The hottest is based on msp430f2012 and ia4420

2022-07-29
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Active RFID tag design based on msp430f2012 and ia4420

overview

radio frequency identification (power-off RFID) is one of the fastest-growing wireless technologies in recent years. It brings the advantages of bar code and wireless technology into asset management, product tracking, shipping and transportation identification, inventory control and positioning detection. Most RFID systems use passive tags that receive power from the reader via RF. This will help to reduce the label size and cost, but will limit the reading range and data storage capacity. Active tags with batteries offer a wide range of readability and greater reliability, but they are larger and more expensive. Using the latest low-power MCU and wireless data transmission chip, the purpose of this design is to design an active RFID tag which not only has long reading distance, high reliability, but also has lower cost and longer service life

analysis of design scheme

the active RFID completed in this design shall have the characteristics of low cost, low power consumption, long reading distance and adjustable distance, battery power supply, etc. By analyzing these characteristics of active RFID, a design scheme is formed as follows:

low cost: in terms of the general RFID based electronic identification system, RFID tags used to mark objects are always used in a large amount. The unit price of the label directly affects the overall cost of the system. Although active RFID has many advantages over passive RFID, such as long recognition distance, fast recognition speed and good anti-collision performance, if the spring on the piston breaks or the spring force is too small and the price difference is large, it will also become an obstacle in the application and promotion. Therefore, the label cost should be reduced as much as possible

starting from the selection of devices, the MCU and wireless data transmission chip with high integration of 6 and 3 extended wedge clamps are selected to minimize the number of peripheral devices, which can not only reduce the hardware cost, but also avoid the unified adjustment in the production process and reduce the production cost. Msp430f2012 single chip microcomputer is selected in this design, and the internal PLL circuit can save the external crystal oscillator necessary for general single chip microcomputer; The built-in power supply voltage monitoring/undervoltage reset module (BOR) eliminates the external reset circuit; Ia4420 wireless data transmission chip is selected, which is one of the least peripheral components in similar wireless data transmission chips at present (only one 10MHz crystal oscillator is required); The differential antenna interface can directly connect the microstrip antenna designed on the PCB. All these make the hardware cost of this design to the lowest

low power consumption: since the active RFID tag supplies power to the battery, in order to prolong the service life of the battery, the system has strict requirements for low power consumption performance. MSP430 MCU has 0.5mA hold mode standby current and 250ma/mips operating power consumption. It is recognized as a low-power MCU in the industry at present; The low power standby mode current consumption of ia4420 is as low as 0.3mA. It provides a basic guarantee for the low power performance of this design. Low power design, on the one hand, starts with the selection of components, on the other hand, it is necessary to design and optimize the reasonable operation sequence, so that the circuit can be in standby state most of the time on the premise of completing the label function

long distance and adjustable distance: the line of sight transmission distance of wireless signal in free space is directly proportional to the log logarithm of the total gain of the system. The transmission distance can be increased by selecting a wireless data transmission chip with high receiving sensitivity without increasing the strength of the transmitted signal

ia4420 has a receiving sensitivity of -109dbm and a maximum RF signal output power of 8dbm. The measured transmission distance in outdoor open ground is more than 200 meters. According to the "6dB" rule, in a wireless system, the transmission distance will be doubled or shortened for every 6dB increase or decrease in the total gain. The signal output power of the ia4420 has 8 levels of 0, -3dbm, -6 DBM, -9 DBM, -12 DBM, -15 DBM, -18 DBM, -21 DBM, which can be adjusted in combination with 0, -6, -14, -20 adjustable LAN gain at the receiving end, realizing a wide range of multi-level adjustment of the label reading distance

battery power supply: a single CR2032 button type lithium manganese battery is selected in this design. The nominal voltage of the battery is 3V, the capacity is 200MAH, and the recommended intermittent discharge current is 15mA. CR2032 has an internal ultra-low leakage of less than 1% per year and an extremely flat discharge curve (these two characteristics are ideal for extending the service life of the battery). This design eliminates the voltage stabilizing circuit between the battery and the device, and directly supplies power to the system by the battery. It also saves the static current consumption caused by the voltage stabilizing circuit, and further extends the battery life. In order to prevent the transient reduction of battery voltage caused by large current in emission state, a large capacity capacitor is used in parallel with the battery

a noticeable problem is that when the battery is replaced, the mechanical contact of the battery wire will produce power supply noise, which will cause the incomplete reset of the single chip microcomputer and random error operation. Msp430f2012 is internally integrated with zero power undervoltage reset (BOR) protection function, which can completely reset when the voltage is lower than the safe operating range, and this problem is well solved

hardware circuit design

msp430f2011

msp430 is an ultra-low power MCU series of TI company, which perfectly integrates low power consumption, speed and on-chip peripheral devices: the CPU adopts 16 bit reduced instruction set, integrates 16 general registers and constant generators, and greatly improves the code execution efficiency; This series of microcontrollers also integrate a large number of peripheral modules into the chip, which is suitable for forming a more complete system on chip; Five low power consumption modes are provided, mainly for battery powered applications. Msp430f2012, a new type of MCU with lower cost and higher performance in MSP430 series, is selected in this design

ia4420

ia4420 is an integrated wireless data transmission chip launched by integration company. RF functions are all built-in, and only one 10MHz crystal oscillator can work externally

see Figure 1 for the circuit diagram of active RFID tag

Figure 1 circuit diagram of active RFID tag

communication protocol

all tags and readers work on the same radio frequency for wireless data transmission. When there is only one tag within the reading range (wireless signal coverage) of the tag reader, the tag and the reader conduct point-to-point wireless communication, and the radio signal will not conflict. However, if there are multiple tags in the reading range of the reader, it is necessary to consider the radio signal conflicts caused by multiple tags sending data (multiple access) at the same time, and formulate corresponding anti-collision mechanisms to solve them

the design complies with all the agreements on the physical layer and data link layer of the active RFID tag communication protocol in iso/iec 433 MHz active RFID Air interface communication parameters

conclusion

by reasonably selecting components, optimizing the circuit around the characteristics of low cost, low power consumption, long distance, battery power supply, and complying with the iso/iec standard communication protocol in the design, the active RFID tag has great advantages in performance index, stability, compatibility with international standards and low hardware cost

the RFID tag completed by this design, together with the supporting reader, can form an electronic identification/positioning system for people or objects, which is widely used in many fields such as mining, industrial production, road traffic, logistics and transportation, medical treatment, medicine, national defense and security

reprinted from: Design Innovation

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