RC522 RFID with Arduino Uno R3

Wiring for the RC522 RFID reader (13.56 MHz) on the Arduino Uno R3 (ATmega328P, 5 V logic), chosen with the same pin rules BoardPilot uses: default buses first, and no pins that are used for flash, USB, the debugger or booting.

Wiring

RC522 RFID pin	Role	Arduino Uno R3 pin	Notes
SDA	SPI chip select	~10 (PB2)	This is the SPI chip select (CS), despite the SDA label
SCK	SPI clock	13 (PB5)
MOSI	SPI MOSI	~11 (PB3)
MISO	SPI MISO	12 (PB4)
IRQ	Interrupt	2 (PD2)	Interrupt, optional. Leave unconnected
GND	Ground	GND
RST	Input to the part	~3 (PD3)	Reset, active LOW
3.3V	Power	3.3V	3.3 V only. Never 5 V

Check before you power it on

Supply: 3.3 V from the 3.3V pin.
The RC522 RFID is a 3.3 V part and the Arduino Uno R3 uses 5 V signals. Power it from 3.3 V and put a level shifter on the signal wires, or buy a 5 V version of the module.

Test code (Arduino)

// Library: MFRC522 (miguelbalboa)
#include <SPI.h>
#include <MFRC522.h>

MFRC522 rfid(10, 3);  // SDA is the SPI chip select

void setup() {
  Serial.begin(115200);
  SPI.begin();
  rfid.PCD_Init();
  rfid.PCD_DumpVersionToSerial();  // 0x91 or 0x92 means the reader answers
}

void loop() {
  if (!rfid.PICC_IsNewCardPresent() || !rfid.PICC_ReadCardSerial()) return;
  for (byte i = 0; i < rfid.uid.size; i++) Serial.print(rfid.uid.uidByte[i], HEX);
  Serial.println();
  rfid.PICC_HaltA();
}

Arduino board: arduino:avr:uno.

Questions

Which Arduino Uno R3 pins do I use for the RC522 RFID?

SDA → ~10 (PB2), SCK → 13 (PB5), MOSI → ~11 (PB3), MISO → 12 (PB4), IRQ → 2 (PD2), GND → GND, RST → ~3 (PD3), 3.3V → 3.3V.

Does the RC522 RFID work with the Arduino Uno R3 at 5 V?

The RC522 RFID is a 3.3 V part and the Arduino Uno R3 uses 5 V signals. Power it from 3.3 V and put a level shifter on the signal wires, or buy a 5 V version of the module.

BoardPilot checks this wiring in 3D as you build it, and finds crossed or missing wires on the real board.

Download BoardPilot

Full Arduino Uno R3 pinout · RC522 RFID reader (13.56 MHz): all pins and data

The RC522 RFID on other boards

ESP32 DevKit Arduino Mega 2560 R3 Arduino Nano WeAct Black Pill STM32F411CE ESP32-C3-DevKitM-1 ESP32-S3-DevKitC-1 Nordic nRF52840 DK NUCLEO-F401RE Raspberry Pi Pico 2 Raspberry Pi Pico W Raspberry Pi Pico Teensy 4.1

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