How to Connect a Push Button to Arduino: Pull-up, Pull-down and Debounce

A button is the simplest part for bringing a user's touch into an Arduino project. Pressed, it joins two contacts; released, it separates them. Simple as it looks, wired wrongly it reads random values or counts one press several times. In this guide we cover how to connect and read a button correctly.

Inside a 4-leg button

The 6×6 mm tactile button you'll use most on a breadboard has 4 legs but only 2 connection points: opposite leg pairs are already connected inside. Pressing the button joins the two pairs. If you seat the button across the center channel of the breadboard, each pair lands in separate rows and the right orientation is easy.

Why do you need a pull-up or pull-down resistor?

When the button isn't pressed, the Arduino's input pin isn't connected to anything; this is called a floating input. Such a pin picks up electrical noise and reads random HIGH or LOW values. The fix is to pull the pin to a fixed level through a resistor:

The most practical way is pinMode(pin, INPUT_PULLUP): the Arduino's internal resistor of about 20–50 kΩ is enabled and you just connect the button between the pin and GND. The only difference is that the logic is inverted: a press reads LOW.

Debounce: why does one press count several times?

The moment the button's metal contacts touch, they vibrate for a few milliseconds and the circuit opens and closes many times. Because the Arduino reads so fast, it can see one press as 3–5 presses. This is called contact bounce. To fix it in software, new changes are ignored for about 50 ms after the last change.

const int BUTTON_PIN = 2;   // buton pin ile GND arasında / button between pin and GND
const int LED_PIN = 13;     // karttaki LED / onboard LED

bool ledOn = false;
int lastReading = HIGH;
int stableState = HIGH;
unsigned long lastChange = 0;

void setup() {
  pinMode(BUTTON_PIN, INPUT_PULLUP); // dahili pull-up / internal pull-up
  pinMode(LED_PIN, OUTPUT);
}

void loop() {
  int reading = digitalRead(BUTTON_PIN);
  if (reading != lastReading) lastChange = millis();   // değişti / changed
  if (millis() - lastChange > 50 && reading != stableState) {
    stableState = reading;                              // 50 ms kararlı / stable for 50 ms
    if (stableState == LOW) {                           // basıldı / pressed
      ledOn = !ledOn;                                   // LED'i değiştir / toggle LED
      digitalWrite(LED_PIN, ledOn ? HIGH : LOW);
    }
  }
  lastReading = reading;
}

This code toggles the LED once per press; holding the button doesn't keep toggling it. Because it uses millis() instead of delay(), the loop never waits and can do other jobs at the same time.

Common mistakes

• Inserting the button the wrong way: if you use an already-connected pair of legs, the button always reads as pressed. Turn it 90°.
• Not using a resistor: without a pull-up or pull-down the reading changes randomly.
• Expecting the wrong logic with INPUT_PULLUP: a press reads LOW, not HIGH; write your conditions accordingly.
• Using a long delay() for debounce: the program can't do anything during that time; timing with millis() is better.
• Using pins 34–39 on an ESP32: these pins have no internal pull-up; add an external resistor or pick another pin.

To place the button and resistor correctly on a breadboard, see What Is a Breadboard?, and to understand pull-up resistor values, What Is a Resistor?.