All about car tuning

A device for automatically turning on headlights. Automatic low beam switching on and off

The vast majority of modern foreign-made cars, especially prestigious versions, are equipped with a device that automatically turns on the headlights when certain or specified conditions are created.

Often this device is combined with a rain sensor or is triggered when the light level decreases, controlled by sensitive photocells. However, the use of the above options becomes insufficient when it comes to a car operated in Russian Federation. The “Road Rules” (hereinafter referred to as traffic rules) in force on its territory require the inclusion of low beam headlights while the vehicle is moving, regardless of the time of day and degree of illumination.

The appearance of this requirement in traffic regulations has caused the need for significant improvements in the electrical supply system not only for domestically produced cars, but also for foreign cars of the older age category.

The main requirements for a device or system that ensures automatic switching on of low beam headlights are:

  • Guaranteed automatic switching on of headlights when the vehicle starts moving.
  • Turning off the low beam when the vehicle is parked.
  • Economical consumption of electrical energy in all operating modes of the power unit.

Filling the created niche in the automotive spare parts market, the development of these devices was undertaken not only by enterprises specializing in electrical equipment for automobiles, but also by the so-called “traditional craftsmen”. The devices they offer, both ready-made and at the same level circuit diagrams, a great many. The devices differ not only in the principle of operation, but also in the complexity of their implementation.

1. Diagrams of automatic headlight switching devices

Let's look at a few possible options, providing automatic switching on of vehicle headlights.

1.1 One of the simplest and most effective schemes for protecting against turning on headlights when the car is not running is a circuit that provides supply voltage to the button (relay) for turning on the headlights through. Turning off the engine (starter) opens the headlight power supply circuit. The fears of some motorists about increasing the load on the chain are unfounded, provided correct connection devices.


1.2 The method of organization described below automatic switching on low beam provides for connecting an additional relay or relay electromagnet that turns on the headlights to the “battery charging” signal lamp circuit. The practical implementation looks like this (see diagram in Fig. No. 1):

  • add a five-pin relay to the circuit (type 90.3747);
  • We connect contacts “30” and “85” to the ignition switch;
  • contact “86” is connected to the terminal of the generator connected to the charge control lamp;
  • contact “88” is connected to the relay that turns on the headlights (or the headlight circuit fuse);
  • turning on the ignition ensures the supply of current to the windings of the relay electromagnet coil and its flow (through the generator winding) to the negative terminal;
  • the relay operates to open contacts “88” and “30”;
  • as a result of starting the engine and the subsequent start of operation of the generator, positive current comes to the terminal of the generator warning lamp;
  • disabling the relay leads to the closure of contacts “88” and “30”, that is, the low beam headlights are automatically turned on.

Using a diode in series with the relay coil and directed towards the generator will help prevent the occurrence of a "harmful" circuit. The headlights will light only if the circuit is unbroken, which is monitored by the “battery charging” lamp.

Figure No. 1

1.3 The third connection method is based on the use of an emergency oil pressure sensor in the power plant in the automatic headlight switching circuit. In fact, this method is a variation of the one described above. The difference is that the relay coil is connected to the pressure sensor rather than to the generator. The headlights turn on immediately after the pressure in the lubrication system rises to the required level.

A significant disadvantage of this scheme is the blinking of the headlights when the oil pressure in the system decreases and, as a result, the sensor is triggered (coasting, idling mode, etc.).

The schemes and methods discussed above that ensure automatic switching on of headlights are simple in technical design and do not require significant material costs for implementation. This is their undoubted advantage. However, a fairly large group of domestic car enthusiasts, due to lack of free time, technical illiteracy and other objective reasons, prefer to use factory-made devices.

2. The “AvtoSvet AS” device, as an alternative to homemade schemes

The functional purpose of the AutoLight AS device is to smoothly turn on the low beam headlights at the moment:

a) the vehicle begins to move;

b) starting the engine and achieving 10-100% of the rated power.

This allows you to significantly extend the service life of incandescent lamps.

The low beam headlights automatically go out when the side lights are turned on (mains voltage< 12,7 Вольт), зажигания. Схема подключения контроллера предполагает коммутацию «+», то есть включение в цепь «+» выключателя или реле.

