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Automatic Vehicle Headlight Dipper/Dimmer Circuit

Automatic Vehicle Headlight Dipper/Dimmer Circuit

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.

 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.

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.


About the Author

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!

40 thoughts on “Automatic Vehicle Headlight Dipper/Dimmer Circuit”

  1. 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..

    • 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.

  2. 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

    • 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

  3. 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

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

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

    • 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…

  6. 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

  7. 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

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

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