Aim:

Simulate a real traffic light system with programmed timing.

Requirements:

• Arduino Uno or Raspberry Pi Pico

• Red, yellow, and green LEDs (1 each)

• 3 × 220 Ω resistors

• Breadboard and jumper wires

• USB cable and computer with Arduino IDE (or Thonny for Pico)

Working Principle:

Traffic lights use fixed cycles to manage traffic flow:

1. Red → STOP

2. Green → GO

3. Yellow → Get ready to STOP

We will program LEDs to turn ON/OFF for specific durations, simulating real-world traffic control.

Circuit Diagram:

    Arduino Pin 2 → [220Ω] → Red LED → GND  

     Arduino Pin 3 → [220Ω] → Yellow LED → GND  

     Arduino Pin 4 → [220Ω] → Green LED → GND

(Visual diagram can be included in the printed book)

Step-by-Step Instructions

Step 1: Wiring

1. Place all three LEDs on the breadboard.

2. Connect a 220 Ω resistor to each LED’s positive leg (anode).

3. Connect the resistor ends to Arduino pins:
   • Red → Pin 2

   • Yellow → Pin 3

   • Green → Pin 4

4. Connect all LED cathodes (negative legs) to Arduino GND.

Step 2: Arduino Code (Delay Version)

void setup() {

  pinMode(2, OUTPUT); // Red LED

  pinMode(3, OUTPUT); // Yellow LED

  pinMode(4, OUTPUT); // Green LED

}

void loop() {

  // Red light – 5 seconds

  digitalWrite(2, HIGH);

  delay(5000);

  digitalWrite(2, LOW);

  // Green light – 5 seconds

  digitalWrite(4, HIGH);

  delay(5000);

  digitalWrite(4, LOW);

  // Yellow light – 2 seconds

  digitalWrite(3, HIGH);

  delay(2000);

  digitalWrite(3, LOW);

}

Step 3: Upload and Test

• Open Arduino IDE → Select board → Upload code.

• Observe LEDs switching in the red → green → yellow order repeatedly.

Upgrading to a Timer (Non-Blocking) Version

Using millis() allows other actions (like reading a button) while lights run.

unsigned long previousMillis = 0;

int state = 0;

void setup() {

  pinMode(2, OUTPUT);

  pinMode(3, OUTPUT);

  pinMode(4, OUTPUT);

}

void loop() {

  unsigned long currentMillis = millis();

  if (state == 0 && currentMillis – previousMillis >= 5000) {

    digitalWrite(2, LOW);

    digitalWrite(4, HIGH);

    previousMillis = currentMillis;

    state = 1;

  }

  else if (state == 1 && currentMillis – previousMillis >= 5000) {

    digitalWrite(4, LOW);

    digitalWrite(3, HIGH);

    previousMillis = currentMillis;

    state = 2;

  }

  else if (state == 2 && currentMillis – previousMillis >= 2000) {

    digitalWrite(3, LOW);

    digitalWrite(2, HIGH);

    previousMillis = currentMillis;

    state = 0;

  }

}

Real-World Variations of This Project:

1. Pedestrian Crossing Button – Add a push button that triggers a special sequence for pedestrians.

2. Smart Traffic Light – Use sensors to detect cars and change timing dynamically.

3. Night Mode – Only blink yellow light during late hours.

Troubleshooting: