As shown in the figure, the voltage detection circuit takes 555 as the core to form a bistable mode. Normally, VDD 6 is connected to VDD through R1, so 3 is low. The trigger pin 2 of the 555 is connected to the monitored point through a Zener diode DW. If the DW with different voltage regulation values ​​is used, the switch control is turned on, and the different measured voltage values ​​can be discriminated.
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