🛠 Bouton poussoir et console USB

Objectives

Wire a push button to a digital pin on the MKR GSM 1400 (3.3 V logic), read it using an internal pull-up resistor (INPUT_PULLUP), debounce the signal, and display each press on the USB console. This is a fundamental skill for any local interface: pins D0–D7 are digital, including 8 external interrupt-capable inputs.

Hardware

• Arduino MKR GSM 1400 board
• 1 push button
• 1 breadboard and jumper wires
• USB power supply (the radio module remains off, so USB is sufficient for this setup)

Complete Code

// Bouton sur D2 (vers GND) + console USB
const uint8_t BTN = 2;
volatile uint32_t appuis = 0;
uint32_t dernierMs = 0;

void onAppui {
  uint32_t maintenant = millis;
  if (maintenant - dernierMs > 50) {  // anti-rebond 50 ms
    appuis++;
    dernierMs = maintenant;
  }
}

void setup {
  pinMode(BTN, INPUT_PULLUP);          // logique active a l'etat BAS
  attachInterrupt(digitalPinToInterrupt(BTN), onAppui, FALLING);
  Serial.begin(9600);
  while (!Serial) {}                   // attend l'ouverture du moniteur USB
  Serial.println("MKR GSM 1400 - test bouton D2");
}

void loop {
  static uint32_t dernierAffiche = 0xFFFFFFFF;
  noInterrupts;
  uint32_t n = appuis;
  interrupts;
  if (n != dernierAffiche) {
    dernierAffiche = n;
    Serial.print("Appuis : ");
    Serial.println(n);
  }
  delay(10);
}

Expected Verification

Each single press prints a line "Presses: N" with a counter that increases by 1; a firm press must never create duplicates. The while (!Serial) statement shows that the MKR GSM 1400 has native USB CDC: the program waits for the serial monitor to open.

Common Errors

• Button wired to 3.3 V instead of GND while the code uses INPUT_PULLUP: the counter increments continuously; wire it to ground or switch to INPUT with an external pull-up resistor to 3.3 V.
• Forgetting that the logic level is 3.3 V: never inject 5 V into a GPIO pin on the board.
• Using a pin that does not support interrupts: only some pins accept attachInterrupt (8 external interrupt pins on the MKR); D2 is one of them.
• Not including while (!Serial): the first lines are lost if the monitor opens after startup.
• Bouncing: without the 50 ms window, a single press may count 3 to 5 events.