Read a Button

Part of the First Circuits section of Coddy's Arduino journey. Lesson 22 of 22.

A pin can also be an input: the board reads whether it is HIGH or LOW.

This button connects pin 2 to ground (0 volts) while you hold it. When it is up, the pin is connected to nothing and would read random values. INPUT_PULLUP turns on a pull-up resistor inside the board, which holds the pin HIGH until the button pulls it LOW:

pinMode(2, INPUT_PULLUP);

digitalRead(2) gives the pin's level. With a pull-up, a pressed button reads LOW:

if (digitalRead(2) == LOW) {
  // the button is pressed
}

The rest is what you know: if and else to choose, digitalWrite() for the LED, Serial.println() to report.

Challenge

Easy

The button is on pin 2 and the LED on pin 13. Make the LED light while the button is held:

set pin 2 to INPUT_PULLUP
when digitalRead(buttonPin) is LOW, turn the LED on, print Pressed and wait 200 ms (so the monitor is not flooded)
else, turn the LED off

Press Run, hold the green button on the board, then Check.

Try it yourself

const int buttonPin = 2;
const int ledPin = 13;

void setup() {
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {

}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in First Circuits

1Hello, Board

Blink an LED Setup and Loop Change the Blink Speed An LED of Your Own Two LEDs Taking Turns Comments in Your Sketch

4Decisions

Decisions with if Choosing with if and else Comparing Values Combining ConditionsRead a Button

2Talking to Your Computer

Hello, Serial Monitor Print Versus Println Printing Numbers Your First Variable Counting Up When an Int Runs Out

3Math on the Board

Named Constants Arithmetic Operators Integer Division Decimals with float A Blink That Speeds Up

Practice on your own: Arduino playground