This paper introduces the design concept of active tags, and designs RFID tags based on the principle of low power consumption and high efficiency for the general small-area space RFID positioning requirements in coal mines. The system uses the low-power combination of MSP430F2012 microcontroller and nRF24L01 RF chip on the hardware; the software combines the characteristics of RFID positioning, introduces the design method different from the general identification label, 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 [1]. Passive tags acquire energy by capturing electromagnetic waves emitted by readers, which has the advantages of low cost and small size. Active tags are usually powered by batteries and have communication. The advantages are far distance, fast reading speed and good reliability [2], but in order to meet the underground positioning of coal mine, it is necessary to consider the low power consumption 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 band. The system structure block diagram is shown in Figure 1.
Figure 1 System block diagram
2.2 chip selection and low power design
TI's MSP430 series of microcontrollers is a 16-bit Flash RISC instruction set microcontroller [3], known for its ultra-low power consumption.
MSP430F2012 chip operating voltage is only 1.8~3.6V, consumption current is 0.1μA in power-down mode, and consumption current is only 0.5μA in standby mode. In this design, MSP430F2012 is placed in standby mode for a long time, wake-up by interrupt The way it is put into a working state to save energy. The MSP430F2012 has three independent clock sources: on-chip VLO, off-chip crystal, and DCO. The off-chip clock is based on an external crystal oscillator; 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.
nRF24L01 is a 2.4GHz ultra-low power single-chip wireless transceiver chip developed by Nordic. The chip has 125 frequency points, which can realize point-to-point and point-to-multipoint wireless communication. The maximum transmission rate is up to 2Mbps, and the working voltage is 1.9~3.6. V[4]. In order to highlight its low power performance, the chip presets two standby modes and one power down mode. What's more worth mentioning is that the ShockBurstTM mode and the enhanced ShockBurstTM mode of the nRF24L01 [4] truly realize the low-speed high-speed output, that is, the MCU sends the data to the nRF24L01 on-chip FIFO at a low speed, but transmits it at a high speed of 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.
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