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Introduction
Build a traffic light simulation with red, yellow, and green LEDs. Optionally add a pedestrian button to trigger a safe crossing phase.
Overview
- Difficulty: Beginner level — requires a basic understanding of Arduino concepts, components, and simple coding. Learners should already know how to connect sensors and upload basic sketches
- Estimated Time: 45–60 minutes
- Concepts:
- Digital Output
- Timing
- State Machines
- Debouncing
Components Required
| Item | Quantity | Notes |
|---|---|---|
| Arduino Uno (or compatible) | 1 | Main controller |
| LEDs (Red, Yellow, Green) | 1 each | 5mm |
| Resistors 220Ω | 3 | LED current limit |
| Push Button (optional) | 1 | Pedestrian request |
| Breadboard & Jumpers |
Circuit Connections
| Arduino Pin | Connection |
|---|---|
| D8 | Red LED (+ via 220Ω) |
| D9 | Yellow LED (+ via 220Ω) |
| D10 | Green LED (+ via 220Ω) |
| GND | All LED negatives |
| D2 | Button to GND (INPUT_PULLUP) |
Arduino Code
const int RED = 8, YELLOW = 9, GREEN = 10, BUTTON = 2;
void setup(){
pinMode(RED, OUTPUT); pinMode(YELLOW, OUTPUT); pinMode(GREEN, OUTPUT);
pinMode(BUTTON, INPUT_PULLUP);
}
void phase(int r, int y, int g, unsigned long ms){
digitalWrite(RED, r); digitalWrite(YELLOW, y); digitalWrite(GREEN, g);
delay(ms);
}
void normalCycle(){
phase(HIGH, LOW, LOW, 3000); // Red
phase(HIGH, HIGH, LOW, 1000); // Red+Yellow
phase(LOW, LOW, HIGH, 3000); // Green
phase(LOW, HIGH, LOW, 1000); // Yellow
}
void pedestrianCycle(){
// Ensure safe stop
phase(HIGH, HIGH, LOW, 1000);
phase(HIGH, LOW, LOW, 4000); // Red for crossing
}
void loop(){
if (digitalRead(BUTTON) == LOW) {
pedestrianCycle();
} else {
normalCycle();
}
}Assembly Steps
- Place LEDs on a breadboard with resistors to Arduino pins D8, D9, D10.
- Wire a pushbutton to D2 and GND; use INPUT_PULLUP in code.
- Upload the sketch and test the cycle; press the button to trigger crossing.
Tips
- Use long delays first, then refactor to non-blocking millis() logic.
- Swap LEDs for a 4-way junction model by duplicating channels.
- Enclose in a small cardboard model for a fun display.
