View Code#include <avr/interrupt.h>
#include <avr/sleep.h>

// Pin 4 has an mosfet connected on most Arduino boards.
int mosfet = 4;
// interrupt counter
int count = 0;

ISR(WDT_vect) {
digitalWrite(mosfet, LOW); // turn the mosfet off - keep it off
count = count +1;
if (count >111) //roughly 15 minutes sleep
{
digitalWrite(mosfet, HIGH); // turn the mosfet on (HIGH is the voltage level) till the next interrupt
delay(3000);
count = 0;
}

}

// the setup routine runs once when you press reset:
void setup() {
// initialize the digital pin as an output.
pinMode(mosfet, OUTPUT);

(ADCSRA &= ~(1<<ADEN)); // disable ADC (before power-off) // ADC uses ~320uA

digitalWrite(mosfet, HIGH); // turn the mosfet on (HIGH is the voltage level)
delay(3000);
count = 0;

//SET timer for 8s
WDTCR |= (1<<WDP3 )|(0<<WDP2 )|(0<<WDP1)|(1<<WDP0); // 8s

// Enable watchdog timer interrupts
WDTCR |= (1<<WDTIE);
sei(); // Enable global interrupts
// Use the Power Down sleep mode
set_sleep_mode(SLEEP_MODE_PWR_DOWN);

for (;;) {
sleep_mode(); // go to sleep and wait for interrupt...
}
}

// the loop routine runs over and over again forever:
void loop() {
// wait for a second

}

/*
Values for the watchdok interrupt
16MS (0<<WDP3)|(0<<WDP2)|(0<<WDP1)|(0<<WDP0)
32MS (0<<WDP3)|(0<<WDP2)|(0<<WDP1)|(1<<WDP0)
64MS (0<<WDP3)|(0<<WDP2)|(1<<WDP1)|(0<<WDP0)
125MS (0<<WDP3)|(0<<WDP2)|(1<<WDP1)|(1<<WDP0)
250MS (0<<WDP3)|(1<<WDP2)|(0<<WDP1)|(0<<WDP0)
500MS (0<<WDP3)|(1<<WDP2)|(0<<WDP1)|(1<<WDP0)
1S (0<<WDP3)|(1<<WDP2)|(1<<WDP1)|(0<<WDP0)
2S (0<<WDP3)|(1<<WDP2)|(1<<WDP1)|(1<<WDP0)
4S (1<<WDP3)|(0<<WDP2)|(0<<WDP1)|(0<<WDP0)
8S (1<<WDP3)|(0<<WDP2)|(0<<WDP1)|(1<<WDP0)
*/