🛠 Bouton utilisateur et console série USB

Objectives

Read the state of the USER button on the Feather nRF52840 and display it on the USB serial console. The nRF52840 has a native USB controller: the Serial object in the Arduino core is a CDC-TinyUSB implementation, so there is no external serial chip. You will also learn about software debouncing (millis) and non-blocking delays.

Hardware

• 1× Adafruit Feather nRF52840 Express
• 1× micro-USB data cable
• Arduino IDE with the Adafruit nRF52 Boards core

Complete Code

// nrf52840-bouton-console-uart.ino
const uint8_t BUTTON_PIN = 9;   // bouton USER (alias D9)
// > 
// sa broche exacte (D9 vient d'exemples CircuitPython) ; vérifier au multimètre
// ou avec le schéma officiel si rien ne se passe.

uint8_t lastState = HIGH;
uint32_t lastDebounce = 0;
uint32_t pressCount = 0;

void setup {
  Serial.begin(115200);          // console USB CDC native
  pinMode(BUTTON_PIN, INPUT_PULLUP); // le bouton USER relie la broche à GND
  Serial.println("Console Feather nRF52840 prete");
}

void loop {
  uint8_t state = digitalRead(BUTTON_PIN);
  uint32_t now = millis;
  if (state != lastState && (now - lastDebounce) > 30) {
    lastDebounce = now;
    lastState = state;
    if (state == LOW) {
      pressCount++;
      Serial.print("Appui n°");
      Serial.println(pressCount);
    }
  }
  if (Serial.available) {      // echo de la console vers la carte
    char c = Serial.read;
    Serial.print("Recu: ");
    Serial.println(c);
  }
}

Expected Verification

Open the serial monitor at 115200 baud: each press of the USER button displays "Press n°N" without spurious bounces (no duplicates within 1 ms). Any character typed into the console is echoed back.

Common Errors

• INPUT without pull-up: the pin floats and the console fills with false presses — use INPUT_PULLUP.
• Debouncing with delay(30): you miss subsequent presses; compare timestamps using millis as shown above.
• Incorrect USER pin: if nothing reacts, test D9 and neighboring pins, as the exact reference is not confirmed in the documentation.
• Monitor closed during upload: with native CDC, close the monitor if the port is busy.