The Research And Development Of School Bus Occupant Safety Monitoring System

In recent years,school buses are widely used in China for the convenience of students' commuting. However, due to the backward technology and management,China's school bus accidents occur frequently, attracting great attention in recent years.According to school bus safety monitoring system functional requirements and its actual situation, a practical school bus occupant safety monitoring system is researched and developed in this paper which can monitor the school bus seat belt use,its speed and the number of people in it in real time and prevent such events that some students are forgotten so as to be suffocated in the school bus after parking. This system has high stability, good real-time performance, easy migration and extension and low cost.At first, overall scheme of this system which includes topology construction,definition of every module functions and system communication application layer protocol is designed.Then hardware designs of this system are completed. The low power consumption and high performance 8 bit microcontroller STC89C52 RC is chosen as MCU. Constituted with SJA1000 CAN communication controller and PCA82C251 CAN bus driver, CAN bus interface circuit can work in 24 V electrical environment.Central control module's on-off input is achieved by photoelectric isolation circuit with photoelectric coupling chip EL817. Output circuits are made of photoelectric isolation circuits and power relays. The intelligent serial port LCD screen is selected for display. Display content is completed by using the host computer software. Seat information is got by pellicle contact sensors and seat belt switches. Before entering the seat information acquisition module's MCU, their signals are processed by isolation circuits and logic gate circuits made of Nor Gate and Or Gate. Through external interrupt expansion circuit, infrared reflecting sensors' signals get into statistical MCU of people number which can calculate the number of the people in the bus. Power supply circuit is built by LM22676 chip which can convert voltage from24 V to 5V and supply power for MCU and other chips.After that, software programs are designed referring to the system structure andhardware circuit design. The common computer programming language C language is used for programming language.The software development environment is Keil C51.Programs involve CAN initialization, sending and receiving program,central control module program about speed and switch data acquisition, display control and so on, seat information acquisition program, statistical procedures of people number and so on. Some programs are used to simulate in Proteus ISIS simulation platform. Simulation results show that these programs are in correct operation.Following the hardware and procedures design, the system prototype and function debugging and test such as debugging of the local functions of unit module,the message sending and receiving between units and tests of system function are finished. CAN debugging platform and function test platform are built for the convenience of test. Debugging and test results show that functions of each module are realized, CAN bus communication is normal and the overall functions of the system are completed. The developed school bus occupant safety monitoring system achieves a better effect and meets the development requirements.Finally, system cost accouting is done. Compared to similar products on the market, this system has certain advantages for its cost controlled within 1000 yuan.