Figure No. 2

  1. The device can operate in several ways:

The control wire of the controller is connected to the injector or hall sensor circuit;

Connection to the speed sensor circuit

2.2 Installation of the “AvtoSvet AS” controller on a car is carried out as follows:

  • disconnect the “-” battery terminal;
  • the red wire (D=1.5 mm) is connected through a 15-amp fuse to the power source (12 Volts);
  • a black wire (D=1.5 mm) is connected to the “╧” (“ground”) terminal;
  • a blue wire (D=1.5 mm) is connected to the low beam headlight circuit (“+” terminal ≤ 9 Amperes) after the relay;
  • a brown wire (D=0.35 mm) is connected to the input contact of the speed sensor;
  • The blue wire (D=0.35 mm) is connected to the input contact of the side lights or connected via a toggle switch to the “+” terminal of 12 Volts.

The conditions that determine the automatic activation of low beam headlights depend on the state of the controller loop:

The cut loop ensures that the light turns on when the vehicle starts moving;

The whole loop ensures that the headlights are turned on when the power plant is started.

Attention! Connecting the brown wire directly to the coil contacts Absolutely forbidden, since high voltage values ​​will lead to loss of controller functionality.

  • Avoid getting moisture inside the device;
  • prevent deformation of the controller due to mechanical and temperature loads;
  • Do not use gas-discharge lamps in the vehicle electrical system.


The law on the mandatory use of low-beam headlights when driving a car during daylight hours came into force a long time ago, but it happens that even professional drivers forget to turn on their headlights and start driving without light. Low beam headlights can be replaced with fog lights (FF) or daytime running lights (DRL), but this does not exclude the possibility of forgetting about the need to turn them on.

The proposed device is designed to automatically turn on headlights, DRLs or other light sources on a car. Its peculiarity is that it implements the “polite light” function, used on some expensive cars. The device can be connected to any car and configured to turn on any light source.

The polite light function has three main features:

Delay in turning on the headlights for the period of engine starting;

Delay for turning off the light after stopping the engine;

Forced switching off of headlights when starting the engine.

A delay in turning on the headlights is needed to facilitate engine starting in the cold season, while the headlights turn on 15 seconds after starting, allowing the engine to stabilize its operation. The light switch-off delay is convenient for those who leave the car in a parking lot or garage without an additional source of lighting. After turning off the engine, the headlights light up for about 2 minutes and then go out, allowing you to slowly get out of the car, pick up your things and leave the parking lot. Forcibly turning off the headlights at the moment of starting also makes it easier to start the engine, while saving headlight bulbs, especially xenon ones. Additionally, the device is equipped with an LED headlight indicator.

The device diagram is shown in Fig. 1. Pin 6 of the XP1 connector of the device is supplied with +12 V on-board voltage of the vehicle, and pins 1 and 2 are connected to the common wire (ground) of the vehicle. Pin 4 is connected to the ignition switch so that voltage appears on it only when the engine starts. Pin 5 is connected to any wire on which voltage appears after the engine starts. On some cars, this may be the control output of the generator; if there is no such output, you can connect pin 5 to the turn-on wire of an audio device, such as a radio. Then the headlights will turn on 15 seconds after turning the key in the ignition, regardless of whether the engine is running or not. Pins 7 and 8 are connected in parallel with the car's headlight switch.

After power is applied, transistor VT2 is closed, relay K1 is de-energized and the headlights are turned off, as indicated by LED HL1 starting to glow. After starting the engine, a voltage of +12 V appears on pin 5 and capacitor C1 begins to slowly charge. The charging time, and therefore the time after which the headlights turn on, depends on the resistance of resistor R3 and the capacitance of the capacitor. After charging capacitor C1 to the threshold voltage of transistor VT2, the latter opens, relay K1 is activated and the headlights turn on, and LED HL1 stops shining. Since +12 V is present at pin 5 while the engine is running, the headlights are constantly on. After stopping the engine, the voltage on it disappears and capacitor C1 begins to slowly discharge through resistor R4. The time the headlights remain on after the engine is stopped depends on the time constant of circuit R4C1. After the capacitor is discharged to a voltage below the opening threshold of transistor VT2, the latter closes, de-energizing relay K1, and the headlights go out. If, after stopping the engine, it becomes necessary to start it again, then at the moment the starter is turned on, +12 V is applied to pin 4 and transistor VT1 opens, quickly discharging capacitor C1 and blocking the activation of relay K1, i.e., the headlights are forced to turn off at the moment the engine starts .

