chrispeng [ad_1]
1 Principles and main features of radio frequency identification technology
Radio frequency identification technology is a non-contact automatic identification technology that emerged from the 1990s. Its basic recognition principle is to use radio frequency wireless way for non-contact two-way communication, so as to automatically recognize the target object and obtain relevant data information. At the same time, it has many advantages such as strong anti-interference, strong ability to adapt to the environment, high precision, and fast operation.
1.1 Working principle
The non-contact access control card reader base station in this system is based on radio frequency identification technology. This base station is a small size, light weight, and an ID card radio frequency base station with a maximum operating distance of 10 cm. When the access control card reader base station is working, the coil antenna connected to the dedicated radio frequency base station (MFRC-522) continuously sends a set of fixed-frequency electromagnetic waves (13.56 M) around. When a non-contact ID card approaches, at this time The excited frequency can resonate with a set of fixed LC series resonant circuits stored in the card. When the resonant frequency is the same as the frequency emitted by the read-write base station, it is known from the principle of resonance that the charge will be excited by the resonance to generate the amount of charge. The stored data is sent out and decoded by the radio base station to obtain the card number. The principle of the ID card is that when the frequency sent by the radio frequency base station is received, the built-in capacitor of the card is in a state of excitation and charging to generate an excitation charge. At the other end of the capacitor, an electronic pump with unidirectional conductivity is connected at the same time. , The electronic pump can send the charge in the excitation capacitor to another unexcited capacitor for charge storage.When the charge of the storage capacitor reaches 2 V, the storage capacitor can be used as the power supply on the card to provide working voltage for other circuits, and the card
The internal data is transmitted out. In this access control system, when an ID card enters the sensing area of the antenna transmission frequency of the radio frequency base station, the access control card reader base station will read the card number of the non-contact ID card and send the read card number to the microprocessor through the serial port When the password verification is correct, the door lock will be activated. If the password verification error exceeds three times, a warning will be given. When the ID card is not detected by the access control card reader base station antenna, the emblem processor will enter the idle time mode, read the clock information of the real clock circuit, and display the current date and time on the display.Research on Access Control System Based on RFID Technology
Compared with the traditional access control system, it has the following intelligent features:
1) The radio frequency identification card is small, light in weight, and easy to carry. The radio frequency base station can realize the identification and reading of the card number within a range of about 10 cm;
2) The ID card is made closed and has good dustproof, waterproof and anti-fouling performance;
3) There is no need to contact the door lock during operation, which reduces mechanical wear;
4) The radio frequency wireless signal has strong penetrating ability, can penetrate obstacles in life, and the card number data transmission is small and easy to read;
5) Compared with the serial number in the IC card, the ID card is just like an ID card, and it is unique. The manufacturer has solidified this serial number before the card leaves the factory, which has high security;
2 System design and implementation
2.1 The overall design of the system
The design of the entire access control system is to use radio frequency identification technology (RFID), the key is to use a lightweight ID card as the access control card, and the control unit uses a low-cost, high-stability, and relatively mature technology single-chip microcomputer as the control core of the system At the same time, in order to increase the anti-theft coefficient of the access control, the system adds a password verification function to the traditional radio frequency access control system solution, performs double verification of the card reading key, and adds a display screen as a human-computer interaction interface, and also adds a voice prompt function With the clock source as the idle time display function, the entire operation process of this system is the same as the bank ATM operation process in daily life. The specific operation design process is as follows: when the key ID card is close to the reader base station of the controller, the reader base station can accurately recognize and read the card number, and send its serial card number to the control through the serial port data. Then the microprocessor calls the database information through the interrupt service program to match the user information corresponding to the card number. If the card number has been registered as a user, it will pass the card number verification and notify the microprocessor to check The verification is successful, and then the voice prompt is correct and the user is prompted to enter the keyboard to verify the password. If the password verification is successful, the door lock control is triggered to start the door; if the card reading fails or the card number information does not match the information registered in the database and the number of card swiping exceeds Three times, the voice will give a warning prompt; if the card number verification is successful, but the password verification fails and the number of password entries exceeds three times, the alarm device will be activated to prohibit the passage and inform the cardholder to leave quickly; if the two password verifications are both After the failure, the ultrasonic detection device is activated to detect whether the person currently operating is still within the ultrasonic detection range in the alarm state; at the same time, when the system is idle, the current clock signal will be read through the clock circuit to display the time.
