Research on RFID Livestock Information Reader!NFC metal Wholesaler

　　Livestock product traceability system is of great significance to strengthen the informatization construction of livestock industry, realize high-quality and high-price livestock products, and then regulate the continuous, stable and healthy development of the livestock product market. After the animal is born, the "ear tag" is used as the record carrier to give the tag a unique identification code, to record the necessary information of the animal in each link of circulation and use the corresponding reader to read it as the information input of the animal product traceability system. At present, the technology commonly used in the traceability system of livestock products. However, the frequent movement of animals will cause rapid changes in the reading/writing angle and reading/writing distance, and often make errors in the reading/writing process. The currently widely used RFID readers are difficult to solve this problem due to their low operating frequency. This paper designs a high-reliability reader/writer that works in the microwave frequency band, which solves this problem well.

　　1 The working principle of RFID reader

　　1.1 Introduction to RFID system

　　RFID system consists of electronic tags, readers, and antenna systems. When the tag is in the reading and writing range of the reader, the tag and the reader can communicate through the antenna they carry, and the computer can communicate with the reader through the serial port. The label instruction) is transmitted to the reader, and the reader completes the write (or read) operation of the label (see Figure 1).

　　1.2 Introduction to RFID Reader

　　RFID reader is an important part of the RFID system. Its core device is the radio frequency chip. The radio frequency chip determines the data encoding and the communication protocol with the electronic tag, thereby determining the scope of use of the reader. The design of the reader directly affects the convenience, ease of use and the reliability of reading and writing information. It can generally communicate with a computer, and with the support of the human-machine interface, the computer's host computer software can control the reader to read and write/operate the electronic tag.

　　First, configure the system to a suitable environment, then enter the ID number of the tag to be read/write, find the corresponding tag, and then transfer to the subroutine to read/write the tag for corresponding processing.

　　2 The basic composition of the reader

　　RFID reader is generally composed of control unit, radio frequency unit, communication interface, man-machine interface, memory and power circuit. Among them, the control unit, radio frequency unit and communication interface are the basic components of the reader, and they are introduced separately below.

　　2.1 Microcontroller ATmega128

　　The control unit is an important part of the reader, which is responsible for coordinating the work of each unit module of the system and providing some communication interfaces. Here we choose ATmega128 from Atmel as the control unit of the reader. ATmega128 is a low-power CMOS 8-bit microcontroller based on AVR RISC. It has a wealth of peripheral interfaces, 128 KB of FLASH program memory, 4 KB of E2PROM, 4 KB of SRAM, 53 programmable I/O lines, internal and external interrupt sources, programmable USART, programmable gatekeeper Dog timer, SPI port, etc. Its USART, SPI, IIC ports and higher operating frequency meet the needs of this design. In addition, its abundant pins provide conditions for system expansion. [next]

　　2.2 RF module

　　2.2.1 RF chip interface

　　The radio frequency module is the core component of the reader. Its working frequency, coding, communication protocol, etc. determine its performance. In order to design a reader with long reading and writing distance and ensuring reliable communication, nRF2401 chip with higher working frequency is selected. It is a single-chip radio frequency transceiver chip produced by Nordic Company in Norway. It works in the 2.4-2.5 GHz ISM frequency band. The chip has built-in functional modules such as frequency synthesizer, power amplifier, crystal oscillator and modulator, and its output power and communication channel can be Configure through the program.

　　The radio frequency chip is mainly used to exchange information with the electronic tag through the antenna. The single-chip microcomputer mainly controls its CS, CE, DR1, PWR_UP, CLK1, DATA and other pins to operate it. The circuit principle of the chip's peripheral components and pin connection mode is shown in Figure 3.

　　2.2.2 RF chip programming

　　To use nRF2401 to send and receive data, it must be configured first. In this design, the chip is configured to ShockBurstTM transceiver mode. In this mode, the programming of the system will be simpler and the system stability will be higher. The configuration process is as follows: set CS to high level, CE to low level to make the chip enter the configuration mode, the delay is more than 5μs, the microcontroller writes the configuration data into nRF2401 through the I/O pin, and then sets the CS pin to low level The configuration of nRF2401 can be completed. When configuring the chip for TX mode, set the CE pin of nRF2401 to high level, after a delay of more than 5μs, write the data to be sent into the transmit data buffer of nRF2401, and then set the CE pin of nRF2401 to low level The data to be sent can be transmitted through the antenna.

　　The process of receiving data is similar to the process of sending data, and nRF2401 is configured in RX mode. Then set the CE pin to high level. After a delay of 200μs, the chip enters the receiving state. When the DR1 pin is detected to be high, it indicates that the FIFO buffer of nRF2401 has received data, and the microcontroller executes the data read subroutine to change nRF2401 All the data in the data is read out. When all the data is read, the DR1 pin becomes low level. At this time, the state transition jump of the DR1 pin can be used to execute other processing programs.

　　2.3 Communication interface design

　　2.3.1 Serial port circuit design

　　In this design, the communication between the reader and the PC is through the RS 232 serial interface, but the level of the I/O pin of the single-chip microcomputer is TTL level and the PC cannot be directly communicated, and the level conversion is required through the chip. Communication. In this design, MAX232E is used to complete the level conversion. T1IN and R1OUT are connected to the serial transmission port and serial reception port of the microcontroller. T1OUT and R1IN are connected to the RXD and TXD ports of the PC COM port through the DB9 connector, and the circuit is connected The way is shown in Figure 3 of the circuit principle.

　　2.3.2 Serial programming

　　After the single-chip microcomputer and the PC are connected through the handshake signal, under the action of the control status signal sent by the PC, the single-chip microcomputer transmits and receives data through the USART to communicate with the PC's serial port. In this design, USART works in asynchronous transceiver mode, the operation process is as follows, first initialize USART, then put the data to be sent in the data register, configure the relevant bits of the control register so that the data can be sent out through the pins; the situation of receiving data is similar, After initializing the control register, enable the corresponding control bit of the receiving control register, and then go to the data register to read the data.

　　2.4 Schematic diagram of basic system composition

　　3 Expansion of the reader system

　　The above is the basic composition of the reader. In order to design a convenient and complete reader, the man-machine interface, memory, power supply circuit, etc. must be added. The man-machine interface provides an interface that requires human intervention during the read/write process, which can be realized by an independent keyboard and LCD12864; the storage circuit is used to temporarily store the data read by the reader or the data to be written to the electronic label. In the reader, the reader sends the electronic label, which can be realized by the AT24C08 chip, which is an I2C interface device. The power circuit provides power for each chip of the entire reader, and various voltage stabilizing modules can be selected to obtain the required power through transformation.

　　4 Conclusion

　　In the process of realizing the design, the problem of electromagnetic interference is very prominent. The PCB of the reader is designed as a double-layer board, the bottom layer is used as the ground layer, no components are placed, the empty space on the top layer is covered with copper, and the copper is connected to the ground of the bottom layer through via holes, which can greatly reduce electromagnetic interference. After the whole system has been processed for anti-electromagnetic interference, the reader/writer working in the microwave frequency band can have very high reliability in the state of long-distance and fast-moving animals.

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