RC522 RFID reader (13.56 MHz) with ESP32

Supply 3.3 V Bus SPI

Pins and ESP32 wiring

Pin	Role	ESP32 pin	Notes
SDA	SPI chip select	D5	This is the SPI chip select (CS), despite the SDA label
SCK	SPI clock	D18
MOSI	SPI MOSI	D23
MISO	SPI MISO	D19
IRQ	Interrupt	D35	Interrupt, optional. Leave unconnected
GND	Ground	GND
RST	Input (the ESP32 drives it)	D25	Reset, active LOW
3.3V	Power	3V3	3.3 V only. Never 5 V

Suggested wiring for the 30-pin ESP32 DevKit, avoiding flash, input-only and strapping pins. BoardPilot checks it for you as you wire.

void setup() { pinMode(25, OUTPUT); }  // RST

void loop() {
  digitalWrite(25, HIGH);
  delay(500);
  digitalWrite(25, LOW);
  delay(500);
}

Part data: CC BY 4.0, free to reuse with credit to BoardPilot.