Driving a RGB LED with Arduino Uno

Here's a simple way to drive a RGB LED with Arduino Uno. The microcontroller generates a multiplexed PWM signal in software. The PWM is generated in an interrupt routine so the main program and LED update frequency are completely independent. The only requirements is that main program does not use hardware timer 1.

Components required: one common cathode RGB LED, one 330 ohm resistor.

	// 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);
	}
	}

view raw Arduino Multiplex RGB Led Demo hosted with ❤ by GitHub