introduction
In today's college canteens, due to the large number of students and frequent mobility, traditional paper meal tickets, cash or consumer payment methods based on contact IC card technology have low service efficiency, poor convenience, high management cost, and vulnerable cards. And so on. As an important part of the school's logistics service, college canteen consumption will use a lot of manpower and material resources, and there will be many cumbersome tasks in management, which is not conducive to better serving the teachers and students. And the management of the school. In order to solve this problem, more and more colleges and universities now use smart card technology and network technology to build a school cafeteria card system.
Contactless smart card technology and CAN bus technology are the products of the rapid development of science and technology in the world today. Smart card technology is widely used in various industries, especially in the fields of public transportation, wireless communication, identification, financial transactions and security defense. The CAN bus has outstanding advantages in terms of reliability, real-time and flexibility. If the non-contact IC card technology and CAN bus technology are combined into two hotspot technologies, a CAN bus-based college canteen credit card system will be developed to optimize the life of teachers and students and improve the management level and service quality of college canteens. Very good promotion.
1, the overall design of the system
1.1 System Design Principles
According to the background of the design and the design tasks and requirements of the system, the system must follow four principles in the research and design process: safety, reliability, ease of use, and ease of maintenance.
1.2 System main technical options
The main technical solutions that need to be first determined in the design of the system are: selection of communication bus, selection of cards, and selection of technical solutions for card reading and writing operations. Through sufficient comparative argumentation, the system uses CAN bus to build the system network. The MifarelS50 non-contact IC card designed by Philips is used as the information carrier of the college canteen credit card system. In order to improve the reliability, stability and compatibility of the system, The system uses the YHY502ATG RF card reader module of Beijing Yihuoyan Company to read and write the RF card.
1.3 system design main device selection
According to the market conditions, the development tools and the actual needs of the design, the card issuing node and the card swiping node of the system all use the single chip AT89S52 as the main control chip. Considering that SJA1000 supports CAN2.0A/B protocol, PCA82C250 can support 110 CAN nodes, and Philips has more product models and convenient purchases in the domestic market. Therefore, Philips SJA1000 is used as CAN controller and PCA82C250 as CAN bus. transceiver.
1.4 system overall structure
According to the technical solution determined by the system design, the overall structure of the system is shown in Figure 1.
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1.5 system function module division
According to the functional tasks and requirements of the system design, the system can be divided into three major functional modules: the card issuance module, the card swipe module and the system upper computer module, as shown in Figure 2.
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2, system hardware circuit design
2.1 hardware overall design
The hardware part of the college cafeteria card system is divided into card issuing machine and card swiping machine. According to the system function module, the system hardware circuit is composed of 7 parts: AT89S52 minimum system peripheral circuit, RF card reading and writing module YHY502ATG circuit, serial communication circuit, CAN bus communication Circuit, LCD12864 display circuit, keyboard input circuit and alarm prompt circuit. The system hardware circuit composition is shown in Figure 3.
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2.2 RF card read / write module circuit design
The communication between the YHY502ATG RF card read/write module and the microcontroller is realized through the I2C bus. The application circuit can be designed with reference to the technical application manual of YHY502ATG. The YHY502ATG read/write module provides a set of communication protocols for card operations, regardless of the processing of the underlying communication data, but must comply with these communication protocols and modify the corresponding program on the control side according to the design requirements.
2.3 Serial communication interface circuit design
The design uses a 9-pin RS232C interface to communicate between the lower computer and the upper computer. The AT89S52 itself has a full-duplex UART serial channel. In the hardware circuit design, in order to make the input and output TTL level of the AT89S52 microcontroller and the PC The electrical specifications of the configured RS232C standard serial interface are the same. The system uses the MAX232 chip to realize the conversion between the AT89S52 and the RS232C standard interface level of the PC.
2.4CAN bus interface circuit design
The system uses CAN communication controller SJA1000 and CAN transceiver PCA82C250 to design CAN bus node interface circuit. In the hardware circuit design, the two 120Ω resistors at the end of the bus play a very important role in matching the bus impedance. If you ignore them, the anti-interference ability and reliability of data communication will be greatly reduced, and even communication will not be possible.
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