Sound Pressure Meter

Here is a simple circuit of “Sound Pressure Meter” to check the pressure of sound. An am-meter of few micro-amperes is used in its output in order to show the deflection corresponding to intensity of sound.

Circuit description

The circuit sound pressure meter utilizes a microphone, an operational amplifier, and a moving coil am-meter. Microphone pick-up the sound to be measured and change it into electrical signal corresponding to intensity of sound. The output of microphone is given to pin 2 of IC1 (TLC272) through bipolar capacitor C1, where IC1 is a 2-operational amplifier. Variable resistor VR1 is used to select the amplification power connected to pin 1 and 2. The reference voltage is given to non-inverting pin (pin 3) of IC1 through resistor R3 and R4. As TLC272 (IC1) is a combination of two individual operational amplifier, so for further amplification of half voltage of voltage at non-inverting input (pin 3) second operational amplifier is used.

A moving coil am-meter of 30 µA range having internal resistance of 6.5 KΩ is used in its output.

circuit diagram of sound pressure meter


Resistors (all ¼-watt, ± 5% Carbon)

R1 = 10 KΩ

R2 = 220 Ω

R3, R4 = 100 KΩ

R5 = 8.2 KΩ

VR1 = 500 KΩ (preset)


C1 = 10 µF/40V

C2 = 470 µF/16V

C3 = 4.7 µF/63V

C4 = 15 pF

C5 = 100 KpF


IC1 = TLC272 (2-operational amplifier)

D1 – D4 = BAT85

D5 = 1N4148


SW1 = On/Off switch

M1 = 30 µA/6.5 KΩ (am-meter)

MIC1 = MCE2000

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