void setup() {
  Serial.begin(9600);
  pinMode(13, OUTPUT);
}

void loop() {
  int A[30];
  float sum = 0;

  for (int i = 0; i < 30; i++) {
    A[i] = analogRead(A0);
//    Serial.println(A[i]);
    delay(3);
    sum = sum + A[i];
  }

  float avg = sum /30.0;
  sum = 0;
  for (int i = 0; i < 30; i++) {
    sum = sum + (A[i] - avg)*(A[i] - avg);
  }
  Serial.println(sum);

  digitalWrite(13, (sum > 50000));
}