At the end of 200 1, the Ministry of Public Security, the Ministry of Communications and the State Administration of Work Safety jointly issued the Notice on Strengthening Highway Passenger Traffic Safety Management, requiring long-distance passenger and freight vehicles to gradually install and use driving recorders that meet relevant national standards. The vehicle traveling recorder introduced in this paper is a product designed and developed by Jiangsu Hangtai Electronic Technology Co., Ltd., and it is one of the vehicle traveling recorders selected by Shaanxi Heavy Duty Truck Co., Ltd.
I. Introduction of Vehicle Driving Recorder
Car traveling recorder, commonly known as "car black box", is a digital electronic recording device that records and stores the state information such as vehicle traveling speed, time and mileage, and can realize data output through an interface. It unifies the advancement and practicability of microcomputer with the running state of vehicles, and provides a reliable scientific basis for analyzing and judging the running state of vehicles and handling traffic accidents. The vehicle traveling recorder produced by Jiangsu Hangtai Electronic Technology Co., Ltd. is one of many varieties imported by Shaanxi Heavy Duty Truck Co., Ltd., with P89C668 single chip microcomputer as the core processor, large-capacity E2PROM memory as the storage carrier, timing data acquisition and storage are realized through external precise timing interrupt, and data communication with microcomputer is realized through serial port interrupt or USB. The data sent by the automobile driving recorder is sent in the form of binary files and stored on the computer hard disk, and the historical driving state of the automobile is simulated and reproduced in the form of graphics by special computer software.
Second, the system composition of driving recorder
See figure 1 for the overall block diagram of the system. P89C668 single chip microcomputer is the core processor, which completes information collection, dynamic information storage and data processing, and realizes communication with microcomputer through serial port. Because of the time characteristics of various state information in the process of automobile driving, the data must be sorted according to time coordinates, and the data storage and memory adopt the combination of E2PROM solid-state storage and FRAM dynamic storage.
Third, the working principle of the information acquisition module
The recorder records two kinds of state information of automobile running: pulse signal from speed sensor and switch signal containing braking signal.
10 switch signals, such as turn signal, headlight, door opening signal and brake light signal, are isolated by photoelectric coupler and output by 74HC244 to single chip microcomputer for processing. In order to make the driving recorder record the information of automobile driving state in real time, the system uses the clock chip RX8025 to provide the time signal. RX8025 can automatically acquire and update the current time. The microcontroller can get the current time and calendar by reading the internal time scale register of RX8025, and can also initialize the chip's 10 time scale registers by selecting binary code or BCD code.
Speed sensors include electromagnetic induction, magnetic, photoelectric and Hall. No matter what kind of sensor, it outputs speed signal in the form of pulse. At present, most cars often use Hall sensors. The voltage generated by this sensor is very small, but the single chip microcomputer can only recognize the square wave signal of 0 ~ 5V. Therefore, after this voltage signal is input to the driving recorder, it must be converted into its output pulse signal through the amplification and shaping circuit, as shown in Figure 2. The principle is that the Hall sensor outputs a pulse signal Ui, which is amplified by an amplifier A, and then converted into a square wave signal of 0 ~ 5V by a Schmidt trigger and a transistor T, so that it can be recognized by a single chip microcomputer.
The system uses frequency method to measure the vehicle speed, that is, the number of pulses per unit time is accumulated, so as to calculate the vehicle speed at that moment. By counting the 32768Hz frequency output of RX8025, the sampling time of speed measurement is 0. 125s, and the number of pulses is recorded by setting the counting memory count. When 4096 pulse signals are accumulated, the CPU responds to the interrupt, clears the counting memory count, and the memory re-counts, and cycles in turn. Then the program calculates the vehicle speed according to the following formula. The formula for calculating the speed per125ms is
Where: VS—— driving speed per 125ms; The number of pulses in PS-125ms; T—— Vehicle characteristic coefficient.
Fourthly, information storage and processing module.
The data in the recorder should include two parts, one is the real-time data of the car (storing the data before and after the accident), and the other is the historical data of the car (storing the driving conditions of the car and the driver). Real-time automobile data is mainly used to analyze the cause and responsibility of accidents. Historical automobile data is used as a reference for accident analysis and evaluation of the running state of automobiles and drivers. Historical data is based on current real-time automobile data. The storage system for storing historical data is E2PROM(AT24C 1024) of ATMEL Company. Because the storage frequency of real-time data is higher than that of historical data (the national standard requires data to be collected at most once every 0.2s, with 20s as a storage unit, and real-time data needs to be stored at 10 times of 20s), the FRAM(FM 1808) of RAMTRON Company is selected as the system.
A Real-time data includes time, speed, 8 switches and * * * 10 semaphores. Set an address pointer of 1 in FM 1808, and save the real-time speed data of 20 seconds before the current time before stopping every time. The address pointer will be automatically incremented by 1, counting 10 times. Historical data includes time and speed. When processing, set the data buffer of 1 h in FM 1808. If the recorded data is overtime, save the data in this buffer to AT24C 1024. If the vehicle is powered off at this time, when it is powered on again, the hourly data will be saved immediately when it is powered on, and the buffer will be cleared. After counting in E2PROM for 360 hours, the data pointer will be cleared for cycle counting.
Verb (abbreviation of verb) serial communication module
The computer can read the data stored in the driving recorder at any time through the serial port. The serial communication between the driving recorder and the computer follows the RS- 232 serial communication protocol. During serial communication, the microcontroller reads out the real-time data stored in FRAM and the historical data stored in E2PROM in turn, sends them through serial port, and then sends them to the computer through MAX232 level converter.
6. The application of vehicle driving recorder in heavy-duty vehicles.
Steyr and F2000 Delong cars produced by Shaanxi Heavy Duty Truck Group Co., Ltd. can be equipped with driving recorders according to users' needs. The driving recorder introduced in this paper is one of the imported varieties of the company, and its external structure is shown in Figure 3. The recorder has simple installation and reliable performance. Main indicators: ① The nominal voltage of the main power supply is 24V, the range is 18 ~ 32V, the overvoltage is 36V, and the reverse resistance is 28±0.2V. ② The recorder can automatically enter the protection state after power failure, and the data stored before power failure will not be lost for 15 days. ③ The recorder can continuously record 24-hour data, and the recording time error is within 5 s ... ④ The recorder continuously records and stores the vehicle speed value and vehicle braking state signal corresponding to the real-time time time of 20 seconds before parking at intervals of 0.2s, and the recording times are 10. ⑤ The speed recorded by the recorder is km/h, the measuring range is 0 ~ 180 km/h, and the measuring resolution is equal to or better than1km/h ... ⑤ The recorder can record and store 8 channels of 360h data of different types of switches. ⑦ The recorder can continuously record the cumulative mileage of vehicles in kilometers, ranging from 0 to 0~999999.9 kilometers, and the resolution is better than 0. 1 kilometer. ⑧ The data analysis software of the recorder can display real-time corresponding data such as vehicle speed and turnout status in the form of graphs and tables, and can print out graphs and tables.