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How to Realize the Control of Photosensitive Switch by LDR Sensors

How to Realize the Control of Photosensitive Switch by LDR Sensors

LDR sensors are widely used in various industries. This article gives you a brief introduction and application of photoresistor sensor.

Brief Introduction of LDR Sensors

Ldr sensor is a kind of special resistor made of special material, which has a rapid decrease of resistance value under the irradiation of specific wavelength. Its working principle is based on the internal photoelectric effect. It is very sensitive to light. With the increase of illumination, the resistance value decreases. In the absence of illumination, it presents a high resistance state. Using this characteristic, ldr photoresistor can be widely used in making light-controlled switch circuits, as well as monitoring cameras, light-controlled toys, dimming circuits and indoor light control. The following pictures show the shape of LDR sensors and the symbols of circuit diagrams.


This is a LDR sensor with two electrodes. The surface of the photoconductor is serpentine. It is similar to wireless communication circuit board antenna such as WIFI. This LDR sensor is encapsulated in epoxy resin. It has the characteristics of small size, fast reaction speed, high sensitivity and fast reaction speed.


Application of LDR Sensors

LDR sensors can be used in light controlled switch. LDR light sensor and resistor R1 are connected in series. When there is no light, that is, the voltage at both ends of R1 does not reach the open voltage of Q1 triode. Once illuminated, the resistance value of LDR sensors drops rapidly, the voltage at both ends of R1 increases, and the transistor turns on, which leads to the conduction of the rear Q2 triode. The final switch K turns on and the light bulb works.