MFRC522 RFID Reader

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

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

Pins

3.3V · power

Voltage supply (3.3V)

RST · input

Reset (active low)

GND · ground

Ground

IRQ · output

Interrupt request (active low)

MISO · spi

SPI data out

MOSI · spi

SPI data in

SCK · spi

SPI clock

SDA · spi

SPI chip select (active low)

Attributes

uid · string · default: ""

Custom UID (for Blue Card only)

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.

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:

Index	Preset	Color	UID	Card Type
0	Blue Card	Blue	01:02:03:04	MIFARE Classic 1K
1	Green Card	Green	11:22:33:44	MIFARE Classic 1K
2	Yellow Card	Yellow	55:66:77:88	MIFARE Classic 1K
3	Red Card	Red	AA:BB:CC:DD	MIFARE Classic 1K
4	NFC Tag	Gray	04:11:22:33:44:55:66	MIFARE Ultralight
5	Key Fob	Orange	C0:FF:EE:99	MIFARE 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.

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.

Keyboard shortcuts

Click on the control panel to focus it, then use these shortcuts:

Key	Action
b	Select Blue Card
g	Select Green Card
y	Select Yellow Card
r	Select Red Card
n	Select NFC Tag
k	Select Key Fob
t	Tap (present card briefly)

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

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);
}

Arduino Uno wiring

MFRC522	Arduino Uno
VCC	3.3V
RST	9
GND	GND
MISO	12
MOSI	11
SCK	13
SDA	10

ESP32 wiring

MFRC522	ESP32
VCC	3.3V
RST	GPIO 21
GND	GND
MISO	GPIO 19
MOSI	GPIO 23
SCK	GPIO 18
SDA	GPIO 5

Automation controls

The MFRC522 reader can be controlled using Automation Scenarios. It exposes the following controls:

Control	Type	Description
card	int	Card preset index (0-5, see table)
tagPresent	int	1 to present card, 0 to remove

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'

Simulator examples

• MFRC522 Basic Reading - Basic RFID card detection with ESP32