Automatic Dark Detector




About: I have some interest in electronic. you can find me at

I made a project on this platform and It's not that much effective. So this project is all about the some minor upgrade to increase the effectiveness. If you are following me then you know that what I am talking about.

Or If you seen my projects for the first time then just stick with this project.

So lets start....

Step 1: Parts Required

First Step in a project is planning and gathering materials.

So now lets gather the items to make the project.

Electronic components required:-

10K resistors - 1 nos

BC548 NPN Transistor - 1nos

LED's - 4 nos

LDR (400Ohm or 1000lux) - 1nos


Prototyping PCB board - 1 nos

5v DC Power Source

Tools required:-

Soldering Iron


Soldering Lead

Step 2: What Is LDR?

A photoresistor (or light-dependent resistor, LDR, or photocell) is a light-controlled variable resistor. The resistance of a photoresistor decreases with increasing incident light intensity; in other words, it exhibits photoconductivity. A photoresistor can be applied in light-sensitive detector circuits, and light- and dark-activated switching circuits.

A photoresistor is made of a high resistance semiconductor. In the dark, a photoresistor can have a resistance as high as several megohms (MΩ), while in the light, a photoresistor can have a resistance as low as a few hundred ohms. If incident light on a photoresistor exceeds a certain frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electrons (and their hole partners) conduct electricity, thereby lowering resistance. The resistance range and sensitivity of a photoresistor can substantially differ among dissimilar devices. Moreover, unique photoresistors may react substantially differently to photons within certain wavelength bands.

Step 3: Schematic for Automatic Dark Detector

Follow the circuit diagram and you will be able to make this project. Its a good start for beginners. And by This circuit you can lots of another things. In my future projects I will show you how.

The circuit is very simple and very easy to make. You just have to connect one terminal of 10K Ohm resistor to 5V Dc supply and another terminal to Base of NPN transistor, similarly connect one terminal of LDR to base of NPN and another terminal to the emitter of NPN transistor and then connect emitter terminal to GND.And add some LED's in parallel and +ve terminal to 5V DC supply and -ve terminal to collector of NPN transistor.

Here I am attaching PDF file if you need PCB Layout and circuit diagram on paper. If you are interested in PCB etching and need Printed Circuit.

Step 4: Watch This Video for Demo Purpose

Hope you like the video and like this project and I am waiting to see yours.

Step 5: Some Imgs



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    14 Discussions

    Raj wadia

    2 years ago

    The actual name of this project should be automatic night light or night lamp

    1 reply

    2 years ago

    This project isn't "Dark Detector", it is more like "Automatic Lamp"


    2 years ago

    Nice and simple.

    One note: the resistor at the picture is 10M ohm, schematics have 1K Ohm and in the description you have used 10K Ohm... I think, it is not correct.

    Thank you.

    2 replies
    Tech WorksCharlyeZ

    Reply 2 years ago

    thanks @CharlyeZ It's totally my mistake... I used 10K resistor and forget to change the value in schematic and as I downloaded the resistor picture from google so from color code you thought its 10M but I already mention over there its 10K..after all thanks a lot...

    CharlyeZTech Works

    Reply 2 years ago

    Anyway, this is a perfect instructable for the basics of the electronic.

    Thank you man... :-)


    2 years ago

    My porch light is controlled by an LDR alone and comes on at dusk and turns off when the sun comes up. Thus, the LDR resists current flow in when light shines on it, but allows current to flow when not lighted. The poster's own video bears this out.

    1 reply
    Tech WorksGrantLevy

    Reply 2 years ago

    Ya.. this is a very simple application for this circuit.. thanks for your comment


    2 years ago

    As simple as it can be. Note: them LDR's come with a wariety of values, mind that when buying them.

    A hint in the build: For the LDR I use a LED-distance/holder (to be used in PCB-mount), they come in a wariety of lenghts.

    1 reply