please explain this digital stethoscope circuit operation.

digital stethoscope circuit

dear friends.. can any one help me about explaining this circuit..?

this is a "digital stethoscope" circuit.
the heart beats can be heard in the speaker attached at the end.
the heart sound is taken by the microphone.

please explain me this circuit operation.

Thanks in advance..

the ckt. is as follows.........

stethoscope circuit

It is very simple:

Mic1 biased by R3 catch the heartbeat. Alternating voltage from R3 through C3 input to the amplifier U1. R4 gives DC bias for noninverting input of U1.

This amplifier has 1V/V amplification for DC part (due to capacitor C5) and about 22 V/V (+27 dB) for AC part of signal (from about 18Hz to 20 kHz)

Low corner frequency is set by values of R3, R4, C3, R2 and C1. Upper corner is set by R5 and C4 and frequency parameters of U1.

There is tone and volume control net between U1 and U2.
R7,C8 establish low pass filter and C7, R9 establish high pass filter. R8 potentiometer allow to continously pass between low or high pass filtered signal from Mic1. R10 is for volume control.

Amplifier U2 works as output (headphone) amplifier and amplifies signal 45 times (+33 dB)

R13 works in case of short circuit of output.

R1, R2 gives ground level due to powering from one battery. C2 short circuits R1 and R2 for AC signals (lower ground impedance).