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Running lights control unit. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices

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From November 20, 2010, drivers were required to drive during the daytime in cars with dipped headlights or daytime running lights (DRLs) on. It is clear that driving with the headlights on is unprofitable from a financial point of view, so DRLs remain the best way out of the situation. They should turn on when the ignition is turned on or in such a key position that does not exclude the operation of the engine.

In many vehicles, the cigarette lighter socket only works when the ignition is turned on. Which contacts would seem to be the easiest to connect DRL, but many different accessories are often connected to this socket (power supplies, mobile phone chargers, etc.) and, turning on the ignition to supply power to this equipment, we, not wanting to In addition, let's turn on the DRL.

Running lights control unit
Fig. 1

I have developed a running lights control unit that automatically turns them on when the engine is running and turns them off when the dipped or main beam headlights are turned on. Its scheme is shown in Fig. 1. When the ignition is turned on, the + 12 V voltage of the on-board network is supplied through the closed contacts of the SA1 switch of the ignition lock to the upper DRL power wire according to the scheme. The engine is not running, and the contacts of the emergency oil pressure sensor (DADM) are closed to a common wire (to the housing), as evidenced by the corresponding indicator (lamp or LED) on the instrument panel. On the resistor R1, the voltage is zero, the transistor VT2 is closed and the running lights are off. After starting the engine, the oil pressure increases, the sensor opens and the +12 V voltage through the indicator goes to the resistor R1 and the capacitor C1 is slowly charged with a time constant R1d equal to 4,4 s. Transistor VT2 starts to open, and DRLs ignite smoothly.

Running lights control unit
Fig. 2

When the high or low beam headlights are turned on, a voltage of +12 V is supplied to the anode of the diode VD1 or VD2, the transistor VT1 opens and the capacitor starts to discharge through the resistor R3 to the common wire. The reverse process occurs - the transistor VT2 begins to close, and the DRLs gradually go out. When "blinking" the main beam, the capacitor C1 does not have time to discharge and turn off the running lights.

All parts indicated in the diagram are mounted on a printed circuit board with dimensions of 18x20 mm (Fig. 2). Resistors MLT-0,125 are used, the capacitor is imported, the transistor VT1 is any of the KT315 series, except for KT315Zh. The field effect transistor VT2 is installed without a heat sink and will be replaced, for example, by IRFZ46N or similar. The fusible insert FU1 is made in the form of a short piece of copper wire with a diameter of about 0,08 mm, taken from the MGTF-0,35 wire. On the printed circuit board, it is soldered from the side of the conductors, as shown in Fig. 2 thin "snake".

Running lights control unit
Fig. 3

Capacitor C1 and transistor VT2 (as far as the length of its leads allows) are mounted parallel to the board surface over the elements VD1, VD2, R1 and VT1, R3, respectively. The board is placed and fixed in the housing of the 75.3777 series automotive relay with a switching group of contacts. It is better to take the housing version of the relay with a flange for ease of fastening (Fig. 3). The internal stuffing of the relay is removed, and the released contacts are connected with flexible conductors with a cross section of about 0,5 mm2 with contact pads on the board. The DRL pads and the common wire are connected to pins 85 and 86, diodes VD1, VD2 - to 87, 88, and the output of the resistor R1 - to pin 30. The length of the conductors is selected locally, after which the board is fastened with hot glue to the lower part of the case (where there are contacts). The case may not be sealed if it is fixed vertically with the contacts down.

It should be noted that since DRLs are ignited when their negative terminal is shorted to a common wire, their cases should not have electrical contact with the metal parts of the car chassis, however, the bumpers of modern cars are made mainly of plastic, so this problem will not arise.

Connecting the unit to the car's electrical network is relatively easy. It is necessary to find a wire under the hood, on which the mains voltage +12 V appears when the ignition is turned on, from which running lights will be powered, as well as wires coming from the low and high beam headlights. In this case, if the dipped beam lamps continue to burn when switching to high beam, then the signal wire can only be removed from the dipped beam lamp, and the diodes VD1, VD2 should not be installed by applying a signal to resistor R2.

Next, you should decide where to get the signal to turn on the navigation lights after starting the engine. There are two options. The first is an emergency oil pressure sensor (DADM). This option should be tested for suitability. You will need a 20 kΩ resistor. We disconnect the wire from the DADM, connect one terminal of the 20 kΩ resistor to the wire, and the second to the "mass" of the car and turn on the ignition. If at the same time a low oil pressure signal is displayed, then the first option is not suitable. The second option is to use a contact to connect a lamp that indicates the health of the generator. The contact designations for the various generators are: D, D+, 61, L, WL, IND. This is a guaranteed option.

The display unit was repeatedly installed on cars and showed its best side. Everyone to whom it was installed was satisfied with its work, which I expect from those who want to repeat it.

Author: A. Baikov

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