🛠 Lire un bouton et afficher dans la console

Objectives

Wire a push button to the Raspberry Pi 5 and display a message in the console on each press, using gpiomon (libgpiod) and then a small Shell script. This introduces GPIO inputs, internal pull-up resistors, and edge detection.

Hardware

• Raspberry Pi 5 running Raspberry Pi OS 64-bit
• 1 push button
• Dupont cables
• Pinout: physical pin 7 = GPIO4 (input), physical pin 6 = GND. No external components are needed thanks to the internal pull-up resistor.

Complete code

# Écouter les fronts sur GPIO4 (libgpiod v2)
sudo apt install -y gpiod
gpiomon --num-events=0 --rising-edge gpiochip0 4

# Script bouton.sh : journaliser chaque appui
cat > bouton.sh <<'EOF'
#!/usr/bin/env bash
# Bouton sur GPIO4 (broche physique 7), pull-up interne : appui = niveau 0
echo "Surveillance de GPIO4... Ctrl-C pour terminer"
gpiomon --num-events=0 --falling-edge --debounce-period 0.05 gpiochip0 4 | while read -r _; do
    echo "$(date '+%H:%M:%S') - bouton pressé !"
done
EOF
chmod +x bouton.sh
./bouton.sh

Expected verification

Each press of the button displays a timestamped line "button pressed!" in the terminal. With gpiomon --rising-edge, it is the release that triggers the event.

Common errors

• Button wired to 3.3 V without a resistor: short circuit when pressed if the pin is configured as an output. Here we wire to GND with a pull-up, which is safe.
• Mechanical bouncing: multiple events for a single press; the --debounce-period 0.05 option in gpiomon filters these out.
• Wrong pin: GPIO4 = physical pin 7. Verify with the pinout command (provided with gpiozero) or gpioinfo gpiochip0.
• Running without sufficient privileges: on some configurations, accessing the GPIO requires being in the gpio group or using sudo.
• Confusing libgpiod versions: the syntax gpiomon gpiochip0 4 corresponds to v2 (Bookworm).