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You are here: Home / Car and Motorcycle / Automatic Vehicle Headlight Dipper/Dimmer Circuit

Automatic Vehicle Headlight Dipper/Dimmer Circuit

Last Updated on November 8, 2021 by Swagatam 53 Comments

caution electricity can be dangerous

The circuit described here can be built and used in your vehicle for an automatic dipping and dimming operation of the vehicle headlamps, in response to the intense lights coming from an opposite vehicle headlamps.

What's a Dimmer/Dipper in Automobiles

An automobile headlight dimmer/dipper is a circuit which automatically switches the headlight intensities of vehicles arriving from opposite directions in a controlled manner.

This prevents the drivers from the blinding glares of the opposite side headlights, and allows the drivers to have proper control of their vehicles, and avoid serious accidents.

 Why an Automatic Headlight Dimmer/Dipper is so Important in Vehicles

You must have come across this irritating situation while driving at night when you find the headlight lamp focus from an opposite vehicle coming straight to your eyes, making things difficult to assess, and giving rise to a situation of a collision or a possible accident.

Incidentally, the driver of the opposite vehicle might be going through the same situation due to the headlight focus from your vehicle.

Such situations are normally tackled by using manual dipper switch mechanism, where the driver is prompted to "dip" the focus of his headlight, thus giving the opposite vehicle a chance to adjust his vehicle and also an indication that he too needs to "dip" his vehicle lamps.

However, doing the above operation manually, every now and then can become horribly laborious and troublesome, therefore if some kind of automatic system is Incorporated, can help to save this headache of the driver, especially while he is driving in stressful conditions and on dangerous highways.


You maybe also interested in reading a PWM based self-adjusting dimmer/dipper circuit


Circuit Operation

The following diagram describes a simple yet effective auto head lamp dipper or dimmer circuit. The transistor is used as a comparator, which compares the preset resistance level and the LDR resistance level with reference to ground.

Circuit Diagram

Automobile automatic dimmer dipper circuit with a single transistor, LDR and DPDT relay

DPDT Relay Connection Diagram with Dipper Bulb

DPDT Relay Connection Diagram with Dipper Bulb

How the LDR Operates

Light falling over the LDR from the headlight of the vehicle coming from the front instantly lowers its resistance and allows more current to flow to the base of the transistor.

The transistor conducts and activates the relay, which in turn flips the contacts such that the host vehicle's headlamps gets connected with the dipper filament, changing its intensity.

The whole circuit may be enclosed in a small box and installed somewhere near the driver's dashboard area, however the LDR needs to be wired and placed out of the enclosure, in some corner of the wind shield, so that it is able to "see' the light from the opposite vehicles just as the driver would see them.

Parts List

R1 = 1K,
P1 = 10 K,
LDR = With resistance @ around 10 to 50 K when illuminated in daylight (under shade).
T1 = BC547,
D1 = 1N4007
Relay = coil 400 Ohms, DPDT, 12 volts

Making a vehicle dimmer/dipper without Relay

The above automatic dipper circuit can be modified for operating with mosfets:

Automobile dimmer dipper lamp using mosfet and IC 555

Dimmer Dipper with Cellphone Charger

The following brief explanation was provided by Miss Surya for getting a better view of the proposed circuit design of an automobile dimmer/dipper head light switch circuit with an optional cell phone charger circuit for facilitating the charging of a cell phone also on board.

Circuit Operation

Here the IC 555 has been used not as a charging indicator rather as a comparator for controlling the dipping action of the head lamps.

The use if IC 555 as a charging indicator would have made the circuit unnecessarily complicated, therefore a novel and simpler way is selected for the charging ON indication.

The LED connected across the 5 Ohm  watt current limiting resistor effectively indicates the charging status of the cell phone and switches OFF the moment the charging process stops.

The IC 555 works like a comprartor here, when light falls on the LDR, voltage at PIN#2 rises above the set internal threshold which prompts the IC to change its output PIN#3 voltage from 0 to 12, triggering the connected relay.

The relay contacts immediately transfer the positive supply from the "high" filament to the "low" filament of the head lamps, resulting in an instant dipping of the lamp intensity.

The LDR must be positioned in such a way that it only receives light rays coming from front of the vehicle, which will be mostly the  lights from another vehicle's head lamps.

Using Photo Transistor

When photo-transistor Q1 detects the headlights of an approaching vehicle, the circuit gets operational and starts executing the dimming/dipping function. The 22 M resistor, R5, sets the sensitivity to approximately half a foot-candle. A 12 V, 0.3A coil is utilized for the relay. The photo transistor L14C1 comes with an one-inch lens with a 10° angle of view and a 1 inch diameter.

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About Swagatam

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials.
If you have any circuit related query, you may interact through comments, I'll be most happy to help!

