Design of car wireless black box based on MG2455 microprocessor

　　0 Introduction

　　The car black box is also called the car driving status recording system, which is mainly composed of a car driving status recorder, a handheld code reader and a management computer. The recorder is installed on the car to monitor and record the vehicle's driving data in real time; the handheld code reader consists of a handheld computer and application software, which is used to control and operate the recorder and read the data from the recorder through the RS232 serial port; the management computer is used to count, report, store and query the original recorded data.

　　1 System Principle and Structure

　　1.1 System Introduction

　　This system uses the MG2455 microprocessor as the core and designs a car wireless black box based on Zigbee wireless radio frequency technology. The detection of tire pressure and temperature communicates with the host through Zigbee technology. The system includes a wireless monitoring transmission device installed on the tire rim and a digital receiving and display device that can be installed in the driver's seat of the vehicle body. When the tire pressure and temperature exceed the standard, the system will sound an alarm.

　　The system also has a fatigue driving warning and recording function, which can effectively curb driver fatigue driving and ensure the safety of long-distance transportation driving.

　　1.2 Functions and indicators

　　(1) The vehicle operation and status information (such as temperature, tire pressure, etc.) at different times during driving is stored and displayed on the LCD screen. The storage frequency is 30 times/hour.

　　(2) The reference value can be set arbitrarily, and an alarm will be triggered if the indicator exceeds the normal range.

　　(3) When driving data is needed, the data can be directly read to a personal terminal such as a PC or PDA through the USB interface. The USB interface is a universal USB2.0 interface.

　　1.3 Implementation Principle

　　In the control system with the microcontroller as the core, all the processing of automobile signals and LCD display are completed by the MG2455 microcontroller. After A/D conversion, the sensing signals such as tire pressure and acceleration are transmitted to the microcontroller through Zigbee wireless communication. The wireless monitoring and transmission device includes: a pressure sensor, a temperature sensor, a differential amplifier connected to the pressure sensor, an attenuator connected to the temperature sensor, a microcontroller that receives the pressure signal from the differential amplifier and the temperature signal from the attenuator for calculation and processing, and transmits the signal to the digital receiving display through a transmitter and a filter through a resonant antenna, so that the driver can grasp the tire pressure and temperature status at any time. The microcontroller stores the clock signal and temperature signal received by the I/O port together with the tire pressure and acceleration signals received wirelessly in the FlashROM and displays them on the LCD module LCD6029. When the signal exceeds the standard, the system can actively alarm. The USB interface is connected to the serial port of the microcontroller through the conversion chip, and the information stored in the system can be exported to personal terminals such as PCs or PDAs.

　　1.4 Hardware Block Diagram

　　The system can be functionally divided into data acquisition part, data processing part, data storage part, communication part (USB communication), display part, tire pressure module, temperature module, and clock module. The hardware block diagram is shown in Figure 1.

　　1.5 Software Process

　　After receiving the data from the tire pressure monitoring module, temperature module, and clock module, the main microcontroller MG2455 transmits it to the controller via the SPI port. While receiving the data, the controller also needs to verify and process the data with complex algorithms, and judge the processed results. If the data exceeds the pre-determined range (such as overpressure, timeout, overtemperature, etc.), the alarm is immediately activated, and the driver is prompted by the buzzer that there is an abnormality; otherwise, the car is prompted to operate normally. In addition, the serial port is used to realize communication with the computer, which is convenient for querying and analyzing the recorded data, providing a basis for optimizing the control algorithm and analyzing traffic accidents. [page]

　　The system software mainly performs two functions: 1) Realize real-time detection and recording of vehicle driving status and alarm when fault is detected. 2) Upload recorded data to the host computer through RS232 port for daily management and accident diagnosis.

　　The program mainly includes: main program, digital quantity acquisition program, switch quantity acquisition program, pulse quantity acquisition program, data storage program, clock processing program, fault processing program, fault alarm program and serial communication program.

　　The main program flow chart is shown in Figure 2.

　　2 System Testing

　　2.1 Test Data

　　Data analysis shows that tire wear increases by 2% for every 1°C increase in tire temperature. Generally, the temperature should not exceed 80°C. When the temperature reaches 95°C, the tire is in very dangerous condition. Moreover, when the air pressure is too high, the tire cord is overstretched, the tire body elasticity is reduced, the rigidity is increased, the unit pressure is increased, the crown contact area is reduced, and the wear increases. The tread pattern is prone to cracks. Once it is hit by an obstacle during driving, it will cause internal cracks or explosions. At the same time, this system has fatigue driving (time monitoring), so when the tire pressure temperature exceeds the preset value and the driving time exceeds 4 hours, the system will sound an alarm. In terms of errors during transmission, the tire pressure measurement accuracy is ±0.5kpa, and the tire temperature is ±1°C.

　　2.2 Functionality

　　(1) It has the functions of collecting, recording and storing time, date and driving time. It can record continuous driving time. Since the traffic safety law stipulates that drivers must rest for at least 20 minutes every 4 hours of driving, it can monitor the driver's fatigue state. Once a violation is found, an alarm will sound and the information will be transmitted to the monitoring center. (2) The function of measuring, recording and storing the temperature and tire pressure of the vehicle while driving: a. The temperature measurement system detects the engine temperature of the vehicle and displays it in real time. It can alarm for abnormal high temperature conditions, thereby improving driving safety. b. The main function of the tire pressure and temperature detection system is to monitor the pressure and temperature data inside the tire and display it in real time. It can alarm for abnormal high pressure, high temperature and low pressure conditions, thereby improving driving safety. c. The running data is stored in a large-capacity serial Flash memory. Even if the power is off, the data will not be lost. d. It is equipped with a USB interface, and the data can be read directly with a USB flash drive or connected to a computer for reading.

　　3 Conclusion

　　This system has the functions of collecting, recording and storing time, date and driving time; car tire pressure, temperature, etc.

　　The monitoring system communicates with the host through Zigbee wireless radio frequency technology; the Flash memory stores data, and the data will not be lost even if the power is off; the USB interface is configured to read data directly with a USB flash drive or connect to a computer for reading; it has timeout (fatigue) alarm and recording functions, which can effectively curb driver fatigue driving and ensure the safety of long-distance transportation driving.