🛠 Clavier USB : taper du texte avec la bibliothèque Keyboard

Objectives

Leverage the feature that defines the Leonardo: the ATmega32u4 integrates the USB transceiver, so the board can pretend to be a HID keyboard to the host computer, without any auxiliary USB processor. You will send a sentence when a button is pressed, with the two official precautions: a startup guard window and a call only on the rising edge.

Hardware

• 1 Arduino Leonardo + micro-USB cable
• 1 push button between pin 2 and GND (internal pull-up)
• A deliberate keyboard focus in a text editor for testing

Complete code

#include <Keyboard.h>

const uint8_t BUTTON_PIN = 2;
bool wasPressed = false;

void setup {
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  Keyboard.begin; // énumère la carte en clavier HID standard
  delay(3000);      // fenêtre de garde : le temps de placer le focus
}

void loop {
  bool pressed = (digitalRead(BUTTON_PIN) == LOW);
  if (pressed && !wasPressed) {           // front montant uniquement
    Keyboard.print("Hello, Leonardo!");   // les frappes partent vers l'OS hôte
    Keyboard.releaseAll;                // aucun key remain held
  }
  wasPressed = pressed;
}

Expected verification

Place the cursor in a text editor during the first 3 seconds, then press the button: the sentence “Hello, Leonardo!” is typed once in the focused application. In the IDE, the serial monitor will show nothing here: Serial is not used, and the current USB device is a keyboard.

Common errors

• Runaway HID: calling Keyboard.print in a tight loop floods the computer with keystrokes and can make the board very difficult to reprogram. Arduino explicitly warns: test first with Serial.print and only trigger HID calls behind a button or a condition.
• Forgetting Keyboard.releaseAll: a key left pressed causes a character to repeat indefinitely.
• No guard window: the board types immediately into the focused window upon enumeration, sometimes the IDE itself.
• Wrong component selected: “Pro Micro” clones share the chip but require their own board entry in the IDE.
• Waiting for the serial monitor: once enumerated as HID, the board may no longer expose a CDC port if the sketch only declares the keyboard.