How to build Decibel Meter
The post explains a very handy little decibel meter circuit which may be built by any new hobbyist at home. Description Decibel (dB) is a unit of sound pressure. In this particular circuit three LEDs or lamps are employed to indicate the pressure of a available audio input. When the three lights are ON, the audio level would be 4x. When two lights are ON it would be 2x and when one light ON it would be x. the circuit is built around a quad OP-AMP LM324. One section of the IC is being used as an amplifier whereas the other three OP-AMPs have been used as voltage comparators. Here in this case the audio sensor is a standard 8ohm speaker. One side of the speaker is grounded and the other pin of the speaker is connected to the negative pin of a 10μF electrolytic capacitor. The positive pin of the electrolytic capacitor is connected to the base of a switching transistor of high gain. In this case 2N2222 or 2N3904 is recommended. The first OP-AMP which is used as an amplifier as a trim p...