Robotics Lab / Experiment 02

Arduino Traffic Light Simulator

Set the red, green and amber light durations, assign Arduino pins and watch the simulated traffic lights change. Compare breadboard wiring with a circuit schematic.

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01 Experiment parameters

Yellow code values follow your settings

Red duration (seconds)

Green duration (seconds)

Amber duration (seconds)

Red LED pin

Green LED pin

Amber LED pin

02 Live circuit view

Stopped · all LEDs OFF

Full cycle: 12 s

03 Arduino code

C++ / Arduino IDE

Yellow values are controlled by the parameters above. Each LED has its own 220 Ω series resistor.

// Experiment 02: Traffic lights
const int redPin = 8;
const int greenPin = 9;
const int amberPin = 10;

const unsigned long redTime = 5000;
const unsigned long greenTime = 5000;
const unsigned long amberTime = 2000;

void setup() {
  pinMode(redPin, OUTPUT);
  pinMode(greenPin, OUTPUT);
  pinMode(amberPin, OUTPUT);
}

void loop() {
  digitalWrite(redPin, HIGH);
  delay(redTime);
  digitalWrite(redPin, LOW);

  digitalWrite(greenPin, HIGH);
  delay(greenTime);
  digitalWrite(greenPin, LOW);

  digitalWrite(amberPin, HIGH);
  delay(amberTime);
  digitalWrite(amberPin, LOW);
}

Yellow = user-controlled program value.

Understand the logic

04 How does the traffic light work?

The Arduino activates one output at a time. When the programmed delay finishes, it switches that LED off and activates the next. The loop() function repeats the sequence.

Configure three outputs

pinMode() configures pins 8, 9 and 10 to drive three LEDs through separate resistors.

Red: stop

Only the red LED is ON for 5 seconds, then it switches OFF.

Green: go

Only the green LED is ON for 5 seconds, then it switches OFF.

Amber: prepare to stop

The amber LED stays ON for 2 seconds, then the sequence restarts.

Engineering connection: A traffic controller is a finite-state machine: RED → GREEN → AMBER → RED. One cycle takes 12 seconds. This beginner example uses blocking delay() calls; more advanced projects use millis() so the Arduino can respond to pedestrian buttons while timing the lights. Actual traffic signal sequences and safety interlocks vary by jurisdiction.