int temperature;

void setup() {

  // put your setup code here, to run once:
  pinMode(4, OUTPUT);
  
  Serial.begin(9600);

}

void loop() {
  // put your main code here, to run repeatedly:
  int sensorValue=analogRead(A4);
  float voltValue=sensorValue/1023.0*5;
  float temperature = 1 / (log(1 / (1023. / sensorValue - 1)) / 3950 + 1.0 / 298.15) - 273.15;
  Serial.print(temperature);
  Serial.println(" C");
  
  if (temperature<20){
    digitalWrite(4, HIGH);
    delay(500);
  }
  else{
    digitalWrite(4, LOW);
    delay(500);
  }
}