Design Of OBD-? Universal Vehicle Diagnostic System Based On ARM

With the improvement of people's quality of life,the rapid development of transport,more and more people can enjoy the convenience of the car.meanwhile,the car also caused a lot of problems.The environmental pollution caused by the car is becoming more and more serious,and more and more traffic accidents happen frequently.Although the relevant departments has taken a single or double limit line,optimize travel routes,etc.,the better way to solve these problems is to develop good driving habits after understanding the operation of the car,and timely maintenance of the car.This paper designs a vehicle fault detection system based on OBD-II diagnostic protocol,which can help the driver understand the situation of the car.This diagnostic device can be used between large vehicles and small vehicles,and taking the Android phone as the display interface,through Bluetooth to complete the communication between them.In this paper,the vehicle diagnostic technology has been studied and analyzed.CAN bus technology and K-line technology are selected as the research object according to the bus technology currently used.The application formats and some key technologies are introduced respectively,The last,there has a comparative study of the three diagnostic protocols,including their detection principle,the format of data communication,meanwhile,also showing the meaning of the vehicle diagnostic fault code and the diagnostic interface standards.Vehicle diagnostic terminal is based on embedded technology,and use STM32F407VGT6 as processor.In the design of the use of two methods to collect the data of the car's ECU;the first is for the use of car CAN line,SAEJ1939 diagnostic protocol and ISO15765 diagnostic protocol,to obtain data,this approach mainly by the MCU controller and TJA1050 transceiver and the OBD Diagnosis interface of the car is connected to achieve two parts function of the data processing;one part is the communication between transceiver and the car,the car is receiving the message responding the request of upper computer,the requested service type determined by the mobile terminal,which using the Bluetooth on phone to inform the main control module;The other is the CAN controller to capture and process the data on the CAN bus.The second way is to obtain data for the KWP2000 diagnostic protocol of K-Line,to design the circuit of level conversion which establish a communication to the car's ECU,and finally the bus level is compatible with the MCU level.The collected data is hierarchically analyzed according to the corresponding the frame format of diagnostic protocol.The design also uses the GPS and GSM module to communicate with the user,in the event of a failure,notify the user by message.The interface of data displaying uses Android system and simplify design.The home page are made of the medule of real-time data,fault diagnosis,driving habits and driving warning;We can see the collected data by entering into the corresponding interface,which establish a connection by Bluetooth between the mobile phone and the vihicle diagnostic equipment Bluetooth,and can achieve data transmission and processing by designing program.Finally,the paper makes a number of experiments on each module of the design,and uses the OBD simulator to simulate the data,and the data sent is compared with the data displayed on the mobile phone side,which indicates that the system can meet the design requirements.