CAN bus engineering vehicle remote monitoring system based on GPS/GPRS technology

　　With the rapid development of industrial modernization, there are more and more types of engineering vehicles and their functions are becoming more and more powerful. Engineering vehicles play a vital role in engineering construction. Their operating conditions and working conditions are complex and changeable, and the working environment is harsh, which greatly increases the failure rate. How to remotely monitor the operating parameters of engineering vehicles through various advanced technologies and to scientifically command and dispatch them is an important research topic in the engineering vehicle industry and has very important practical significance.

1 Overall system structure

The CAN bus engineering vehicle remote monitoring system 　　proposed in this paper obtains vehicle operation information through the CAN bus of the on-board electronic control unit ECU , and uses GPRS wireless network communication means to remotely monitor and dispatch the vehicle.

　　The architecture of the engineering vehicle remote monitoring system is mainly composed of a control center and a vehicle-mounted mobile terminal . The vehicle- mounted terminal device obtains the real-time operating parameter information of the vehicle through the CAN bus interface module, and after combining the GPS positioning information, sends the information to the monitoring center through GPRS. The control center analyzes the received data and displays the specific location and other parameter information of each vehicle on the screen in real time. At the same time, the control center transmits corresponding control instructions according to the specific situation of each vehicle to remotely control the vehicle in real time.

Figure 1 Overall system diagram

2 Hardware Design

　　The system uses C8051F040 as the core module, and combines GPS module, GPRS communication module, CAN bus module, storage module and power module to realize the monitoring, display, recording and alarm of the operation process status of engineering vehicles. The system structure block diagram is shown in Figure 2.

Figure 2 System structure diagram

　　2.1 MCU Module

　　This system uses Xinhualong's C8051F040 microcontroller as the core control unit. The chip has an instruction core that is fully compatible with MCS-51 and uses pipeline processing technology to improve instruction execution efficiency; it integrates JTAG and supports online programming; it uses low-voltage power supply (2.7-3.6 V), because the on-board power supply of engineering vehicles is 24V, which must be converted to the voltage required by each module of the system through a power conversion module. It has multiple bus interfaces, and the two UART ports can realize full-duplex communication. The communication baud rate can be set separately, which can be used for GPS signal reception and GPRS communication interaction respectively.

　　In addition, the CAN controller integrated in it complies with the CAN2.0B protocol and has 32 message objects. Each message object has an independent address and can be configured to send or receive data. The working bit rate can reach 1Mpbs. The CAN bus controller is used to communicate with the ECU of the engineering vehicle to obtain the real-time operation data and fault data of the vehicle. It can be seen that the selection of this chip can fully utilize the existing functions and greatly simplify the design of the system peripheral circuit.

　　2.2 GPS Positioning Module

　　The engineering vehicle remote monitoring system uses GS-87 as the GPS module, which is a high-performance, low-power intelligent satellite receiving module. The operating voltage of GS-87 is 3.3V, and it can be directly connected to the microcontroller for serial communication; GS-87 follows the NMEA_0183 standard, and the positioning accuracy can reach within 10m, which can meet the positioning requirements of the vehicle. The microcontroller is connected to GS-87 through the serial port, and the information received by GPS is processed through programming, and the information required by the user is extracted to communicate with the monitoring center and stored in the external expansion memory module.

　　2.3 GPRS Communication Module

　　The engineering vehicle remote monitoring system uses MC55I as the GPRS module, which is an important part of establishing communication between the vehicle-mounted mobile terminal and the monitoring center. Its advantages are permanent online and fast data storage. Its GPRS is charged by traffic and the working voltage is 3.3 to 4.8V. The module is embedded with TCP/IP protocol stack and connected to the microcontroller through the serial port. The microcontroller uses AT commands to control the GPRS module to communicate with the monitoring center server , and sends the real-time information of the vehicle to the monitoring center through the GPRS module of the vehicle-mounted mobile terminal and receives the command information from the monitoring center.

