chrispeng [ad_1]
Identification (Radio Frequency Identification) technology is a non-contact automatic identification technology that uses wireless radio frequency communication to achieve long-distance identification. Compared with the barcode technology commonly used in modern logistics, it has significant advantages in terms of reading distance, confidentiality, intelligence, environmental adaptability and service life.
At present, there are two coding systems for RFID logistics applications worldwide, one is the UID coding system proposed by the UID (Ubiquitous ID) Center of Japan, and the other is the UID coding system proposed by the U.S. EPC (Electronic Production Code, Electronic Product Code) Universal Association. EPC electronic product coding standard. The two standards differ in the wireless frequency bands used, the number of bits of information, and the fields of application. my country does not have its own formal standard yet, but the electromagnetic detection work related to the application of RFID in the 900MHz frequency band has been basically completed. my country is most concerned about the ISO1800-6 standard. In essence, the EPC standard and IS018000 are not contradictory. For logistics applications, the EPC standard is more complete.
In addition, for logistics applications, cost is the most concerned issue for enterprises. On the premise of meeting the needs, choosing the lowest cost is the first to bear the brunt. The UHF (915MHz) radio frequency has a working distance of about 10m, which can already meet the needs of logistics applications, and the cost is much lower than that of the microwave range.In particular, UHF radio allows the use of relatively small directional antennas, which will direct the radiation beam of the reader to a specific area. This feature enables the reader to resist potential from other readers or transmitters. Interference
In view of the above situation, in order to promote the large-scale application of RFID system in the field of logistics and warehouse management in our country, this paper proposes a reader design method based on the application of logistics and warehouse management. The design of the reader refers to the EPC standard, adopts 915MHz operating frequency, and aims at the reading and writing of a certain company’s RFID tag chip. The circuit design is simple, the application is flexible, and the production cost is low.
1 Introduction to label function
The tags used in this design are long-distance passive tags that work at 860MHz ~ 960MHz, conform to IS018000-6 standard, and have a working distance of up to 8.4m (depending on the antenna situation), which is especially suitable for logistics supply chain management and logistics in the United States Guarantee system. The label mainly has the following characteristics:
(1) Convert the energy received by the antenna into electricity through the analog circuit of the RF front-end to supply power to the internal circuit.
(2) The 16-bit CRC (cyclic redundancy check) code is included inside, which has high data integrity.
(3) It has a fast anti-collision mechanism and uses its own anti-collision algorithm to realize true internal conflict judgment and anti-collision.
(4) It adopts 64-bit EPC encoding and contains 216 bytes of user-defined storage space inside.
When the tag enters the RF zone, the tag is activated. If the signal strength in the RF area meets the energy requirements of the tag, the tag enters the ready-to-work state and waits to receive instructions sent by the reader. The data received and sent by the tag will go through CRC for error checking. At the same time, the data is further protected by Manchester encoding and FM0 encoding to ensure data security. The reader can read and write data from multiple tags at the same time by combining external commands with the tag’s internal anti-collision algorithm.
2 RFID reader design
2.1 Hardware design
RFID readers are used in warehouse management. In addition to completing simple radio frequency signal sending and receiving processing, they also need to be connected to the upper warehouse management system (Warehouse Management System, WMS) to transfer the received label information to WMs to facilitate the system Complete warehouse storage, inventory, and outbound management operations. At the same time, information such as the location of the item is written into the item tag through WMS. Therefore, the overall structure of the reader includes four modules: receiving/sending module, control module, external interface module and power supply management module. The transmitting and receiving modules of the radio frequency circuit are composed of two units: radio frequency signal formation and signal processing. The radio frequency power amplifier powers the formed radio frequency signal, and the linear amplifier linearly amplifies the received radio frequency signal. The selected chips are shown in Table 1.
In the design of radio frequency circuits, preventing and suppressing electromagnetic interference and improving electromagnetic compatibility are very important links. It is necessary to select a substrate with a small permittivity tolerance, and perform block processing on the radio frequency and digital parts of the circuit. The radio frequency part should try to use SMT (surface mount) components, reduce via holes, and add a grounded metal shielding layer on the surface. The specific design of each module is as follows.
2.1.1 Receiving/sending module
The functional block diagram of the receiving/sending module is shown in Figure 1. The receiving/transmitting and modulation and demodulation chip selects TI’s TRF6901, the power amplifier chip selects Freescale Semiconductor’s MW4IC915GMBR1 chip, and the linear signal amplifier chip selects RF Micro Devices’ RF2132. The TRF6901 chip integrates a complete radio frequency receiving and transmitting circuit, which can form a half-duplex radio frequency transceiver circuit. Its operating frequency can be fine-tuned by programming, and the frequency range is 860MHz~930MHz. MW4IC915 is a wide-band power amplifier chip designed for GSM applications. It uses Freeseale’s latest high-voltage LDMOSIC technology. It can work in the 750MHz ~ 1000MHz frequency band with linear performance covering almost the entire application frequency band. RF2132 is a gallium arsenide heterojunction device (HBT), which can well meet the requirements of radio frequency circuits for amplification power, efficiency and supply voltage.
The operating frequency of each chip in this design is 915MHz. The modulation mode of TRF6901 is OOK, which can be realized by setting the 4th bit of the internal B register to zero. TRF6901 sends the required transmission signal to the REIN pin of MW4IC915 through the PA pin. After power amplifying the signal, it is transmitted by the antenna; the signal received by the antenna is linearly amplified by RF2132, and then enters the LNA of TRF6901. Pin, TRF6901 processes the received signal to complete the data exchange task at the front end of the reader.
