2.C 17 can isolate DC, and the latter 1k can be regarded as a high-pass filter.
3. The second stage TL084 B constitutes a low-pass reverse amplifier, which is used to amplify the received signal. The magnification is1m/1k.
1~3 is a two-stage amplifier bandpass circuit. The center frequency is about 5khz.
4 U7A is a threshold comparison circuit. When the output of TL084 B exceeds the voltage threshold set by VR2, INT0 = 0INT0= 1 is lower than the set threshold.
5 C 19~VR4 is a diode detection circuit.
6 U6C Shaped Amplified Output.
7 U7B is a threshold comparison circuit. When the output of U6B exceeds the voltage threshold set by VR3, int1= 0; INT 1= 1 is lower than the set threshold.