This code sleeps atmega16a for 4s and wake up then do the job and sleep again. This helps to reduce the power consumption.

code:

// CPU speed 1MHz @ Atmega16A,
// gives 4s timeout for each timer1 overflow
// This code shows how to go into deep sleep for 4s and wake up after
// every 4s and do the job

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/power.h>
#include <avr/sleep.h>
#include <util/delay.h>

volatile uint8_t f_timer = 0;

ISR(TIMER1_OVF_vect)
{
if (f_timer == 0)
{
f_timer = 1;
}
}

int main()
{
DDRB |= (1 << PB3);
TCCR1B |= (1 << CS11) | (1 << CS10);// | (1 << CS12); //prescalar = 64
TCNT1 = 0;

TIMSK |= (1 << TOIE1); //enable timer1 overflow interrupt
PORTB |= (1 << PB3);
_delay_ms(1000);
PORTB &= ~(1 << PB3);
_delay_ms(1000);
sei();

while (1)
{
if (f_timer == 1)
{
PORTB ^= (1 << PB3);
f_timer = 0;

//sleep mode routine
//sleep bro!
// only IDLE and SLEEP_MODE_ADC seems to work
set_sleep_mode(SLEEP_MODE_IDLE);

sleep_enable();
power_all_disable();

//now enter into sleep mode
sleep_mode();

// you will wake up in every 262 ms ;)
//wake up
sleep_disable();
power_all_enable();
}
}

return 0;
}