2.1.2 External interface module
The external interface module shown in Figure 2 is a level conversion circuit, and the main component is ICL232. The ICL232 chip completes the conversion between the TTL level and the RS-232 level inside the reader, and is connected to an external computer through a standard 9-pin serial port. It is a two-way RS-232 sending and receiving interface chip that complies with EIA RS-232 standards and V28 specifications. It is responsible for completing the conversion of the TTL/CMOS level of the circuit to the standard serial port level, and can improve the noise of data reception through hysteresis inhibition. A 1μF capacitor is connected between pins l and 3, and pin 2 is connected to a 5V power supply through a 1μF capacitor. The three pins constitute a conversion circuit from +5V level to +1OV level; a 1μF capacitor is connected between pins 4 and 5. 6 Ground through a lμF capacitor, and three pins form a conversion circuit from +IOV level to -10V level.
2.1.3 Control module
The structure of the control module is shown in Figure 3. The internal control task of the reader is mainly completed by the W77E58 chip, which is an 8-bit CMOS fast MCU compatible with 8051. Compared with 8051, it reduces the execution time and storage cycle of machine instructions, and reduces power consumption. It contains 32KB Flash EPROM, supports on-chip 1KB SRAM without external storage components, and saves more I/O pins. It has four 8-bit I/O ports and an additional 4-bit I/O port and wait state control signals, three 16-bit timers, counters, 12 interrupt sources with two interrupt priority levels, and two enhanced full dual Industrial serial communication port and programmable watchdog timer; only need to add reset, crystal oscillator circuit and power supply circuit.
In this design, the working frequency of W77E58 is 40MHz. Its P1 port is connected to the various control pins of TRF6901 to complete the control of the transceiver chip and provide clock signals required for data transmission; serial port 1 is connected to the data transceiver end of TRF6901 to realize serial communication of data. MCU serial port 0 is connected to chip ICL232, and data transmission is completed through asynchronous communication. Just set w77E58 serial port 1 to work in mode 1, and select the same baud rate as the computer. This part of the design is mainly concentrated in the program design part, and the Pl port can be used as an ordinary I/O port.
2.1.4 Power supply management module
The schematic diagram of the power supply management module circuit is shown in Figure 4. LM317T is a three-terminal voltage regulator, which can provide 1.2V～37V power supply voltage by changing the value of variable resistor R6. At the same time, IC load overload protection is provided. The input end and output end of the power supply management module circuit are connected in parallel with a tantalum capacitor suitable for filtering low-frequency noise and a monolithic capacitor suitable for filtering high-frequency noise to improve the quality of the power supply.
2.2 Software design
The software design of the reader mainly includes two parts: the main program design and the tag read-write anti-collision program design.
2.2.1 Main program design
The reader is used in logistics warehouse management and needs to be connected to the upper WMS system, so the reader works under the supervision of the PC, and the PC and the reader communicate in a master-slave manner. As shown in Figure 5, in this design, because the internal working mode of the transceiver chip is connected to the MCU to control the internal register programming through external pins, the main program also includes a working mode modification program, which improves the flexibility of reader applications; at the same time It also includes RSSI (Signal Strength Detection), which greatly improves the accuracy of reading data. After the MCU completes the normal power-on reset and initialization process, the PC prompts the user whether to set and modify the internal working mode, if necessary, then transfer to the working mode modification program, otherwise the MCU enters the ready-to-work state and is ready to receive Relevant execution instructions sent by the PC. After receiving the instruction, the MCU transfers to processing related programs. After the processing is completed, the result information is returned and the waiting state is entered again.
2.2.2 Anti-collision program design
Anti-collision programming is an important part of the programming of readers. When the reader enters the working state, all tags within the coverage area of its antenna will be activated, in a waiting state, ready to respond to reader commands at any time, which causes tag read-write conflicts. To solve this problem. The tag is designed with its own anti-collision mechanism, and only needs to use the relevant instruction set to assist in the design of an anti-collision program. The flow chart of the anti-collision program is shown in Figure 6. When the tag in the active state receives the reader SELECT command, it sends its own UID to the reader. At this time, if there are more than one tag sending UID at the same time, the reader will always conflict with each other and send the FAIL command to the tag, and the tag will modify its own related parameter values through the internal anti-collision algorithm. After that, the qualified tags will send the UID to the reader again, and the reader will determine the conflict, and repeat the above operation until only one tag meets the conditions, then it will jump out of the anti-collision program and enter the tag subsequent processing program. At the same time, the remaining tags will be automatically processed. Modify the relevant value of itself to prepare for the next reading; if there is no tag that meets the conditions at this time, the reader will send the SUCCESS command, and the tag will modify its own parameters and wait for the reader to detect the command.
Based on the in-depth analysis of the application background of the current RFID system in the field of logistics warehousing management, this paper proposes a design method for readers based on logistics warehousing management. The reader has simple design, flexible application and low production cost. In the future, the reader will be used in actual logistics and warehousing management, and in view of the problems of reading and writing speed, distance, confidentiality and other aspects that appear in actual applications, the reader design will be further improved to make the overall The performance has been greatly improved, which promotes the large-scale application of RFID systems in the field of logistics and warehouse management in my country.
Shanghai Nanqing Intelligent Technology Co., Ltd.
Contact: Yao Jinsheng
Phone: 13817705453/021-64826702
QQ: 765079947
[ad_2]
