Light Dependent Resistor (LDR) Activated Transistor Switch Driving a Motor Demonstration

This is a demo of a light activated switch based on the light dependent resistor (LDR). This is a transistor based LDR circuit. The light operated transistor switch triggers another power transistor to drive a higher load. Blocking the light falling over the LDR activates the first transistor to turn on. The emitter of the first transistor is directly connected to the base of the next transistor. The second transistor is a power transistor that can tolerate higher current and load. The emitter voltage of the first transistor triggers the second transistor that drives a motor or higher load current. This circuit can be used to switch on lights automatically when it gets dark, and operate devices such as DC motors, light bulb, etc. You can also use a relay in place of the motor to switch higher load or high voltage circuits.