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Arduino Uno · Button

Arduino Uno Button Simulator: Wiring, Code and a Live Circuit

This is a pushbutton wired to an Arduino Uno, with a debounced press counter running live: hold the button on the drawing and the serial monitor counts each press exactly once.

Two wires and no resistor: pin 2 to one side of the button, GND to the other, and the Arduino Uno’s internal pull-up does the rest.

Run it in the editorRead the code
  • 5 V logic
  • No library
  • Input on pin 2
  • Internal pull-up, 20 ms debounce
Arduino Uno · Buttonlive0.000 s 0.00x
Hold the button
The circuit itself, running on the simulator with the sketch below. Press what can be pressed; click anything else to open it in the editor.

Wiring the Button to the Arduino Uno

Every connection in the circuit above, with the board’s own pin names.

Button pinArduino Uno pinWhy
One side (1a)pin 2With INPUT_PULLUP the ATmega328P’s own resistor holds the pin high.
The other side (2a)GNDPressing connects the pin to ground, so it reads LOW.

No resistor and no supply wire: the ATmega328P’s internal pull-up ties the pin to 5 V until the button pulls it to ground.

Pins to leave alone on the Arduino Uno

Pins 0 and 1 are the USB serial port on a real Uno, so anything wired there fights the upload and the serial monitor. Pin 13 carries the onboard LED.

On a real bench

On a real bench the Uno stands beside the breadboard: the Button goes into the breadboard and male-to-male jumpers run from the Uno’s female headers to its rows. Power the Uno from USB while you build, and unplug it before you move a wire.

The code

The sketch the circuit above runs. Open it in the editor, change a line and press Run: it compiles in your browser.

Debounced button on Arduino Uno pin 2
const int BUTTON_PIN = 2;   // pin 2 to the button, the button to GND
const unsigned long DEBOUNCE_MS = 20;

int lastReading = HIGH;
int state = HIGH;
unsigned long changedAt = 0;
unsigned int presses = 0;

void setup() {
  Serial.begin(9600);
  pinMode(BUTTON_PIN, INPUT_PULLUP);   // HIGH when up, LOW when pressed
  Serial.println("Press the button");
}

void loop() {
  int reading = digitalRead(BUTTON_PIN);
  if (reading != lastReading) changedAt = millis();
  lastReading = reading;
  if (millis() - changedAt > DEBOUNCE_MS && reading != state) {
    state = reading;
    if (state == LOW) {
      presses++;
      Serial.print("Pressed, count ");
      Serial.println(presses);
    }
  }
}

pinMode(BUTTON_PIN, INPUT_PULLUP) turns on the pull-up inside the chip, so the pin reads HIGH while the button is up and LOW while it is held. That is backwards from what most people expect the first time, and it saves a resistor.

A real button bounces: for a few milliseconds after it closes, the contacts open and close many times. The sketch notes the time of every change and only accepts a new state once the reading has stayed put for 20 ms, so one press counts once. The simulated button bounces like a real one, so you can see it fail by setting DEBOUNCE_MS to 0.

Serial.begin(9600) opens the serial monitor. Serial goes over the USB cable, and the serial monitor in the editor reads it at whatever baud rate the sketch sets.

Common mistakes with the Button on the Arduino Uno

A floating input

With plain INPUT and no resistor, the pin reads whatever noise is nearby and the sketch sees presses nobody made. Use INPUT_PULLUP, or a 10 k resistor to the supply.

Counting the bounce

Without a debounce, one press can count as three or four. The simulated button bounces for a few milliseconds the way real contacts do, so the fix here is the fix on a desk.

Using pins 0 and 1

Pins 0 and 1 carry the USB serial port on a real Uno. the button wired there fights every upload and every Serial.print(). Start at pin 2.

Questions and answers

Can I simulate a button with an Arduino Uno?

Yes. The circuit at the top of this page is an Arduino Uno with a pushbutton, running in your browser on a simulated ATmega328P. Hold the button on the drawing to press it; the contacts bounce like a real switch. Press Run it in the editor to change the wiring or the code; it is free and needs no account.

Why does the button read LOW when pressed?

Because the pull-up holds the pin HIGH and the button connects it to ground. Compare with LOW in the code, or wire the button to the supply with a pull-down resistor if you want the opposite.

Should I use attachInterrupt() for a button?

You can, but an interrupt fires on every bounce too, so it still needs a debounce. Polling every pass of loop() is simpler and fast enough for a person.

Is there a library for buttons?

Bounce2.h, OneButton.h and AceButton.h all compile here. The sketch above does the same job in a dozen lines, which is worth understanding before reaching for one.

Build your own Button project

Open this circuit in the editor, change the wiring or the code, and keep your version in a free account.

Start building freeOpen the editor