🛠 Lire un bouton et afficher l'état dans la console

Objectives

Read the state of a push button on the ODROID-N2 GPIO and display it in the console. We use the internal pull-up resistor (libgpiod bias pull-up), so no external resistor is needed: the button connects the pin to ground when pressed.

Hardware

• ODROID-N2/N2+ running Armbian (mainline)
• 1 push button
• 2 Dupont cables
• Pin used: PIN_11 (GPIOX_3), GND on PIN_25

Complete code

#!/usr/bin/env bash
# bouton.sh — état du bouton sur PIN_11 en temps réel (libgpiod v2)
set -e
gpiomon --num-events=0 --falling-edge --rising-edge gpiochip0 PIN_11 &
MON=$!
trap "kill $MON" EXIT
while true; do
    etat=$(gpioset --quiet --state gpiochip0 PIN_11 2>/dev/null || true)
    lu=$(gpioget gpiochip0 PIN_11)
    [ "$lu" = 0 ] && echo "BOUTON APPUYÉ" || echo "relâché"
    sleep 0.1
done

C version (libgpiod) with event handling: gcc bouton.c -o bouton -lgpiod, requesting PIN_11 as input with GPIOD_LINE_REQUEST_FLAG_BIAS_PULL_UP, then reading at 10 Hz.

Expected verification

At startup, the console displays "released" in a loop (the internal pull-up keeps the line at 1). While holding the button pressed, the lines become "BUTTON PRESSED". With gpiomon gpiochip0 PIN_11, each press/release produces a timestamped event.

Common errors

• Button between PIN_11 and 3.3 V instead of GND: without software pull-up, the line floats and the state is random.
• Missing debounce: a few bounces are displayed in addition to the press; filter by logic (ignore changes < 50 ms).
• Confusing PIN_11 (physical pin 11) and GPIO 11: the PIN_xx names in the device-tree are physical, verify with gpioinfo gpiochip0.
• gpioget returns an error: the line might be occupied by another process (gpioinfo shows the consumer).
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