Table of Contents

• Table of Contents
  • Traffic Light (v1)
  • Traffic Light (v2)
  • Traffic Light (v3)
  • Traffic Light (v4)
  • Traffic Light (v5)

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Traffic Light (v1)

We make a simple program that cycles between the colours, like a traffic light!

/*
  Title:              MakerLab1-RGB-Task1
  Organisation:       UCD ElecSoc - MakerLab
  Author(s):          Joe Biju
  Created:            24/09/2025

  Description:
  - Control a Common Anode RGB LED using Serial Monitor.

  Ingredients:
  - Arduino Uno
  - RGB LED with common anode configuration
  - 330Ω resistor
  - Breadboard
  - Jumper cables

  Notes:
  - Use the 5V pin for powering the LEDs
  - Be careful not to get injured on the sharp LED pins!
  - Please use a 330Ω resistor in series with the anode.
  - Since grounding a pin will turn on that colour, logic HIGH in code actually turns OFF an LED.

  Edit History:
  - 
*/

/*Global Declarations*/
const int RED_PIN = 3;
const int GREEN_PIN = 5;
const int BLUE_PIN = 6;

void setup() {
  pinMode(RED_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
  pinMode(BLUE_PIN, OUTPUT);

  // Start with all off
  digitalWrite(RED_PIN, HIGH);
  digitalWrite(GREEN_PIN, HIGH);
  digitalWrite(BLUE_PIN, HIGH);
}

void loop() {
  // Red ON
  digitalWrite(RED_PIN, LOW);
  digitalWrite(GREEN_PIN, HIGH);
  digitalWrite(BLUE_PIN, HIGH);
  delay(3000);

  // Green ON
  digitalWrite(RED_PIN, HIGH);
  digitalWrite(GREEN_PIN, LOW);
  digitalWrite(BLUE_PIN, HIGH);
  delay(2000);

  // Orange (Red + Green)
  digitalWrite(RED_PIN, LOW);
  digitalWrite(GREEN_PIN, LOW);
  digitalWrite(BLUE_PIN, HIGH);
  delay(1000);
}

Traffic Light (v2)

Now we make a function to do the repetive parts

/*
  Title:              MakerLab1-RGB-Task1
  Organisation:       UCD ElecSoc - MakerLab
  Author(s):          Joe Biju
  Created:            24/09/2025

  Description:
  - Control a Common Anode RGB LED using Serial Monitor.

  Ingredients:
  - Arduino Uno
  - RGB LED with common anode configuration
  - 330Ω resistor
  - Breadboard
  - Jumper cables

  Notes:
  - Use the 5V pin for powering the LEDs
  - Be careful not to get injured on the sharp LED pins!
  - Please use a 330Ω resistor in series with the anode.
  - Since grounding a pin will turn on that colour, logic HIGH in code actually turns OFF an LED.

  Edit History:
  - Added function to control colours
*/

/*Global Declarations*/
const int RED_PIN = 3;
const int GREEN_PIN = 5;
const int BLUE_PIN = 6;

// Function to control LED states (0 = off, 1 = on)
void setLEDColour(int redValue, int greenValue, int blueValue) {
  // Red control
  if (redValue == 1) {
    digitalWrite(RED_PIN, LOW);   // ON
  } else {
    digitalWrite(RED_PIN, HIGH);  // OFF
  }

  // Green control
  if (greenValue == 1) {
    digitalWrite(GREEN_PIN, LOW);   // ON
  } else {
    digitalWrite(GREEN_PIN, HIGH);  // OFF
  }

  // Blue control
  if (blueValue == 1) {
    digitalWrite(BLUE_PIN, LOW);   // ON
  } else {
    digitalWrite(BLUE_PIN, HIGH);  // OFF
  }
}

void setup() {

  pinMode(RED_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
  pinMode(BLUE_PIN, OUTPUT);

  // All LEDs off at the start
  setLEDColour(0, 0, 0);
}

void loop() {
  // Red for 3 seconds
  setLEDColour(1, 0, 0);
  delay(3000);

  // Green for 2 seconds
  setLEDColour(0, 1, 0);
  delay(2000);

  // Orange (red + green) for 1 second
  setLEDColour(1, 1, 0);
  delay(1000);
}

---

Traffic Light (v3)

Now we add debug statements to better understand what’s happening in the code at any moment. We use Serial Monitor to do this. (This will come in handy when making our Arduino’s talk to each other!)

