Multi-point control corridor light circuit

The control button switches
SB1-SB4 can be installed at different positions in the corridor. As long as
any button SB1-SB4 is pressed, the lighting EL will
light up immediately. At the same time, it will be decompressed, rectified and filtered by the transformer to supply power to
the 555 integrated circuit .
The initial voltage on the 220yF capacitor connected to pins ② and ⑥ of the 555 integrated circuit is zero,
so the pin ③ of the 555 integrated circuit outputs a high level, and the relay
K actuates, causing the normally open contact K to close, and the entire circuit enters
a timed self-locking state. state. After that, the power supply charges the capacitors on the ② and ⑥ pins of the 555 integrated circuit
, and the voltage rises. When the
capacitor charges about 2/3 of the DC power supply voltage
, it takes about 3 minutes. At this time, the output of pin ③ of the 555 integrated circuit
flips to low level, so K is released, the contact switch K is automatically disconnected, and the light EL goes out. Just press any button among SB1-SB4 again, and the fork will re- time and turn on the light.