Introduction: 5 LDR Circuits: Latching, Timers, Light & Dark Sensors

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Light Dependent Resistor, aka LDR, is a component that has a (variable) resistance that changes with the light intensity that falls upon it. This allows them to be used in light sensing circuits.

Here, I have shown five simple circuits that can be made using a LDR:

1. Dark Sensor Circuit – LED (output) glows when darkness detected

2. Light Sensor Circuit – LED glows when light detected

3. Latching Circuit – LED glows until any obstacle cuts the latching mechanism

4. Dark Timer Circuit – LED glows for some time after darkness detection

5. Light Timer Circuit – LED glows for some time after light detection

Step 1: Components Required

These are the Components Required for:

1. Dark Sensor Circuit

• LDR

• Transistor: BC547

• Resistors: 47K, 330Ω

• LED

2. Light Sensor Circuit

• LDR

• Transistor: BC547

• Resistors: 1K, 330Ω

• LED

3. Latching Circuit

• LDR

• Transistor: BC547

• Resistors: 1K, 330Ω

• LED

4. Dark Timer Circuit

• LDR

• IC 555

• Capacitor: 47μF

• Resistors: 47K, 4.7K, 330Ω

• LED

5. Light Timer Circuit

• LDR

• IC 555

• Capacitor: 47μF

• Resistors: 47K, 4.7K, 330Ω

• LED

Other Requirements:

• Battery: 9V and battery clips

• Breadboard

• Breadboard Connectors

Step 2: Circuit Diagrams

Step 3: Step-by-step Tutorial