   if (nfc.readPassiveTargetID(PN532_MIFARE_ISO14443A, &uid[0], &uidLength)) {
     String hexId = String("");
     for (uint8_t i=0; i < uidLength; i++) {
+      if (uid[i] < 0x10) {
+        hexId += '0';
+      }
       hexId += String(uid[i], HEX);
     }
     hexId.toUpperCase();

    return;
  }

  configNfc();
  Serial.println(F("PN532 initialized"));
}

// Set the max number of retry attempts to read from a card.
// This prevents us from waiting forever for a card, which is the default behaviour of the PN532.
void configNfc() {
  nfc.setPassiveActivationRetries(1);
  nfc.SAMConfig();  
}

void initializeTimer() {

  if (enable) {
    Serial.println("Enable NFC");
    digitalWrite(NFC_RESET_PIN, HIGH);
    initializeNfc();
  } else {
    Serial.println("Disable NFC");
    digitalWrite(NFC_RESET_PIN, LOW);    
