RFID-Triggered Timed Alarm System

#include <Arduino.h>
// =====================================================================
//  RFID + RTC + Relay Siren Alarm + I2C LCD — Arduino Uno
//
//  LCD (16x2 I2C, address 0x27)  → A4 (SDA), A5 (SCL)  [shared with RTC]
//  RTC (DS3231, address 0x68)    → A4 (SDA), A5 (SCL)
//  RFID (MFRC522)                → SPI  D10/D11/D12/D13, RST D9
//  Relay                         → D8   (NO → 240V AC siren Live)
// =====================================================================

#include <SPI.h>
#include <MFRC522.h>
#include <Wire.h>
#include <RTClib.h>
#include <LiquidCrystal_I2C.h>

// ---- Pin Definitions ------------------------------------------------
#define RFID_SS_PIN   10
#define RFID_RST_PIN   9
#define RELAY_PIN      8

// ---- I2C Devices ----------------------------------------------------
// LCD  : 0x27  (PCF8574 I2C backpack, standard address)
// RTC  : 0x68  (DS3231 fixed address)
LiquidCrystal_I2C lcd(0x27, 16, 2);
RTC_DS3231        rtc;
MFRC522           rfid(RFID_SS_PIN, RFID_RST_PIN);

// ---- Authorised UIDs ------------------------------------------------
// Replace the example UID with your card's actual UID (read from Serial Monitor)
const byte authorisedUID[][4] = {
  {0xDE, 0xAD, 0xBE, 0xEF}
};
const int numAuthorised = sizeof(authorisedUID) / sizeof(authorisedUID[0]);

// ---- Alarm timing ---------------------------------------------------
const unsigned long ALARM_DURATION_MS = 5000;
unsigned long alarmStartTime = 0;
bool alarmActive = false;

// ---- Forward declarations -------------------------------------------
bool isAuthorised(byte *uid, byte size);
void printDateTimeSerial();
void showDateTimeLCD();
void triggerAlarm();
void stopAlarm();
String uidString(byte *uid, byte size);

// =====================================================================
//  Helpers
// =====================================================================

String uidString(byte *uid, byte size) {
  String s = "";
  for (byte i = 0; i < size; i++) {
    if (uid[i] < 0x10) s += "0";
    s += String(uid[i], HEX);
    if (i < size - 1) s += ":";
  }
  s.toUpperCase();
  return s;
}

bool isAuthorised(byte *uid, byte size) {
  if (size != 4) return false;
  for (int i = 0; i < numAuthorised; i++) {
    if (memcmp(uid, authorisedUID[i], 4) == 0) return true;
  }
  return false;
}

void printDateTimeSerial() {
  DateTime now = rtc.now();
  Serial.print(now.year(),  DEC); Serial.print('/');
  Serial.print(now.month(), DEC); Serial.print('/');
  Serial.print(now.day(),   DEC); Serial.print("  ");
  Serial.print(now.hour(),  DEC); Serial.print(':');
  if (now.minute() < 10) Serial.print('0');
  Serial.print(now.minute(), DEC); Serial.print(':');
  if (now.second() < 10) Serial.print('0');
  Serial.print(now.second(), DEC);
}

// Show current date on LCD row 0, time on LCD row 1
void showDateTimeLCD() {
  DateTime now = rtc.now();

  // Row 0: DD/MM/YYYY
  lcd.setCursor(0, 0);
  if (now.day()   < 10) lcd.print('0'); lcd.print(now.day());
  lcd.print('/');
  if (now.month() < 10) lcd.print('0'); lcd.print(now.month());
  lcd.print('/');
  lcd.print(now.year());
  lcd.print("      ");   // clear trailing chars

  // Row 1: HH:MM:SS
  lcd.setCursor(0, 1);
  if (now.hour()   < 10) lcd.print('0'); lcd.print(now.hour());
  lcd.print(':');
  if (now.minute() < 10) lcd.print('0'); lcd.print(now.minute());
  lcd.print(':');
  if (now.second() < 10) lcd.print('0'); lcd.print(now.second());
  lcd.print("  Ready ");
}

void triggerAlarm() {
  Serial.print("[ALARM] Unauthorised card at ");
  printDateTimeSerial();
  Serial.println();

  digitalWrite(RELAY_PIN, HIGH);   // Energise relay → 240V siren ON
  alarmActive    = true;
  alarmStartTime = millis();

  // LCD: show alarm message
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("!! ALARM ACTIVE !!");
  lcd.setCursor(0, 1);
  lcd.print("ACCESS  DENIED  ");
}

void stopAlarm() {
  digitalWrite(RELAY_PIN, LOW);    // De-energise relay → siren OFF
  alarmActive = false;
  Serial.println("[ALARM] Alarm stopped. RFID reader ready.");

  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("Alarm Stopped   ");
  lcd.setCursor(0, 1);
  lcd.print("Scan Card...    ");
  delay(2000);
}

// =====================================================================
//  Setup
// =====================================================================
void setup() {
  Serial.begin(9600);
  while (!Serial);

  // Relay — start LOW (siren off)
  pinMode(RELAY_PIN, OUTPUT);
  digitalWrite(RELAY_PIN, LOW);

  // I2C
  Wire.begin();

  // LCD
  lcd.init();
  lcd.backlight();
  lcd.setCursor(0, 0);
  lcd.print("RFID Alarm Sys  ");
  lcd.setCursor(0, 1);
  lcd.print("Initialising... ");
  delay(1500);

  // RTC
  if (!rtc.begin()) {
    Serial.println("ERROR: DS3231 RTC not found!");
    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("RTC ERROR!      ");
    lcd.setCursor(0, 1);
    lcd.print("Check I2C wiring");
    while (1);
  }
  if (rtc.lostPower()) {
    Serial.println("RTC lost power - setting to compile time.");
    rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
  }

  // SPI & RFID
  SPI.begin();
  rfid.PCD_Init();
  Serial.print("RFID firmware: ");
  rfid.PCD_DumpVersionToSerial();

  // Ready
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("System  Ready   ");
  lcd.setCursor(0, 1);
  lcd.print("Scan Card...    ");
  delay(1000);

  Serial.println("System ready. Waiting for RFID card...");
}

// =====================================================================
//  Loop
// =====================================================================

// Update LCD clock every second
unsigned long lastClockUpdate = 0;

void loop() {
  // ---- Manage active alarm ----------------------------------------
  if (alarmActive) {
    if (millis() - alarmStartTime >= ALARM_DURATION_MS) {
      stopAlarm();
    }
    return;
  }

  // ---- Refresh clock on LCD every second --------------------------
  if (millis() - lastClockUpdate >= 1000) {
    showDateTimeLCD();
    lastClockUpdate = millis();
  }

  // ---- Poll for RFID card -----------------------------------------
  if (!rfid.PICC_IsNewCardPresent() || !rfid.PICC_ReadCardSerial()) {
    return;
  }

  // Print UID to Serial
  String uid = uidString(rfid.uid.uidByte, rfid.uid.size);
  Serial.print("Card UID: ");
  Serial.print(uid);
  Serial.print("  at ");
  printDateTimeSerial();
  Serial.println();

  if (isAuthorised(rfid.uid.uidByte, rfid.uid.size)) {
    Serial.println("Access GRANTED.");

    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("Access GRANTED  ");
    lcd.setCursor(0, 1);
    lcd.print(uid);
    delay(2000);

  } else {
    Serial.println("Access DENIED - triggering siren alarm!");
    triggerAlarm();
  }

  rfid.PICC_HaltA();
  rfid.PCD_StopCrypto1();
}