🛠 Bouton et console USB

Objectives

Read a push button and display presses on the USB serial console. Understand that the MKR NB 1500 has native USB (no FTDI chip): Serial is the USB CDC port, and the GPIO logic is at 3.3 V.

Hardware

• 1 MKR NB 1500 board + micro-USB data cable
• 1 push button
• 1 connecting wire (pin D2 → button, other leg → GND); the internal INPUT_PULLUP resistor eliminates the need for any external resistor

Complete code

// Bouton sur D2 + console USB — MKR NB 1500
#include <MKRGSM.h>
GSM gsm;                       // sert uniquement a eteindre le modem

const uint8_t BTN = D2;        // D2 accepte aussi l'entree analogique (AIN18)

void setup {
  Serial.begin(9600);
  while (!Serial);             // USB natif : attendre l'ouverture du port CDC
  pinMode(BTN, INPUT_PULLUP);

  // Couper le modem pour eviter qu'il cherche un reseau en pure perte
  gsm.begin;
  gsm.shutdown;
}

void loop {
  static uint8_t last = HIGH;
  uint8_t now = digitalRead(BTN);
  if (now != last) {
    Serial.println(now == LOW ? "Bouton appuye" : "Bouton relache");
    last = now;
  }
  delay(20);                   // petit anti-rebond logiciel
}

Expected verification

Open the serial console (9600 baud) after uploading: "Button pressed" / "Button released" are displayed on each press. No additional components are required thanks to the internal pull-up resistor.

Common errors

• Forgetting while (!Serial);: on native USB, the first Serial.print calls occur before the port opens and seem "lost".
• Wiring the button to 5 V with an external resistor to D2: possible, but unnecessary here, and note that all MKR pins are 3.3 V max.
• Not turning off the modem: it consumes power and may interfere with measurements; gsm.shutdown silences it.
• Console set to 115200 while the code uses Serial.begin(9600): with USB CDC, the baud rate matters little, but keep it consistent.