A Vehicle System For Prompting Road Condition Based On Spread Spectrum Communication

With the auto industryincreasingly closed to people's lives,the technology is more and more advanced.Auto control systems,GPS,car radio,auto Bluetooth and other electronic equipment have become a standard configuration of the car.The combination of traffic information and automotive electronic systems has also evolved to practical applications in recent years.Most of the vehicle systems are embedded systems,each of which has specific functions,including surveillance,assistanceand so on.The application of embedded systems in the field of weak electricity is more and more extensive and diverse.And its concept shows that it is designed for the specific application.The system is developed for prompting road conditions.The knowledge of electronic circuits,computer technology,singnal processing,software development and so on have applied in the system.The development of these disciplines provides the theoretical basis for this vehicle system.Safety is the key element to consider when the driver is driving.Observing the driving environment and understanding the traffic information are very important to the safe driving,especially for the first driver of the convoy.The driver of the lead has an impact on the entire team.At present,the walkie-talkie is used as a toolfor exchanging information in most of the teams,but there will be a situation of string or band occupancy,as long as one of the use of the channel,then the rest of the walkie-talkie cannot be used.This situation will affect traffic and traffic informationbroadcasted by the first car.In view of this shortcoming,the design of the road conditions based on spread spectrum communication system has come up with,mainly for mountain mode and high-speed mode.In addition to prompt traffic information,but also transmission of driver orders and requests,the maximum possible consideration of the traffic encountered in the process problem.The system sends information by trigger the keys,eliminating the one hand to grasp the steering wheel of insecurity,but also to avoid the attention of the driver's attention.LoRa spread spectrum communication technology is used for wireless transmission,LoRa technical standards released in 2013,the application target directed at the Internet of things program.LoRa is different from the direct spread spectrum system and the frequency hopping system which need to insert pseudo-random code(PN code)to expand the frequency band.Through the characteristics of the frequency of the chirp signal with time,a single frequency signal is extended to disperse the energy to a wider frequency band.At present market,LoRa wireless chip is providedin SemTech Company,the size are SX1276 and SX1278 RF chip,so the choice of wireless transmission module is AS62-DUT2 module with SX1278.The transmission frequency is Free application frequency segment,410MHz-441 MHz,transmission distance range is 3km.Because of its high sensitivity and superior signal to noise ratio,the signal anti-interference ability is stronger than other spread spectrum communication.In this paper,the study is LoRa spread spectrum technology in automotive applications,combined with STM32 embedded development board,completed the initial construction of the system.The improvement of the circuit diagram mainly depends on the circuit design software altium designer 10,and software design and debugging work is completed in the KEIL MDK platform.The main research work is as follows: first of all,the featuresof the system are designed.The data transfer module AS62-DUT2 is selected to transfer the information,SD card is used for storing data,while the voice playback module is connected on development board for voice prompts.Second,the hardware modules and development board interface are designed for connect,the data transfer module carries on the data exchange through the serial port and the MCU on the development board.MCU connects to the SD card via SPI communication mode.The SD card is not set in the receiver,the information that the receiver send to the transmitterwill be recorded in the transmitter's SD card.Voice playback module and the key system are directly controlled by MCU IO port,active low.The hardware flow of the whole system is the driversselect the mode according to the driving environment,sending traffic information or command by pressing the key.This information is transmitted by aerial through the data transmission module,The receiver determines which IO port to transmit the low level to the corresponding voice prompt by identifying the received data.The last step is to complete the system software design work.Transmitter and receiver of the process is different,but generally includes the system module initialization,real-time clock,DMA configuration and so on.The sender side of the hardware set up the SD card,which also implanted FATFS file system,avoiding difficult to record a valid data location and cannot determine the remaining space SD card.The data transmission and reception work is completedin main program,data is sentby key recognition,data reception in receiver achieved by setting the serial port interrupt.There is no SD card in the main process of the receiver.The data sent by the transmitter and the request of the receiver are written to the SD card through the SPI interface,the date is the file name,and the information of the data transmission and reception is recorded in this file.The test results show that it avoid too much hardware in the system because of the rich peripherals of STM32,the data receiving and sending functions are achieved under the "high-speed mode" through the software settings,and information from transmitter is successfully written to SD Card.The transmitter and receiver are separated by 3km or more,and the data transmission module is verified that the information transmission function is accurate and efficient.This shows that the system has a wide range of practical application significance and safe driving support.