#include <SPI.h>
#include <MFRC522.h>
const byte selectPin = 10, resetPin = 9;
MFRC522 reader(selectPin, resetPin);

void setup() {
  Serial.begin(9600);
  SPI.begin();
  reader.PCD_Init();
  Serial.println("Present a compatible 13.56 MHz tag");
}

void loop() {
  if (!reader.PICC_IsNewCardPresent() || !reader.PICC_ReadCardSerial()) return;
  Serial.print("UID ("); Serial.print(reader.uid.size); Serial.print(" bytes): ");
  for (byte i = 0; i < reader.uid.size; ++i) {
    if (reader.uid.uidByte[i] < 0x10) Serial.print('0');
    Serial.print(reader.uid.uidByte[i], HEX);
    if (i + 1 < reader.uid.size) Serial.print(':');
  }
  Serial.println();
  reader.PICC_HaltA();
  reader.PCD_StopCrypto1();
}