🛠 Bouton poussoir et messages dans la console

Objectives

Read a logical state on a GPIO input and react in the console. You will wire a push button, enable the internal pull-up resistor to avoid an external component, then poll the pin in a loop to display a message on each press.

Hardware

• Raspberry Pi 2 Model B running 32-bit Raspberry Pi OS
• 1 push button
• Breadboard, 2 jumper wires
• Pins: GPIO4 (pin 7 on J8) and GND (pin 9)
• gpiod package installed (sudo apt install gpiod)

Complete code

#!/bin/bash
# bouton.sh — surveille GPIO4 (actif au niveau bas, pull-up interne)
CHIP=gpiochip0
while true; do
  etat=$(sudo gpioget --pull-up $CHIP 4)
  if [ "$etat" = "0" ]; then
    echo "$(date +%T) : bouton appuye !"
    while [ "$(sudo gpioget --pull-up $CHIP 4)" = "0" ]; do sleep 0.05; done
    echo "$(date +%T) : bouton relache"
  fi
  sleep 0.05
done

Save as bouton.sh, then run: chmod +x bouton.sh && ./bouton.sh

Expected verification

Each press displays a timestamped line "button pressed!" followed by "button released" upon release. Without any press, the loop remains silent. Stop with Ctrl+C.

Common errors

• Forgetting the pull-up: without it, the pin floats and displays random states; the --pull-up option (or a resistor to 3.3 V) is essential.
• Wiring GPIO4 to 3.3 V instead of GND: you then need to invert the logic (active high).
• Confusing the physical pin number (7) with the GPIO number (4): always program using the GPIO number.
• Message spam: mechanical bounce of the button causes duplicates; the 50 ms delay after detection filters them out.