Reader Interactions

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  1. Mino says

    April 28, 2022

    Thank you for your time
    Yes what should be done on the headlamps
    The negative pulse is provided by the alarm system, which behaves as follows: negative pulse output on unlocking and negative pulse output on locking .

    Reply
    • Swagatam says

      April 29, 2022

      OK, I will try to design them soon…

      Reply
    • Swagatam says

      April 29, 2022

      Here’s the circuit you can try:

      car headlamp delay using LDR and negative trigger

      Reply
      • Mino says

        April 30, 2022

        Thank you very much,
        I will tru this circuit while waiting for ideas for a circuit combining serval lightning fonctions.

        Reply
        • Swagatam says

          April 30, 2022

          Sure, no problem!

          Reply
  2. Mino says

    April 28, 2022

    Hi,mr swagatam, first of all, I would like to congratulate you on your achievements, which are very, very useful!

    I have a request to make regarding the automatic lighting circuit (which I have already made thanks to you)

    I want to make a circuit combining several features!

    1 – automatic lighting of the lights at night when unlocking the car with the alarm ( negative pulse) and turning off when the contact is put on.

    2 – extinguishing the lights after a certain time after stopping the engine (delay)

    3 – coming home/leaving home function only when it’s dark

    Note: my alarm has several power latching and delayed output functions I send you the alarm schema if you want.

    Thank you for your help and good luck <3

    Reply
    • Swagatam says

      April 28, 2022

      Thank you Mino,

      On which lamp these needs to be done? Is it the head lamps.
      The 1st one looks difficult since I do not know from where I should extract the trigger pulse.

      Reply
  3. Anuraj says

    November 4, 2021

    Hi, please let me know the suitable position for the photo transistor?
    Is there is any chance to interfere with street light or any other side lights?
    Is that possible to build a flashing of high beam in case the opposite vehicle is not dimming there headlamp?

    Reply
    • Swagatam says

      November 4, 2021

      Hi, you will have to enclose the light detector inside a suitable pipe like encloser so that it is able to “see” only the light beam focused from the front vehicles. Yes it is also possible to flash the high beam bulb after a few seconds, through an additional circuit.

      Reply
  4. Dip says

    November 10, 2019

    What are the components for this Project..
    Please reply me..

    Reply
    • Swagatam says

      November 11, 2019

      The values are given in the diagram itself

      Reply
    • Anuraj A V says

      November 4, 2021

      Can u support to figure it out .Also am looking of a headlamp auto leveling system but not available in the market. I hope you can support me on that as well.
      Some high end vehicles having that system but it’s bit complicated but I was looking for a simple one with the support of an inclinometer.

      Reply
      • Swagatam says

        November 5, 2021

        I will try to figure it out soon. Yes auto adjusting is also possible through a PWM circuit!

        Reply
  5. kemn says

    July 5, 2019

    , nice one please can you explain to me how it works please

    Reply
  6. project group says

    January 13, 2019

    Hello sir, we made college project of “automatic headlight dim and bright controlled using ldr” from ur first ckt Diagram.. For 4 wheeler… Are u suru it really works? Pls sir reply its too imp for us..

    Reply
    • Swagatam says

      January 13, 2019

      Hello Project Group, as you can see the design is very basic and therefore it will work exactly as described without any problems.

      To ensure that the relay does not stutter at thresholds you can add a 1000uF/25V capacitor in parallel to the relay coil or the diode D1.

      Test the circuit on your work bench using flashlight first, before actually installing it in a vehicle.

      To make the circuit more sensitive you can upgrade the transistor into a Darlington transistor by adding another BC547 to it.

      Reply
    • project group says

      January 13, 2019

      Thank u so much for ur reply… And I hope it really work for me

      Reply
      • Swagatam says

        January 13, 2019

        You are welcome!

        Reply
  7. MOHAMED Reswan says

    October 16, 2017

    I would like to have a detailed circuit design using relay…

    rezdude07@gmail.com

    Reply
  8. Jinu says

    September 27, 2017

    May be two vehicles have headlight with different intensity .like 2 car uses two types of light one is led and other is halogen in this situation is it possible

    Reply
    • Swagatam says

      September 27, 2017

      the circuit will respond to all forms of light, it doesn’t matter whether it is from LED or halogen….

      Reply
  9. Jinu says

    September 27, 2017

    Pls help to do dis idea for our project

    Reply
    • Swagatam says

      September 27, 2017

      what is your question?

