🛠 Bouton poussoir avec anti-rebond

Objectives

Read a push button on PA0 and control the LED on PC13 by toggling its state on each press, filtering mechanical bounce in software (time-based debouncing). You will learn how to configure an input, the active-HIGH logic of a button wired with a pull-down resistor, and the limitations of millis-based debouncing when handling rapid presses.

Hardware

• GD32F103C8T6 / GD32F103CBT6 board compatible with Blue Pill
• Push button between 3.3 V and PA0, with a pull-down resistor to ground (the verified pinout uses PA0; press = HIGH level) >
• On-board LED on PC13 (active-LOW)
• 3.3 V power supply (the circuit operates between 2.6 V and 3.6 V)

Complete Code

// bouton_antirebond.ino — GD32F103C8, core CommunityGD32Cores
#include <Arduino.h>

const uint8_t BTN = PA0;      // appui = HIGH (pull-down externe)
const unsigned long DEBOUNCE_MS = 50;

bool etatStable = false;      // état filtré du bouton
bool dernierLu = false;       // dernière lecture brute
unsigned long dernierChangement = 0;
bool ledAllumee = false;

void setup {
  pinMode(BTN, INPUT_PULLDOWN); // pull-down interne : pas obligatoire si R externe
  pinMode(PC13, OUTPUT);
  digitalWrite(PC13, HIGH);     // LED éteinte (active-LOW)
}

void loop {
  bool brut = digitalRead(BTN);
  unsigned long maintenant = millis;

  if (brut != dernierLu) {
    dernierChangement = maintenant;   // le signal bouge : on repart
    dernierLu = brut;
  } else if (maintenant - dernierChangement >= DEBOUNCE_MS
             && brut != etatStable) {
    etatStable = brut;                // état confirmé après 50 ms stables
    if (etatStable) {                 // front montant = appui
      ledAllumee = !ledAllumee;
    }
  }
  digitalWrite(PC13, ledAllumee ? LOW : HIGH);
}

Expected Verification

A firm press turns the LED on (if it was off), a second press turns it off, with only one state change per press. When gently shaking the button, the LED should not "flicker": the debouncing is working. You can add a Serial output to count the presses and verify that there are never two counts for a single action.

Common Errors

• Button counting 2 to 5 presses: debouncing is missing or too short; 30 to 50 ms is a good range for a mechanical button.
• Inverted logic: without a pull-down (internal or external), the PA0 input floats and the state changes randomly; add INPUT_PULLDOWN or a 10 kΩ resistor to ground.
• Pin confusion: the verified documentation lists the button on PA0; if your board has its user button on PA1 (classic Blue Pill wiring), adapt the pin. >
• millis "overflow": always compare using now - lastChange >= D and not now >= lastChange + D, which breaks upon overflow after 49 days.
• Forgetting the active-LOW LED: writing HIGH to turn the LED on leaves it off.