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May 24, 2008
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Revision of LEDs: Inputs and Outputs from Wed, 09/12/2007 - 23:24

Project Members: 


Build a three-LED circuit using three Pulse Width Modulation (PWM) pins on
the Arduino board to control the brightness of several LEDs simultaneously.

The modified code uses Arduino’s Serial Communication feature, and allows
the user to increase the brightness of each LED by 10% each time he inputs the
key “r” for red, “g” for green, and “b” for blue. The code also prints the brightness of each LED as a percentage.

Components Used

Blue LED
Green LED
Arduino board
Three 220-ohm Resistors (red, red, brown, gold)

Arduino Code


* Serial RGB LED

* ---------------

* Serial commands
control the brightness of R,G,B LEDs


* Command structure
is "<colorCode>*", where "colorCode" is

* one of
"r","g", or "b".

* E.g.
"r" increases the red LED
brightness by 10

* "rrr" increases the red LED brightness by 30

* "ggb" increases the green LED brightness by 20 and
the blue by 10


* Created 18 October

* copyleft 2006 Tod
E. Kurt <



* Adapted 13
September 2007

* modified by
Kimberly Lau


//include support for manipulating strings.

//for a useful string comparison function, see the bottom of
this file... stringsEqual()

#include <stdio.h>

#include <string.h>

char serInString[100];
// array that will hold the different bytes of the string.

// -> you must state how long the array will be else it won't work

char colorCode;

int colorVal;

int redPin = 9; // Red LED,
connected to digital pin 9

int greenPin = 10; //
Green LED, connected to digital pin 10

int bluePin =
11; // Blue LED, connected to digital pin 11

int redValue = 127;

int greenValue = 127;

int blueValue = 127;

void setup() {

pinMode(redPin, OUTPUT);
// sets the pins as output


pinMode(bluePin, OUTPUT);


redValue); // set them all to
mid brightness

analogWrite(greenPin, greenValue);
// set them all to mid brightness

blueValue); // set them all to
mid brightness

Serial.println("enter color command (e.g. 'rrrrrrrrbbbb')


void loop () {

//read the serial
port and create a string out of what you read

readSerialString(serInString, 100);

processRepeatKeyCommands(serInString, 100);

//Erase anything
left in the serial string, preparing it for the

//next loop

resetSerialString(serInString, 100);

delay(100); // wait a bit, for serial data


void resetSerialString (char *strArray, int length) {

for (int i = 0; i
< length; i++) {

strArray[i] =



//read a string from the serial and store it in an array

//you must supply the array variable

void readSerialString (char *strArray, int maxLength) {

int i = 0;

if(!Serial.available()) {



(Serial.available() && i < maxLength) {

strArray[i] =;




//go through the string, and increase the red value for each

//the green value for each 'g', and the blue value for each

//For example "rrrg" increases red by 30 and green
by 10.

void processRepeatKeyCommands(char *strArray, int maxLength)

int i = 0;

//loop through the
string (strArray)

//i = the current
position in the string

//Stop when either
(a) i reaches the end of the string or

// (b) there is an empty
character '\0' in the string

while (i <
maxLength && strArray[i] != '\0') {

//Read in the
character at position i in the string

colorCode =

//If the character
is r (red)...

if (colorCode ==
'r') {

//Increase the
current red value by 10, and if you reach 255 go back to 0

redValue = (redValue + 25) % 255;

analogWrite(redPin, redValue);

Serial.print("setting color r to
brightness percentage ");

brightness as a percentage

int redPercent =

redPercent =
(((redValue * 100) / 255) + redPercent) % 255;


//If the character
is g (green)...

} else if
(colorCode == 'g') {

greenValue =
(greenValue + 25) % 255;

analogWrite(greenPin, greenValue);

Serial.print("setting color g to brightness percentage ");

brightness as a percentage

int greenPercent
= 0;

greenPercent =
(((greenValue * 100) / 255) + greenPercent) % 255;


//If the character
is b (blue)...

} else if
(colorCode == 'b') {

blueValue =
(blueValue + 25) % 255;


Serial.print("setting color b to brightness percentage ");

brightness as a percentage

int bluePercent
= 0;

bluePercent =
(((blueValue * 100) / 255) + bluePercent) % 255;



//Move on to the
next character in the string

//From here, the
code continues executing from the "while" line above...




//compare two strings to see if they are equal

//compares the first 'numCharacters' characters of string1
and string2 to

//see if they are the same


//E.g. stringsEqual("hello","hello",5)
=> true

stringsEqual("hello","helaabbnn",3) => true

stringsEqual("hello","helaa",5) => false

boolean stringsEqual(char *string1, char *string2, int
numCharacters) {

if (strncmp(string1,
string2, numCharacters) == 0) {

return true;

} else {

return false;




Homemade diffuser was made of a water bottle cap, a lotion
bottle cap, and a piece of napkin respectively taped onto a cylinder of paper
and placed on top of the lights.


3 LEDs3 LEDs

Water Bottle Cap DiffuserWater Bottle Cap Diffuser

Napkin DiffuserNapkin Diffuser

Lotion Bottle Cap DiffuserLotion Bottle Cap Diffuser

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