November 24, 2007
Reading for November 27th, are now posted. Enjoy!

October 2, 2007
To upload your thoughtless acts, create a new assignment page like any other lab. You'll see "Thoughtless Acts" listed as one of the assignment options.

May 24, 2008
This site has been archived and is no longer editable. Stay tuned for the next version, coming in the fall!

Lab 2

Project Members: 
Eun Kyoung Choe

Control the RGB value

Use the Arduino to control the RGB value of the lights with multiple keypresses. When you press r, g, b N times, it increases the brightness by 10%*N, and when you reach its maximum brightness (100%), it goes back to 0% brightness.

Components Used

Light Emitting Diode (LED) * 3

Resistor * 3

6 yellow wires, 1 black wire

Arduino Code

* Serial RGB LED
* ---------------
* Serial commands control the brightness of R,G,B LEDs
* rrrrrCommand 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 <>
* Modified 12 September 2007
* iSchool Tangible User Interfaces Lab2 Homework
* Eun Kyoung Choe (
//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 = 50; // default value: 50%
int greenValue = 50; // default value: 50%
int blueValue = 50; // default value: 50%

int red; // value varies from 0 to 255
int green; // value varies from 0 to 255
int blue; // value varies from 0 to 255

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);

//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] = '\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 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 = serInString[i];
//If the character is r (red)...
if (colorCode == 'r') {
//Increase the current red value by 10%, which is 25.5 in RGB value, and if you reach 255 go back to 0
redValue = (redValue + 10) % 100;
red = (redValue * 255) / 100;
analogWrite(redPin, red);
Serial.print("setting color red to brightness % ");
//If the character is g (green)...
} else if (colorCode == 'g') {
greenValue = (greenValue + 10) % 100;
green = (greenValue * 255) / 100;
analogWrite(greenPin, green);
Serial.print("setting color green to brightness % ");
//If the character is b (blue)...
} else if (colorCode == 'b') {
blueValue = (blueValue + 10) % 100;
blue = (blueValue * 255) / 100;
analogWrite(bluePin, blue);
Serial.print("setting color blue to brightness % ");
//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 string
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;

I used my translucent white board made of glass as a diffuser.


GSI Comments

Nice work. I like the scale of your diffuser -- it has the beginnings of something "architectural"... I wonder if it would be possible to get the LEDs to illuminate more of the glass, even when the lights are on in the room, perhaps by building a reflector box behind the glass?

Your code is fine, but trying to make a few more modifications to the code is definitely a great way to learn more about Arduino programming. Being creative with code and with physical components (like the diffuser) can create really interesting results.

Powered by Drupal - Design by Artinet