Button controls an LED

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 signal import pause

led = LED(17)
button = Button(27)

button.when_pressed = led.on        # run led.on when pressed
button.when_released = led.off      # run led.off when released

print("Press and hold the button on the screen")
pause()                             # keep the program alive

The same program with RPi.GPIO

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)
GPIO.setup(27, GPIO.IN, pull_up_down=GPIO.PUD_UP)   # button to GND

try:
    while True:
        pressed = (GPIO.input(27) == 0)     # pulled up: 0 means pressed
        GPIO.output(17, pressed)
        time.sleep(0.02)
finally:
    GPIO.cleanup()

How the code works

• Button(27) watches GPIO27. gpiozero turns on the internal pull-up resistor for you.
• when_pressed and when_released are events. You give them a function and gpiozero calls it at the right moment.
• pause() stops the script from ending while it waits for events.

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.