Traffic light with a walk button

Parts in this circuit

Wiring, pin by pin

Red = 5 V, orange = 3.3 V, black = GND, other colours = signals. “Pin” is the position on the 40-pin header; the GPIO number is what the code uses. Power the Pi from a 5.1 V supply and wire with the power off.

Python code (gpiozero)

from gpiozero import LED, Button
from time import sleep

red = LED(22)
yellow = LED(23)
green = LED(24)
walk = Button(27)

def show(colour, seconds):
    for led in (red, yellow, green):
        led.off()                    # all off first
    colour.on()
    sleep(seconds)

while True:
    show(green, 1)
    print("Green. Press the walk button to cross.")
    walk.wait_for_press(timeout=10)  # stay green until pressed (max 10 s)
    show(yellow, 2)
    show(red, 5)
    print("Walk now!")

The same program with RPi.GPIO

import RPi.GPIO as GPIO
import time

RED, YELLOW, GREEN, WALK = 22, 23, 24, 27

GPIO.setmode(GPIO.BCM)
GPIO.setup([RED, YELLOW, GREEN], GPIO.OUT)
GPIO.setup(WALK, GPIO.IN, pull_up_down=GPIO.PUD_UP)

def show(pin, seconds):
    GPIO.output([RED, YELLOW, GREEN], GPIO.LOW)
    GPIO.output(pin, GPIO.HIGH)
    time.sleep(seconds)

try:
    while True:
        show(GREEN, 1)
        print("Green. Press the walk button to cross.")
        GPIO.wait_for_edge(WALK, GPIO.FALLING, timeout=10000)
        show(YELLOW, 2)
        show(RED, 5)
        print("Walk now!")
finally:
    GPIO.cleanup()

How the code works

• show(colour, seconds) turns every LED off, then switches on one colour and waits.
• walk.wait_for_press(timeout=10) pauses the program until the button is pressed or 10 seconds pass.
• The order green, yellow, red is a small state machine, the same idea as a PLC sequence.

Parts to buy

The links open a search on each store, so you see what is in stock today. Check the model, voltage and price before you order.