Photoresistor sensors are particularly sensitive to light, the stronger the light, the smaller the resistance value; the darker the light, the greater the resistance value. So this feature can be used to build a photosensitive circuit, and cooperate with a relay/transistor/MOS tube to realize a light-controlled switch. The following describes the circuit that uses photoresistors, transistors, and relays to realize photoelectric switches.
Connect the photoresistor sensor and the sliding rheostat in series, and connect the common point to the base of the NPN transistor through the current limiting resistor. The collector of the NPN is connected to the base of the PNP through the current limiting resistor and the relay is connected to the emitter of the PNP for switch output. When it's in dark, adjust the sliding rheostat to reduce the resistance until the relay is in action. When the light is very strong, the resistance value of the photosensitive sensor starts to decrease, so that the NPN triode is not enough to conduct to a certain extent, then the base level of PNP triode is high, leading to the cut-off of PNP triode to reset relay.
If the light is connected to the output of the relay, it can be automatically turned on when the light becomes dim, and the light can be automatically extinguished when the light reaches a certain intensity, thus realizing the function of the light control switch.
Senba Sensing Technology Co., Ltd., with its own R&D center, conducts a large amount of basic researches and uses unique technology to develop sensors and other products. We are very concerned about the quality of our products. Our photoresistors and other products have passed international certifications and are worthy of your trust!