ATtiny_deep_sleep_fade.ino

//unknown days
//AKleindolph 2025 (with ChatGPT)

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

// Define pins for the LEDs
#define LED_PIN0 0
#define LED_PIN1 1

// Sleep and wake management
volatile uint8_t sleepCounter = 0;  // Count the number of 8-second cycles
const uint8_t maxSleepCycles = 4;   // 4 x 8 seconds = 32 seconds 

void setup() {
  pinMode(LED_PIN0, OUTPUT);  // Set LED_PIN0 as output
  pinMode(LED_PIN1, OUTPUT);  // Set LED_PIN1 as output

  // Disable ADC to save power
  ADCSRA &= ~(1 << ADEN);

  // Set up Watchdog Timer for 8-second intervals
  setupWatchdogTimer();
}

void loop() {
  // Fade LED on PIN1
  fadeInOut(LED_PIN1);

  // Fade LED on PIN0 immediately after
  fadeInOut(LED_PIN0);

  // Enter deep sleep until 7.5 minutes have passed
  sleepCounter = 0;
  while (sleepCounter < maxSleepCycles) {
    enterDeepSleep();
  }
}

void fadeInOut(uint8_t pin) {
  // Fade in to 60% brightness in smaller steps for slower fade
  for (int brightness = 0; brightness <= 153; brightness += 2) { // 60% of 255 = 153
    analogWrite(pin, brightness);
    delay(12);  // Slower fade-in with adjusted delay
  }

  // Fade out from 60% brightness in smaller steps for slower fade
  for (int brightness = 153; brightness >= 0; brightness -= 2) {
    analogWrite(pin, brightness);
    delay(12);  // Slower fade-out with adjusted delay
  }

  // Ensure LED is completely off at the end
  analogWrite(pin, 0);
}

void setupWatchdogTimer() {
  // Clear the WDRF flag in MCUSR (reset if watchdog reset occurs)
  MCUSR &= ~(1 << WDRF);

  // Set the Watchdog Timer for 8-second intervals
  WDTCR = (1 << WDP3) | (1 << WDP0);

  // Enable Watchdog Timer interrupt mode (not reset mode)
  WDTCR |= (1 << WDIE);
}

void enterDeepSleep() {
  // Set the sleep mode to Power Down
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
  sleep_enable();

  // Disable brown-out detection for lower power consumption
  MCUCR |= (1 << BODS) | (1 << BODSE);
  MCUCR &= ~(1 << BODSE);

  // Enter sleep mode
  sleep_cpu();

  // Wakes up here after Watchdog Timer interrupt
  sleep_disable();
}

void delayWithLowPower(unsigned long ms) {
  unsigned long start = millis();
  while (millis() - start < ms) {
    // Idle briefly to save power
    set_sleep_mode(SLEEP_MODE_IDLE);
    sleep_enable();
    sleep_cpu();
    sleep_disable();
  }
}

// Watchdog Timer Interrupt Service Routine
ISR(WDT_vect) {
  // Increment the sleep counter each time the Watchdog Timer triggers
  sleepCounter++;
}