DIY relay for daytime running lights

Manufacturing the controller of daytime running lights

Traffic rules require that the car in the daytime was equipped with daytime running lights (DRL, foreign designation – DRL). Not every car has them by design, so the role of flasher lights often perform the lights included in the standard equipment of the car – fog lights, dipped beam headlights, etc. Some motorists install homemade DRLs on vehicles. To control them, you need a separate device – a controller.

What is a controller of DRLs?

The controller of DRLs is an electronic system that controls the glow of the DRL. Its functions may include:

  • Automatically switching on the daytime running lights – the basic and mandatory service;
  • On and off DRLs depending on the voltage on-board power system of the car;
  • stepless supply voltage to the DRLs – if they are used incandescent dumps, it can increase their life;
  • adjusting the brightness of the lights (manual or automatic).

Other service functions are also possible – everything is limited only by the designers’ imagination.

Manufacturing instructions

You can buy a control unit for daytime running lights. You can make it yourself. There are several schemes of different control units for daytime running lights – depending on the availability of components and skills of the master, you can choose the best option.

Controller DRLs based on a relay

The simplest DRL controller can be assembled on a single relay. True, and it will perform only basic functions:

  • turning on the sidelights when the ignition is turned on;
  • Lights turn off when the starter;
  • switching off the DRL when the headlights, lights, fog lights are on (you may need a little complication).

The controller operation is tied to the ACC (accessories) key position in ignition locks of many cars, designed to turn on auxiliary equipment (car audio, cigarette lighter, etc.). The lock has a separate output (a wire with a large cross-section is connected to it), there is voltage on it when the ignition is on, but not when the starter is on. This algorithm correlates well with the conditions of DRL switching on, so it is convenient to use this wire for switching on the DRLs.

Manufacturing of a daytime running lights controller

When voltage appears on the wire A, the relay is triggered, the contacts open and the DRLs turn off. Connection of this conductor depends on the circuit of the car’s electrical equipment. The voltage can be selected as an extinguishing signal:

  • switching on the fog lights;
  • low or high beam;
  • lights.

If the scheme of the car’s lighting equipment is built so that a separate wire (which is then branched off) goes to the regular lighting, then you can use it. If this is not possible, there are two options:

  • Apply only one signal (high beam only, fog lights only, etc.) to extinguish the exhaust lights;
  • combine all the necessary signals using diodes (OR circuit).
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In the latter case, the circuit will be a little more complicated – you will need several diodes by the number of signals, by which the DRLs should turn off.

Manufacturing of a daytime running lights controller

In this scheme, switching on any of the specified lighting equipment will cause the relay to operate, the contacts to open, and the DRLs to be de-energized.

Important: The use of diodes to decouple circuits is mandatory. In their absence, turning on one equipment will turn on the other light sources.

Specific connection points will vary from car to car, depending on the scheme and topology of the on-board network. There is no need for a separate enclosure to accommodate this variant of the control unit. The relay can be placed in any convenient location. If diodes are needed, they can be soldered directly to the relay coil pin.

With a comparator

You can find a schematic of a comparator controller on the Internet. Its operation is based on monitoring the on-board voltage. With battery power it is about 12 volts, and with the engine running and the generator power about 13,5 volts. When the voltage crosses the threshold, the comparator will switch the lights on or off via the power switch. The turn-on level is set with a trimmer resistor.

Manufacturing of a daytime running lights controller

The problem here is that the DRLs should not turn on when the motor is running, but when the ignition is turned on. And this moment is not tracked in this circuit. But if someone wants to build it, it can be made as a module. The electronic components and the connector for the connection must be placed on the board and put it all in a housing. Preferably a metal one. Those who know how to make printed circuit boards at home (LUT, photoresist) can design and etch the board. The rest can assemble the circuit on a piece of breadboard. The block is mounted in a convenient place and connected according to the schematic.

