Arduino Starter Series - Colour Mixing Lamp

Arduino Aug 19, 2015

This is a project from my Arduino starter series.

This project comes from the Arduino Starter Kit Projects Book. The project uses photo-resistors to control an RGB LED. This is a great project for beginners. Enjoy!

Project Requirements
  • Arduino Uno/Duemilanove/Diecimila
  • USB cable to program Arduino
  • Breadboard
  • RGB LEDS (Looks like a white LED)
  • Three Photoresistors
  • Three 220 Ohm Resistors
  • Three 10k Resistors
  • Wires to power the components on the breadboard
The Breadboard Setup

Colour Mixing Lamp Breadboard Setup

The Code

As usual I try comment as much of the code as possible. Also be aware that I change the code for the project from what is defined in the Arduino Projects Book. It's not that I don't think the code is good or bad, I just find that there are more interesting ways to tackle these projects and providing an alternative method to approaching this project always leads to better understanding.

// The pins that the RGB LED connects to.
// I tested the RGB LED light first by connecting the different legs to power first.
// This gave me an indication of which leg was for which colour
const int greenLEDPin = 4;
const int redLEDPin = 5;
const int blueLEDPin = 6;

// The photoresisters get connected to analog pins
const int redSensorPin = A0;
const int greenSensorPin = A1;
const int blueSensorPin = A2;

// These values will be generated by the photoresistors for each of the three colors
int redSensorValue = 0;
int greenSensorValue = 0;
int blueSensorValue = 0;

// These will be the values that are used to set the LED colour.
int redValue = 0;
int greenValue = 0;
int blueValue = 0;

void setup() {
  // Fire up the Serial monitoring so we can debug the code

  pinMode(redLEDPin, OUTPUT);
  pinMode(greenLEDPin, OUTPUT);
  pinMode(blueLEDPin, OUTPUT);

void loop() {
  // The first thing to do here is to read the sensor data using the analogRead function
  // The delay gives the analog to digital conversion (ADC) time to process
  redSensorValue = analogRead(redSensorPin);
  greenSensorValue = analogRead(greenSensorPin);
  blueSensorValue = analogRead(blueSensorPin);

  // We need to convert the 10-bit data provided by ADC into 8-bit.
  // This is easy  to do by simply dividing the value by 4
  redValue = redSensorValue / 4;
  greenValue = greenSensorValue / 4;
  blueValue = blueSensorValue / 4;

  // Now that we have the correct values we can output them to the Serial monitor 
  // and see how the photoresisters work when you interact with them.
  Serial.print("Mapped sensor Values \t red: ");
  Serial.print("\t green: ");
  Serial.print("\t Blue: ");

  // Finally we need to update the pins on the RGB LED to control the LED colour
  analogWrite(redLEDPin, redValue);
  analogWrite(greenLEDPin, greenValue);
  analogWrite(blueLEDPin, blueValue);

I have uploaded this project onto my Github page

Nicholas Bester

I have 15 years of experience in design, development and implementation of digital marketing solutions ranging from virtual reality, 3D projection mapping, mobile apps and massive web platforms.