#include <PinChangeInterrupt.h>

#define IRQPIN 8

volatile int button_changes = 0;

void setup() {
  pinMode(IRQPIN, INPUT_PULLUP);
  attachPCINT(digitalPinToPCINT(IRQPIN), pinisr, CHANGE);
  Serial.begin(115200);
}

void pinisr() {
  button_changes += 1;
}

void loop() {
  static int last_changes = 0;
  if (last_changes != button_changes) {
    last_changes = button_changes;
    Serial.print("Changed: ");
    Serial.println(button_changes);
  }
}