Only the one on the left can explain the principle of the circuit. On the right is the 51 microcontroller (basically a minimal system). Its functions are implemented by internal software, so no further analysis is possible. The following mainly talks about the circuit on the left side

1. The main functions of the upper and lower parts on the left side are basically the same. They compare and shape the input analog signals (completed by the 393 comparator) and output digital The pulse signal is provided to the 51 microcontroller for processing.

2. The upper side is the photoelectric input, and the changing light is converted into an electrical signal by the photodiode D1.

3. The lower side is the sound input, and the microphone MK1 converts the sound signal into an electrical signal.

It is estimated that this circuit is to judge the input sound and light signals, maybe to judge the frequency, or maybe to judge the number of times (specifically implemented by the microcontroller software), and then indicate it through the LED on the right

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