// Example of sleeping and saving power
//
// Author: Nick Gammon
// Date:   25 May 2011

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

#define LED 13

// watchdog interrupt
ISR(WDT_vect)
  {
  wdt_disable();  // disable watchdog
  }

void myWatchdogEnable(const byte interval)
  { 
  MCUSR = 0;                          // reset various flags
  WDTCSR |= 0b00011000;               // see docs, set WDCE, WDE
  WDTCSR =  0b01000000 | interval;    // set WDIE, and appropriate delay

  wdt_reset();
  set_sleep_mode (SLEEP_MODE_PWR_DOWN); 
  sleep_mode();            // now goes to Sleep and waits for the interrupt
  }

void setup()
{
pinMode (LED, OUTPUT);
}  // end of setup

void loop()
{
  digitalWrite (LED, HIGH);  // awake
  delay (2000);    // ie. do stuff here
  digitalWrite (LED, LOW);  // asleep

  // sleep for a total of 20 seconds
  for (int i = 0; i<5; i++) {
    myWatchdogEnable (0b100001);  // 8 seconds
  }
    
 
}  // end ofloop

// sleep bit patterns:
//  1 second:  0b000110
//  2 seconds: 0b000111
//  4 seconds: 0b100000
//  8 seconds: 0b100001