Automatic switching on of car headlights and parking lights. Scheme, description

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Automatic switching on of car headlights and parking lights. 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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The design of devices for automatically switching on the external lighting of a car when driving continues to be of interest to our readers and authors. This article continues this topic. The author made his device on a PIC16F628-04I/P microcontroller with a small number of attachments.

As you know, since November 2010, an addition to the Road Traffic Rules has been in force, obliging drivers to drive with low beam headlights on when driving at any time of the day. The magazine provided a description of a device that allows you to automatically turn on and off the fog lights of a Zhiguli car (Dolgodrov A. “Automatic switch/switch of fog lights.” - Radio, 2011, No. 5, pp. 43, 44). The device turns on the headlights when the car's generator is running, when the voltage in the on-board network is above a specified threshold, and turns off if the voltage drops below this threshold. In my opinion, this is not the most successful operating algorithm, since in this case the car’s headlights will shine when parked with the engine running and, on the contrary, may turn off while driving. This situation is quite possible at minimum engine speeds, especially if powerful consumers of electricity are turned on, and even in winter.

Foreign-made cars and some modern domestic ones can be equipped with a device that works on a different principle. The automatic machine we bring to the attention of readers turns on the side lights and headlights of the car when it starts moving and turns them off a minute after stopping. It can be installed in cars that have an electronic speedometer that receives information from a speed sensor.

Rice. 1 (click to enlarge)

The schematic diagram of the machine is shown in Fig. 1 and is surrounded by a frame of dash-dotted lines.

Outside the frame in Fig. 1 shows: SA1 - car ignition switch; SA2 - switch for its external lighting; K1 - relay for turning on side lights; K2 - relay for turning on the low beam headlights. When the power is turned on, the microcontroller (MK) program DD1 PIC16F628-04I/P configures the RA0 port line (pin 17) as the input of the comparator built into the MK, and the RB1 port line (pin 7) as the output. With the start of movement, pulses from the path sensor through the circuit C1, R1, VD1, VD3 charge the storage capacitor C2. The voltage from this capacitor is supplied to the input of the comparator built into the MK. After the voltage on capacitor C2 reaches 1,25 V - the threshold of the comparator (set by software), a high level voltage will appear at the output of RB1. In this case, transistor VT1 will open and trigger relays K1 and K2. When the car stops, the pulses from the distance sensor will stop and capacitor C2 will begin to discharge through resistor R4.

After the voltage on capacitor C2 is below the operating threshold of the built-in comparator, the MK will begin counting the delay time for turning off the lighting. It is necessary so that the headlights do not turn off when the car stops briefly at intersections and in front of pedestrian crossings. After the delay expires, the MK will set the RB1 output low. Transistor VT1 will close and de-energize the relay windings K1 and K2. The lighting will be turned off. If capacitor C2 is charged again before the delay expires (i.e., the car resumes movement), the lighting will not be turned off. The duration of the lighting switch-off delay can be adjusted by changing the corresponding constant in the source code of the program and retranslating it. The necessary program lines are marked with appropriate comments.

Circuit R2, VD2, VD4 limits the voltage on capacitor C2 to a level safe for the microcontroller. As soon as the voltage on this capacitor exceeds the stabilization voltage of the zener diode VD2, a current will flow through the diode VD4, which will prevent further charging of capacitor C2. Zener diode VD7 protects transistor VT1 from breakdown by self-induction voltage pulses of relay windings K1, K2.

Based on the voltage level at input RB6 (pin 12), the microcontroller checks whether the lighting is turned on, which can also be turned on manually with switch SA2. If the lighting is already turned on when the movement begins, then no actions will be performed on the part of the MK. If the level on RB6 is high, when the movement begins, the MK will set a high level at output RB1 - the lighting will be turned on automatically.

To avoid false alarms of the second MK comparator from interference from the on-board network, current leakage along the surface of the printed circuit board (due to moisture, dust, etc.), the RA1 port line is connected to a common wire. Lines RB4, RB5, RB7 are also connected to common to avoid false interrupt calls when the signal level at these inputs changes.

Automatic switching on of car headlights and parking lights
Fig. 2

The required +5 V supply voltage is supplied from the DA1 L78L05CZ integrated stabilizer, the input of which is connected to the vehicle’s on-board network. The machine is assembled on a printed circuit board, the drawing of which is shown in Fig. 2. All resistors are MLT-0,25 type, capacitor C1 is K73-17, the rest are imported oxide ones with an operating temperature range of at least -40...+85°C. Instead of the 1N4754A zener diode, you can use any other one with a stabilization voltage of about 36 V. Since the device must operate over a wide temperature range, an industrial microcontroller is used. Instead of the PIC16F628-04I/P microcontroller, you can use the PIC16F628-20I/P.

The designs of modern cars are very diverse, and it is impossible to give specific recommendations for installing this device in the scope of one article. The general principles are as follows. After assembly, the board is placed in a small plastic box and installed under the dashboard of the car. It is most convenient to supply the supply voltage to the board from the dashboard, for example, from the “positive” power output of the speedometer or tachometer. Also, a signal from the speed sensor must be sent from the corresponding output of the speedometer to the input of the device. Then you need to find the connector for the side lights and low beam headlights switch. By turning the side lights on and off, use a voltmeter to find the connector contact, at which the on-board voltage is present when the lights are off, and zero when the lights are on. The wire from the anode of the VD5 diode is connected to the found contact of the connector. In the same way, turning the headlights on and off, find another contact of the connector, to which the wire from the anode of the VD6 diode is connected.

With serviceable parts, error-free installation and correct connection to the vehicle’s on-board network, the automatic control should start working immediately and does not require adjustment.

The microcontroller program can be downloaded from ftp://ftp.radio.ru/pub/2013/03/avtomat.zip.

See other articles Section Automobile. Electronic devices.

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