int rele = 8;

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

void loop() {
  int holat = map(analogRead(A0), 0, 1023, 0, 100);
  Serial.println(holat);
  if (holat >= 50) {
    digitalWrite(rele, HIGH);
    tone(5, 400);
  } else {
    digitalWrite(rele, LOW);
    noTone(5);
  }
}