I feel like I am finally getting somewhere with this electronics thing.

A month ago I bought an ATMega168 microcontroller from Spark Fun Electronics. Having programed for several years now I felt like venturing into microcontrollers.
So far I have made an LED blink, read the value of a potentiometer and now I have a tri color LED fading between all the different colors.

My next challenge is to control the speed of a motor, which is proving to be a bit difficult.

This is all hopefully leading to something useful. I have been thinking about an RC helicopter with an attached camera for arial photography but that is a little ways down the road to say the least.

To get the tri color led to work I used PWM (Pulse Width Modulation). as long as you keep the micro running fast enough it will not look like it’s blinking.

The key was that the led has 1 positive pin and 3 ground pins that control the individual colors. So when the voltage is lower, it is actually brighter.

I wired the positive lead (the longest) to VCC and each of the three grounds to an output pin on the ATMega168 through an appropriate resistor. the colors are a little uneven because I didn’t have precise enough resistors (red takes a different current than green and blue).

Source Code:

#include <avr/io.h>

#define STEPS 255

//change these to the pins you have connected to the led
#define RED 5
#define BLUE 4
#define GREEN 3

void ioinit(void);      //Initializes IO
void fadePin(int pin, int destination);
//gentally fades a pin to destination. assumes starting at oposite value.

int main (void) {
	ioinit(); //Setup IO pins and defaults

	//zero is fully on because output pins are connected to ground pins

	PORTC |= (1 << RED);
	PORTC |= (1 << GREEN);
	PORTC |= (1 << BLUE);
	//start with red
	fadePin(RED, 0);

	//loop forever
	while(1) {
		fadePin(BLUE, 0);	//purple

		fadePin(RED, 1);	//blue

		fadePin(GREEN, 0);	//turquist

		fadePin(BLUE, 1);	//green

		fadePin(RED, 0);	//yellow

		fadePin(GREEN, 1);	//red
	}

    return(0);
}

void fadePin(int pin, int destination) {
	if(destination == 0)
		destination = -1;

	//i controls the PWM
	int i=0;
	for(float j=0.0f; j<1.0f; j+=0.0001f) {
		i++;
		if(i>STEPS)
			i=0;

		//destination makes everything negative if it is zero (before we change it)
		if(i * destination < STEPS * j * destination) {
			//turn pin on
			PORTC |= (1 << pin);
		} else {
			//turn pin off
			PORTC &= ~(1 << pin);
		}
	}

	//make sure to end with the desired value
	if(destination == 1) {
		//turn pin on
		PORTC |= (1 << pin);
	} else {
		//turn pin off
		PORTC &= ~(1 << pin);
	}
}

void ioinit (void) {
    //1 = output, 0 = input
    DDRC = 0b11111111; //All outputs on Port C
}

Filed under: Electronics