Previous
Next

2. Add a button

2.1. A look on the sketch

// constants won't change. They're used here to set pin numbers:
const int buttonPin = 2;     // the number of the pushbutton pin
const int ledPin =  13;      // the number of the LED pin

// variables will change:
int buttonState = 0;         // variable for reading the pushbutton status

void setup() {
  // initialize the LED pin as an output:
  pinMode(ledPin, OUTPUT);
  // initialize the pushbutton pin as an input:
  pinMode(buttonPin, INPUT);
}

void loop() {
  // read the state of the pushbutton value:
  buttonState = digitalRead(buttonPin);

  // check if the pushbutton is pressed. If it is, the buttonState is HIGH:
  if (buttonState == HIGH) {
    // turn LED on:
    digitalWrite(ledPin, HIGH);
  } else {
    // turn LED off:
    digitalWrite(ledPin, LOW);
  }
}

Let's now examine the code of the Button sketch.

Constants
The very first lines of this program introduce constants, which are similar to variables in that they store a piece of information. However, constants don't change throughout your program, and are therefore great for things like pin numbers. They take up less memory space than variables.
const int buttonPin = 2;

digitalRead()
In the main loop, a function called digitalRead() checks/reads the state of pin 2 (which is initialised as INPUT) and stores that state in a variable called buttonState.
buttonState = digitalRead(buttonPin);


Previous
Next