RC522 RFID with Teensy 4.1

Wiring for the RC522 RFID reader (13.56 MHz) on the Teensy 4.1 (MIMXRT1062DVJ6B, 3.3 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	Teensy 4.1 pin	Notes
SDA	SPI chip select	10 (GPIO_B0_00)	This is the SPI chip select (CS), despite the SDA label
SCK	SPI clock	13 (GPIO_B0_03)
MOSI	SPI MOSI	11 (GPIO_B0_02)
MISO	SPI MISO	12 (GPIO_B0_01)
IRQ	Interrupt	2 (GPIO_EMC_04)	Interrupt, optional. Leave unconnected
GND	Ground	G
RST	Input to the part	3 (GPIO_EMC_05)	Reset, active LOW
3.3V	Power	3V	3.3 V only. Never 5 V

Check before you power it on

Supply: 3.3 V from the 3V pin.

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: teensy:avr:teensy41. Press the white program button once if the upload waits for the board.

Questions

Which Teensy 4.1 pins do I use for the RC522 RFID?

SDA → 10 (GPIO_B0_00), SCK → 13 (GPIO_B0_03), MOSI → 11 (GPIO_B0_02), MISO → 12 (GPIO_B0_01), IRQ → 2 (GPIO_EMC_04), GND → G, RST → 3 (GPIO_EMC_05), 3.3V → 3V.

Does the RC522 RFID work with the Teensy 4.1 at 3.3 V?

Yes: the RC522 RFID runs at 3.3 V and the Teensy 4.1 uses 3.3 V signals, so no level shifting is needed.

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

Download BoardPilot

Full Teensy 4.1 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 Arduino Uno R3 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

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