#include <avr/sleep.h>


//Brown-out disable
//Another power saving can be made by disabling the brown-out detection.
//To detect low voltages the processor must generate a voltage source for 
//comparison purposes. You can change the "extended fuse" (efuse) by using AVRdude,
//like this:
//avrdude -c usbtiny -p m328p -U efuse:w:0x07:m
//
//In SLEEP_MODE_PWR_DOWN mode, with brown-out disabled, the power went down 
//from 360 µA to 335 µA, a saving of 25 µA.
//
//Another way of turning off brown-out detection is to temporarily disable it like this:

void setup () 
{
  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);  // turn on brown-out enable select
  MCUCR = bit (BODS);        // this must be done within 4 clock cycles of above
  interrupts ();             // guarantees next instruction executed
  sleep_cpu ();              // sleep within 3 clock cycles of above
}  // end of setup

void loop () { }