RFID Module, MFRC522 with UART, SPI, I²C Interface

Overview

The RobotDyn MFRC522 RFID Module is a 13.56 MHz RFID reader/writer based on the NXP MFRC522 IC. It can read and write to ISO/IEC 14443 Type A tags — most commonly MIFARE Classic 1K (1 KB storage), MIFARE Ultralight (64 bytes), and NTAG21x series.

This module is distinctive because it supports three interfaces (SPI, I²C, UART), making it flexible for projects on different MCU platforms or where pin count is limited.

Pinout

Default mode is SPI. To switch:

• I²C mode: Connect EA (pin selectable on chip) to VDD, set address jumpers
• UART mode: Pull EA high; data via MISO (TX) / SDA (RX)

Most libraries (including the popular MFRC522 Arduino library) assume SPI mode — easiest for getting started.

Arduino Code Example (SPI Mode)

#include <SPI.h>
#include <MFRC522.h>

#define SS_PIN  10
#define RST_PIN 9

MFRC522 rfid(SS_PIN, RST_PIN);

void setup() {
  Serial.begin(9600);
  SPI.begin();
  rfid.PCD_Init();
  Serial.println("Tap a card...");
}

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

  Serial.print("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();
}

Install the MFRC522 library from the Arduino Library Manager.

SPI Wiring (Arduino Uno)

For Mega/Nano/ESP8266/ESP32, MOSI/MISO/SCK pins differ — check your board’s SPI pin mapping.

Read Range Notes

Realistic read distance is 30–50 mm, often less through plastic enclosures or metal-backed surfaces. Tips for maximum range:

• Keep the module away from metal (especially the antenna coil area)
• Don’t enclose in a metal case — RFID won’t work through aluminum/steel
• Lower-quality clone cards may have weaker antennas (shorter range)

Common Uses

• Access control systems
• Time-attendance trackers
• Inventory / asset tracking
• Custom NFC tag readers
• Maker projects (RFID-activated lockboxes, music triggers, etc.)

Where to Buy in 2026

MFRC522 modules are among the cheapest RFID readers — typically $1–3 each. Look for boards with all 8 pins broken out (some cheaper ones omit IRQ or interface-selection pins).

Documentation

• Pinout PDF — coming soon
• Interface selection guide (SPI vs. I²C vs. UART) — coming soon