About: Just a Simple Maker.

Hi, guys....!
I'm back with some more cool DIY projects.

In this instructable, I'm sharing with you about my new modified
# Modified Automatic night light Circuit

This is one of the Cool Circuits I have made....
I think you people would probably like my project.

As explained earlier this is the modified version of my previous project . But the change is that THE CIRCUIT HAS BECOME MORE POWERFUL & YOU CAN EVEN CONTROL YOUR HOUSE LIGHTS OR STREET LIGHTS ( Or just anything that comes to your mind) by just connecting an appropriate relay.
(In the old circuit this cannot be done because it did not work perfectly with a relay on it )

I had connected everything that I could get my hands on and made them on - off by the swish of my hands ( blocking the light to LDR using my hands).It was so Cool.Somewhat like a motion sensor activated things

Children can use this at their science fair to show off Automatic street light controller based street lights.which turns on automatically at night and switches off automatically when it's morning or whatever idea that strikes in their mind.

Step 1: To the Building Procedure......!

Working of the circuit is as of the previous project that I had published earlier but now its power has's more advanced compared to the other which could only control LEDs

Step 2: Gathering Materials......

First Step in a project is planning and gathering materials.
So now let's gather the items to make the project

Electronic components required:

1. 1K resistors - ×2
2. SL100 Transistor - ×1
3. BC107 Transistor - ×1
4. 100K preset - ×1
5. Wires
6. Prototyping PCB board
7. An LED
8. 9v Battery & battery connector
9. 5v relay

Tools required:

1. Soldering Iron
2. Wirecutter
3. Soldering Lead

Step 3: Building.....

Follow the circuit diagram.

First solder the smaller things like resistors , preset and transistors and But it's better to continue as in the circuit diagram.

Step 4: Step - 1

Solder the preset to the PCB.Presets have 3 legs,one middle one and other 2 on sides join anyone and middle leg and follow as in the circuit diagram

Step 5: Step - 2

Solder BC 107 Transistor as in the Circuit.Take note of the pin-outs of the transistor given in figure 2.

Step 6: Step - 3

Solder the 2 Resistors as in the circuit diagram.

Step 7: Step - 4

Now solder the SL100 Transistor as in the circuit diagram.Take note of the pinout of transistor given in figure 2 before soldering.
After this, our building process is almost finished.

Step 8: Step - 5

Now the wiring part.

Leave wires so as to connect the battery,relay and LDR as in the diagram.
Connect the battery connector to the 2 wires coming out to the battery.
Connect the LDR & relay to its respective wires.

Step 9: Testing.... !

Connect the battery and adjust the preset with a plastic screwdriver (using a metal one would affect its tuning). Turn it till the LDR is adjusted to the surrounding light and the moment when bulb switches off leave tuning it . Now try to cover the LDR blocking it from light.
If everything is right LED should light.if not adjust the preset and try again.

Tuning is same as in the previous project.But here we have to insert a screwdriver to turn it,that is the only difference.

Step 10:

Now reconnect the relay and you can use this to replace the switch of your garden light.So that it will light up automatically when night and then turn off automatically when it's morning.

Place the circuit in a box and leave the LDR out so as it is facing the light outside.

Now it is ready to work for you...

Not only this you can do anything with this like,

1. motion activated switch
2. motion activated burglar alarm
3. automatic street light controller

...."Let your imaginations loose and start building anything that comes to your mind" ...

For more about the technical stuff of this project, check out my previous instructable:

A simple circuit for every electronic beginners #Automatic night lamp with LDR - Check out this Instructable.


Press start simulation above and tap on the LDR, you can see a movable slider pointing to the sun and the moon

Move the slider to the moon, you can see that the LED lights

Do the opposite the LED turns off .

To make circuits like this visit

And here is the pdf of this project for those who do not have pro membership.



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24 Discussions


3 years ago

Sir can you please explain the working and use of the 2 transistors in this circuit?

1 reply
techno manmanveen26

Reply 3 years ago

Here transistor BC107 works as a automatic trigger ones the LDR detects darkness BC107 gets fired then in turn it fires the SL100 which wrks as a relay driver [ Amplifies the signals from BC107]


3 years ago

how to power the circuit directly with 220 AC , so both the LDR and relay will have the same power supply?

i don't want to use a transformer, i want to use cheaper components with smaller size.

shall i use full wave rectifier with the 4 diodes, capacitor, and a voltage divider after that? is there a better approach?

2 replies
techno manMeena_Bassem

Reply 3 years ago

U Can try it but keep in mind the circuit will not operate perfectly if it does not get 9v dc supply

Meena_Bassemtechno man

Reply 3 years ago

well, i know that, but still my question. is there a good and cheap way to get 9V DC supply from 220 AC without using a transformer?


3 years ago

Thank you for sharing

What kind of software did you use for the schematic?

Thank you in advance

2 replies

3 years ago

Is there a specific reason that you choose a 1K resistor for the collector resistor?

This means that 9mA is flowing when the BC107 is turned on (daylight hours). An average 9v battery when new has about 560 mAh ( ) which will only give you just over 60 hours of daylight operation.

If you dropped that 9 ma to 1 ma, you would have closer to 560 hours of daylight operation

1 reply
techno manpcarew

Reply 3 years ago

Mm, i didn't think of that

I would surely try it out soon


3 years ago

I really love your project. Thanks for sharing your hard work.

I am a beginner and I wanted to learn such things. Please help me out.

Do email me at

Thanks you very much.

1 reply
techno manpavanram

Reply 3 years ago

Tnx pavan ram for showing interest on my project and electronics

I would sent you the mail as soon as possible


3 years ago

An efficient simple circuit but without hysteresis. This will produce flickering if transition between day and night is smooth, as it is normally.

3 replies
techno manrafununu

Reply 3 years ago

Yes ,I think you are right, i to had experienced that.

Any solutions ?

Sleutel13 techno man

Reply 3 years ago

i think a delay capacitor will solve that problem


3 years ago

Hi, for all of you. I like Electronic and I'm beginner. And like to start learning to do some night light, blinking light whatever about Led light. So please I will apreciat it if any one of you can help me or send me,thank you.


3 years ago

It is not missing a diode in parallel with the coil of the relay ??

1 reply

3 years ago

You need to add the relay to your parts list.

With the relay in place you should put a diode (say a 1N4001) across the relay coil. The inductive kickback from the coil in the relay will kill your output transistor -- perhaps you've already experienced this? .]

Here is a good explanation and schematic.

When the field in the relay coil collapses you have to give the energy a place to go to protect the switching transistor, that's what the added diode will do.

If you use a solid state relay instead it will act just like an LED -- that's what a solid state relay IS (some of them) -- an optically coupled switch triggered by an LED.

THANK YOU for not incorporating an ARDUINO in your project! Nothing like using 100,000 transistors when TWO can do the job.