Lantern light control automatic switch

During the Spring Festival, the big red lanterns add a lot of festive and auspicious atmosphere to the festival. However, most lanterns are turned on and off manually, which is inconvenient to use. In fact, electronics enthusiasts only need to make a practical light-controlled automatic switch to make the lanterns automatically light up when it gets dark and automatically go out when it gets light, fully realizing the automatic on/off function.

Working Principle The circuit principle is shown in the attached figure. R1, R2, D1, D2, Cl, C2 form a 12V power supply to provide power supply voltage for the whole machine. NE555 and peripheral components form a Schmitt trigger with delay. RG in the circuit is a photoresistor, which is used to detect the brightness of the surrounding environment. At dusk, the brightness of the surrounding environment gradually dims, and the resistance value of RG also increases. The potential of IC1's ② and ⑥ pins gradually decreases. When the potential is less than 1/3Vcc, IC1's ③ pin outputs a high level, and the bidirectional thyristor Q1 is triggered to turn on, and the light in the lantern is powered and lit. In the morning, the sky gradually becomes brighter, the resistance value of RG gradually decreases, and the potential of IC1's ② and ⑥ pins gradually increases. When the potential is higher than 2/3Vcc, ③ pin outputs a low level, Q1 is cut off, and the light in the lantern goes out. Because the hysteresis voltage of the Schmitt trigger composed of NE555 and peripheral components reaches 1/3Vcc, the flickering phenomenon of the light can be eliminated when the critical brightness is near. At the same time, in order to avoid the sudden change of surrounding brightness when setting off fireworks on festival nights, which may cause the lights to flicker on and off, a delay capacitor C3 is specially added to the circuit.

The parameters of each component in the production and debugging circuit are marked as shown in the figure. Because the circuit is very simple, it is easy to make it successfully as long as the welding technology is good and the quality of the components is not a problem. Put the welded circuit board into a plastic box of suitable size, connect the pins of the photoresistor with the wires, and install it in a plastic tube of about 5cm in length (you can cut a ballpoint pen rod of suitable length instead). When installing, the photosensitive surface of the photoresistor should avoid the light of the lantern, and adjust the resistance value of RP1 to make the critical brightness of the light on or off appropriate. When using, just connect the lights in the two lanterns to L1 and L2 respectively. Switch K1 is usually in the off state. Once the switch is turned on, the light control circuit can be used normally.

Note: Since a capacitor step-down circuit is used, the entire circuit board is energized. During the debugging and installation process, attention should be paid to safety to prevent electric shock accidents.