This wave of operations makes your car's headlights more "smart"

No matter how cars evolve, there is one element that must be ranked at the top priority, and that is safety. Therefore, many efforts to make cars smart are centered around safety-related vehicle components. As one of the most important safety components of a car, the headlights of a car , commonly known as "headlights", are naturally also on this list of smart features.

The core function of car headlights is to provide drivers with sufficient illumination to ensure visibility for driving safety when ambient light conditions are poor. Therefore, in many anthropomorphic cartoon car images, headlights are portrayed as the eyes of the car, which is not an exaggeration. Even in autonomous driving with millimeter-wave radar and lidar, car headlights are still indispensable, because in terms of object and traffic signal recognition, there must be sufficient visibility to ensure that the camera can quickly and accurately obtain visual information.

However, the position and angle of traditional car headlights are fixed, which will inevitably cause some troubles in actual driving. For example, when the vehicle turns, the direct headlights cannot effectively illuminate the blind spots inside the curve, which will cause a safety hazard. For another example, when the vehicle goes uphill or speeds up, the headlights will appear too close; while when going downhill or slowing down, the headlights will be far away.

To solve this problem, people have come up with a solution called Adaptive Front- lighting System (AFS) . As the name suggests, it allows the headlights to automatically adjust the angle of the light according to the actual conditions such as the steering angle of the car, the posture of going uphill and downhill, acceleration, etc., to obtain the best lighting range and brightness.

Specifically applied to the two typical scenarios mentioned above - when the vehicle turns, AFS will obtain data from the steering wheel angle sensor, and then control and drive the headlights to rotate an angle to the inside of the curve in the horizontal dimension, so that the road ahead is filled with lights; when the vehicle goes uphill or downhill or accelerates or decelerates, AFS will adjust the illumination angle of the headlights up and down according to the data transmitted from the front/rear body height sensors and acceleration sensors, raising the illumination angle when going uphill or accelerating, and lowering the illumination angle vice versa, to obtain a reasonable visibility distance.

Figure 1: Using AFS to adjust the left and right illumination angle of the headlight (Image source: ON Semiconductor)

Figure 2: Using AFS to adjust the up and down angle of the headlight (Image source: ON Semiconductor)

As an active safety technology, a typical AFS system is an intelligent control system composed of sensors, main controllers, actuators and stepper motors. Usually, a headlight will have two sets of actuators and stepper motors to drive the headlight to adjust the direction in up/down and left/right dimensions.

In order to promote the application development of AFS technology, Avnet has launched an AFS demonstration board system, which is a very valuable reference design for users when developing products.

Figure 3: AFS demonstration board system launched by Avnet

From the system block diagram of Avnet's AFS demonstration board, we can see that the solution includes two core devices: the main controller and the stepper motor driver.

Main controller MC9S08AW32 from NXP is used. It communicates with the on-board sensors via the LIN bus and sends control instructions to the stepper motor driver via the SPI interface. MC9S08AW32 belongs to NXP's low-cost, high-performance HCS08 series 8-bit MCU family. It integrates an enhanced S08 core. When the main frequency is 20 MHz, it can achieve a minimum instruction cycle time of 50ns at a low voltage of 2.7V. MC9S08AW integrates third-generation flash memory, and peripheral resources such as clock, ADC, and interface are also very rich, which is very suitable for industrial control and automotive industry applications.

Another core device in the solution is the stepper motor driver , which uses STMicroelectronics' L9942, a bipolar stepper motor driver with different subdivision modes and programmable current configuration tables. The supported stepping modes include full step, half step, fine step, and micro step. Users can also set low speed, high speed, mixed and automatic attenuation modes through programming, with high control accuracy and flexibility. The direction adjustment of car lights is one of the typical applications of L9942.

Figure 4, Avnet's AFS demo board system block diagram

Based on these two high-performance chips, the functions implemented by Avnet's AFS demo board system include:

• MC9S08AW32 controls the stepper motor driver chip L9942 through the SPI bus to adjust the headlight position in both horizontal and vertical directions.

• The 4 buttons on the board can control the headlights to move in 4 directions

• The data of L9942 register can be sent to the computer through URAT to monitor the working status of the stepper motor in real time

• LED circuit board allows the stepper motor to be displayed running or stopped

• L9942 Bipolar stepper motor driver with subdivision drive (1/8)

• Each output has short-circuit protection measures such as no-load, overload current, temperature alarm and thermal shutdown

• Current fully programmable

Such a solution can obviously lay a good foundation for developers to explore AFS. In the future, with the development of vehicle intelligence, the connotation of AFS will become richer. For example, in addition to direction adjustment, the headlights can also adjust the intensity of light in time according to the speed and direction of the other vehicle when meeting (data provided by the on-board radar) to avoid safety risks caused by glare. AFS can also be expanded from the control of a single headlight to the control of an on-board LED matrix.

In short, after a series of "operations" by AFS, the car's headlights and even the entire vehicle lighting system will become more "smart", giving you a different experience.