int sensorPin = A0;
int sensorValue = 0;
int tresholdValue = 700;
int relayPin= 8;
void setup() {
  pinMode(relayPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  sensorValue= analogRead(sensorPin);
  Serial.println(sensorValue);
  if(sensorValue<tresholdValue)
    digitalWrite(relayPin, HIGH);
  else
    digitalWrite(relayPin, LOW);
}