rfid_code.cpp

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

#define SS_PIN 53  // Change this to reflect your setup
#define RST_PIN 5  // Change this to reflect your setup

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

void setup() {
    Serial.begin(9600);   // Initiate a serial communication
    SPI.begin();          // Initiate SPI bus
    mfrc522.PCD_Init();   // Initiate MFRC522
    Serial.println("Approximate your card to the reader...");
    Serial.println();
}

void loop() {
    // Look for new cards
    if (!mfrc522.PICC_IsNewCardPresent()) {
        return;
    }

    // Select one of the cards
    if (!mfrc522.PICC_ReadCardSerial()) {
        return;
    }

    // Show UID on serial monitor
    Serial.print("UID tag: ");
    String content = "";
    byte letter;
    for (byte i = 0; i < mfrc522.uid.size; i++) {
        Serial.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");
        Serial.print(mfrc522.uid.uidByte[i], HEX);
        content.concat(String(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " "));
        content.concat(String(mfrc522.uid.uidByte[i], HEX));
    }
    Serial.println();
    Serial.print("Message: ");
    content.toUpperCase();
    if (content.substring(1) == "YOUR_CARD_ID_HERE") {  // Change this to reflect your card ID
        Serial.println("Authorized access");
        Serial.println();
        delay(3000);
    }
    else {
        Serial.println("Access denied");
        delay(3000);
    }
}