Manufacturing of a daytime running lights controller

Using the ATmega8 board

Many motorists themselves develop schematics of controllers for their own needs and put the materials on the internet. Here is one of the variants on the popular ATmega8 microcontroller. Its use allows you to greatly expand the functionality of the control circuit.

Hand made headlight protectant

When the ignition is turned on the board is powered and the controller waits for the engine to start. When the start signal is received the control circuit checks the operation of one of the turn signals. If at least one turn signal is on, the brightness of the running light on the corresponding side is reduced. The level of illumination is controlled by pulse width modulation. Also monitored by turning on the dipped beam, the presence of this signal also serves as a reason to turn off the parking lights. Activation of fog lights indicates bad weather conditions, so the brightness of the DRLs, on the contrary, becomes maximum when the dipped beam is on. If the hazard lights are switched on, the DRLs blink in counter-phase with them. And also a very useful function is implemented – if the ignition is off and the dipped beam is left on, the running lights start flashing, reminding that the battery may be discharged.

Manufacturing of a daytime running lights controller

In this case, the controller also does not switch on the lights when the ignition is on, but waits for the engine to start. But this disadvantage is easy to eliminate programmatically (you can ask the developer to do so). Connection and assignment of the board contacts to external circuits are given in the table below.

contact number designation Function
1,3 LED+ DRL power line (output)
2,4 VCC Circuit board power supply
6 Lled Left light
8 Rled Right light
5 lbm Middle beam
7 fog Fog light
9 Rin Right turn signal
11 Run Signal from alternator
13 Lin Left turn signal
15 Ign Ignition
12,14,16 GND Common wire

You can download the firmware for ATMeg here. It is better to assemble the controller on a printed circuit board, and the use of SMD elements will greatly reduce the size of the module. This design is intended for qualified specialists, so it is easy to design and make a printed circuit board for them. You can also find many other hobby designs to control DRL with other microcontrollers, including the popular “baby” ATTiny13. The functionality of the devices depends on the capabilities of the chip and the imagination of the developer.

What you need to make

To make a simple dcho controller with your own hands, you will need a relay. You can use any 12 volt car relay with a normally closed or change-over contact group. The advantage of such a relay is its closed design. The housing is good protection from external factors (water, dirt), so you do not need to take additional measures and the relay can be installed in any convenient place. When using another relay (it is possible to use any model for the suitable voltage with the corresponding contact group), additional protection measures have to be taken.

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Manufacturing of a daytime running lights controller

You can use any diode from 1N400X series or any other diode with suitable dimensions. Almost any semiconductor device will pass the voltage, but the current should be enough to operate the relay.

Manufacturing of a daytime running lights controller

For more complex circuits, you will need the electronic components shown in the schematics (any operational amplifier suitable for the supply voltage can be used as a comparator), as well as a board for the assembly. For microcontroller firmware you will need a programmer.

How to install the controller in your car correctly

First of all you need to find the wiring diagram of the car and thoroughly understand it. You need to determine which circuits the homemade controller should be connected to. Then you should determine the points where it is more convenient to connect (not all circuits are easily accessible, to access some you will have to disassemble some part of the car structure, remove panels, etc.).

The next step is to determine the routing of wires from the connection points to the controller terminals. It is difficult to give specific advice here – scheme and design of electrical equipment in different cars can differ greatly. When this question is clear, you can choose optimal place for controller board installation. It must be as protected as possible from high engine temperature, water or dirt ingress. The latter factor can be eliminated by putting the controller board in a casing, but the casing should not interfere with the cooling of the electronic key transistors. Therefore, a nice-looking option to wrap the board in a heat shrink is not a good idea.

The power circuit that supplies power to the LEDs must be equipped with a fuse for the appropriate current regardless of the version of the controller.

If you decide to make your own LED controller, you should immediately realize that the manufacturing and installation process is creative. It is not easy to find ready-made advice because of the differences in the design of the machine. It is necessary to be ready to make technical decisions. If this is not intimidating, you can proceed to the selection of the circuit and fabrication of the device.