The overall system is composed of five parts: ID card, read-write base station, keyboard matrix, microprocessor and clock circuit. The microprocessor is the control core of the system, and the read-write base station communicates wirelessly with the ID card through radio frequency technology to complete the card number reading and data transmission. When sent through the serial port, the microprocessor receives the communication data and communicates with The card number information that has been registered in the database is verified. If it is successful, the keyboard password verification function will be activated. After the double security verification is successful, the control terminal will respond accordingly, thereby realizing the entire work flow.
2.2 Hardware composition
The card reader base station of the access control system is equivalent to an intelligent node, which can independently complete a series of operations such as door status and lock status monitoring, card type determination, real-time monitoring of card swiping actions, and control of electromagnetic door locks and alarms. The hardware part of the entire access control system mainly includes the microprocessor responsible for controlling and monitoring the identification part, radio frequency base station circuit, clock circuit, alarm device (acousto-optic alarm circuit), ultrasonic detection circuit, reset circuit, and button matrix circuit. The hardware block diagram of the circuit is shown as in Fig. 2. The control unit uses the STC STC12C5A60S2 single-chip microcomputer as the control unit. This single-chip is an enhanced version of the commonly used MCS-51 series of single-chip microcomputers. It has good low power consumption, anti-interference and high cost performance characteristics. In this case, the more common MCS-51 main frequency processing speed is 8 to 12 times, 1280 bytes of RAM are integrated on the chip, there are 8 10-bit high-precision AD acquisition channels, 4 16-bit timers, and more common 8051 Added two timers, two PWM functions, two standard serial communication ports, and has a P4 port, supports ISP program download, and is compatible with traditional 8051 single-chip microcomputers; the ultrasonic module adopts HC-SR04, which has stable performance, It has high ranging accuracy, small detection blind area, and simple programming operation; LCD1602 is used as the human-computer interaction screen on the display screen, which has low power consumption, light weight, and rich display content; the keyboard adopts 8×8 matrix keys; the clock circuit adopts DS1302 is used as a real-time clock circuit with high performance and low power consumption. It also comes with RAM as a real-time clock. It also counts the year, month, day, week, hour, minute, and second, and has a leap year self-correction function; RF base stations adopt the market The more common MFRC-522 used above, the radio frequency module integrates code demodulation and demodulation code transceiver functions, the effective distance of reading ID card data can be up to 10cm, and it integrates parallel and serial port control. The circuit can automatically detect the port type of the external microcontroller connected to it, and has a 64-byte FIFO buffer register for the input and output of the data stream between the microprocessor.
The hardware circuit of the entire access control system is relatively simple, with fewer auxiliary circuits, and each module response unit is relatively independent, which can improve the stability of the system during operation; at the same time, the device selection is a module circuit with relatively mature technology and performance. System hardware is low in price, low in power consumption, high in stability, high in security, and easy to market.
2.3 Software design
The program of the access control unit includes: door detection and lock status monitoring program of the access control unit, communication program of MFRC-522 radio frequency base station and ID card, serial communication process between microprocessor and MFRC-522, access control number information and database registration Information verification and interrupt service program, keyboard password verification interrupt service program, clock circuit read and write and LCD display program, etc.
The design of the access control system adopts the C language as the programming language, and KeiluVision4 as the programming software for programming, debugging, compiling, linking, and generating machine code. The hardware serial port debugging is carried out through stc-isp.
3 Conclusion Research on the access control system based on RFID technology
At present, with the rapid maturity and development of radio frequency technology, the branch of the security field based on radio frequency technology has also been rapidly developed, and the application field has shown a popular trend from high-security banks and companies to homes. The access control system combines the monitoring system and the alarm system to realize a transition from non-intelligence to intelligent in the modern security field, and also strengthens the security of the access control. The structure of the system is based on radio frequency identification technology, which organically combines traditional access control and alarms, so as to realize the intelligentization of man-machine operation, alarms, and real-time monitoring.
[ad_2]
