🛠 Faire clignoter la LED intégrée de l'UNO R3

Objectives

Discover the reference board of the Arduino ecosystem: the UNO R3 (ATmega328P, 8-bit AVR, 16 MHz, 32 KB of flash, with 0.5 KB reserved for the bootloader). You will upload your first program and make the built-in LED blink, without any wiring.

Hardware

• 1 Arduino UNO R3 board (or compatible)
• 1 USB-B cable (the square connector on the UNO; USB-to-serial conversion is handled by the onboard ATmega16U2)
• A PC with the Arduino IDE (or arduino-cli)
• Optional for later steps: External LED + 330 Ω resistor on pin 13 — remember: 20 mA maximum per pin, always design with caution.

Complete code

// Blink — LED intégrée sur la pin 13 (LED marquée "L")
const uint8_t LED = 13;

void setup {
  pinMode(LED, OUTPUT);      // la broche devient une sortie
}

void loop {
  digitalWrite(LED, HIGH);   // LED allumée
  delay(500);                // 500 ms (blocant, c'est OK pour débuter)
  digitalWrite(LED, LOW);    // LED éteinte
  delay(500);
}

In the IDE: Tools > Board > Arduino Uno, then select the displayed serial port, and click Upload.

Expected verification

The "L" LED blinks every 0.5 s as soon as the upload is complete, and continues even when you unplug the USB and power via the barrel jack (6–20 V, 7–12 V recommended): the program is burned into the flash, it runs autonomously.

Common errors

• Wrong board type selected (e.g. "Arduino Nano"): the upload fails with a bootloader timeout.
• Serial port not found on clones: some R1/R2 or third-party clones use a different USB-to-serial chip, install the appropriate driver (CH340, etc.).
• Confusing the power LED (ON, steady) and the user LED "L" (pin 13).
• Overloading the pin: never wire an LED without a resistor; the per-pin spec is 20 mA.
• Forgetting that delay blocks the entire program: useful here, but to be avoided as soon as you do two things at once (see the multitasking tutorial).