lostModelAlarm.ino

#include <avr/sleep.h>
#include <avr/wdt.h>

const int buzzerPin = 0;       // Physical Pin 5 (PB0)
volatile int sleepCounter = 0; // Counts how many 8-second cycles have past
const int targetCycles = 75;   // 75 cycles * 8 seconds = 600 seconds (10 minutes)

// Watchdog Timer Interrupt Service Routine
ISR(WDT_vect) {
  sleepCounter++; // Increment our 8-second interval counter
}

void setup() {
  pinMode(buzzerPin, OUTPUT);
  digitalWrite(buzzerPin, LOW);
  
  // ─── NEW: PRE-FLIGHT STATUS FEATURE ───
  // 1. Wait 10 seconds before giving the status beep
  delay(10000); 
  
  // 2. Sound a long confirmation beep for 3 seconds
  digitalWrite(buzzerPin, HIGH);
  delay(3000);
  digitalWrite(buzzerPin, LOW);
  // ──────────────────────────────────────
  
  setupWatchdog(); // Configure the hardware watchdog timer after the beep
}

void loop() {
  // If we haven't reached 10 minutes yet, go back to deep sleep
  if (sleepCounter < targetCycles) {
    goToSleep();
  } 
  // Once 10 minutes hits, stay awake and execute the loud alarm loop
  else {
    triggerAlarm();
  }
}

void setupWatchdog() {
  cli();                  // Disable all interrupts while configuring
  MCUSR &= ~(1 << WDRF);  // Clear the Watchdog Reset Flag
  
  // Start timed sequence to allow changing configuration
  WDTCR |= (1 << WDCE) | (1 << WDE);
  
  // Set Watchdog settings: Interrupt mode enabled, Timeout = 8.0 seconds
  WDTCR = (1 << WDIE) | (1 << WDP3) | (0 << WDP2) | (0 << WDP1) | (1 << WDP0);
  
  sei();                  // Re-enable interrupts
}

void goToSleep() {
  set_sleep_mode(SLEEP_MODE_PWR_DOWN); // Set to maximum power savings
  sleep_enable();                      // Enable the sleep function
  sleep_cpu();                         // Actually put the MCU to sleep here...
  
  // ─── THE CHIP LIVES HERE IN DEEP SLEEP FOR 8 SECONDS ───
  sleep_disable();                     // Execution resumes here after WDT barks
}

void triggerAlarm() {
  // Active Buzzer Alert Pattern: 2 rapid beeps every 10 seconds
  digitalWrite(buzzerPin, HIGH);
  delay(150);
  digitalWrite(buzzerPin, LOW);
  delay(100);
  
  digitalWrite(buzzerPin, HIGH);
  delay(150);
  digitalWrite(buzzerPin, LOW);
  
  delay(10000); 
}