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MFRC522 RFID/NFC reader module with SPI interface for reading 13.56 MHz MIFARE cards and tags.

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Pins

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3.3V
power
Voltage supply (3.3V)
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RST
input
Reset (active low)
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GND
ground
Ground
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IRQ
output
Interrupt request (active low)
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MISO
spi
SPI data out
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MOSI
spi
SPI data in
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SCK
spi
SPI clock
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SDA
spi
SPI chip select (active low)

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Attributes

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uid
string
default:""
Custom UID (for Blue Card only)

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UID format

The UID can be specified in the following lengths:
  • 4 bytes: 01:02:03:04 (MIFARE Classic)
  • 7 bytes: 04:11:22:33:44:55:66 (MIFARE Ultralight)
Each byte must be two hexadecimal characters (00-FF), separated by colons.

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Card presets

The simulator provides built-in card presets for quick testing. Click on the MFRC522 to open the control panel where you can select a card:
IndexPresetColorUIDCard Type
0Blue CardBlue01:02:03:04MIFARE Classic 1K
1Green CardGreen11:22:33:44MIFARE Classic 1K
2Yellow CardYellow55:66:77:88MIFARE Classic 1K
3Red CardRedAA:BB:CC:DDMIFARE Classic 1K
4NFC TagGray04:11:22:33:44:55:66MIFARE Ultralight
5Key FobOrangeC0:FF:EE:99MIFARE Mini
The uid attribute only affects the Blue Card (index 0). Other cards always use their preset UIDs. This lets you customize your main card while keeping the others for multi-user testing.

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Controlling the reader

The control panel provides two ways to present a card:
  • Tap button - Presents the card briefly (500ms), simulating a quick tap
  • Hold switch - Keeps the card presented until you toggle it off
This allows testing both tap-and-go scenarios and scenarios where the card needs to stay on the reader.

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Keyboard shortcuts

Click on the control panel to focus it, then use these shortcuts:
KeyAction
bSelect Blue Card
gSelect Green Card
ySelect Yellow Card
rSelect Red Card
nSelect NFC Tag
kSelect Key Fob
tTap (present card briefly)

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Using the MFRC522

The MFRC522 communicates via SPI (Mode 0) and is commonly used with the MFRC522 library by Miguel Balboa or the Arduino_MFRC522v2 library. Common use cases:
  • Access control systems
  • Attendance tracking (multi-user)
  • Smart home door locks
  • NFC tag reading projects

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Arduino code example

The example below uses the MFRC522 library to detect and read card UIDs. On ESP32, the default SPI pins are used with GPIO 5 for chip select and GPIO 21 for reset. 
#include <SPI.h>
#include <MFRC522.h>

#define SS_PIN  5
#define RST_PIN 21

MFRC522 rfid(SS_PIN, RST_PIN);

void setup() {
  Serial.begin(115200);
  SPI.begin();
  rfid.PCD_Init();
  Serial.println("MFRC522 Ready");
  Serial.println("Scan a card...");
}

void loop() {
  if (!rfid.PICC_IsNewCardPresent()) {
    return;
  }

  if (!rfid.PICC_ReadCardSerial()) {
    return;
  }

  Serial.print("Card UID:");
  for (byte i = 0; i < rfid.uid.size; i++) {
    Serial.print(rfid.uid.uidByte[i] < 0x10 ? " 0" : " ");
    Serial.print(rfid.uid.uidByte[i], HEX);
  }
  Serial.println();

  rfid.PICC_HaltA();
  delay(1000);
}

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Arduino Uno wiring

MFRC522Arduino Uno
VCC3.3V
RST9
GNDGND
MISO12
MOSI11
SCK13
SDA10

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ESP32 wiring

MFRC522ESP32
VCC3.3V
RSTGPIO 21
GNDGND
MISOGPIO 19
MOSIGPIO 23
SCKGPIO 18
SDAGPIO 5

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Automation controls

The MFRC522 reader can be controlled using Automation Scenarios. It exposes the following controls:
ControlTypeDescription
cardintCard preset index (0-5, see table)
tagPresentint1 to present card, 0 to remove

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Example scenario: Multi-user attendance

The following scenario tests an attendance system with multiple cards: 
name: Attendance System Test
version: 1

steps:
  - wait-serial: 'System Ready'

  # Select Blue Card and present it
  - set-control:
      part-id: rfid1
      control: card
      value: 0

  - set-control:
      part-id: rfid1
      control: tagPresent
      value: 1

  - wait-serial: 'Welcome, Alice'

  # Remove card
  - set-control:
      part-id: rfid1
      control: tagPresent
      value: 0

  - delay: 500ms

  # Select Red Card (unauthorized)
  - set-control:
      part-id: rfid1
      control: card
      value: 3

  - set-control:
      part-id: rfid1
      control: tagPresent
      value: 1

  - wait-serial: 'Access Denied'

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Simulator examples

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