Car steering wheel control system based on Bluetooth technology

Most of the objects controlled in the slave control system use 5V signal level, so the STC89C516 microcontroller with 5V signal level is selected. Since the Bluetooth module uses 3.3V, a 100Ω resistor needs to be added between the serial port lines to match the voltage when the Bluetooth is connected to the STC89C516.

3.2.2 CAN bus control

Modern automobile control systems have many nodes, large numbers, and high real-time requirements, and a large amount of data information needs to be shared between different electronic devices [2]. The CAN bus is a serial multi-master controller area network bus. It has high network security, communication reliability and real-time performance, is simple and practical, and has low network costs. It can not only reduce wire connections, but also enhance diagnostic and monitoring capabilities. It is suitable for automobiles and general industrial environments. In this design, the CAN controller uses the SJA1000 of PHILIPS. The schematic wiring diagram of the in-vehicle system is shown in Figure 2.

3.2.3 Display module

The display module of the system adopts a 12864 LCD display module with ST7920 driver chip as the core, with 64*16-bit character display RAM and 64*256-bit graphics display RAM. The system displays the status mode called by the main control device and the progress of the function in real time on the screen in the form of pictures and characters. It has strong intuitiveness, which makes it easy for the driver to understand the parameters of various electronic equipment in the car in time and makes operation more convenient.

4 System Software Design

Software programming mainly includes two parts: Bluetooth communication software design and master-slave device application design.

Complete the initialization of the Bluetooth module on the PC, set it as master or slave, assign an address to the Bluetooth, and determine its baud rate to complete accurate and timely data transmission.

BC219159 and STC89LE516 communicate through the serial port. Data can be transferred to each other by using the serial port function in the program. Bluetooth is equivalent to an invisible wire that connects the master and slave devices.

4.1 Bluetooth communication software design

Data communication between two Bluetooth modules is achieved through HCI packets. HCI packets include command packets, event packets, and data packets. The data communication process generally includes the following six steps: Bluetooth module initialization, HCI flow control setting, query, connection establishment, data transmission, and disconnection.

This part of the program is mainly developed and implemented in C language under Windows XP environment with the help of CSR's BlueLab development platform.

4.2 Bluetooth Master-Slave Control System Application Design

The application programs of Bluetooth master and slave devices are relatively complex, and the software design follows the modular design concept. Figures 6 and 7 respectively show the flow charts of the master and slave systems. All program modules are developed and implemented in C language under Windows XP environment.

Figure 6 Flowchart of the master control device.

Figure 7 Flowchart of slave control device.

5 Conclusion

The steering wheel control system designed with the above scheme is powerful, cost-effective, stable, easy to maintain and develop. Experiments show that the whole system has good versatility and scalability and has application value.