Unit A - Foundations

03. Arduino IDE 2 & First Upload

Install Arduino IDE 2, select board and port, Verify, Upload, and blink the onboard LED.

Estimated time 2 hours

Learning outcomes

Install and navigate Arduino IDE 2
Select the correct board definition and serial port
Explain the difference between Verify (compile) and Upload
Run the Blink sketch on LED_BUILTIN and diagnose common upload faults
Know when Library Manager is needed for later lessons

Parts and preparation

Arduino Uno, USB data cable and Arduino IDE 2 (desktop). No breadboard required for Blink.

Before power: inspect wiring, confirm supply voltage and ensure all connected circuits share GND.

Arduino IDE 2 & First Upload instructional connection diagram

Your first reliable workflow

Arduino IDE 2 is where you write sketches, compile them, and send them to the board. A repeatable habit prevents most beginner frustration: correct board, correct port, Verify until clean, then Upload, then observe.

Write, Verify, Upload, Observe workflow — Write -> Verify -> Upload -> Observe. Fix the first error before hunting later ones.

Verify vs Upload

Verify (tick icon) compiles your C++ sketch on the computer and reports syntax or type errors. It does not change what is running on the Uno.

Upload compiles (if needed) and transfers the binary through the selected port. The board resets and then runs the new program from setup() into loop().

Verify compiles only; Upload compiles and transfers to the board — Verify fixes code errors. Upload needs board + port and updates the flash.

Board and port

Tools -> Board selects the hardware definition (Arduino Uno for classic R3, or UNO R4 Minima if that is your board). Wrong board choice causes confusing compile or upload failures.

Tools -> Port selects which USB device receives the upload. The port usually appears only when a data cable is connected. Charge-only cables look plugged in but never enumerate a port.

Board selects hardware definition; Port selects the USB device — Both Board and Port must match the hardware on your desk.

Blink and LED_BUILTIN

The classic first sketch blinks the onboard L LED. LED_BUILTIN is a named constant for that pin (usually 13 on Uno). The board already includes a series resistor for L - no breadboard required.

setup() runs once after reset and configures the pin. loop() turns the LED on, waits, turns it off, waits, and repeats.

LED_BUILTIN maps to the onboard L LED near pin 13 — Watch the L LED after a successful Upload.

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);
  delay(1000);
  digitalWrite(LED_BUILTIN, LOW);
  delay(1000);
}

Reading error messages

Always read the first compiler error - later messages are often knock-on effects. Missing semicolons are often reported on the next line. Case matters: setup, pinMode, HIGH and LOW must match exactly.

Upload errors such as not in sync or port busy: close Serial Monitor and other programs using the port, recheck Board/Port, try another USB socket or data cable, then retry.

Symptom	Likely fix
No port listed	Data cable; reconnect; drivers; another USB socket
Wrong board	Tools -> Board -> Arduino Uno (or R4 Minima)
Compile error	Read first error; check ; and spelling
Upload not in sync	Close Monitor; correct port; retry

Library Manager (preview)

Later lessons install third-party libraries with Tools -> Manage Libraries. Each of those lessons names the exact Library Manager title and author. Install only that package - similarly named libraries often use different APIs.

Blink itself needs no extra library.

Wiring and safe build sequence

Connect Uno to the PC with a USB data cable
Tools -> Board -> Arduino Uno (or UNO R4 Minima if that is your board)
Tools -> Port -> choose the port that appears when the Uno is connected
Open File -> Examples -> 01.Basics -> Blink (or paste the worked sketch)
Click Verify, then Upload; watch the onboard L LED

Power rule: switch off before moving wires. Arduino I/O pins are control signals; high-current loads require a driver and suitable external supply.

Worked sketch

Download .ino sketch

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);  // LED on
  delay(1000);
  digitalWrite(LED_BUILTIN, LOW);   // LED off
  delay(1000);
}

How the code works

LED_BUILTIN maps to the board onboard LED pin (usually 13).
setup runs once after reset; loop repeats for as long as the board is powered.
delay(1000) waits one second - fine for Blink; later lessons introduce millis for multi-task timing.
No breadboard is required for this first upload.

Test and record evidence

Expected result: After Upload, the onboard L LED is on for about one second and off for about one second, repeating.

Practical evidence checklist

Labelled wiring or block diagram Uploaded sketch and observed result At least one measured/tested value Fault or improvement recorded in logbook

Common faults and checks

Port not found: reconnect with a known data cable; try another USB port.
Not in sync: verify Uno and port selections, close other serial programs, retry.
Compilation error: read the first error, not only the final summary.
Upload OK but no blink: confirm you uploaded Blink (not an empty sketch) and look at the L LED near pin 13.

Extension challenge: Change the sketch to produce two short flashes (200 ms on) followed by a one-second pause, then repeat.

Check your understanding

Q1. What does Verify do?

Show answer

Compiles the sketch and reports errors without uploading.

Q2. What is the difference between board and port selection?

Show answer

Board selects the target hardware definition; port selects the connected USB device.

Q3. What does LED_BUILTIN refer to?

Show answer

The pin connected to the board onboard LED (usually pin 13 on Uno).

Q4. Name one common cause of a missing port.

Show answer

A charge-only USB cable, missing drivers, or the board not connected.

Q5. Why read the first compiler error first?

Show answer

Later errors are often knock-on effects of the first mistake.