gistfile1.cpp

int redPin   = 9;
int greenPin = 10;
int bluePin  = 11;
int hue = 0;

void setup()
{
    pinMode(redPin,   OUTPUT);
    pinMode(greenPin, OUTPUT);
    pinMode(bluePin,  OUTPUT);
}

void loop()
{
    int r, g, b;
    int s = 1, v = 1;

    hue++;
    if (hue > 360)
        hue = 0;

	int hf = hue / 60.0;
	int i = floor(hf);
	int f = hf - i;

	int pv = v * (1 - s);
	int qv = v * (1 - s * f);
	int tv = v * (1 - s * (1 - f));

	switch(i) {
	    case 0:
	        r = v;
	        g = tv;
	        b = pv;
	        break;

	    case 1:
	        r = qv;
	        g = v;
	        b = pv;
	        break;

	    case 2:
	        r = pv;
	        g = v;
	        b = tv;
	        break;

	    case 3:
	        r = pv;
	        g = qv;
	        b = v;
	        break;

	    case 4:
	        r = tv;
	        g = pv;
	        b = v;

	    case 5:
	        r = v;
	        g = pv;
	        b = qv;
	    break;

		default:
			break;
	}

	analogWrite(redPin,   max(0, min(255 * r, 255)));
	analogWrite(greenPin, max(0, min(255 * g, 255)));
	analogWrite(bluePin,  max(0, min(255 * b, 255)));

    delayMicroseconds(50);
}