Arduino Multiplex RGB Led Demo

// Multiplexed PWM RGB Led Demo
// By Petri Hakkinen
// 24th November 2014
//
// Arduino Uno driving a single RGB led with only one resistor.
//
// Make the following connections:
// * Connect Arduino pins D2,D3,D3 to anodes of a RGB led.
// * Connect cathode of the RGB led to 330 ohm resistor.
// * Connect the other end of the resistor to ground.
//
// A multiplexed PWM signal is generated by a timer interrupt routine.
// 
// Uses TimerOne library, download from here:
// http://playground.arduino.cc/Code/Timer1

#include <TimerOne.h>

volatile uint8_t color[3];		// R,G,B led intensities in range [0,255]
volatile uint8_t phase = 0;		// phase of the PWM signal, counts from 0 to 255
volatile uint8_t led = 0;		// which led to update, counts from 0 to 2

// Look up table of sin values for mega demo effect.
uint8_t sintab[64];

// The interrupt routine that updates the states of leds.
void interruptRoutine()
{
	// turn all leds off
	PORTD &= B11100011;

	// sample pwm and turn on one led
	if(phase < color[led])
		PORTD |= 1<<(led+2);

	led = (led + 1) & 3;
	phase++;
}

void setup()
{
	pinMode(2, OUTPUT);
	pinMode(3, OUTPUT);
	pinMode(4, OUTPUT);

	// attach interrupt routine
	Timer1.initialize(50);
	Timer1.attachInterrupt(interruptRoutine);

	// init sin table for mega demo effect
	for(uint8_t i = 0; i < 64; i++)
		sintab[i] = (uint8_t)(sin(i * M_PI * 2 / 64) * 127.0f + 128.0f);
}

void loop()
{
	const uint8_t speed = 13;

	color[0] = 0;
	color[1] = 0;
	color[2] = 0;

	// fade red
	for(int i = 0; i < 256; i++) {
		color[0] = i;
		delay(speed);
	}

	// fade green
	for(int i = 0; i < 256; i++) {
		color[1] = i;
		delay(speed);
	}

	// fade blue
	for(int i = 0; i < 256; i++) {
		color[2] = i;
		delay(speed);
	}

	// mega demo effect
	for(int i = 0; i < 500; i++) {
		color[0] = sintab[i & 63];
		color[1] = sintab[(i*2 + 123) & 63];
		color[2] = sintab[(i*2/3 + 35) & 63];
		delay(speed);
	}
}