#define BUTTON_PIN 4

/**
 * Initialize a new OneButton instance for a button
 * connected to digital pin 4 and GND, which is active low
 * and uses the internal pull-up resistor.
 */

OneButton btn = OneButton(
  BUTTON_PIN,  // Input pin for the button
  true,        // Button is active LOW
  true         // Enable internal pull-up resistor
);