Car steering wheel control system based on Bluetooth technology

Abstract: This paper introduces a design scheme of steering wheel control system based on Bluetooth technology. The electronic optimization design of the steering wheel panel switch of the car is realized by using Bluetooth transmission technology, which overcomes the disadvantage of having to look down to find the switch during traditional driving, so that most operations can be realized on the steering wheel, making car driving more convenient. The control system adopts a Bluetooth module based on the BC219159 Bluetooth chip; the main control device uses STC89LE516 as the controller, collects and processes the signal of the button on the steering wheel and sends it to the Bluetooth chip for wireless transmission; after the Bluetooth module of the slave control device receives the signal of the master control device, the slave control chip STC89C516 sends corresponding instructions according to different signals to control the use of the four major systems of air conditioning, audio, cruise control, and lights in the car through the CAN bus, and connects to the LCD display at the same time, which can facilitate the driver to control various devices. This system uses PWM to control the strength and weakness of each function to reduce hardware costs. Tests show that this system has the advantages of low cost, good reliability, high safety and strong versatility.

1 Introduction

High-tech applications have changed people's lives. While cars are basic means of transportation, people hope that driving them will be simpler and more convenient, and that they can communicate and exchange information with the outside world in a timely manner in the car.

Bluetooth technology can provide technical support for the realization of this new automotive electronic information system. Bluetooth technology can be used to connect various electronic devices in the car wirelessly to form a "vehicle area 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 short-range wireless spread spectrum communication technology, Bluetooth has the characteristics of small size, low power consumption, openness and interoperability. Compared with the traditional data transmission by cable and infrared, it has the following advantages:

(1) Strong anti-interference ability; when wireless laptops, mobile phones and other electronic devices with wireless communication functions are working, there will be a lot 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 one connection, the radio transceiver continuously "hops" from one channel to another according to a certain code sequence. Only the sender and receiver communicate according to this rule, thus avoiding interference; the instantaneous bandwidth of frequency hopping is very narrow, but through the spread spectrum technology, this narrow bandwidth can be expanded hundreds of times into a wide bandwidth, making the possible impact of interference very small. (2) No signal line connection is required, reducing costs and reducing the space occupied. (3) It has the basic characteristics of electromagnetic waves, has a large power, can increase the transmission distance, and has no angle and directionality restrictions. It has the ability to penetrate walls and can reflect and diffract between objects. (4) The power consumption is very low, many components can be connected at the same time, and the transmission speed is fast.

This article introduces a steering wheel control system based on Bluetooth technology, which uses a network solution that combines wired and wireless to form the entire control system.

2 System Design

This system realizes control functions such as cruise control, audio, in-car air environment, headlight lighting, etc. through buttons installed on the steering wheel.

The control system is designed based on Bluetooth technology, and its hardware components mainly include two parts: Bluetooth master device and Bluetooth slave device. The master device collects key signals through ZLG7289, and then sends them to the microprocessor STC89LE516 for processing. The microprocessor sends corresponding instructions and data to the Bluetooth module BC219159B according to different key signals. The Bluetooth module transmits instructions and data after establishing a link between the Bluetooth modules of the master and slave devices through the wireless network. The microprocessor of the slave device sends different instructions and data to the CAN bus according to the corresponding signals. Other vehicle systems connected to the CAN bus implement related functions according to the instructions, and the LCD displays various functional states. The hardware block diagrams of the Bluetooth master and slave devices are shown in Figure 1 and Figure 2 respectively.

Figure 1: Hardware block diagram of Bluetooth master device.

Figure 2: Bluetooth slave device hardware block diagram.

3 System Hardware Design

3.1 Main control equipment hardware design

3.1.1 Button part

The button positions are shown in Figure 3, which are divided into 4 areas, with 4 buttons in each area. To make the operation comfortable and simple, one-button multi-function is used to reduce hardware equipment and simplify operation, and 16 function buttons are set on the steering wheel.

Figure 3 Distribution of steering wheel button locations.

Function description: Key 1 is the cruise control switch button. Press key 1 once to enter the cruise control. Press key 2 to enter the setting or reset function. Keys 3 and 4 are the up and down option movement keys. Press key 1 again to exit the cruise control. Key 5 is the audio system start and stop button, and can switch FM/CD mode. The selection is based on the number of button presses (on→FM→CD→off). Key 6 is the program selection key. The related item is also selected based on the number of button presses. Keys 7 and 8 are volume adjustment keys. Key 9 is the air conditioning start and stop button. Key 10 is the temperature mode switch key. Keys 11 and 12 are temperature adjustment keys. Key 13 is the high and low beam switch control key. Key 14 is the fog lamp switch control key. Keys 15 and 16 are the headlight intensity adjustment keys.

3.1.2 Key signal processing module

The key signal processing is implemented by the keyboard scanning management chip ZLG7289. ZLG7289 uses the SPI serial bus to communicate with the microprocessor. /CS, CLK, and DIO are respectively connected to the three I/O pins of the microprocessor. KEY is connected to /INT0. The serial data is sent to the chip from the DATA pin and synchronized by the CLK end. When a key is pressed and the chip select signal becomes low, the data on the DATA pin is written into the buffer register of ZLG7289 at the rising edge of the CLK pin, and the key value is only allowed to be read when the /INT0 pin has a falling edge. In the absence of any key, the LED is on, and when any key is pressed, the LED is off.

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

Figure 4: Pin diagram of ZLG7289 chip.

Figure 5 Keyboard logic array diagram.

3.1.3 Bluetooth module

The core of BC219159 is the single-chip RF chip BlueCore2-External launched by CSR, which includes a radio transceiver, baseband controller hardware circuit and the protocols necessary to implement the Bluetooth application framework. The chip contains automatic calibration and built-in self-test procedures, which simplifies development, application, and product testing. When an external Flash with CSR Bluetooth protocol stack software is added, BlueCore2-External can form a complete Bluetooth system for audio and data communication [1].

The chip has few external components, and the RF receiver has a near-zero intermediate frequency structure. The high enough out-of-band cutoff performance index at the input of the low-noise amplifier allows the RF module to be used close to GSM and W-CDMA mobile phone transmitters. The chip uses an FSK monitor and has excellent performance in the presence of noise. The internal power amplifier has a maximum power output of +6dBm. The RF synthesizer is fully integrated in the core and does not require an external voltage-controlled oscillator, varactor tuning diode or LC tuner. The system's reference clock is generated by a built-in crystal oscillator with a clock range of 8~40MHz.

The Bluetooth module supports multiple communication interfaces such as USB, UART, PCM voice interface and SPI interface. There is 32KB RAM on the chip, which is used as a ring buffer to store the audio/data of each valid connection and the memory of the Bluetooth protocol stack function, and 8MB Flash; it supports point-to-point and point-to-multipoint network topologies, and can form piconet and scatternet.

The Bluetooth module of this system converts data into corresponding codes according to the Bluetooth protocol and sends them to the other party's Bluetooth device. Since BC219159 provides a standard UART interface, it can directly connect to the UART port of STC89LE516 in this system for communication.

3.2 Slave control equipment hardware design

The hardware design of the slave control device includes Bluetooth communication, CAN bus control, display and other modules. Due to space limitations, a brief introduction is given below.

3.2.1 Bluetooth module

The Bluetooth chip BC219159 of the slave device is connected to the microcontroller STC89C516. When Bluetooth starts working, its LED will flash quickly. If the Bluetooth module of the master device is searching for the Bluetooth slave module at this time, the two will automatically establish connection and communication through the automatic search function.