setup() ทำงานครั้งเดียว

Every Arduino program is built from two functions. The first one is setup(), and getting it right makes everything else click. 🙂

The big idea: setup() runs a single time, right after your board powers on or resets. It never repeats on its own.

It is a function with empty parentheses and curly braces. Everything you write between those braces is your startup code.

The word void means setup returns no value. You are just running commands, not handing a result back to anyone.

setup is where you announce how each pin behaves. Use pinMode() once here so the board knows a pin sends or receives signals.

Talking to your computer also starts here. Serial.begin() opens the USB link once, ready for messages later.

Put things here that should happen a single time: setting pin modes, starting Serial, or initializing a sensor. Setup is your launch checklist.

No matter what else is in your sketch, setup() always runs before any repeating logic. It is the very first thing the board does.

Press the board's reset button or cut and restore power, and setup() fires once more. A fresh start means a fresh setup.

You can stack many one-time tasks inside setup. The board runs them top to bottom, then moves on for good.

A sketch can have an empty setup() if nothing needs preparing. The braces must still be there, even with nothing inside.

Let's test how setup() behaves.

You learned that setup() runs once at startup, returns void, and is where you prepare pins and Serial. It is your board's launch checklist. 🎉