RFID
We will use the RFID Card Reader (RC522) module to read data from RFID tags and key fobs.
RFID is commonly used in systems like apartment access keys, office entry cards, smart parking setups, hotel keycards, toll passes, and contactless credit cards. These systems all work in a similar way. You bring a card or tag close to a reader, and the reader identifies it wirelessly.
We will do a similar thing using the Raspberry Pi Pico, but instead of just reading data, we will also learn how to write data to RFID tags and understand how the system works.
What is RFID?
RFID stands for Radio Frequency Identification. It is a wireless technology used to identify objects using radio waves.
An RFID system has two main parts. One is the reader, and the other is the tag. The reader generates a radio field. When a tag comes close to this field, the tag is powered by it and sends data back to the reader. Most basic RFID tags do not have a battery.
The data stored on a tag can be as simple as a unique ID, or it can include small blocks of memory that can be read from and written to. The reader handles all the radio communication, and your microcontroller talks to the reader using a standard interface like SPI.
In this book, we will focus on short range RFID, where the tag needs to be very close to the reader. This is the type commonly used for access cards, key fobs, and similar systems.
Categories By Range
RFID systems can be categorized by their operating frequency, which directly affects communication range, data rate, and typical use cases. The three main categories are Low Frequency (LF), High Frequency (HF), and Ultra High Frequency (UHF).
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Low Frequency (LF)
LF RFID operates around 125 kHz. These systems have a very short read range, typically up to about 10 cm. Data transfer is slow, but LF RFID is relatively tolerant to interference from metal and liquids. Because of this, it is commonly used in simple access control systems and livestock tracking. -
High Frequency (HF)
HF RFID operates at 13.56 MHz and typically offers a read range from about 10 cm up to 1 m, depending on antenna size and power. HF systems provide moderate data rates and support more complex protocols, allowing both read and write operations. This category is widely used in access control systems for offices, apartments, and hotels, as well as in ticketing, contactless payments, and short range data transfer.We are going to use this category in this book, specifically the RC522 module, which operates at 13.56 MHz.
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Ultra High Frequency (UHF)
UHF RFID operates in the 860 to 960 MHz range and supports much longer read distances, often up to 12 m or more. These systems offer higher data rates and can read multiple tags simultaneously. UHF RFID is commonly used in retail inventory management, logistics, supply chain tracking, and anti counterfeiting applications.
Categories By Power source
RFID tags can be categorized based on how they are powered. The two main types are active and passive tags.
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Active RFID Tags
Active tags include an internal battery, which allows them to transmit signals on their own. This enables much longer communication ranges compared to passive tags. Active RFID tags are commonly used for tracking large assets such as rail cars, shipping containers, and equipment that must be monitored over long distances. -
Passive RFID Tags
Passive tags do not have a battery. Instead, they draw power from the electromagnetic field generated by the RFID reader. Once powered, the tag sends its data back to the reader using radio waves. Passive RFID tags are the most widely used type and are found in access cards, key fobs, and contactless payment systems.
The RC522 module used in this book works with passive RFID tags.
RFID System Components
The RFID reader is technically referred to as the PCD (Proximity Coupling Device). In passive RFID systems, the reader generates an electromagnetic field that powers the tag and enables communication.
The tag itself is called an RFID tag, or in technical terms, a PICC (Proximity Integrated Circuit Card). It is good to know these technical terms as well. They will come in handy if you want to refer to datasheets and other documents.
RFID readers typically include internal components such as FIFO buffers and non volatile memory like EEPROM. Many readers also include cryptographic features to support secure communication with tags, allowing only authenticated readers to interact with protected data. For example, RFID readers from NXP Semiconductors use the Crypto-1 cipher for authentication.
Each RFID tag has a hardcoded UID (Unique Identifier). Depending on the tag type, this UID can be 4, 7, or 10 bytes in size and is used to uniquely identify the tag.