The device is assembled on a printed circuit board made of foil fiberglass laminate with dimensions of 45x25 mm (Fig. 2). Field-effect transistor VT2 can be replaced with another powerful one with low open channel resistance (no more than 0.15 Ohm), for example, IRF540, IRFZ44. It is not required to install it on a heat sink. Transistor VT1 - any low-power n-p-n structures. The HL1 LED can be of any color; using a flashing LED is useful to attract the driver’s attention. Mount it in any place convenient for the driver. Relay K1 - ELZET LR-T78-12VDC or other low-power with a winding voltage of 12 V. The parameters of the timing circuits R3C1 and R4C1 are selected individually. No changes in their parameters were observed when the vehicle was operated in the cold season at low ambient temperatures. Appearance devices is shown in Fig. 3.

Additionally, for the convenience of controlling the device, you can include a three-position switch in the executive circuit of relay K1 by connecting it to the vehicle’s on-board network so that in one extreme position the device turns on fog lights or daytime running lights, in the other extreme position the low beam headlights would turn on, and in the middle (neutral) position the device had no effect on the vehicle's lighting.


Publication date: 24.07.2014

Readers' opinions
  • Viktor Bayakov / 04/21/2017 - 09:33
    or without a diagram - wire the speedometer speed sensor through the relay winding to the security system unit, the function of closing the doors at the beginning of the movement - let's go - the headlights are on - the lights are off
  • Viktor Bayakov / 04/21/2017 - 09:20
    or just one relay - without a circuit - starter - the ignition is not lit - 5 and 6 are lit, disconnect the jumper in all cases except the 1st
  • Victor / 04/21/2017 - 09:14
    It is advisable to place a switch-repair, etc.-forest swamp-garage in a break with the ground
  • Viktor Bayakov / 04/21/2017 - 09:10
    The 5th is simply connected to the sixth - the transistor vt1 and the divider are removed from the circuit - there is no need for extra ones because as on the ignition switch, when you turn the key to the starter position, terminal 5 is de-energized and the relay will turn off the lights - after starting, terminal 6 will be de-energized - the relay will turn on the headlights 3 15 sec - when the ignition is turned off, terminal 5 will be de-energized and the headlights will immediately go out.
  • Sergey / 07/26/2014 - 05:12
    The prefix is ​​certainly not superfluous for a certain type of people who get behind the wheel. my nephew assembled a couple of these, spending several hours (and he was constantly distracted from work). but I think that if you are forgetful, first of all, before you get behind the wheel, you need to see a doctor. otherwise you can forget everything in the world. a relative immediately wanted to install switches, but forgot to do so. I remembered when his wife reminded him of the need to clean the table. everyone into the forest! the berries are gone! ! !

Daytime running light (DRL)

DRL (Day Running Light) - control of car daylight

Finished, debugged and tested the DRL. I am posting the results for free repetition by anyone interested. The device is designed to automatically turn on the low beam when the vehicle starts moving and adjust the voltage on the low beam lamps depending on the driving mode. Increases traffic safety and extends lamp life.

Corrected diagram


DRL operation algorithm.
At the beginning of the movement, when the car reaches a speed of 6 km/h, the device smoothly turns on the low beam lamps up to 75% of the on-board voltage and maintains this value until a speed of 69 km/h.
In the range from 70 km/h to 94 km/h, 85% of the on-board network voltage is set.
In the range of 95 km/h and above, 95% of the on-board network voltage is set.
After stopping the car for more than 22 seconds, the voltage drops to 30%.
When movement is resumed, the voltage is again set in accordance with the algorithm described above.

When the driver turns on the low beam using the standard switch, the voltage is set to 100%.
After turning off the ignition, the lamps remain on for a few seconds and then go out.

If we take into account only the fact that to increase safety, constant operation of the car with the lights on is required, then:
- It’s nice when the neighbor turns on and off automatically.
- Halogen lamps last much longer due to smooth switching and reduced voltage.
- Dimensions last much longer due to the fact that they are not turned on during the day when they are not needed.
- The generator belt lives longer due to the fact that the load on it is halved.
- Generator bearings last longer for the same reason.
- Fuel consumption decreases slightly. According to some data, gasoline savings reach $15...25 per year on average per driver.

