Use NE555 to make automatic door-controlled lights at night

The power circuit of this machine is composed of VDI ~ VD5 and vs. When the thyristor vs is in the off state, the 220V
AC power is rectified by the bulb H, VD1 ~ VD4, R2 step-down current limiter, VD5 voltage stabilizing and capacitor Cl After filtering,
about 6V DC voltage can be obtained at both ends of the capacitor Cl , which is used to power the whole machine. At this time, the current flowing through the bulb H is very small, only about 2mA, so
the lamp H will not be lit. The time base circuit NE555 is connected as a typical monostable trigger. The trigger is usually in a stable state, and its
output pin 3 outputs a low level . The resistors Rl and R3 form a voltage divider to supply forward voltage to the thyristor vs gate. , because
the resistance of Rl is much larger than R3, the vs gate is at a low level, vs is turned off, and the light does not light up.
    The door control switch is composed of a reed tube K and a small magnet ZT. ZT is fixed on the door, and K is installed on the door frame. When the door
is closed , ZT is exactly aligned with the reed tube K, thus making the two contacts in the reed tube Magnetization attracts, the trigger terminal 2 pin of the time base circuit
is high level, and the trigger is in a stable state. If you go home and open the door at night, because ZT leaves the reed tube, the two contacts in the reed tube
will trip due to their own elastic reset. Since the resistance of RP is much smaller than that of the photoresistor RG, pin 2 of the time base circuit will receive a negative pulse.
level (less than 1/3 VDD), the monostable trigger flips into the transient state, that is, the circuit is set, and pin 3 of the output terminal outputs a high level, so
the level of the right end of the resistor R3 is raised, and the voltage divider of Rl and R3 At this point, the gate level of vs rises, and vs is triggered to turn on,
so there is normal current flowing through the bulb H (via VD1-VD4, vs and VD5 forming a loop). The lamp was lit and glowed.
When vs is turned on, the voltage-reducing resistor R2 no longer works. Since current flows directly through vs and VD5,
a voltage drop of about 6V will be generated at both ends of VD5 and filtered by CI to supply power to the whole machine. From the above analysis, it can be seen that no matter whether the thyristor VS is turned on or
not, a DC voltage of about 6V can be generated at both ends of the capacitor CI, thus ensuring that the circuit can always work normally. After the owner enters
the house, he will close the door. At this time, the contacts in the reed switch will be magnetized again, and pin 2 of the time base circuit will return to high level, but the circuit
is still in a transient state and the light will still light up. At this time, the positive power supply charges the capacitor C3 through R4. IR4C3, time base
The level of pin 6 of the min value end of the circuit rises to 2/3 VDD, the circuit is reset, the transient ends, pin 3 returns to low level, vs loses its
due trigger voltage, when the alternating current crosses zero. When turned off, the light goes out and the circuit returns to its original resting state.
    The light control circuit is composed of RG and RP. During the day, RG has a low resistance due to being illuminated by indoor natural light. At this time, even if
the door is opened and ZT leaves the reed switch, the resistance of RG is much smaller than RP, so pin 2 of the time base circuit is The level is always higher than 1/3 VDD, so
the time base circuit will not trigger a flip. Only after night falls, the RG resistance value increases, and when the RG resistance value is greater than twice the RP, ZT
leaves the reed switch to make the level of pin 2 of NE555 lower than l/3 Vcm, and the light will be triggered to light up. .