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automatically recognizes target objects and obtains relevant information data.

- May 08, 2018 -

Wireless communication technology that automatically recognizes target objects and obtains relevant information data. It can achieve rapid recognition of moving targets and multi-target recognition. The recognition distance can reach several tens of centimeters to tens of meters; according to the way of reading and writing, it can input thousands of bytes of custom information to electronic tags, and indirectly manages the incidental RFID-enabled product information; RFID technology is non-contact, requires no manual intervention for identification work, and has extremely high confidentiality; RFID electronic labels are different from magnetic or IC cards, have no exposed contacts, and are not easily damaged. Long, can work in various harsh environments.

Based on the above characteristics, RFID technology has been widely used in various parts of the world, mainly including product anti-counterfeiting, transportation, automatic control, industrial production, identification, warehouse management, safety management, medical care, health, animal husbandry management, and book archives management. Defense military and many other applications.

Radio frequency identification system is generally composed of reader, electronic tag, antenna and host four parts, as shown in Figure 1.



Figure 1 Passive RFID System Block Diagram

The work flow of the RFID system is not complicated: the host sends user commands through the data transmission channel with the reader; the reader receives the commands, encodes and modulates the signals, and sends them through the transmitting antenna in a certain area; After entering the magnetic field, it receives the RF signal from the reader and inducts the current to obtain energy, completing the storage, transmission or other operations of the data: the reader receives the data returned by the electronic tag through the receiving antenna to perform decoding and demodulation. The processed data is sent to the host; the host receives the data returned by the reader and performs related processing.

Overall design

In order to design a passive RFID reader that can work stably in the UHF band and increase its read/write distance as much as possible, the passive RFID read/write module can be well integrated with the construction equipment IoT to realize the inside of the construction equipment. The personnel detect and locate and provide energy information for building electrical equipment. The program refines the development process of the radio frequency identification system.

The program is designed according to the modular idea, which facilitates development, management, system upgrade and maintenance. In general, passive RFID readers consist of three major components: RF transceiver modules, MCU control modules, and peripheral circuits. The RF transceiver module handles data communications between the reader and the RFID tag. The design goal of this module is to design a universal RF transceiver module for 915MHz, and contact the control part through custom I/O interfaces and functions. In the peripheral circuit, according to the design and practical application needs, they are further subdivided into: MCU control module, passive RFID radio module, reset circuit module, power management module, RS232 interface, and expansion I/O port.

UHF band passive RFID reader system structure shown in Figure 3:


Figure 2 UFH band passive RFID reader system block diagram

In the entire reader/writer system, the function of the RFID RF transceiver module is to receive commands from the host computer, encode and modulate the information according to the commands, and send them out through the antenna to control the electronic tag to perform related read/write operations and receive tags from the electronic tags. The signal is demodulated and decoded to determine the person who is wearing the tag. When selecting radio frequency chips, we mainly refer to the following indicators:

The transmit power of the chip determines the signal coverage of the RF chip. The higher the transmit power, the wider the signal coverage. Therefore, to ensure effective communication under the same conditions, the higher transmit power and larger power adjustment range should be selected. product. Chip anti-jamming capability Wireless communications are susceptible to interference. Therefore, to ensure the reliability of data communications, a chip with strong anti-interference capability should be selected. The power consumption of the chip should be based on the premise of ensuring effective data communication. The number of peripheral components of the chip The number of peripheral components of the chip affects the cost of the product on the one hand, and on the other hand it affects the soldering and debugging of components. Therefore, chips with fewer peripheral components should be selected.

The ease of use should use chips that are easy to use and program, reducing the difficulty and cycle of product development.

According to the above principle of indicators, at the same time, according to the actual needs of the design, such as price, performance parameters and many other considerations, nRF905 has a good advantage in terms of extended functions, peripheral components and ease of use, so the program uses nRF905 as a Design the main chip used in the RF transceiver module.

The nRF905 single-chip radio transceiver operates in the 433/868/915 MHz ISM band and consists of a fully integrated frequency modulator, a receiver with a demodulator, a power amplifier, a crystal oscillator, and a regulator. On-chip hardware can be used to automate Manchester encoding/decoding without the need for users to write code/decoder programs. With the SPI interface, it is easy to communicate with a microcontroller with an SPI interface through this interface. The programming configuration is very convenient; the current consumption is very low.

This design uses the STC12C5A60S2 microcontroller from STMicroelectronics. The STC12C5A60S2 microcontroller has the following features: The STC12C5A60S2 microcontroller and the MCS-51 series of microcontrollers are fully compatible with the instruction system and pins; there is an on-chip 8k byte on-line reprogrammable flash Program Memory; Full Static Operation, Operating Range: 0Hz to 24MHz; Level 3 Program Memory Encryption; 512 Bytes of Internal RAM; 32 Bit Bidirectional Input/Output Lines; Two 16-Bit Timers/Counters; Five Interrupt Sources, Two Levels Interrupt priority; a full-duplex asynchronous serial interface; intermittent and power-down modes of operation. The use of this single-chip microcomputer is sufficient to meet the needs of the design program.

The RF transceiver module NRF905 passes the TRX_CE, PWR_UP, CD, AM, DR, MISO, MOSI, SCK, CSN, TX_EN and other control pins as well as the data and always pins respectively and the single-chip microcomputer P1.0-P1.7 and P2.0, P2.1 and so on connected to achieve NRF905 control. The hardware circuit is shown in Figure 4.

The control module provides the external circuit of the STC12C5A60S2 microcontroller, as shown in Figure 5. The T extension introduces some I/Os for later application expansion and communication with the host through the serial port. The part of the hardware circuit shown in Figure 6. The NRF905 operating power hardware is used to generate a 3.3V power supply for the NRF905 RF chip. Its hardware circuit is shown as in Fig. 6.

This program has conducted in-depth research and design and development of UHF RF modules. It has designed NRF905 RF module hardware circuits, RFID main control module hardware circuits, and other auxiliary and extended hardware circuits. In the process of design and development, the data collection and design work of the RF module part was successfully completed, and certain results were achieved.


Figure 3 NRF905 radio frequency transceiver module hardware circuit


Figure 4 External Circuit of STC12C5A60S2 Microcontroller


Figure 5 extended part of the hardware circuit