If you don’t care about safety and don’t turn on the lights during the day, then there’s no point in installing the device, because... all its bonuses are only in comparison with simply turning on the low beam and dimensions using the standard means of the car. In this case, there is only one plus - smooth start lamps

“Follow me home” mode - guide me home, 30-second delay to turn off the neighbor - so you can walk home in the dark.
In my scheme, this mode turned out by itself. The fact is that after turning off the ignition and de-energizing the DRL continues to work on the energy accumulated in the capacitor and the low one continues to burn even after I set the car alarm and am already on my way home. With the capacitor indicated in the diagram, DRL works for approximately 8-10 seconds, depending on humidity and air temperature. If you install a capacitor with a larger capacity, the light will last even longer. I think that the glow time can easily be increased to one minute if you install a 3000...4000 uF capacitor. So, we can confidently say that this “follow me home” in this scheme is not a bug, but a feature.

And walking home in the dark has actually become much more convenient. True, the neighbors are already fed up with their constant hints that I forgot to turn off the lights.

Notes on the manufacture of the device.

The conductors on the board between legs 1,5,3 of the BTS555 key and the corresponding terminal block contacts must be carefully soldered and reinforced with copper wire soldered on top of the conductors.
The jumper wires marked on the board are soldered in first.
You can program the microcontroller through the ISP connector located on the board. The ISP connector pinout is shown in the ISPHEADER.JPG file.
The installation of microcontroller fuses is shown in the fuses.jpg file.

Connecting the device to the car.

Pin 1 (SPD input) is connected to the output pin of the speed sensor with a resolution of 6 pulses per meter.
Contact 2 (ON - input) is connected to the standard wiring wire that supplies +12 volts to the low beam lamps, which must be disconnected from the lamps in advance.
Pin 3 (GND - input) ground.
Pin 4 (IGN - input) +12 volts, which appear when the ignition is turned on and disappear when turned off. Under the hood you can take it directly from the speed sensor.
Pin 5 (BAT - power input) +12 volts from the battery. Connect to the battery through a 15 amp fuse.
Pin 6 (OUT - power output) +12 volts. PWM control for low beam lamps.
It is connected to the lamps instead of the standard wire disconnected from them, connected to pin 2 (ON).

Archive (circuit diagram, firmware - corrected) of the entire device is possible.

The device must be manufactured by ourselves; we do not supply manufactured boards and components; soon a commercial version of DRL will be on sale, completely different from this one.

Changes to the traffic rules introduced in November 2010 oblige the driver of a vehicle to turn on daytime running lights, or low beam headlights, or fog lights, regardless of the time of day and visibility conditions.

This device will be a good addition for those vehicles that are not equipped with automatic low beam headlights. The circuit presented in this article is designed to automatically turn on the headlights when the car engine starts. As you know, a running generator creates a voltage in the on-board network in the region of 14...14.4 V, and this is higher than the battery voltage (12V).

The machine’s circuit monitors the voltage in the car’s network, and if it exceeds 13.2 V, then after about 1 second it activates two relays. The first relay is used to power the side lights and instrument panel, the second is used for daytime running lights. running lights or low beam headlights. After the engine is turned off, the lighting turns off.

The schematic diagram is shown below. Comparator DD1.1 () compares the reference voltage coming from the 5.6 V zener diode (VD2) with the voltage coming from R1, R2, R3. R3 is used for fine tuning so that the machine responds to an input voltage in the range of 13.2...13.3.


Resistor R5 between the comparator output and the non-inverting input contributes positively feedback, ensuring the comparator operates with hysteresis. For the comparator state to change again, the voltage must drop below 10.6 V.

Therefore, there is no fear that as a result of any heavy load on the vehicle's on-board network, the headlights will turn off. This will happen only after the ignition is turned off, or, for example, when you try to start the engine with the starter.

The chain of elements R6, C3 is responsible for the delay in turning on the headlights after starting the engine. For the specified values, the delay is approximately 1 second. To implement this delay, the second comparator DD1.2 is designed. It compares the voltage across capacitor C3 with the reference voltage obtained from the zener diode VD2.

A transistor is connected to the output of comparator DD1.2, which controls the output relay. Diodes VD3 and VD4 are connected to the relay coils, parallel in the opposite direction, protecting the transistor from voltage surges when the relay is turned off. Diode VD1 protects against power connection errors (reversal). The load capacity of the circuit depends on the relays used.

