Traffic light
You build a real traffic light with a red, a yellow, and a green LED. They turn on one by one, just like on the street.
🧰 What do you need?
🗺️ Wiring diagram
Follow the wires from the Arduino to each part. You can choose the wire colors yourself.
| From | To |
|---|---|
Arduino UNO · D4 |
220Ω · 1 |
220Ω · 2 |
LED red · ANODE |
LED red · CATHODE |
Arduino UNO · GND |
Arduino UNO · D3 |
220Ω · 1 |
220Ω · 2 |
LED yellow · ANODE |
LED yellow · CATHODE |
Arduino UNO · GND |
Arduino UNO · D2 |
220Ω · 1 |
220Ω · 2 |
LED green · ANODE |
LED green · CATHODE |
Arduino UNO · GND |
🛠️ This is how you build it
- Put the three LEDs next to each other in the breadboard.
- Give each LED its own 220 Ω resistor to its pin: red to 4, yellow to 3, green to 2.
- Connect all short legs to the minus strip (−) of the breadboard.
- Connect the minus strip to GND of your Arduino.
💻 The code
// Traffic light
// Three LEDs do exactly what a real traffic light does: green, orange, red.
const int RED = 4; // Red LED on pin 4
const int ORANGE = 3; // Yellow/orange LED on pin 3
const int GREEN = 2; // Green LED on pin 2
void setup() {
pinMode(RED, OUTPUT);
pinMode(ORANGE, OUTPUT);
pinMode(GREEN, OUTPUT);
}
// Turn one light on and the other two off
void setLight(int on) {
digitalWrite(RED, on == RED ? HIGH : LOW);
digitalWrite(ORANGE, on == ORANGE ? HIGH : LOW);
digitalWrite(GREEN, on == GREEN ? HIGH : LOW);
}
void loop() {
setLight(GREEN); // Green: you may go
delay(5000);
setLight(ORANGE); // Orange: watch out, it will turn red
delay(2000);
setLight(RED); // Red: stop!
delay(5000);
}
🧠 What does the code do?
- Each LED has its own pin: red on 4, yellow on 3, and green on 2.
- The function
setLight()turns one light on and the other two off. - In
loop()we go from green to orange to red, with a wait in between.
🎯 Try this…
- Make the orange light blink three times before it turns red
- Add a button: when you press it, the light goes to red faster (a pedestrian button)
- Make a night mode where only the orange light blinks
🚀 Build this project with Codey: open codey.online/starter-kits/uno/projects/traffic-light and click MAKE THIS. Then the code and the wiring diagram are ready right away.
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