How to Make a "Dark Sensor."




Introduction: How to Make a "Dark Sensor."

About: Hi. I'm Troy Araujo and welcome to my page. I upload content related to simple electronic projects, home made things, DIY tutorials, breadboard circuits, life hacks and much more. My YouTube channel name is...

A 'Dark Sensor' is a device which senses the presence of darkness. It senses the presence of darkness with the help of the LDR. Whenever light is focused on the LDR...the L.E.D will not glow. As soon as you cover the LDR or keep the dark sensor in a dark room without lights...the L.E.D will glow.

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Step 1: Components Required:-

Electronic Components Required:- LDR (Light Dependant Resistor), L.E.D (Light Emitting Diode), 10k ohm resistor, 9v battery with battery clip, BC547 Transistor and some wires.

First connect all the elements on the breadboard to check if it works and then you can solder it to make it permanent. You can even attach a switch to the "Dark Sensor" to turn it "ON" and "OFF" when required.

Step 2: Steps of Construction:-

Steps of construction:-

1.Connect the LDR to the 'base' and 'emitter' of the BC547 transistor.

2.Then connect one end of the 10k ohm resistor from the 'base' of the BC547 transistor and the other end of the 10k ohm resistor to anode (+) side of the L.E.D.

3.The cathode (-) side of the L.E.D will get connected to the 'collector' of the BC547 transistor.

4.The positive (+) side of the battery will get connected to the 10k ohm resistor and anode (+) of the L.E.D while the negative (-) side of the battery will get connected to the 'emitter' of the BC547 transistor and the other end of the LDR.

Step 3: Testing:-

Once you connect the battery, switch the lights "OFF" in the room and you'll see the L.E.D coming "ON" The L.E.D will come "ON" as soon as the LDR detects the presence of darkness.

Congrats! Your "Dark Sensor" is ready! Have fun!

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    3 Discussions


    Question 1 year ago on Introduction

    sir, I am interest to know the following 2

    1. how do we know 10 k resistor is value require here in tis circuit.

    2. Can we use BC548 transistor instead of Bc547?

    thank you


    3 years ago

    is it possible to use a diffrent transistor?


    3 years ago

    If you replace the resistor with a potentiometer, you'll be able to set a threshold for the "darkness".