The Research Of Wireless Vehicle Detecting System Based On Three-axis AMR Sensor And ZigBee

With the rapid development of economy,it become more and more diffcult to find a parking spaces in everyday life[1].In order to solve this problem,a wireless vehicle detecting system based on three-axis AMR sensor and ZibBee was studied,which enhance the efficient use of parking spaces by improving the accuracy of parking identification.The wireless vehicle detecting system consists of hardware and software.To realize the real-time detection and control of parking spaces,the hardware is designed for signal acquisition,signal processing and the formation of communications network.At the same time,the software is designed for data integraion,system control and the optimization of filtering and parking identification algorithm.In hardware,the key of signal acquisition is to reduce electromagnetic interference from three-axis AMR sensor assembled by HMC1022 and HMC1021 which manufactured by Honeywell.To reduce EMI from the rear end of the circuit, both power supply terminal and ground terminal of the sensor circuit are connected to filter capacitor. In the other hand,the PI-type filter circuit is used to reduce EMI from the front end of the circuit.The key of signal processing is to ensure that the signal amplification without distortion,which depends on the selection of the amplifier.By comparing various amplifier circuit,the amplifier circuit based on AD623 is used to signal amplification,which known with high accuracy and single supply.The formation of communications network should gain the balance between communication speed and network capacity.According to the actual application scenarios,ZigBee and Wi-Fi Direct are designed to adapt to different environment which includes vehicle detection of parking spaces and road. The research is focus on the vehicle detection of parking spaces.At last, tree topology achieve the coordination of networking flexibility and transmission efficiency,which improve the network load capacity.In software, the key of data integration is data integrity,data validity and network communication efficiency.By comparing various filtering algorithm,weighted average filtering algorithm meet the requirements of data validity and network communication efficiency.At the same time,it has faster response. On the server, regular expressions is used to match the data which ensure data integrity.The core of system control is functional partition and system capacity.Hierarchical design makes the system into the data layer,the interface layer, application layer,which reducing coupling of software and Improving system stability.The system capacity is increased by the load balancing of each layer.The optimization of algorithms based on the managment of sample data and parameters.By using SQLite3 database and configuration files to organize data and parameters,the Algorithm adaptability, stability and accuracy achieve improvements.Eventually, on the basis of hardware and software, we constructed a wireless parking detection system. In the laboratory, the linearity of three-axis AMR sensor was measured within-1Gs- 1Gs range. In the parking lot, the different orientations of the magnetic field distribution of parking spaces was measured, According to the distribution of the magnetic field, the parking identification algorithm was designed.Furthermore, the parking identification system was optimized by comparing with algorithms, compared with the fixed threshold algorithm, sliding threshold algorithm has higher accuracy above90%.With small size, fast response and high precision, it has wide application value in the field of parking lot management and traffic flow control.