The scheme uses the low-power combination of MSP430F2012 microcontroller and nRF24L01 RF chip in hardware; the software combines the characteristics of RFID positioning, which is different from the design method of label which is generally used for identification, and analyzes its software design. Process and simple anti-collision capabilities. With a well-matched antenna, the design can effectively read distances of up to tens of meters, enough to meet the needs of positioning in general space.
1 Introduction
Radio Frequency Identification (RFID) technology uses wireless radio frequency to realize two-way data exchange and identify identity. RFID positioning utilizes this identification feature to locate the space by using parameters such as communication signal strength between the reader and the tag. RFID tags are divided into active and passive according to the power supply mode. Passive tags acquire energy by capturing electromagnetic waves emitted by the reader, which has the advantages of low cost and small size. The active tags are usually powered by batteries and have a long communication distance. Fast reading speed and good reliability, but need to consider low power design to enhance the battery life. Starting from the design concept of active tags, this paper designs the RFID tags according to the requirements of low power consumption and high efficiency for the requirements of RFID positioning in small-scale space, and expounds its hardware components, software processes and anti-collision capabilities.
2. System hardware design
2.1 System Structure
In addition to the low cost and miniaturization of active tags, the most important thing is to adopt a low power design. From the overall structure, the RFID tag usually includes two parts: the control terminal and the RF terminal. Therefore, when selecting the control chip and the RF chip, priority should be given to its low power consumption performance. Based on this, the MSP430F2012 control chip and nRF24L01 RF chip are selected. The antenna is selected from Nordic's PCB single-ended antenna; the tag is powered by 3V-500mAh button battery. The system operates in the 2.4 GHz global ISM band. The system structure block diagram is shown in Figure 1.
2.2 Chip selection and low power design
TI's MSP430 series of microcontrollers are 16-bit Flash RISC instruction set microcontrollers, known for their ultra-low power consumption. The MSP430F2012 chip operates at a voltage of only 1.8~3.6V, consumes 0.1μA in the power-down mode, and consumes only 0.5μA in standby mode [4]. In this design, the MSP430F2012 is placed in the waiting mode for a long time, and it is temporarily put into the working state by interrupting the wake-up to save power. The MSP430F2012 has three independent clock sources:
On-chip VLO (Ultra Low Power Oscillator), Off-Chip Crystal, DCO (Digital Controlled Oscillator). Among them, the off-chip clock is based on an external crystal; the DCO is generated on-chip and the frequency is adjustable. Obviously, the clock frequency of the main system determines the power consumption of the system, especially when a high-speed off-chip crystal is selected. Therefore, the MSP430F2012 provides the function of switching between different clock sources.
In the actual design, the basic clock control register is real-time reconfigured to switch between the main system clock and the auxiliary system clock, without losing performance and saving energy.
MSP430F2012 has five low-power modes of LPM0~LPM4. Reasonable use of these five preset modes is the key to reduce the power consumption of MCU. In this design, MSP430F2012 will enter LPM3 mode directly after power-on configuration, and open interrupt at the same time. Wait for the external interrupt signal. In addition, because the MSP430F2012 is a multi-function general-purpose single-chip microcomputer, it integrates many function modules on the chip. When the power-on configuration is stopped, all the unused function modules can also reduce the power consumption of the system.
Since nearly two-thirds of the energy consumed by RFID tags is used for wireless transmission and reception, it is crucial to choose an ultra-low-power wireless transceiver chip.
nRF24L01 is a 2.4GHz ultra-low-power single-chip wireless transceiver chip developed by Nordic. The chip has 125 frequency points and can realize point-to-point and point-to-multipoint wireless communication. The maximum transmission rate is up to 2 M bps and the working voltage is 1.9. ~3.6V. In order to highlight its low power performance, the chip presets two standby modes and one power-down mode. More worth mentioning is the ShockBurstTM mode and the enhanced ShockBurstTM mode of the nRF24L01. The Sock BurstTM mode truly realizes low-speed high-speed output, that is, the MCU sends data to the nRF24L01 on-chip FIFO at low speed, but transmits it at 1Mbps or 2Mbps. . This design utilizes the enhanced ShockBurstTM mode, which enables the MSP430F2012 to transmit data at high speed through the RF terminal even under the 32768Hz low-speed crystal oscillator, which reduces power consumption, improves efficiency, and enhances system anti-collision and coping with movement. Target ability.
2.3 Circuit Design
This system is mainly used in RFID positioning. In addition to simple identification, the focus is on the reader's measurement of the signal strength of the tag. Therefore, there is no large amount of data read and write between the reader and the tag, which can be omitted in the circuit design. Off-chip EEPROM. At the same time, the voltage regulator circuit can be omitted to save static current consumption. The hardware schematic is shown in Figure 2.
3. System software design
The system software design uses the C language programming environment under the IAR EmbeddedWorkbench V4.11B platform. The design considers the low power performance, stability and program execution efficiency of the MSP 4 3 0 F 2 0 1 2 and nRF24L01 chips.
Tinned Copper Clad Steel,Professional Tinned Copper Clad Steel,Heat-Resistant Tinned Copper-Clad Steel,Tinned Copper Clad Steel Metal Wire
changzhou yuzisenhan electronic co.,ltd , https://www.ccs-yzsh.com