The circuit was designed to detect and identify audible sound signals within the boundary limits of the device.
Sound may be termed as a fluctuation or alternation in pressure, stress, particle displacement, or other physical characteristics, in an elastic medium. In measuring an audio intensity, there are sound-level meters that are complete, self-contained, portable and normally battery-driven. It consists of a sound-pressure transducer (microphone), amplifier, standardized weighting networks, a calibrated attenuator and an indicating meter.
The circuit for audio monitoring can be designed by using a regular dynamic microphone. It must be water-proofed together with the circuitry, which can be located distantly and anywhere as desired. Dynamic microphones are tough, cheap and humidity-free. Using the microphone converts the sound into an electrical signal. For security purposes, there are very sensitive microphone sensors (acoustic sensors) that are installed on walls, ceilings and floors to sense any sound during a burglary or any unwanted incident.
The transistors are responsible for amplifying the signal output coming from the microphone. The output from the micrphone traveling across the 220uF capacitor is restored at the power supply. This in turn supplies small amplifiers to drive small speakers.
During the identification of sound, the system may not function well if the noise level is very high. Noise refers to those unwanted and undesirable sound.