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

const int RST_PIN = D0;     // Reset pin
const int SS_PIN = D1;      // SDA / Chip Select

MFRC522 mfrc522(SS_PIN, RST_PIN);   // Create instance

void setup() {
  Serial.begin(9600);
  while (!Serial);  // Wait for Serial Monitor (optional)
  SPI.begin();       // Init SPI bus
  mfrc522.PCD_Init(); // Init MFRC522
  Serial.println("Scan an RFID tag...");
}

void loop() {
  if (!mfrc522.PICC_IsNewCardPresent() || !mfrc522.PICC_ReadCardSerial()) {
    return;
  }

  Serial.print("UID tag: ");
  for (byte i = 0; i < mfrc522.uid.size; i++) {
    Serial.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");
    Serial.print(mfrc522.uid.uidByte[i], HEX);
  }
  Serial.println();
  mfrc522.PICC_HaltA();
}