FREE SIMULATOR EXAMPLE · BEGINNER

Nano: Button + LED

This example lights the Arduino Nano’s built-in LED on pin 13 while you hold a pushbutton wired to pin 2 — press for on, release for off, no latching. The response is effectively instant because the loop contains no delay at all. A one-line banner on the Serial Monitor at 9600 baud confirms the sketch is running.

Board	Arduino Nano (ATmega328P, 16 MHz)
Difficulty	beginner
Category	basics
Libraries	None — just the Arduino core
Runs in	Sensbench browser simulator — free, no account

The exact circuit you get when you open this example — already wired, ready to run.

The sketch

// Arduino Nano — Button controls LED

const int BTN = 2;
const int LED = 13;

void setup() {
  pinMode(BTN, INPUT_PULLUP);
  pinMode(LED, OUTPUT);
  Serial.begin(9600);
  Serial.println("Button LED ready — press button on pin 2");
}

void loop() {
  bool pressed = digitalRead(BTN) == LOW;
  digitalWrite(LED, pressed ? HIGH : LOW);
}

How it works

The button pin is configured as pinMode(BTN, INPUT_PULLUP), which enables the ATmega328P’s internal pull-up resistor — roughly 20–50 kΩ to 5 V. That means the button’s other leg goes to GND, and the pin reads LOW when pressed. The sketch makes that inverted logic explicit: pressed = digitalRead(BTN) == LOW.

The loop is two lines: read the button, write the LED. There is no delay() anywhere, so the Nano re-evaluates the button tens of thousands of times per second and the LED tracks the switch in real time. Lighting an LED also needs no debouncing — a few milliseconds of contact bounce is invisible on a lamp. It only becomes a bug when you start counting presses.

Before you build it for real

Get the parts

Related examples

FAQ

Why does the LED turn on when the pin reads LOW?

Because INPUT_PULLUP holds the pin at 5 V until the button connects it to ground — pressed pulls the line LOW, so the sketch treats LOW as pressed. It feels backwards for one day, then you never think about it again: nearly every Arduino button circuit works this way.

Do I need to debounce this button?

Not for driving an LED — bounce just makes the LED stutter for a few microseconds, invisible to the eye. The moment you count presses or toggle state per press you do need debouncing, either 20–50 ms in software or a small capacitor across the switch.