//Intervalometer from 1 second to 1 minute
 
//Author: Patrick Sebastien Coulombe
//Website: www.workinprogress.ca
//Date: 2010-07-24
 
#define F_CPU 8000000
#include <avr/io.h>
#include <util/delay.h>
 
// use PB2 for led, pin 7
#define LED_BIT 2
// select ADC2, PB4, pin 3
#define CHANNEL 2
// shutter on (in ms)
#define HOLD 300 
 
// Return the 10bit value of the selected adc channel.
uint16_t get_adc(uint8_t channel) {
 
	// ADC setup
	ADCSRA = (1 << ADEN) | (1 << ADPS1) | (1 << ADPS0);
 
	// select channel
	ADMUX = channel;
 
	// warm up the ADC, discard the first conversion
	ADCSRA |= (1 << ADSC);
	while (ADCSRA &#038; (1 << ADSC)); 
 
	ADCSRA |= (1 << ADSC); // start single conversion
	while (ADCSRA &#038; (1 << ADSC)); // wait until conversion is done
 
	return ADCW;
}
 
// Scale
long map(long x, long in_min, long in_max, long out_min, long out_max)
{
  return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}
 
// Main program
int main(void) {
 
	// vars
	uint16_t adcvalue = 0;
	uint16_t i;
 
	// define LED as outputs
	DDRB |= (1 << LED_BIT);	
 
	while (1) {	
 
		//release the shutter
		PORTB |= (1 << LED_BIT);
 
		//exposure length
		for (i=0; i<HOLD; i++) { 
			_delay_ms(1); 
		}
		PORTB &#038;= ~(1 << LED_BIT);
 
		//interval time (using a potentiometer to adjust)
		adcvalue = map(get_adc(CHANNEL), 0, 1023, 1, 60);
		adcvalue = adcvalue * 1000;
 
		//one way to achieve long delay
		for (i=0; i < adcvalue; i++) { 
			_delay_ms(1); 
		}
 
	}
	return 0;
}