attiny13_blinky.c

/*
 * Tiny13Blinky.c
 *
 * Created: 21.04.2017. 11:21:09
 * Author : ivoras
 */ 

#define F_CPU 1000000UL

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

ISR(WDT_vect) {
}

unsigned int measure_adc() {
	ADCSRA = (1 << ADEN) | (1 << ADPS1) | (1 << ADPS0) | (1 << ADSC); // Enable ADC, at 1/8 prescaler, enable conversion
	while (ADCSRA & (1 << ADSC)) {}
	unsigned int lsbyte = ADCL;  // read the low byte first
	unsigned int msbyte = ADCH;
	ADCSRA = 0;
	return lsbyte | (msbyte << 8);
}

int main(void)
{
	DDRB = 1 << DDB4;
	ADMUX = (1 << REFS0) | (1 << MUX1) | (1 << MUX0); // Internal Vref, ADC3

	// prescale timer to 0.5s
	WDTCR |= (1<<WDP2) | (1<<WDP0);
	// Enable watchdog timer interrupts
	WDTCR |= (1<<WDTIE);
	sei();

       // Use the Power Down sleep mode
       set_sleep_mode(SLEEP_MODE_PWR_DOWN);
       sleep_enable();
       sleep_bod_disable();

        while (1) 
        {
		sleep_cpu();
		if (measure_adc() < 512) {
			PORTB ^= 1 << PINB4; // blink light
		} else {
			PORTB &= ~(1 << PINB4);
		}
        }
}