CAN bus is a serial multi-master station LAN bus. Its main principle is to connect the relevant controllers on the vehicle to realize the engine controller, gearbox controller, ABS controller, body controller, instrument and others. Controller communication. In addition to making the whole vehicle wiring harness smaller and more organized, and the weight of the whole vehicle is lighter, the CAN-bus system has the greater advantage of real-time sharing of vehicle information. The developed driving recorder is used to collect the car CAN bus data information in real time during the running of the vehicle, and store the data in the u disk, and transmit it to the PC as the carrier, and analyze the data by using the software on the PC. . Overcoming the previous field data acquisition system must have a computer mode, real-time understanding of various data changes during the operation of the car, synchronous recording of driving conditions, after the vehicle is tested or driven for a long time, the recorded data is used to analyze the driving performance of the vehicle and The operation of each component facilitates the calibration and design work.
System overall structural design
Due to the good characteristics of the CAN serial communication bus, it is widely used in field data acquisition systems, automotive manufacturing and aerospace industries. The CAN bus data recorder designed in this paper is applied to the Chery Automobile A5 model to collect and store the node data on the vehicle CAN network. A5 is the first self-owned brand domestic car that uses CAN bus bus system. Its CAN-bus is mainly used in the transmission department, and there are also a small number of applications in the body part, ITS department and information department. Real-time data acquisition for the A5, which is the first to use CAN technology, can be used to understand the changes in various data information during the operation of the car. It is of great significance for the development of A5 and all subsequent models.
When the CAN bus driving recorder is working, it should be hooked up to the CAN bus of the car to become a CAN node to collect CAN data information. As shown in Fig. 1, the system not only collects CAN bus messages in the car, but also collects analog signal quantities in real time as needed. The LCD screen is used to display the collected signal values, and has a power-down protection function. After power-on, the original data can be restored. The collected data can be stored in the u disk through the USB interface chip CH375 in addition to the real-time display of the LCD screen, which can be used by the experimenter to get back to the laboratory for analysis. To implement the storage function, press the memory switch. can.
Figure 1 System overall structure
According to the overall structure of the system, the hardware circuit mainly has the following major modules: main controller module, liquid crystal module, CAN driver module, power module, CH375 interface circuit module. The system CPU uses the MC9S12XD series of single-chip microcomputers from Freescale. It is the core of the control and communication part, not only responsible for system initialization settings and message reception, but also related data judgment processing and display. The chip integrates almost all analog and digital peripherals and other functional components required to form a microcontroller control system and data acquisition system. The main features are as follows:
(1) The MC9S12XD series has a unique XGATE coprocessor. The CAN signal reception in this system is completed by the interrupt program, and the interrupt handler is handed over to XGATE for processing, which will reduce the CPU load and improve the system's response speed. (2) With l6 analog-to-digital conversion channels, it provides hardware support for acquiring analog signals, and can be programmed to be accurate to 10-bit precision. (3) With 5 MSCAN modules, the CAN controller is integrated internally. The configuration of the CAN module is essentially converted into the configuration of the corresponding registers of the MCU, which is convenient and flexible to use. (4) Background debugging mode BDM support makes the debugging of the chip extremely convenient and speeds up the product development cycle. (5) A rich source of interrupts provides sufficient protection for the system to operate under non-operating system support.
Power module
The power of the recorder is taken from the 12V vehicle battery power supply. In addition to the system operation, the power supply is also responsible for the power supply of ignition, lighting, signal and other equipment. The power supply fluctuates greatly and the interference is serious. Because the car is in the process of driving, it may encounter road surface comparison. In the worst case, the power supply interface of the recorder may be loose or poorly contacted due to severe vibration, so the power module must be carefully designed to meet the demand. The schematic diagram of the power module circuit is shown in Figure 2, where U1 is the 6V backup power supply provided by the battery, U2 (main power supply) is the vehicle 12V power supply, the power supply module is divided into 2 channels, and the +5v voltage is stabilized by the 7805 voltage. Power is supplied to the liquid crystal, and the VCC converted by 4275 supplies power to the entire single chip and the auxiliary circuit. When the system is working normally, D1 is in the off state, and the backup battery does not work. Once the main power supply is lost, D1 is turned on quickly, and the backup power supply automatically starts to supply power to the system.
Figure 2 Power Module
There are two reasons for this design of the power module, as shown below:
(1) Adoption of backup battery. The recorder stores the collected data, and the collected data is sequentially written into the cluster allocated for the record file. When the acquisition ends, the experimenter disconnects the storage switch or the collection is forced to terminate due to the power failure, and the single-chip microcomputer needs to close the record file. An important deal. Closing a file means writing the actual length of the file and the total number of records collected into the file header. If the file is not closed properly, or because the power is too late to close the file, Windows will not be able to find the end of the file, and the PC software will not be able to open the file because it cannot find the end of the collected data. At this time, the collection work will fail. . In order to prevent the file from being closed due to power failure, the system uses a spare battery.
(2) The single chip and the liquid crystal are separately powered. When the main power supply works normally, the power of the whole system is supplied by the main power supply. Once the main power supply is powered off, the backup battery only supplies power to the single chip microcomputer, and the MCU completes the file processing, and the liquid crystal does not work due to power failure. Due to the large power consumption of the liquid crystal and the limited backup battery power, this separate 2-way power supply method not only provides the power supply for closing the file, but also saves battery power. Of course, the backup battery cannot be used for a long time, and can only be used for system emergency shutdown file processing. For this purpose, a power detection signal is designed. Once the main power supply is detected, the buzzer and the light-emitting diode are enabled to remind the user that the power supply is not supplied. Normal, the staff is required to check the recorder power connector.
CI-I375 interface circuit module
The USB interface chip in this system is selected from CH375 of Nanjing Yuheng Electronics Co., Ltd., which supports host mode and device mode. It has an 8-bit data bus and read, write, chip select control lines and interrupt outputs, which can be easily hooked up to the system bus of the microcontroller. It also has built-in firmware for handling the dedicated communication protocol of the Mass-Storage mass storage device. The external MCU can read and write the U disk directly in the sector as the basic unit. The read strobe signal RD#, the write strobe signal WR#, and the chip select signal CS# are both input signals and active low, CS# is the interrupt request output signal, and is also active low. The A0 signal is used to distinguish between commands and data. When A0=1, the command can be written. When A0=0, the data can be read and written. The 8-bit bidirectional data bus is connected to the PA port (PA0-PA7) of the MCU, and the parallel port is transmitted. The hardware supports automatic detection of the USB device connection function. When the host mode is normally connected, the ACT# pin outputs a low level. Therefore, the ACT# I pin is externally connected with a pull-up resistor and connected in series with an LED to indicate whether the USB device is connected. Normal connection.
When laying the PCB, try to make the 7805 chip on the edge of the board and the heat dissipation is better, and away from the LCD screen. Because in the actual process, after testing, the 7805 chip generates a lot of heat, if used for a long time and close to the LCD screen, it will affect the display effect of the liquid crystal. In addition, try to make the LED of the power module close to the power interface. The LED of the USB module is close to the USB module and is separated by color to facilitate user observation. The driving recorder developed by this system has been successfully applied to various road tests such as 30,000 kilometers and 50,000 kilometers of A5 vehicles, accurately recording important data during the driving process, performing performance analysis, fault analysis, and research for researchers. Calibration work provides an important data basis. Using a CAN-based driving recorder on a vehicle with a CAN bus can significantly reduce system complexity and reduce costs. For different models, only a small modification of the software without the need to change the hardware makes the recorder extremely flexible and portable, so it can be widely used in various models.
2.54mm (.100") Pin Headers
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