Time-controlled password electronic doorbell circuit based on 555 chip

The 555 circuit contains two voltage comparators, a basic RS flip-flop, and a discharge switch T. The reference voltage of the comparator is provided by a voltage divider composed of three 5K resistors. They respectively make the non-inverting input of high-level comparator A1 and the inverting input of low-level comparator A2. The reference levels of the input terminals are 2/3VCC and 1/3VCC. The output terminals of A1 and A2 control the RS flip-flop state and Discharge tube switch status. When the input signal is from pin 6, that is, the high level trigger input exceeds the reference level 2/3VCC, the flip-flop is reset, and the output pin 3 of the 555 outputs low level, and the discharge switch is turned on at the same time; when the input signal is from 2 When the pin input is lower than 1/3VCC, the flip-flop is reset, pin 3 of 555 outputs high level, and the discharge switch is turned off at the same time. RD is the reset terminal (pin 4). When RD=0, 555 outputs low level. Normally, the RD terminal is open or connected to VCC.

Time controlled password electronic doorbell circuit diagram