hit_led.c

int pinHit = 2;
int pinLed = 13;
int ledStatus = LOW;

int count = 0;
volatile int flag = 0;
void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  pinMode(pinHit, INPUT);
  pinMode(pinLed, OUTPUT);
  attachInterrupt(0, hitISR, FALLING);
}

void loop() {
  // put your main code here, to run repeatedly:
  Serial.print("HIT : ");
  Serial.println(count);
  flag = 0;
  digitalWrite(pinLed, ledStatus);
  delay(500);
}

void hitISR(void) {
  if(flag == 0) {
    count++;
    flag = 1; 
    ledStatus = !ledStatus;
  }
}