Traffic Light

Expand a single blinking LED into a clear state sequence. This project introduces multiple outputs, reusable functions, readable timing constants, and systematic breadboard wiring.

Last updated July 15, 2026

Build Time: 35-50 minutes
Estimated Cost: $10-$18
Skill Level: Easy

Raspberry Pi PicoRaspberry Pi PicoLEDsGPIOSequencing

Project illustration

A visual reference for this build. Use the parts, wiring, and instruction sections below for exact assembly details.

Recommended for

Middle School
High School
Adult Beginners
Homeschool

Skills

What You'll Learn

Control several GPIO outputs independently
Organize repeated behavior in a function
Build and verify repeated LED circuits
Translate a real sequence into program states

Preparation

Required Parts

Gather these components before starting the build.

QuantityPartNotes

Qty: 1Raspberry Pi PicoMicroPython installed
Qty: 1Solderless breadboardHalf-size or larger
Qty: 3LEDsOne red
Qty: 3220 ohm resistorsOne per LED
Qty: 4Jumper wiresMale-to-male

Wiring

Circuit Diagram

Red, yellow, and green LED anodes connect through 220 ohm resistors to GP15, GP14, and GP13. All cathodes share GND.

Circuit overview

Three-output traffic light circuit. Follow the written connection notes and numbered build steps for exact wiring.

Build

Step-by-Step Instructions

Work through each stage in order and disconnect power before changing the wiring.

1. Build three LED branches

Place the LEDs in traffic-light order. Connect each anode to its assigned GPIO through a separate 220 ohm resistor and connect all cathodes to ground.

2. Test one color at a time

Before running the full sequence, briefly set each GPIO high in Thonny’s shell. Correct any color or polarity mistakes now.

3. Run the sequence

Upload the program and confirm the order is red, green, then yellow. The show function guarantees only one light is active.

4. Tune the timing

Change the duration values to model a faster tabletop demonstration or a more realistic intersection cycle.

Programming

Project Code

Upload traffic-light.py after completing the circuit.

traffic-light.pypython

from machine import Pin
from time import sleep

red = Pin(15, Pin.OUT)
yellow = Pin(14, Pin.OUT)
green = Pin(13, Pin.OUT)

def show(active, seconds):
    for light in (red, yellow, green):
        light.value(light is active)
    sleep(seconds)

while True:
    show(red, 4)
    show(green, 4)
    show(yellow, 1)