To configure the device you need adjustable block power supply or 13.2 V voltage source. Move potentiometer R3 to the extreme left position. Then we drop the power to 13.2 V. Gradually rotate potentiometer R3 to the right until we hear the relay turn on. Then we reduce the voltage and the relay should turn off. We increase the voltage again to check. A correctly adjusted circuit should turn on at a voltage of 13.2...13.4 V.

The operation of this circuit has been tested in Proteus:


(12.6 Kb, downloads: 21)

The wires from the relay must have a minimum cross-section of 1 mm 2. It is worth additionally installing a power switch on the case in order to be able to turn off the machine in some cases.

A small drawback of this scheme is the fact that the low beam headlights will be on even when switching high beam. Operating the lamp this way is not recommended and will significantly reduce its service life. Hence the recommendation - during long night trips, it is recommended to turn off the machine using the switch on the body.

Automatic switching on of headlights is necessary to turn on the headlights in the event of a sharp deterioration in visibility without driver intervention. In some countries, it is necessary to turn on the headlights when the vehicle is moving.

On foreign cars, automatic headlight switching is installed, for which a corresponding sensor is used. Often this sensor is combined with a rain sensor attached to the windshield. The principle of this sensor is based on measuring illumination using photocells.

But this method is unlikely to be suitable for a domestic car owner. According to the rules traffic Low beam headlights must be turned on not only at night, but also during the day. When this requirement arose, there was a need to automatically turn on the headlights when the car is moving and turn them off when parking, for economical use of energy and to prevent leaving the headlights on when parked. According to the laws of the market, electrical equipment companies for automobiles and craftsmen immediately responded to this need. The principle of operation is different for all, depending on what the car owner wants to get and what costs and complications of the scheme he wants to go to. Let's look at some of the most common schemes.

A way to turn on for the forgetful.

The most simple circuit Automatic headlight switching on protects against driver forgetfulness and prevents headlights from turning on when the ignition is off. On most cars this is done during design at the manufacturer, and where it is not implemented it can be easily done. To do this, simply supply power to the power button or headlight relay through the ignition switch terminals, which are closed when the ignition is turned on, but open when the starter is turned on.

This method has a very important advantage: simplicity. There is an opinion that turning on the headlights will cause additional load, but this is not the case. If the connection is made correctly, then when the starter is turned on, the headlights will turn off. Conclusion: a simple, reliable method that does not require costs.

Automatic switching on of headlights via relay.

The second way to implement automatic headlight switching is to connect the electromagnet of the headlight switch relay or an additional relay to the generator excitation circuit, or rather the charging signal lamp circuit. This method is suitable for almost all modern cars.


To implement it, you need to add a five-pin relay of type 90.3747. Connect the wire from the ignition switch to pins 85 and 30. Connect pin 86 to the generator terminal to which the wire from the charge control lamp is connected. Connect pin 88 to the headlight relay or directly to the fuses protecting the headlight circuit.

IN in this case when the ignition is turned on, power from the ignition switch, the relay electromagnet coil, goes to minus through the generator winding, and the relay is activated and opens contacts 30 and 88. After the engine starts and the generator starts operating, a plus appears at the output of the generator warning lamp. The relay turns off and closes contacts 30 and 88, turning on the headlights.

To prevent a harmful circuit in this case, it is advisable to use a diode connected in series with the relay coil directed towards the generator. In this case, the headlights will light only when there is a charging current, subject to the integrity of the circuit, which can be monitored by the battery charge lamp.

Automatic switching on of headlights via a pressure sensor.

In the third connection method, automatic turning on of headlights, Kulibins suggest using an emergency engine oil pressure sensor. The connection diagram is identical to that described earlier, only the relay coil is connected not to the generator, but to the emergency oil pressure sensor. In this case, the headlights will light up immediately after pressure appears in the lubrication system. The disadvantage is that the headlights turn on regardless of the serviceability of the generator. When the oil pressure is low at idle, if the engine condition is not the best, the headlights will begin to flash when the sensor is triggered.

Only the simplest and possibly primitive ways of implementing automatic headlight switching are discussed here. On the Internet you can find many more schemes, both simple and quite complex. Also in stores they can offer you ready-made blocks to implement this function.

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admin 06/06/2013