🛠 Bouton poussoir et retour dans la console

Objectives

Read a digital input: a push button wired to GND with an internal pull-up, and display the state in the console on each press. You will learn about inverted logic (press = low level), mechanical bounce, and simple polling in the shell.

Hardware

• Raspberry Pi 3 Model B+ type board running Raspberry Pi OS
• 1 push button
• 2 Dupont wires (no external resistor needed: internal pull-up)
• Terminal access (SSH or keyboard/screen)

Complete Code

Wiring: pin 13 (GPIO27) → one leg of the button; other leg → pin 9 (GND). The internal pull-up keeps the line at 1 when idle.

#!/usr/bin/env bash
# bouton.sh — affiche un message à chaque appui (GPIO27, broche 13)
# Active le pull-up interne puis boucle sur la lecture de la ligne.
sudo gpioset --quiet --hold-period 0ms gpiochip0 27=0 2>/dev/null || true

echo "Appuyez sur le bouton (Ctrl-C pour quitter)..."
while true; do
    # gpiodetect/gpiget : lecture de la ligne ; 0 = bouton pressé (logique inversée)
    etat=$(sudo gpiget gpiochip0 27 2>/dev/null || echo 1)
    if [ "$etat" = "0" ]; then
        echo "Bouton pressé à $(date +%T)"
        sleep 0.3        # anti-rebond logiciel grossier
        while [ "$(sudo gpiget gpiochip0 27 2>/dev/null || echo 1)" = "0" ]; do
            sleep 0.05   # attend le relâchement
        done
    fi
    sleep 0.02
done

Expected Verification

Each press displays a line "Button pressed" with the time, only once per press despite mechanical bounce. When idle, the line reads 1 thanks to the internal pull-up; when pressed, it drops to 0.

Common Errors

• Forgetting the pull-up: the line floats, the state changes on its own (ghost counting).
• Getting the logic wrong: here pressed = 0, not 1; wiring the button to 3.3 V instead of GND inverts the logic.
• No debouncing: a single press triggers 5 to 20 detections.
• Confusing pin 13 (GPIO27) with GPIO13: check the mapping on the connector diagram.
• Using a PWM/I2C pin already claimed by an overlay: choose a free GPIO pin.