Talk about RFID technology

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Talk about RFID technology [Copy link]

1. Introduction to RFID Radio frequency tags are physical carriers of electronic product codes (EPCs). They are attached to trackable items and can be circulated globally and can be identified, read and written. RFID (Radio Frequency Identification) technology has attracted people's attention in recent years as a key technology for building the "Internet of Things". Radio frequency identification (RFID) is a wireless communication technology that can identify specific targets and read and write related data through radio signals without the need to establish mechanical or optical contact between the identification system and the specific target. Radio frequency identification technology is based on the transformer coupling model (energy transfer and signal transfer between primary and secondary) in the low frequency band and the spatial coupling model of radar detection targets in the high frequency band (the radar transmits electromagnetic wave signals and returns to the radar receiver after hitting the target with target information). The radio signal transmits data from the tag attached to the object through an electromagnetic field tuned to radio frequency to automatically identify and track the object. Some tags can get energy from the electromagnetic field emitted by the identifier during identification, and do not need batteries; some tags have their own power supply and can actively emit radio waves (electromagnetic fields tuned to radio frequencies). Tags contain electronically stored information and can be identified within a few meters. Unlike barcodes, radio frequency tags do not need to be within the line of sight of the identifier and can also be embedded in the tracked object. The reader of the RFID electronic tag communicates wirelessly with the RFID electronic tag through the antenna, and can read or write the tag identification code and memory data. RFID technology can identify high-speed moving objects and can identify multiple tags at the same time, and the operation is quick and convenient. Tag: composed of coupling elements and chips, each tag has a unique electronic code, attached to the object to identify the target object; Reader: a device that reads (and sometimes writes) tag information, which can be designed as handheld or fixed; Antenna: transmits radio frequency signals between tags and readers.

Figure 1: Schematic diagram of RFID system

Passive RFID products are the earliest developed, the most mature and the most widely used products in the market. For example, bus cards, canteen meal cards, bank cards, hotel access cards, second-generation ID cards, etc., which can be seen everywhere in our daily lives, belong to the category of close-range contact identification. The main operating frequencies of its products are low frequency 125KHZ, high frequency 13.56MHZ, ultra-high frequency 433MHZ, and ultra-high frequency 915MHZ. Active RFID products have been slowly developed in recent years. Their long-distance automatic identification characteristics determine their huge application space and market potential. In the field of long-distance automatic identification, such as smart prisons, smart hospitals, smart parking lots, smart transportation, smart cities, smart earth and the Internet of Things, they have important applications. Active RFID has emerged in this field and belongs to the category of long-distance automatic identification. The main operating frequencies of the products are UHF 433MHZ, microwave 2.4GHZ and 5.8GHZ. The air interface communication protocol regulates the information exchange between the reader and the electronic tag, with the purpose of interoperability between equipment produced by different manufacturers. ISO/IEC has formulated air interface protocols for five frequency bands. 2. Passive RFID design case In current technical applications, the most widely used products are passive RFID products. In many circuit designs applied to passive RFID, the 13.56MHZ RC522 module is often selected, which is a widely used passive RFID module. For the application circuit of RC522, a 3V3 DC power supply is used, and then the received information is communicated through the SPI interface. The application schematic is shown in Figure 2:

Figure 2: RC522 application schematic

The 13.56MHZ antenna circuit includes a signal receiving circuit and a signal transmitting circuit. The signal transmitting circuit is divided into an EMC filter part, a matching circuit part, and a coil circuit part. Transmitting circuit: The signal transmitting part can be subdivided into three parts: an EMC filter circuit, a resonance and impedance matching circuit, and a coil. Among them: EMC filter circuit: It is mainly composed of a low-pass filter composed of an LC low-pass filter circuit. The antenna signal sent by the card reader chip through TX1 and TX2 is mainly 13.56Mhz, but it is inevitable that there will be high-order harmonics. Therefore, the main function of the low-pass filter in this part is to filter out useless signals higher than 13.56Mhz. This is conducive to the normal communication between the card reader and the card, and can also reduce the electromagnetic interference of the antenna part to the space or nearby circuits. Matching circuit: This part mainly adjusts the resonant frequency point of the entire antenna transmitting part to around 13.56Mhz, so that the signal amplitude on the coil can be increased, which is conducive to magnetic field radiation. In addition, the matching circuit must also match the resistance of the transmitting part circuit to the output resistance of the card reader chip, typically 50 ohms (different for different chips). This allows the antenna part to obtain maximum power and is conducive to improving the card reading distance. Coil: The coil can be a PCB coil or a copper wire coil. Receiving circuit: The signal receiving circuit is relatively simple and consists of four components. The Cmin capacitor can stabilize the fixed reference voltage Vmin provided inside the card reader chip. R1 introduces this reference voltage to the RX pin, adding a fixed DC level to the chip's receiving signal. CRx introduces the feedback signal from the generating circuit and superimposes it with Vmin and then sends it to the chip. By adjusting the ratio of R2 and R1, the amplitude of the Rx pin signal can be adjusted to optimize the card reading distance of the chip. The following points should also be noted when designing the PCB: The entire transmitting circuit must be designed symmetrically, and the trace lengths of the two signals from Tx1 and Tx2 should be as consistent as possible. The two inductors should be packaged in 0805 or above to ensure that there is enough current passing through (680nH/0805), otherwise it will not be conducive to long-distance card reading. The length and width of the PCB coil depend on the specific situation. If the circuit board is not restricted by the mold, it can be designed to be consistent with the length and width of ordinary cards. If the coil size is limited, the coil area can also be reduced. The general principle is to design it to be consistent with the size of the card being read; as for the number of coils, the length and width should be above 3x3cm and 4 turns are enough. Too many turns will make it difficult to adjust the parameters. If it is less than 3x3cm, the number of turns can be increased to 6 or more; the PCB coil trace width is between 0.5mm and 1mm, and the spacing is the same as the line width. In addition, the corners of the coil are best transitioned with arcs. The coil part cannot be covered with copper over a large area, otherwise it will cause eddy current effects in the magnetic field and cause serious energy loss. It should be noted that there should be no large metal components, metal objects, metal coatings, etc. within the range of the coil (the entire space around the coil). The ground of all devices in the entire transmitting circuit must be connected to the same ground wire and returned to the TVSS pin of the chip. There should be no large area of copper near the antenna circuit devices, and the devices should be connected with wires. 3.Summary In this era of continuous development of Internet of Things technology, RFID, as a perception layer technology used in the Internet of Things, has an inextricable relationship with the Internet of Things. In recent years, RFID technology has greatly increased the functions of the Internet of Things and enriched the connotation of the Internet of Things. The development of the Internet of Things has also promoted the development and application of RFID technology. For example, in response to the special requirements of "things" such as fresh goods and medicines for the Internet of Things, RFID tags can not only provide static information about the goods, but also provide dynamic information such as the location of the goods and the surrounding temperature and humidity, which greatly improves the intelligence of RFID tags. At present, the Internet of Things using the RFID perception layer has realized "people-to-people" communication and "people-to-things" communication, but in order to realize "thing-to-thing" communication and interaction in the future Internet of Things, it is necessary to improve the intelligence level of RFID tags installed on "things" to make "things" intelligent. In addition, standardization, interoperability, protocols, regulations, and connection technologies still need to be improved and perfected.

okby

RC522 is too expensive and I cannot afford it. Now many domestic models can be directly replaced.

okby

For RC522 and RC523, you can contact me to replace them with NZ3801. We have technical support to assist in antenna debugging.