Traffic light system simulation with three LEDs

Last revision • 25/06/2025

Hardware Required

PICUNO Microcontroller board
3 × LEDs (Red, Yellow, Green)
3 × 220Ω resistors
Breadboard
Jumper wires
USB cable

Description

This project simulates a basic traffic light system using three LEDs to represent the red, yellow, and green signals. The lights switch in a predefined timing sequence: Red → Green → Yellow → Red, mimicking real-world traffic signals.

Circuit Diagram

[Fritzing image to be added here]

Circuit

Connect the PICUNO board to the computer using a USB cable.
Connect the red LED anode to one end of a 220Ω resistor, and the other end to GPIO 2.
Connect the yellow LED anode to a 220Ω resistor, and the other end to GPIO 3.
Connect the green LED anode to a 220Ω resistor, and the other end to GPIO 4.
Connect all LED cathodes to GND.

Schematic

GPIO 2 → 220Ω → Red LED Anode

GPIO 3 → 220Ω → Yellow LED Anode

GPIO 4 → 220Ω → Green LED Anode

All LEDs Cathode → GND

Code - C

#define RED 2
#define YELLOW 3
#define GREEN 4

void setup() {
  pinMode(RED, OUTPUT);
  pinMode(YELLOW, OUTPUT);
  pinMode(GREEN, OUTPUT);
}

void loop() {
  digitalWrite(RED, HIGH);
  digitalWrite(YELLOW, LOW);
  digitalWrite(GREEN, LOW);
  delay(5000);

  digitalWrite(RED, LOW);
  digitalWrite(GREEN, HIGH);
  delay(5000);

  digitalWrite(GREEN, LOW);
  digitalWrite(YELLOW, HIGH);
  delay(3000);

  digitalWrite(YELLOW, LOW);
}

pinMode(pin, OUTPUT) - Sets each GPIO as output.

digitalWrite(pin, HIGH/LOW) - Turns each light ON or OFF.

delay(ms) - Waits for the specified duration in milliseconds.

Code - Micropython

from machine import Pin
import time

red = Pin(2, Pin.OUT)
yellow = Pin(3, Pin.OUT)
green = Pin(4, Pin.OUT)

while True:
    red.value(1)
    yellow.value(0)
    green.value(0)
    time.sleep(5)

    red.value(0)
    green.value(1)
    time.sleep(5)

    green.value(0)
    yellow.value(1)
    time.sleep(3)

    yellow.value(0)

Pin(x, Pin.OUT) - Initializes GPIO pins for red, yellow, and green LEDs.

.value(1/0) - Turns each LED ON or OFF.

time.sleep(seconds) - Adds delays to simulate real traffic light timing.