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May 24, 2008
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Revision of Diffuso from Thu, 09/13/2007 - 10:45

Project Members: 


Controls RGB values with multiple key presses, ratcheting up in approximately 10% increments, and looping back to 0 after 255. This code also implements a '0' to turn all LEDs off, and a '1' to crank them all up to full power.

Components Used

red LED

blue LED

green LED

(3) 220 resistors

Arduino Code

* Serial RGB LED
* ---------------
* Serial commands control the brightness of R,G,B LEDs
* Command structure is "<colorCode><colorVal>", where "colorCode" is
* one of "r","g",or "b" and "colorVal" is a number 0 to 255.
* E.g. "r0" turns the red LED off.
* "g127" turns the green LED to half brightness
* "b64" turns the blue LED to 1/4 brightness
* Alternate 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 2006
* copyleft 2006 Tod E. Kurt <
* Adapted 5 September 2007
* copylefter 2007 Ryan Aipperspach <>

//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. 100=100characters;
// -> you must state how long the array will be else it won't work properly
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 = 0;
int greenValue = 0;
int blueValue = 0;

void setup() {
pinMode(redPin, OUTPUT); // sets the pins as output
pinMode(greenPin, OUTPUT);
pinMode(bluePin, OUTPUT);
analogWrite(redPin, redValue); // set them all to mid brightness
analogWrite(greenPin, greenValue); // set them all to mid brightness
analogWrite(bluePin, blueValue); // set them all to mid brightness
Serial.println("enter color command (e.g. 'r43 or rrrrrrrrbbbb') :");

void loop () {
//read the serial port and create a string out of what you read
readSerialString(serInString, 100);


//Uncomment the following line to read commands of the form 'r245' or 'b3'

//Uncomment the following line to read commands of the form 'rrrb'
processRepeatKeyCommands(serInString, 100);

//Or write your own function...

//Erase anything left in the serial string, preparing it for the
//next loop
resetSerialString(serInString, 100);

delay(1); // wait a bit, for serial data

void resetSerialString (char *strArray, int length) {
for (int i = 0; i < length; i++) {
strArray[i] = '\0';

//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()) {
while (Serial.available() && i < maxLength) {
strArray[i] =;

//go through the string, and increase the red value for each 'r',
//the green value for each 'g', and the blue value for each 'b'.
//For example "rrrg" increases red by 75 and green by 25.
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 = serInString[i];

//If the character is r (red)...
if (colorCode == 'r') {
//Increase the current red value by approx 10%, and if you reach 255 go back to 0
redValue = (redValue + 25) % 255;
analogWrite(redPin, redValue);
Serial.print("setting color r to ");

//If the character is g (green)...
} else if (colorCode == 'g') {
greenValue = (greenValue + 25) % 255;
analogWrite(greenPin, greenValue);
Serial.print("setting color g to ");

//If the character is b (blue)...
} else if (colorCode == 'b') {
blueValue = (blueValue + 25) % 255;
analogWrite(bluePin, blueValue);
Serial.print("setting color b to ");

//If the character is 0...
} else if (colorCode == '0') {
blueValue = 0;
redValue = 0;
greenValue = 0;
analogWrite(bluePin, blueValue);
analogWrite(redPin, redValue);
analogWrite(greenPin, greenValue);
Serial.println("turning all LEDs off");

//If the input is 1
} else if (colorCode == '1') {
blueValue = 255;
redValue = 255;
greenValue = 255;
analogWrite(bluePin, blueValue);
analogWrite(redPin, redValue);
analogWrite(greenPin, greenValue);
Serial.println("turning all LEDs on full");

//Move on to the next character in the string
//From here, the code continues executing from the "while" line above...

//change the value of the red, green, or blue LED according to the command received.
//for example, r240 sets the red LED to the value 240 (out of 255)
void processNumericalCommands(char *strArray) {
//read in the first character in the stringrrr
colorCode = serInString[0];

//if the first character is r (red), g (green) or b (blue), do the following...
if( colorCode == 'r' || colorCode == 'g' || colorCode == 'b' ) {
//convert the string to an integer
//(start at the second character, or the beginning of the string '+1')
colorVal = atoi(serInString+1);
Serial.print("setting color ");
Serial.print(" to ");

if(colorCode == 'r')
analogWrite(redPin, colorVal);
else if(colorCode == 'g')
analogWrite(greenPin, colorVal);
else if(colorCode == 'b')
analogWrite(bluePin, colorVal);

//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;


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