Radio frequency identification-based access control system implementation

With the advancement of network technology, digital technology, and especially radio frequency identification technology, access control systems have also achieved considerable development in terms of security, convenience, and manageability, and have become effective measures to ensure the safety of entrances and exits to communities and other important departments. Has been widely used in transportation, logistics management and other fields [1-3]. RS485 bus master scheduling network is still the current medium and small-sized network management system because of its advantages of easy networking, low cost, rich hardware and software, convenient and fast addition of added nodes, reliable and stable data transmission, low bit error rate, and moderate transmission distance. Mainstream form. This work studied a hardware and software implementation of an intelligent access control system based on RS485 bus and RFID technology.

1 overall system configuration

The overall block diagram of the system is shown in Fig. 1. The structure of the system adopts a distributed control mode. Each lower unit monitors the operation status of its own node and is uniformly monitored by the upper computer. The system uses a PC as a host computer, and is mainly responsible for database management of household information, real-time operation monitoring and information recording of each node household, and the specific information includes: RFID card information, household personal information, password information, real-time operation information and history records. And system time. Each subordinate machine adopts W77E58 one-chip computer that WINBOND Company produces as the microprocessor, is responsible for the management of the RFID card in this node, the judgement of user's jurisdiction and the control of the door state. The 485 transceiver MAX485 in each node is responsible for receiving the PC control data from the 485 bus or sending the real-time operation information to the upper computer through the bus. Each access controller reads RFID card information through a serial port and communicates with the 485 bus through another serial port. The upper computer is connected to the 485 bus through the serial port and after the 232-485 level conversion, unified management of the access controller.

The working process of the system is: When the user holds the RFID card close to the reader, the reader recognizes the card information and sends the card information to the single chip controller through the serial port. The user can also enter the password through the keyboard. The single-chip controller compares the card information or the keyboard information with the information stored in the external EEPR0M to verify the user authority and control the door status. The MCU communicates with the upper computer through the serial bus via a 485 transceiver and transmits the card information, operation information at each time, and keyboard information to the bus. The upper computer stores the information and the database via the bus; meanwhile, the upper computer The machine manages the database, password, and personal information of each household in the form of registration or cancellation to facilitate the query.

2 system hardware design 2.1 hardware components

PC hardware is PC and 232-485 adapter card. The lower computer hardware mainly includes RFID reader, 485 transceiver and access controller. Lower machine node structure shown in Figure 3.

The core part of the lower computer is the W77E58 microcontroller microcontroller. Its main characteristic is that it has two independent serial communication ports.

The RFID reader uses the ZLG500CMifare card reading and writing module of Zhou Ligong to ridicule and uses the P1.4 pin of the SCM controller as its reset signal. The interface leads of the card reader and the controller also include power lines, ground lines, and RXD, TXD serial data lines, which are serial communication methods.

The 485 bus transceiver uses the MAX485 from MAXIM. The circuit principle is shown in Figure 2. Optical isolation is added to achieve anti-interference and protection functions. Uses the P2.3 pin of the one-chip computer to control its internal sending and receiving driver, and communicates with it through a serial port of the one-chip computer.

2.2 Working principle
The W77E58 has two serial ports, which is crucial in this system.

The microcontroller controller must communicate with the RFID reader via the serial port and communicate with the 485 bus controller MAX485 through the serial port. Therefore, selecting a microcontroller with two serial ports is the best solution to this contradiction. And at the same clock frequency, its instruction execution speed is 2.5 times faster than the standard 8051, which is also a great advantage for the microcontroller as the core of the access controller.

The keyboard has 12 keys, the function definition of each key is: number key 0-9, confirm key and cancel key. The user can enter the password information through the keyboard or open the door through the keyboard. EEPROM memory AT24C256 is used to store user key information and RFID card card number and password information. It has IIC bus function, which can be read and written under the timing of IIC bus; DS1302 clock chip is used to provide clock to the system. Convenient, the clock should be consistent with the host computer; In addition, the use of MAX813 watchdog chip monitoring program operation; using EA_D20040AR LCD display user input through the keyboard password, real-time operating information and system time information; using DS2Y-S relay control The switch state of the switch.

3 system software design

System software consists of upper computer management platform and lower computer access control program.

PC management software is developed on Windows XP operating platform using Visual C++ 6.0, including functions such as registration and cancellation of RFID cards, adding, deleting, searching, editing, sorting, displaying, real-time monitoring, and administrator login authentication. Friendly human-computer interaction interface, intuitive display, easy operation. When the system is running, each access controller stores the collected card information, keyboard information, and real-time operation information in the host computer in the form of TxT files; the unit household information of each cell is displayed in the form of a “tree” view on the platform interface. In the left window. Clicking on the corresponding node, the household information of each unit is displayed in the form of a database table in the right window of the platform interface. The Tab control below the platform is used to display the real-time operation information of each access controller in real time.

The lower computer control program uses 8OC51 language programming, Wave6000 compiler simulation. The main functions realized in this part include: reading and verification of key password and card information, LCD LCD and LED display, time setting and reading, receiving and sending operation information via 485 bus, etc. The software main program flow is shown in Figure 4.

3.1485 communication

Communication baud rate is set to 9600bit·S-1. The communication protocol is the starting character + local address + function character + data length + data information + ending character where the starting character is '@@@', the ending character is '$$$', and the local address is: 0~ 32 (can be selected according to need); advertising address: Oxffo function characters: '0' ~ 'F'.

3.2 serial port interrupt processing
The functions of the serial port include: Firstly, the upper computer sends operation information, such as swiping card or password authentication information; Second, it receives the password modification and card registration cancellation information sent by the upper computer, and modifies the corresponding contents of the EEPROM accordingly, realizing the real-time update. . The interrupt process is shown in Figure 5.

3.3 Card and Password Management and Authentication Mechanism

Generally, there is only one password for each access control node. The password is stored in both the database of the host computer and the EEPR0M. When the host computer modifies this password, the modified information is sent to the lower computer via the bus to synchronize. modify.

The user's card information storage method is the same as the password. The difference is that the card number information under each node is more than one and can be dozens. When the user registers or deregisters the card through the upper computer, the modified information needs to be sent to the lower computer via the bus to achieve synchronous modification. The authentication process is as follows: When the resident enters a password through the keyboard, the controller collates the information with the password information in the EEPROM. If it is correct, the door is opened through the relay, and the correct information of the password opening door is sent to the upper computer according to the protocol via the bus; otherwise, the operation is reversed. The card swiping operation is almost the same as the password.

3.4 Database and Real-time Information Management

The management of user information (cards, passwords) is in the form of a database. Use Access2000 to create a database, including password tables for all access control nodes and household access information tables for access control nodes. By reading and writing to the database through the member variable In_pSet of the database class, user information can be added or deleted through the management platform. The upper computer records real-time operation information of each access control node in the form of files. The file format is TxT format, and a total of four files are created for storing: real-time operation information, registration and cancellation information, card authentication information and keyboard operation information.

4 Conclusion
The system realizes the functions of radio frequency RFID card identification, access control system password authentication, real-time information display, and host computer database management and storage. The system has a lot of room for expansion. According to need, it can not only expand the nodes of the access controller, but also can add monitoring tools such as cameras. Experiments have proved that the system has reasonable design, reliable operation, low development cost and high cost performance, and has strong application value and broad market prospects.