Vehicle Information Collection System Based On The AMR Sensor

With the development of social economic and the improvement of people’ living standard, car ownership is increasing in China. Although Beijing, Tianjin and other places have taken a series of measures such as private limited number, lottery shopping, reads the subway and so on, it’s difficult to curb this trend. The problem of heavy traffic still exists objectively. The emergence of intelligent transportation system alleviates the problem substantially. The use of AMR magnetic resistance sensor for detecting the vehicle information can effectively alleviate the traffic problems. For example: it can change the traffic-light time to ease the traffic problems by testing the road occupancy rate and testing the speed. In view of the current traffic problems, this paper designs a set of high degree of automation and low cost vehicle information collection system by using AMR magnetic resistance sensor. The main research content of this paper is as follows:First: The in-depth study of the theory of magnetic resistance sensor and cross-axis effect.Due to the interference of various external factors such as the rotation of the earth, Triaxial anisotropic magnetoresistance(AMR) magnetic sensor exists transverse effect. It always makes the measurement change, which has enormous influence on the application of magnetic resistance sensor measurement accuracy. For the cross-axis effect of the AMR sensor, this paper makes a deep study of the theory of magnetic resistance sensor and cross-axis effect. With the same time, through the theoretical analysis and formula derivation this paper puts forward a new rotation error compensation method to compensate the cross-axis. By comparison with the data, the accuracy of the rotation compensation method raised more than twice the non-rotation compensation method.Second: The hardware design of vehicle information acquisition system based on the AMR sensor.The hardware of vehicle information acquisition system based on the AMR sensor mainly consists of those parts that are detection module, power supply module, serial communication module, MCU control circuit and wireless communication module, of which detection module selects the HMC5883 L AMR magnetic resistance sensor to test the change of magnetic field. MCU control circuit select STC89C52 single-chip microcomputer control circuit to read data of sensor HMC5883 L and make data processing according to the demand. By using the antenna, Wireless communication module can make a long distance data transmission, then using the serial communication module transfers to Upper machine.Third: Put forward a new algorithm among the three state machine by studied the common vehicle detection algorithm.This paper has studied the common vehicle detection algorithm, such as fixed threshold algorithm, fixed threshold vehicle detection algorithm based on wavelet change, adaptive threshold algorithm of state machine, and has discussed the main factors of affecting the effect of vehicle detection and putted forward a new algorithm among the three state machine and new double sensor node speed detection algorithm. System programming has been given, including the reading of the AMR magnetic resistance sensor data, the speed detection algorithm, and vehicle detection algorithm design.