Love-O-Metyer.h

const int sensorPin = A0;
const float baselineTemp = 25.0;

void setup(){
  Serial.begin(9600); // open a serial port
  for(int pinNumber = 2; pinNumber<5; pinNumber++){
    pinMode(pinNumber,OUTPUT);
    digitalWrite(pinNumber, LOW);
  }
}

void loop(){
  int sensorVal = analogRead(sensorPin);
  Serial.print("Sensor Value: ");
  Serial.print(sensorVal);

  // convert the ADC reading to voltage
  float voltage = (sensorVal/1024.0) * 5.0;

  Serial.print(", Volts: ");
  Serial.print(voltage);
  Serial.print(", degrees C: ");

  // convert the voltage to temperature in degrees
  float temperature = (voltage - .5) * 100;
  Serial.println(temperature);
  
  if(temperature < baselineTemp){
    digitalWrite(2,  LOW);
    digitalWrite(3,  LOW);
    digitalWrite(4,  LOW);
  }else{ 
    if(temperature >= baselineTemp+2 && temperature < baselineTemp+4){
      digitalWrite(2, HIGH);
      digitalWrite(3, LOW); 
      digitalWrite(4, LOW);
    }else{ 
      if(temperature >= baselineTemp+4 && temperature < baselineTemp+6){
        digitalWrite(2, HIGH);
        digitalWrite(3, HIGH); 
        digitalWrite(4, LOW); 
      }else{ 
        if(temperature >= baselineTemp+6){
          digitalWrite(2, HIGH);
          digitalWrite(3, HIGH); 
          digitalWrite(4, HIGH);
        }
      }
    }
  }
  delay(1);
}