November 24, 2007
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October 2, 2007
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May 24, 2008
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Project Members: 
Joshua Gomez


Use the Arduino to control 3 LEDs and make their brightness adjustable by the using the serial input.

I used Ryan's code to complete the assignment, but I have listed below the code I tried to implement. I wanted to be able to input a percentage value instead a hex value (e.g. r50 would be red at 50%). Unfortunately, this code did not work the way I wanted.

Components Used

Light Emitting Diode (LED)


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
 * Created 18 October 2006
 * copyleft 2006 Tod E. Kurt <
 * Adapted 12 September 2007 by Joshua Gomez

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

void setup() {
  pinMode(redPin,   OUTPUT);   // sets the pins as output
  pinMode(greenPin, OUTPUT);  
  pinMode(bluePin,  OUTPUT);
  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') :"); 

void loop () {
  //read the serial port and create a string out of what you read
  colorCode = serInString[0];
  if( colorCode == 'r' || colorCode == 'g' || colorCode == 'b' ) {
    colorVal = 255 * atoi(serInString+1) / 100;  //This is my change. It allows you to enter the brightness in percentage instead of actual value.
    Serial.print("setting color ");
    Serial.print(" to ");
    serInString[0] = 0;                   // indicates we've used this string
    if(colorCode == 'r')
      analogWrite(redPin, colorVal);
    else if(colorCode == 'g')
      analogWrite(greenPin, colorVal);
    else if(colorCode == 'b')
      analogWrite(bluePin, colorVal);
  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()) {
  while (Serial.available()) {
    strArray[i] =;



Lab 2 pictureLab 2 picture



GSI Comments

Sorry to hear about your code not working -- but thanks for trying it out! My best guess is that, because all three numbers in your code (255 * atoi(serInString+1) / 100;) are integers, the computer is doing integer division, which rounds every result to the nearest integer and might be making your values imprecise. So changing "atoi" to "atof" (for "float" or a decimal number) might work. We'd be glad to take a look during office hours if you'd like.

The diffuser looks like it works pretty well. It would be nice to have a paragraph describing what you did, or a photo showing it working with the room lights off.

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