🛠 Lire un bouton et afficher dans la console

Objectives

Read the state of a push button on the Raspberry Pi 3 Model B GPIO and display a message in the console on each press. Learn how to enable the internal pull-up resistor (the button is wired to GND, active-low logic) and how to avoid mechanical bouncing with a software delay.

Hardware

• Raspberry Pi 3 Model B running Raspberry Pi OS Lite
• 1 push button (tactile switch)
• Breadboard, Dupont wires
• SSH terminal or screen + keyboard on the Pi
• libgpiod-utils package installed (sudo apt install -y libgpiod-utils)

Complete code

The button is wired between physical pin 7 (GPIO4) and physical pin 6 (GND). The internal pull-up keeps the input at 1 when idle; pressing the button brings it to 0:

#!/usr/bin/env bash
# bouton.sh — surveille GPIO4 (broche physique 7), bouton vers GND
# requis : libgpiod-utils (gpiodetect, gpioget)

echo "Surveillance GPIO4 — Ctrl-C pour quitter"

while true; do
  etat=$(gpioget --numeric gpiochip0 4)
  if [ "$etat" = 0 ]; then
    echo "$(date +%T) : bouton appuyé !"
    sleep 0.3   # anti-rebond logiciel
  fi
  sleep 0.05
done

Save as bouton.sh, then run chmod +x bouton.sh and ./bouton.sh. Python alternative: from gpiozero import Button; b = Button(4, pull_up=True) then b.wait_for_press — gpiozero is preinstalled on Raspberry Pi OS.

Expected verification

When idle, gpioget gpiochip0 4 returns 1 (internal pull-up). On each button press held down, the console displays a timestamped line "button pressed!". Upon release, the state returns to 1. Without the pull-up enabled, the input floats and displays random states — this is the best test to understand their usefulness.

Common errors

• Forgetting the pull-up (or wiring an external 10 kΩ one at the same time): the input floats, causing spurious messages.
• Wiring the button to 3.3 V without a resistor and then reading: short circuit to GND when pressed if the pin is set as high output.
• Wrong pin: GPIO4 = physical pin 7, not pin 4 (which is 5 V).
• Mechanical bouncing: without a delay, a single press may produce multiple lines — normal, hence the sleep 0.3.
• permission denied on gpiochip0: add the user to the gpio group and log out/in again.
• Using gpioget in a very tight loop on an old Pi: consumes CPU; keep a short sleep.