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Electrical Engineer. A specialist in the design and operation of electrical products.

Analog or PWM high beam dimmer with an NE555

Schematic at

This article describes how to make with your own hands automatic daytime running lights, hereinafter simply LDL. The creation of running lights is considered on the example of the car, created on the basis of the PWM regulator on the timer 555. When installing this invention changes in the wiring of the car are minimal.

Headlight or main beam PWM dimmer controller on NE555

The problem is that not all cars are equipped with automatic switching off of headlights, if the engine is stopped. And if you leave the car and do not turn off the dipped headlights, the battery can easily run down. In addition, along with the headlights will remain on and the dashboard and tail lights and many other lights.

All this can lead to serious damage. It will have a negative impact on fuel consumption, power consumption. Lamps, especially halogen low-beam lamps, will not last so long after such “stress”. You may even have to repair your dashboard to replace different bulbs.

There is only one way out in this situation – installation of daytime running lights. This is what the light of the lamps used as a daytime running lights should look like:


There are several options to provide your car with exactly this light, corresponding to the traffic regulations:

-first, you can use dipped beam. This option is the easiest, but extremely unprofitable; -secondly, you can install LED daytime running lights in the bumper. But this option is not cheap, so not everyone is available; -third, you can use the high beam headlights as a kind of running lights, only at full throttle.

High beam is better suited for use as an afterburner, as it maximizes the illumination of the road. The difference in low and high beam headlights is shown in the following pictures:


Picture 18

Running Light Diagram.

Dash or PWM-adjuster for driving beam with NE555

In principle, the circuit does not differ anything special, but still there are a few details to pay attention to:

first, the circuit uses a field-effect transistor (p-channel); – second, the circuit uses a diode, which is included in the circuit power supply circuit in series.

If this diode is missing, the chip will burn out.

The printed circuit board.

Here you need a pair of transistors, always in parallel. You can use IRF5305 or IRF4905 transistors, both will do. It will depend on the resistance of the open junction. The lower the resistance, the better the result. There are jumpers on the board, one of them connects the gates of the transistors. The other jumper is under the chip. Any kind of diodes can be used, for example KD522. They are low-power diodes so they will work fine.

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Assembling the LEDs.

This device is assembled in the case of the mains power supply, at which the plug is cut off. The connections need to be plugged, so that later installation can be done easily. It is also necessary for external beauty. Photos of the work in progress:

Headlight or main beam PWM dimmer controller on NE555 Picture20 Making DXRs or PWM regulator for driving beam with NE555

Getting it set up.

If it is assembled correctly then the circuit will not need adjusting. And the device will work immediately after assembly. Such a device will last a long time and will bring only convenience in operation.


In order for the high beam to “blink”, the steering wheel switch has special contacts. The transistor must be connected to these contacts. The minus control pins must be connected to the oil pressure sensor. They should also be connected to the handbrake limit switch. To the headlight, low beam, the plus control leads must be connected.

To be on the safe side, you can make another plus side, it is not connected anywhere. If you want, you can increase the number of control pins and connect them with a diode, while remembering about the polarity.

How the daytime running lights work.

The following photos show how the daytime running lights work on a specific vehicle.

Daytime Running Lights or PWM Headlight Dimmer


Daytime running lights working with high beam.

It is immediately noticeable that the difference is minimal. The only visible difference is the more yellow light in the second picture. A huge plus of the daytime running lights is that the power consumption is many times less than that of the low beam operation.

The device starts working as soon as the engine starts and the oil pressure light goes out. An important point – the running lights will start working provided the dipped headlight is off and the handbrake is not pulled. If one of these prerequisites is not met, the daytime running lights will not work! If the running lights are at rest, the current they consume will not exceed 3 mA.

To be sure that the running lights are working properly, just look at the dashboard. There will be a high beam headlight bulb on, also at half peak. In order to see if the bulb lights up in daylight, you can install a blue LED instead.

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