🛠 Lire un bouton poussoir avec libgpiod (pull-up interne)

Objectives

Read the state of a push button on the Le Potato using libgpiod in C, enabling the internal pull-up resistor (no external resistor required) and displaying the state in a loop.

Hardware

• Le Potato AML-S905X-CC running Armbian mainline
• Push button between physical pin 11 (GPIOX_3 — chip/line to be confirmed with lgpio info 11, example below: gpiochip3 line 8) and a ground pin
• sudo apt install libgpiod-dev gpiod

Complete code

/* bouton.c — gcc bouton.c -o bouton -lgpiod */
#include <gpiod.h>
#include <stdio.h>
#include <unistd.h>
int main(void) {
    /* Chip/ligne à ajuster selon « lgpio info 11 » ou « gpioinfo » */
    struct gpiod_chip *chip = gpiod_chip_open_by_name("gpiochip3");
    if (!chip) { perror("gpiochip3"); return 1; }
    struct gpiod_line *line = gpiod_chip_get_line(chip, 8);
    int flags = GPIOD_LINE_REQUEST_FLAG_BIAS_PULL_UP;
    if (!line || gpiod_line_request_input_flags(line, "bouton", flags)) {
        perror("request"); return 1;
    }
    printf("Appuyez sur le bouton (Ctrl-C pour quitter)\n");
    for (;;) {
        int etat = gpiod_line_get_value(line);
        printf("bouton %s\n", etat ? "relâché" : "APPUYÉ");
        usleep(50000);
    }
}

Expected verification

./bouton displays "released" at rest (the pull-up maintains the high state) and "PRESSED" when the contact to ground is closed. gpioinfo gpiochip3 confirms the pull-up bias on the requested line.

Common errors

• Wrong chip/line: The GPIOAO/GPIOH/GPIOE/GPIODV/GPIOX banks are distributed across several gpiochips; always verify with lgpio info <pin> or gpioinfo.
• Missing pull-up: Without BIAS_PULL_UP, the input floats and displays random states.
• Expected inverted logic: With a pull-up, button pressed = 0 (active low).
• 5 V on the pin: Forbidden, the Le Potato has no 5 V tolerant pins.