🛠 Lire le bouton BOOT sur GPIO0 sans se piéger

Objectives

Learn how to read a digital input on the ESP32-S3 using the BOOT button (GPIO0), while understanding why this pin is special: GPIO0 is a strapping pin that determines the boot mode (flash or execution). You will write a program that detects button presses with software debouncing, and you will understand the golden rule: never force GPIO0 to a LOW state during power-up, otherwise the board will think you want to flash it.

Hardware

• 1 ESP32-S3 board (the BOOT button is present on all of them: DevKitC-1, XIAO, T-Display-S3)
• 1 USB data cable
• Optional: 1 external push button between GPIO1 and GND for comparison

Complete code

// GPIO0 = bouton BOOT embarque (vers GND), pull-up interne obligatoire
// GPIO1 = bouton externe optionnel, entre GPIO1 et GND
const uint8_t BTN_BOOT = 0;
const uint8_t BTN_EXT  = 1;

unsigned long dernierAppui = 0;
const unsigned long ANTI_REBOND = 60;   // ms

void setup {
  Serial.begin(115200);
  pinMode(BTN_BOOT, INPUT_PULLUP);
  pinMode(BTN_EXT,  INPUT_PULLUP);
}

void loop {
  if (digitalRead(BTN_BOOT) == LOW && millis - dernierAppui > ANTI_REBOND) {
    dernierAppui = millis;
    Serial.println("Bouton BOOT (GPIO0) presse !");
  }
  if (digitalRead(BTN_EXT) == LOW && millis - dernierAppui > ANTI_REBOND) {
    dernierAppui = millis;
    Serial.println("Bouton externe (GPIO1) presse !");
  }
  delay(5);
}

Expected verification

Open the serial monitor at 115200 bauds: each press of the BOOT button prints a single line, without duplicates due to bouncing. The second button (if wired between GPIO1 and GND) behaves identically. The board restarts normally after a reset: GPIO0 was never held LOW during power-up.

Common errors

• Floating input: forgetting INPUT_PULLUP and reading random states; the S3 has internal pull-up/pull-down resistors, use them.
• Wiring a load to GPIO0: if this pin is pulled LOW during power-up, the board enters download mode and appears "dead"; this is the classic pitfall of strapping pins (GPIO0, GPIO3, GPIO45, GPIO46).
• Confusing press and hold: the code above detects the level, not the edge; for strict counting, remember the previous state.
• Debounce too short: below 30 ms, mechanical bouncing creates ghost presses; 50 to 60 ms is a good compromise.