      Reply
  10. Jinu says

    September 27, 2017

    We r try to do this idea as our project so pls help and support

    Reply
  11. Amal Vijayan says

    August 20, 2017

    Sir could you please explain the working of mosfets in the circuit…
    and what is the use of 100 K resistor between 5 and 7 terminal of ic555

    Give the complete details about this circuit
    Email: iamamalvijayan9597@gmail.com

    Reply
    • Swagatam says

      August 20, 2017

      Amal, the mosfets are configured to act like SPDT switches, when the right side mosfet pair is ON, the left side pair is off and vice versa.

      the 100K is to create some hysteresis effect between the ON OFF switching

      Reply
  12. Swagatam says

    August 8, 2017

    place the LDR inside a short pipe, such that only light beams coming from the front is able to reach the LDR, and no other light from around or top.

    LDR and photosensor will behave in the same manner, the correct way is to put the sensor inside a pipe like enclosure

    Reply
    • NIRMALSAGAR PATEL says

      July 20, 2019

      Please give circuit diagram of relay point

      Reply
      • Swagatam says

        July 20, 2019

        I have updated the diagram in the article, please check it out

        Reply
  13. Anirudh Madhav Kakkad says

    May 8, 2017

    Can i install this automatic dipper in a scooter?

    Reply
    • Swagatam says

      May 8, 2017

      yes you can

      Reply
  14. Mohammad says

    October 19, 2016

    Arduino version is possible, I have already built it…

    Reply
    • Swagatam says

      October 19, 2016

      Mohammad, please send me the details in my email: admin @ http://www.homemade-circuits.com

      Reply
    • surya virat Molugu says

      October 20, 2016

      Muhammad can u plz forward it to me!! My email is moluguvirat@gmail.com Thank u

      Reply
  15. surya virat Molugu says

    October 3, 2016

    Hello sir, can you please post a circuit of AUTOMATIC HIGH BEAM TO LOW BEAM HEADLIGHT USING ARDUINO. with components required!! plz help me.

    Reply
    • Swagatam says

      October 4, 2016

      Hello Surya, if possible I'll try to produce it in my website

      Reply
    • surya virat Molugu says

      October 4, 2016

      Sir try to produce as soon as possible. Thank you sir.

      Reply
    • surya virat Molugu says

      October 18, 2016

      Sir I'm in a need of ur ckt diagram with components to complete my project. My last date of submission is Oct 21st. So please reply me with the complete details of it, as soon as possible sir. Plz sir. Thank you

      Reply
    • Swagatam says

      October 18, 2016

      Surya, all the details are given in the article, please click the diagram to enlarge.

      you can write the details on paper and show it to the part dealer he will do the needful

      Reply
    • Swagatam says

      October 18, 2016

      ….sorry the arduino version will not be possible…

      Reply
  16. Unknown says

    November 13, 2015

    which bulb is use for this..

    Reply
  17. Sri Dhar says

    October 4, 2015

    What type battery and bulb should be used while submitting as an mini project sir pls kindly requesting u to answer me its urgent

    Reply
    • Swagatam says

      October 4, 2015

      For a realistic look you may want to procure an actual car headlight lamp with double filament, however if you find it difficult then you may simulate the same by tying two small DC bulbs together and wire them up as shown in the first diagram.

      The Dim bulb could be a 24V bulb and the bright bulb could be a 12V bulb…

      Reply
    • Swagatam says

      October 4, 2015

      power could be from a 12V /1amp ac dc adapter

      Reply
  18. Mohammad says

    November 23, 2014

    Hi . Im trying to build automatic headlight beam by using arduino mega 2560 to program the circuit diagram, i want to know if anyone can help me for a clear circuit diagram (12v input)or the connection i mean how to connect arduino to the circuit diagram

    Reply
    • Swagatam says

      November 24, 2014

      if possible we'll try to get it and post it for you

      Reply
  19. Swagatam says

    May 7, 2014

    austin,
    In the second 555 circuit do the following changes:

    remove all the transistors and the pin3 100k resistor.
    now connect white LEDs across positive and pin3, and pin3 to ground
    use 10k series resistors for the ground LED and 1k for the positive LED

    that's it, now the LEDs will respond like dipper lights

    Reply
  20. austin sabu says

    May 7, 2014

    sir i just want to make the model of an autommatic dimming system in a dummy car. how could this be possible?

    Reply
  21. gv rahul says

    July 28, 2013

    we have connected potentiometer in the 1st circuit,so how much of resistance to be applied

    Reply
    • Swagatam says

      July 28, 2013

      R1 can be replaced with a 1M pot.

      Reply
  22. gv rahul says

    July 28, 2013

    what is the use of potentiometer in auto dipper circuit

    Reply
  23. Vivek G says

    July 28, 2013

    hi sir ,
    can you send me the circuit diagram for automatic head lamp control using micro controller please

    Reply
  24. gv rahul says

    July 20, 2013

    Sir will u tell us how to make connections

    Reply

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