/*
  Title:              MakerLab1-RGB-Task1
  Organisation:       UCD ElecSoc - MakerLab
  Author(s):          Joe Biju
  Created:            24/09/2025

  Description:
  - Control a Common Anode RGB LED using Serial Monitor.

  Ingredients:
  - Arduino Uno
  - RGB LED with common anode configuration
  - 330Ω resistor
  - Breadboard
  - Jumper cables

  Notes:
  - Use the 5V pin for powering the LEDs
  - Be careful not to get injured on the sharp LED pins!
  - Please use a 330Ω resistor in series with the anode.
  - Since grounding a pin will turn on that colour, logic HIGH in code actually turns OFF an LED.

  Edit History:
  - Added function to control colours
  - Added serial monitor for debugging
*/

/*Global Declarations*/
const int RED_PIN = 3;
const int GREEN_PIN = 5;
const int BLUE_PIN = 6;

// Function to control LED states (0 = off, 1 = on)
void setLEDColour(int redValue, int greenValue, int blueValue) {
  // Red control
  if (redValue == 1) {
    digitalWrite(RED_PIN, LOW);   // ON
  } else {
    digitalWrite(RED_PIN, HIGH);  // OFF
  }

  // Green control
  if (greenValue == 1) {
    digitalWrite(GREEN_PIN, LOW);   // ON
  } else {
    digitalWrite(GREEN_PIN, HIGH);  // OFF
  }

  // Blue control
  if (blueValue == 1) {
    digitalWrite(BLUE_PIN, LOW);   // ON
  } else {
    digitalWrite(BLUE_PIN, HIGH);  // OFF
  }
}

void setup() {
  Serial.begin(9600);

  pinMode(RED_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
  pinMode(BLUE_PIN, OUTPUT);

  // All LEDs off at the start
  setLEDColour(0, 0, 0);
  Serial.println("All off");
}

void loop() {
  // Red for 3 seconds
  setLEDColour(1, 0, 0);
  delay(3000);
  Serial.println("Red");

  // Green for 2 seconds
  setLEDColour(0, 1, 0);
  delay(2000);
  Serial.println("Green");

  // Orange (red + green) for 1 second
  setLEDColour(1, 1, 0);
  delay(1000);
  Serial.println("Amber (Orange)");
}

---

Traffic Light (v4)

Now instead of 3 arguments, we only use one. This saves space! Welcome to embedded engineering :)

/*
  Title:              MakerLab1-RGB-Task1
  Organisation:       UCD ElecSoc - MakerLab
  Author(s):          Joe Biju
  Created:            24/09/2025

  Description:
  - Control a Common Anode RGB LED using Serial Monitor.

  Ingredients:
  - Arduino Uno
  - RGB LED with common anode configuration
  - 330Ω resistor
  - Breadboard
  - Jumper cables

  Notes:
  - Use the 5V pin for powering the LEDs
  - Be careful not to get injured on the sharp LED pins!
  - Please use a 330Ω resistor in series with the anode.
  - Since grounding a pin will turn on that colour, logic HIGH in code actually turns OFF an LED.

  Edit History:
  - Added function to control colours
  - Added serial monitor for debugging
  - Changed function to use 1 argument instead of 3
*/

/*Global Declarations*/
const int RED_PIN = 3;
const int GREEN_PIN = 5;
const int BLUE_PIN = 6;

// Function to control LED states using a 3-digit number (e.g. 101 = Red ON, Green OFF, Blue ON)
void setLEDColour(int colourCode) {
  int blueValue  = colourCode % 10;          // last digit
  int greenValue = (colourCode / 10) % 10;   // middle digit
  int redValue   = (colourCode / 100) % 10;  // first digit

  // Red control
  if (redValue == 1) {
    digitalWrite(RED_PIN, LOW);   // ON
  } else {
    digitalWrite(RED_PIN, HIGH);  // OFF
  }

