How to program an Arduino?

 

You “program” an Arduino by writing a sketch (a C/C++ program), compiling it, and uploading it to the board over USB. Let’s walk it from zero to blinking LED.

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1. What you need

• An Arduino board (Uno, Nano, Mega, etc.)

• USB cable that matches your board (Uno: USB-B, newer: USB-C/micro-USB)

• A computer (Windows / macOS / Linux)

• Arduino IDE installed

If you don’t have the IDE yet, download it from the official Arduino site (Arduino IDE 2.x). Install it like any normal app.

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2. Connect the Arduino

1. Plug the USB cable into the Arduino and your computer.

2. The power LED on the Arduino should turn on.

3. Windows may install a driver automatically; on macOS and Linux it usually just works.

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3. Open the Arduino IDE and select your board

1. Start Arduino IDE.

2. Go to Tools → Board and choose your board, for example:

   • Arduino Uno

   • Arduino Nano

   • Arduino Mega or Mega 2560, etc.

3. Go to Tools → Port and pick the port that shows something like:

   • COM3 (Arduino Uno) on Windows

   • /dev/ttyACM0 or /dev/ttyUSB0 on Linux

   • /dev/cu.usbmodem… on macOS

If you only see one port, that’s probably it. If you see none, we’ll touch troubleshooting later.

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4. Your first program: Blink

We’ll load the built-in Blink example, then look at the code.

1. In the IDE: File → Examples → 01.Basics → Blink

2. A new window with code opens. It should look like:

// Blink: Turns an LED on for one second, then off for one second, repeatedly.

void setup() {
  // put your setup code here, to run once:
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(LED_BUILTIN, HIGH);  // LED on
  delay(1000);                      // wait 1 second
  digitalWrite(LED_BUILTIN, LOW);   // LED off
  delay(1000);                      // wait 1 second
}

What this means

• setup() runs once when the board powers up or resets.

• loop() runs over and over forever.

• LED_BUILTIN is the on-board LED (on Uno it’s the LED on pin 13).

• pinMode(..., OUTPUT) tells Arduino we want to drive that pin.

• digitalWrite(..., HIGH/LOW) turns it on/off.

• delay(1000) pauses for 1000 ms (1 second).

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5. Compile and upload

1. Click the ✔ Check button (Verify / Compile).

   • The IDE compiles your code. If you made no changes, it should pass.

2. Click the → Upload button.

   • The IDE compiles (again) and uploads over USB.

3. Watch the Arduino:

   • You’ll see the TX/RX LEDs flash during upload.

   • Then the built-in LED should start blinking once per second.

Boom — you just programmed an Arduino.

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6. Change something (so it feels like your code)

Try making the LED blink faster:

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);
  delay(200);              // 0.2 seconds
  digitalWrite(LED_BUILTIN, LOW);
  delay(200);
}

Hit Upload again and watch the change.

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7. Typical workflow after this

Every Arduino project is the same basic pattern:

1. Plan hardware (which pins go to LEDs, buttons, sensors, etc.).

2. In code:

   • In setup(): configure pins (pinMode), start serial (Serial.begin(9600);), start libraries (like Wi-Fi, sensors, etc.).

   • In loop(): read inputs, do logic, control outputs.

3. Use libraries:

   • Example: for an I²C sensor, install its library from Sketch → Include Library → Manage Libraries…

   • Load example from File → Examples → [Library Name].

4. Combine multiple examples into your own sketch.

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8. Quick troubleshooting tips

No COM port / board not found

• Try another USB cable (some are power-only).

• Try another USB port.

• Check Tools → Board and Tools → Port.

• On clones (especially Nanos with CH340), you might need a driver (CH340/CP2102).

Upload error: avrdude: stk500_getsync()

• Wrong board type selected.

• Wrong port selected.

• Board “stuck” from a previous sketch using the serial at high speed → press RESET right before upload.

Code compiles but nothing happens

• Check you used the right pin (e.g. LED_BUILTIN vs 13).

• If driving external components, double-check wiring and ground.