LED Diffusion


After experimenting with and testing out the serial monitor functionality of the Arduino environment and watching the fading color change program work, I chose cone coffee filters as my diffuser of choice. This was after much experimentation–initially, I’d had the three LEDs spaced a few rows apart on the breadboard, but this didn’t allow them to mix very well. So first, I modified my breadboard so that all the LEDs were touching each other.


I tried diffusing with the large cotton balls in class, but those didn’t allow enough light to pass through. I then tried different configurations of coffee filters, lightbulb housings, plastic storage containers, and more. The cone-type coffee filters worked best for me because they maintained structure around the LEDs, and having two stacked on top of each other allowed for more uniform diffusion.


I then modified the code so that a user can press r, g, or b and the LEDs will change based on the following equation: (#key presses/10)*255. This gives the percentage of light, and then applies that to the full value of 255.


  • Arduino Uno
  • Breadboard
  • 3 LEDs (rgb)
  • 3 220Ω Resistors
  • 2 Coffee filters
  • jumper wires
  • USB cable
  • laptop


/* Modified on 9/7/16 by Molly Mahar
* 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 <tod@todbot.com
* http://todbot.com/

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. pressing 'r' 5 times will put red LED at 50% brightness) :");

void loop () {
// clear the string
memset(serInString, 0, 100);
//read the serial port and create a string out of what you read

colorCode = serInString[0];
if( colorCode == 'r' || colorCode == 'g' || colorCode == 'b' ) {
//colorVal = atoi(serInString+1);
colorVal = 0;
for (int i=0; i<strlen(serInString); i++) {
if( colorCode == 'r' || colorCode == 'g' || colorCode == 'b' )
colorVal += 1;
if (strlen(serInString) > 10){
colorVal = 0;

//colorVal = strlen(serInString);
colorVal = (colorVal/10.0)*255;
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] = Serial.read();

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