Practical sensitive light-controlled switch circuit diagram

The sensitive light-controlled switch circuit is mainly composed of photosensitive transistors. As shown in the circuit diagram below, this circuit uses a Darlington phototransistor as the sensitive element, so it is more sensitive to weak light. Suitable for detection of reflected light signals. In the circuit, when the Darlington photosensitive tube is exposed to light, its internal resistance decreases, causing the potential of pin 2 to drop. When it drops to (1/3) Vcc, pin 3 outputs a high level, and the relay is released.