Description:

I made the diffuser from the top of a hat, and propped it up with some square styrofoam from an electronics box, which I punched the top out of. 

I also modified the example program so the user can input 't' for teal, which sets the green and blue LEDs and turns off the red, or 'y' for yellow, which turns off the blue and lights the green and red in proportion to make yellow. I was unsuccessful doing the original assignment with multiple key presses, and even this modified code has some known bugs!

Components used:

hat top and styrofoam for the diffuser
arduino board, breadboard, and usb cable
3 LEDs - red, blue, and green
3 resistors
4 wires

Arduino code:

/*
* Serial RGB LED
* ---------------
* Serial commands control the brightness of R,G,B LEDs
*
* Command structure is "", 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
*
* Created 18 October 2006
* copyleft 2006 Tod E. Kurt 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

void setup() {
  pinMode(redPin,   OUTPUT);   // sets the pins as output
  pinMode(greenPin, OUTPUT);  
  pinMode(bluePin,  OUTPUT);
  Serial.begin(9600);
  analogWrite(redPin,   127);   // set them all to mid brightness
  analogWrite(greenPin, 127);   // set them all to mid brightness
  analogWrite(bluePin,  127);   // set them all to mid brightness
  Serial.println("enter color command (e.g. 'r43')"); 
  Serial.println("or enter 'y' for yellow or 't' for teal"); 
}

void loop () {
  //read the serial port and create a string out of what you read
  readSerialString(serInString);
   
  colorCode = serInString[0];
  if( colorCode == 'r' || colorCode == 'g' || colorCode == 'b' )
 
    colorVal = atoi(serInString+1);{    //I had some trouble modifying/understanding this line (kra)
    if(colorVal != 0) {
      Serial.print("setting color ");
      Serial.print(colorCode);
      Serial.print(" to ");
      Serial.print(colorVal);
      Serial.println();
      serInString[0] = 0;      // indicates we've used this string
      //colorCode = 'z';        //try to prevent the crazy loop I'm getting
    }
   
 
              
    if(colorCode == 'r')
      analogWrite(redPin, colorVal);
    else if(colorCode == 'g')
      analogWrite(greenPin, colorVal);
    else if(colorCode == 'b')
      analogWrite(bluePin, colorVal);
    else if(colorCode == 'y') {         //this was as close to yellow as I found,
      analogWrite(greenPin, 50);        //with the discrepancy in how bright the LEDs are. (kra)
      analogWrite(redPin, 255);
      analogWrite(bluePin, 0);
    }
    else if(colorCode == 't') {          //t is for teal, or blue-green
      analogWrite(greenPin, 100);        //again, I just decided on values based on experimentation (kra)
      analogWrite(redPin, 0);
      analogWrite(bluePin, 100);
    }
  }
 
 
  delay(100);  // wait a bit, for serial data
}

//read a string from the serial and store it in an array
//you must supply the array variable
void readSerialString (char *strArray) {
  int i = 0;
  if(!Serial.available()) {
    return;
  }
  while (Serial.available()) {
    strArray[i] = Serial.read();
    i++;
  }
 
 
}