test_Krawczyk.ino

int index = 0;
bool isPresent = false;
#define THRESHOLD 50
#define BUFFSIZE 25             
int buffer[BUFFSIZE];
void setup() {
  // put your setup code here, to run once:
  pinMode(A0,INPUT);
  Serial.begin(9600);
}

void loop() {

  buffer[idx] = map(analogRead(A0),0,800,0,1024);
  idx= (idx + 1) % BUFFSIZE;
  if ((average() < THRESHOLD) && isPresent)
  {
    Serial.println("Nobody around");
    isPresent = false;
  }
  if ((average() >= THRESHOLD) && !isPresent)
  {
    Serial.println("Somebody Detected!!");
    isPresent = true;
  }
  Serial.println(average());
  delay(100);
}

int average()
{
  int sum = 0;
  for (int i=0; i<BUFFSIZE; i++)
  {
    sum = sum + buffer[i];
  }
  return sum / BUFFSIZE;
}