RC522 RFID Mifare Reader + Writer 13.56MHz with Keychain and Crad Tag


MFRC522 RFID is the wireless technology commonly embedded into key cards to give access to something like a locked door by holding the card up to a reader.

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MFRC522 RFID is the wireless technology commonly embedded into key cards to give access to something like a locked door by holding the card up to a reader.  It is also used in many other applications such as inventory control, animal identification and casino tracking and billing of customers.  MFRC522 is the RFID technology from NXP Semiconductors.


  • MFRC522 RFID Reader Module
  • RFID Key Card
  • RFID Key Ring
  • Straight and right-angle male headers


  • MFRC522 Reader supports MIFARE Mini, 1K, 4K, Ultralight, DESFire EV1 and Plus RF protocols
  • Ships with blank MIFAR 1K Key Card and Key Chain
  • Conforms to parts of the ISO/IEC 14443 Type A 13.56MHz smart card standard
  • 13.56MHz operation
  • SPI Interface
  • 3.3V operation

RFID stands for ‘Radio Frequency Identification’.  This kit is ideal for becoming familiar with RFID technology and it is suitable for implementing a complete basic RFID application.

The RFID Reader which is the circuit board contains the MFRC522 Contactless Reader Integrated Circuit.  The Reader can both read from and write to key cards or key rings.  The Readers are referred to as the Proximity Coupling Device (PCD).

The PCD board includes an RF antenna which is made from PCB traces which is why it is as big as it is.  The RF antenna creates a 13.56MHz electromagnetic field that is used to both power and communicate with a key card or key ring when it comes within about 1 inch distance.  The PCD can read cards placed on either side of the PCB.

The key card and key ring that comes with the kit each contains a small embedded RFID chip. These are referred to as a Proximity Integrated Circuit Card (PICC).  These PICC devices do not contain a battery, but rather the chip inside is powered by the RF energy of the PCD when it comes into close proximity. Once the PICC chip is activated, data can be read from or written to the chip. Every RFID chip has a unique serial number that identifies that particular key card, key ring or whatever else the RFID chip is embedded in.

The MIFARE Classic 1K devices included in this kit provide 1024 bytes of data storage. The first 16 bytes are reserved for the serial number of the card and mfg data. The remaining memory is divided into 16 sectors. Each sector can be protected by two different keys. The first 16 bytes of each sector is reserved for the access keys and conditions.

This shows the typical header info and the content of the last 3 memory sectors of a typical PICC device as reported by the software program down below.

Card UID:  Stands for Card Unique ID and is the unique serial number assigned to that device

Card SAK:  Stands for Select Acknowledge.  This identifies the particular chip type and its level of compliance to the ISO/IEC 18092 Protocol standard.  These PICCs will all report as 0x08

PICC Type:  Identifies the particular technology being used.  In this case it is the MIFARE 1KB Classic

Sector Block:  The 16 sector blocks follow.  The first line of each sector includes the keys for that sector which are set to all 0xFFs from the factory.  The next 3 lines of each sector are the user data bytes are all set to their default 0x00 from the factory.  These blocks can be used to write data to memory and read it back out later.  For instance in some cases it may be desirable to increment a number on the card each time the card is used or to add a dollar amount.

Module Connections

The main connections are via an 8-pin male header.  Both straight and right angle headers are included in the kit.  The header can be soldered to either side of the board or wires can be used for attachment.

1 x 8 Header

  • 3.3V =   3.3V power – Usually powered off 3.3V output of MCU
  • RST =    Reset – Under MCU control
  • GND  =  Ground – must be common with the MCU
  • IRQ  =    Interrupt Request Output.  Not typically used.
  • MISO = SPI MISO – Connect to same on MCU
  • MOSI = SPI MOSI – Connect to same on MCU
  • SCK =    SPI SCK – Connect to same on MCU
  • SDA =    SPI SDA / SS – Connect to same on MCU

The module has 4 holes for mounting.


These modules have good build quality and have worked well in our testing.  Pair it with one of our electric door solenoids below and you are half way to implementing a key card entry setup.

Take note that the RFC522 Reader operates at 3.3V only.  In our example below we are powering it off the Uno 3.3V output.  When using the device with a 5V MCU, the SPI interface signals should be level shifted to avoid possible damage.  In our testing, we have operated these modules off 5V SPI signals without any issues noted, but a level translator is recommended to stay within the published chip specs, especially if putting into permanent operation.  Our TXS0108E 8-Ch Logic Level Translator shown below works well for this purpose.

MFRC522 is an older RFID technology that is easy to use but it is not impervious to hacking.  If you need high security such as in some commercial applications, one of the newer standards such as MIFARE Plus or MiFare DESFire should be used.  With the higher security comes a higher level of difficulty in using those parts which is what makes these parts ideal for getting started with RFID technology and implementing lower security applications.

In our example we are using the MFRC522 library that can be downloaded from the Arduino IDE.  The PCD Reader itself can support the other standards, but the library used here implements support for the RC522 only.

The program shown here is taken from the DumpInfo example program that comes with the library and shows how easy it is to get basically up and running with reading a card.  We use this program to test that the hardware and cards work before shipment.

The library also comes with a number of example programs that illustrate actual applications in considerable detail that can help jump-start a more full featured application.

Pins RST and SS_PIN are connected to D9 and D10 respectively.  This are software configurable and can be changes as needed.  The table below shows the typical connections for different Arduino MCU.

Once everything is hooked up and the program is downloaded and running, open the Serial Monitor window to see the output.  Note that we are using a baud rate of 115200 so set the Serial Monitor window accordingly.  We are using a higher speed link so that we can download the data faster to the window.

Hold the key card up near the antenna of the Reader and you should see the content of the card being downloaded.  If you move the card away during the middle of the data download, you will get a ‘PCD_Authenticate() Failed: error.  If that happens, just move the card back near the antenna and the data download will be restarted.



 Operating Ratings
     Vcc 2.5 to 3.6V
       Imax Reader Module 23mA (measured)
        Data Rates Maximum 848 kBd
     Detection Distance Maximum 25mm  (typical measured)
     Subcarrier Frequency 13.56MHz
Dimensions L x W (PCB) 60 x 40mm (2.4 x 1.6″)
Datasheets NXP MFRC522


Wikipedia – RFID

GitHub – Software Library



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