1 Introduction

High-tech applications have changed people's lives. At the same time as cars are the basic means of delivery, people also hope that the driving operation of cars is simpler and more convenient, and they can communicate and communicate with the outside world in a timely manner.

Bluetooth technology can provide technical support for the realization of this new type of automotive electronic information system. Bluetooth technology can be used to wirelessly connect various electronic devices on the car to form a "vehicle network". These devices include automotive electrical control equipment , Audio and video equipment, vehicle positioning and monitoring equipment, various sensors and their control systems, vehicle security systems and vehicle navigation systems.

As a new type of short-range wireless spread spectrum communication technology, Bluetooth has the characteristics of small size, low power consumption, openness and interoperability. Compared with traditional data transmission by cable and infrared, it has the following advantages:

(1) Strong anti-interference ability; when working on various electronic devices with wireless communication function, such as laptop computers and mobile phones with wireless Internet access, there is a large amount of electromagnetic interference to other electronic devices in the car. Bluetooth technology has the characteristics of fast confirmation and frequency hopping scheme to ensure link stability. It divides the frequency band into several frequency-hopping channels. In a connection, the radio transceiver continuously "hops" from one channel to another channel according to a certain code sequence. Only the transmitting and receiving parties communicate according to this rule, thus avoiding Interference; the instantaneous bandwidth of frequency hopping is very narrow, but this narrow bandwidth is expanded hundreds of times into a wide frequency band by spread spectrum technology, so that the possible impact of interference becomes very small. (2) The connection of signal lines is not needed, which reduces the cost and reduces the space occupied. (3) It has the basic characteristics of electromagnetic waves, has greater power, can increase the transmission distance, and has no restrictions on angle and directionality. It has wall penetration and can be reflected and diffracted between objects. (4) The power consumption is very low, many components can be connected at the same time, and the transmission speed is fast.

The steering wheel control system based on Bluetooth technology introduced in this article adopts a wired and wireless network solution to form the entire control system.

2 System design

This system realizes control functions such as constant speed cruise in the car, sound, air environment in the car, and headlight lighting through the buttons installed on the steering wheel.

The control system is designed based on Bluetooth technology, and its hardware components mainly include Bluetooth master control device and Bluetooth slave control device. The master control device collects key signals through ZLG7289, and then sends them to the microprocessor STC89LE516 for processing. The microprocessor sends corresponding commands and data to the Bluetooth module BC219159B according to different key signals. The Bluetooth module uses the wireless network to connect the master and slave control devices. After the link is established between the Bluetooth modules, the instructions and data are transferred. The microprocessor of the slave device sends different instructions and data to the CAN bus according to the corresponding signals. Other on-board systems connected to the CAN bus implement related functions according to the instructions. LCD Display the status of various functions. The hardware block diagrams of the Bluetooth master and slave control devices are shown in Figure 1 and Figure 2, respectively.

Figure 1 Hardware block diagram of Bluetooth master control device

Figure 2 Bluetooth slave control device hardware block diagram

3 System hardware design

3.1 Hardware design of main control equipment

3.1.1 Button section

As shown in Figure 3, the button position is divided into 4 areas, with 4 buttons in each area. In order to make the operation comfortable and simple, one-key multi-function is adopted to reduce hardware equipment and simplify operation, and 16 function buttons are set on the steering wheel.

Figure 3 Location of the button on the steering wheel

Function description: No. 1 key is the cruise control button, press No. 1 key to enter the cruise control, press No. 2 key to enter the setting or reset function, No. 3 and No. 4 keys are the up and down option moving keys, and then press No. 1 key exits the cruise at fixed speed; No. 5 key is the sound system start and close key, and can switch FM / CD mode, according to the number of keys selected (open → FM → CD → close), No. 6 key is the program selection key, also based on Press the key times to select related items. The 7th and 8th keys are volume adjustment keys; the 9th key is the air conditioner startup and shutdown key, the 10th key is the temperature mode switching key, the 11th and 12th keys are the temperature adjustment keys; the 13th key is the near and far light switch Control keys, key 14 is the fog light switch control key, and keys 15 and 16 are the headlight intensity adjustment keys.

3.1.2 Key signal processing module

The key signal processing is realized by the keyboard scan management chip ZLG7289. ZLG7289 uses SPI serial bus to communicate with the microprocessor, / CS, CLK, DIO are connected to the three I / O pins of the microprocessor, KEY is connected to / INT0, serial data is sent to the chip from the DATA pin, and Synchronized by the CLK terminal. When a key is pressed and the chip select signal goes low, the data on the DATA pin is written to the ZLG7289 buffer register on the rising edge of the CLK pin, and it is only allowed when the / INT0 pin shows a falling edge Read the key value. When there is no button, the LED is on. When any key is pressed, the LED is off.

Figure 4 and Figure 5 are the ZLG7289 chip pin diagram and keyboard logic array diagram, respectively, 4 row lines are connected to the SG, SF, SE, SD pins of ZLG7289; 4 column lines are connected to the ZLG7289 data lines DIG0 ~ 3.

Figure 4 ZLG7289 chip pin diagram

Figure 5 Keyboard logic array diagram

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