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

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

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

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    4 Comments

    0
    MarkD6
    MarkD6

    Question 1 year ago on Introduction

    Hi- I am trying to use a series of your light sensor circuits in one device an have a common 9vdc supply. when separate units are connected this way, they don't respond well. I want to have 24 separate sensors lighting their respective 24 led's when each is exposed to light. am I doing something wrong? is there a better way to do this?
    thanks- mark

    1
    tytower
    tytower

    3 years ago

    Could not find the latching circuit?
    3. Latching Circuit – LED glows until any obstacle cuts the latching mechanism

    0
    DawsonR4
    DawsonR4

    Reply 3 years ago

    It's same as Light Sensor Circuit

    1
    sjlindau
    sjlindau

    Reply 3 years ago

    Described in video.