10 = 5 KΩ

VR1 = 1 KΩ


C1 = 1000 µF/25V

C2, C3 = 0.1 µF

C4 = 0.22 µF

C5 = 4.7 µF/16V

C6 = 1 µF/16V

C7 = 2.2 µF/16V


IC1 = 7809 (voltage regulator)

IC2 = CA3130 (operational amplifier)

IC3 = LM3914 (monolithic IC)

D1, D2 = 1N4148

D3 = 1N4001

T1 = BC558 (PNP)


LED1 – LED4 = Green

LED5 – LED7 = Yellow

LED8 – LED10 = RED

MIC1 = Condenser microphone

PZ1 = Piezo buzzer



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