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

#define SS_PIN  5
#define RST_PIN 22

MFRC522 rfid(SS_PIN, RST_PIN);

void setup() {
  Serial.begin(115200);   // send to XIAO
  SPI.begin();
  rfid.PCD_Init();
}

void loop() {

  if (!rfid.PICC_IsNewCardPresent()) return;
  if (!rfid.PICC_ReadCardSerial()) return;

  String uid = "";

  for (byte i = 0; i < rfid.uid.size; i++) {
    uid += String(rfid.uid.uidByte[i], HEX);
  }

  Serial.println(uid);   // send to XIAO
  delay(1000);
}