Routines for power saving on the Arduino. Posted at http://simonebaracchi.eu/posts/arduino-power-cutter/

power_saving.ino

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

// watchdog interrupt
ISR (WDT_vect)
{
 wdt_disable(); // disable watchdog
}
void
power_saving_sleep()
{
 // disable ADC
 byte old_ADCSRA = ADCSRA;
 ADCSRA = 0;
 power_all_disable();

 PCIFR |= bit (PCIF0) | bit (PCIF1) | bit (PCIF2); // clear any outstanding interrupts
 PCICR = 0;

 TWCR = bit(TWEN) | bit(TWIE) | bit(TWEA) | bit(TWINT);
 digitalWrite (A4, LOW);
 digitalWrite (A5, LOW);

 // clear various "reset" flags
 MCUSR = 0;
 // allow changes, disable reset
 WDTCSR = bit (WDCE) | bit (WDE);
 // set interrupt mode and an interval
 WDTCSR = bit (WDIE) | bit (WDP3) | bit (WDP0); // set WDIE, and 8 seconds delay
 wdt_reset(); // pat the dog

 set_sleep_mode (SLEEP_MODE_PWR_DOWN);
 noInterrupts (); // timed sequence follows
 sleep_enable();

 // turn off brown-out enable in software
 MCUCR = bit (BODS) | bit (BODSE);
 MCUCR = bit (BODS);
 interrupts (); // guarantees next instruction executed
 sleep_cpu (); 

 // cancel sleep as a precaution
 sleep_disable();
 power_all_enable();
 ADCSRA = old_ADCSRA;
}

void
power_saving_init()
{
 for (byte i = 0; i &lt;= A5; i++) {
 pinMode (i, OUTPUT);
 digitalWrite (i, LOW);
 }
}