　　2.4 CAN bus module

　　2.4.1 CAN controller

　　The C8051F040 microcontroller used in this system has an integrated CAN2.0B controller. You only need to program its registers to set its working mode, control its working status, and send and receive data.

　　2.4.2 CAN transceiver

　　C8051F040 integrates a CAN controller. To enable the CAN bus to operate, a CAN transceiver must be connected to the microcontroller to perform electrical conversion and convert the logic level into a balanced differential code. The commonly used CAN transceiver is TJA1050 produced by PHILIPS. To prevent the influence of strong external electrical signals on the system, the microcontroller and TJA1050 are connected after being isolated by a photoelectric isolator 6N137; capacitors and resistors must be added to the nodes at both ends of the CAN bus to absorb the signal and avoid signal reflection.

　　2.4.3 Data transmission line

　　At present, there are two main CAN lines on the car, one is a high-speed CAN for the drive system, with a rate of 500kb/s; the other is a low-speed CAN for the body system, with a rate of 100kb/s. They are bidirectional and transmit the same data, respectively called CAN high line and CAN low line. The main connection objects of the drive system CAN are: engine control unit (ECU), automatic transmission controller, anti-lock brake controller (ABS), anti-skid controller (ASR), airbag controller (SRS), active suspension controller, cruise system controller, electric steering system controller and instrument cluster signal acquisition system, etc., which are all systems directly related to controlling the driving of the car. They require strong real-time, continuous and high-speed signal transmission. The main connection objects of the body system CAN are: front and rear light control switches, electric seat control switches, central door lock and anti-theft control switches, electric rearview mirror control switches, electric window lift switches, air conditioning control switches, etc. They do not require high real-time information transmission, but the number is large. Figure 3 shows the schematic diagram of the CAN bus communication module.

Figure 3 Schematic diagram of CAN bus communication module 

3 Software Design

　　3.1 CAN bus interruption sending and receiving tasks

　　According to the configuration of most automotive CAN buses, the terminal's CAN bus is also configured with a rate of 250K and works in basic CAN mode. The CAN bus receives data in an interrupt mode. The interrupt program puts the received data into a receiving data buffer that can accommodate 10 frames. The CAN bus task scans the buffer and takes out all the buffer data for processing. The CAN bus generally transmits short frames of fixed length of 8 bytes. Each frame of data is accompanied by an ID number, and different data frames are distinguished according to different ID numbers. Generally speaking, the ECU will send out several data frames with different ID numbers at a time. According to the manufacturer's data frame protocol, real-time vehicle operation data and fault alarm data can be obtained from it, including: water temperature, oil temperature, oil level, oil pressure, engine speed, vehicle inclination, alarm value, etc. Send messages to each node at the same time. The CAN bus interrupt receiving and sending task flow chart is shown in Figure 4.

 
Figure 4 CAN bus interruption receiving and sending process

　　3.2 Main program tasks

　　After the vehicle terminal is powered on, each module is initialized and interrupts are enabled. The GPS starts to obtain positioning information. The microcontroller is programmed to process the received data and merge it with the real-time working information of the vehicle obtained by the CAN bus task to form a frame of data. Once the system is running, the GPRS communication task starts to log in to the network through AT commands and stays online. Then it is ready to receive data sending requests from other tasks and send data to the remote server . The remote server parses the data according to the communication protocol and sends it to the database. Remote users can browse the database content through web pages to monitor and dispatch engineering vehicles. The main program flow chart is shown in Figure 5.

Figure 5 Main program flow chart

4 Conclusion

　　The system adopts modular design in hardware, which greatly improves the hardware reliability; the software also adopts modular programming, which makes the system easy to maintain and upgrade. This system uses GPS positioning technology and GPRS wireless network communication technology, combined with the vehicle CAN bus, which can effectively reproduce the location and operation of engineering vehicles in real time on the remote Internet terminal, ensuring the effectiveness, timeliness and safety of synchronous monitoring. After actual application testing, the operation effect is good, and it has good promotion value and application prospects.