  // Green control
  if (greenValue == 1) {
    digitalWrite(GREEN_PIN, LOW);   // ON
  } else {
    digitalWrite(GREEN_PIN, HIGH);  // OFF
  }

  // Blue control
  if (blueValue == 1) {
    digitalWrite(BLUE_PIN, LOW);   // ON
  } else {
    digitalWrite(BLUE_PIN, HIGH);  // OFF
  }
}


void setup() {
  Serial.begin(9600);

  pinMode(RED_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
  pinMode(BLUE_PIN, OUTPUT);

  // All LEDs off at the start
  setLEDColour(0, 0, 0);
  Serial.println("All off");

}
void loop() {
  setLEDColour(100); // Red
  delay(3000);
  Serial.println("Red (100)");

  setLEDColour(10); // Green (Q: why did we not use "010"?)
  delay(2000);
  Serial.println("Green (10)");

  setLEDColour(110); // Orange (Red + Green)
  delay(1000);
  Serial.println("Orange (110)");
}

---

Traffic Light (v5)

Finally, let’s give the user control! Now, we’ll type and set what colour we want through the Serial Monitor

/*
  Title:              MakerLab1-RGB-Task1
  Organisation:       UCD ElecSoc - MakerLab
  Author(s):          Joe Biju
  Created:            24/09/2025

  Description:
  - Control a Common Anode RGB LED using Serial Monitor.

  Ingredients:
  - Arduino Uno
  - RGB LED with common anode configuration
  - 330Ω resistor
  - Breadboard
  - Jumper cables

  Notes:
  - Use the 5V pin for powering the LEDs
  - Be careful not to get injured on the sharp LED pins!
  - Please use a 330Ω resistor in series with the anode.
  - Since grounding a pin will turn on that colour, logic HIGH in code actually turns OFF an LED.

  Edit History:
  - Added function to control colours
  - Added serial monitor for debugging
  - Changed function to use 1 argument instead of 3
  - Removed traffic light sequence. Added ability for user to set colour
  - Added "DEBUG" preprocessor directive
*/
/*Global Declarations*/
#define DEBUG
// #define DEBUG if(false)
const int RED_PIN   = 3;
const int GREEN_PIN = 5;
const int BLUE_PIN  = 6;

// Function to control LED states using a 3-digit number (e.g. 101 = Red ON, Green OFF, Blue ON)
void setLEDColour(int colourCode) {
  int blueValue  = colourCode % 10;          // last digit
  int greenValue = (colourCode / 10) % 10;   // middle digit
  int redValue   = (colourCode / 100);  // first digit
  DEBUG Serial.print("blueValue="); Serial.println(blueValue);
  DEBUG Serial.print("greenValue="); Serial.println(greenValue);
  DEBUG Serial.print("redValue="); Serial.println(redValue);

  // Red control
  if (redValue == 1) {
    digitalWrite(RED_PIN, LOW);   // ON
  } else {
    digitalWrite(RED_PIN, HIGH);  // OFF
  }

  // Green control
  if (greenValue == 1) {
    digitalWrite(GREEN_PIN, LOW);   // ON
  } else {
    digitalWrite(GREEN_PIN, HIGH);  // OFF
  }

  // Blue control
  if (blueValue == 1) {
    digitalWrite(BLUE_PIN, LOW);   // ON
  } else {
    digitalWrite(BLUE_PIN, HIGH);  // OFF
  }
}

void setup() {
  Serial.begin(9600);

  pinMode(RED_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
  pinMode(BLUE_PIN, OUTPUT);

  // All LEDs off at the start
  setLEDColour(0);
  Serial.println("All off");
  Serial.println("Type a 3-digit number (RGB) to set the LED colour, e.g. 101 for Red + Blue");
}

void loop() {
  // Check if data is available in Serial Monitor
  if (Serial.available() > 0) {
    int colourCode = Serial.parseInt();  // Read the typed number
    setLEDColour(colourCode);

    Serial.print("LED set to: ");
    Serial.println(colourCode);

    // Optional: small delay to avoid repeated reads of the same number
    delay(200);
  }
}