int tempPin = A1;
int fanPin = 11;

double tempMeasurement;
double tempError;
int fanPWM;
double pconst = 20;
double desTemp = 27;

void setup() {
  pinMode(fanPin, OUTPUT);
  pinMode(tempPin, INPUT);
  Serial.begin(9600);
}

void loop() {
  tempMeasurement = readTemp();

  if (tempMeasurement < desTemp) {
    fanPWM = 0;
    digitalWrite(fanPin, LOW);
  } else {
    tempError = tempMeasurement - desTemp;
    fanPWM = (int) (pconst * tempError);
    if (fanPWM > 255) {
      fanPWM = 255;
    }
    analogWrite(fanPin, fanPWM);
    Serial.print("Fan percentage is:");
    Serial.println(fanPWM * 100 / 255);
  }
  Serial.print("Temp: ");
  Serial.println(tempMeasurement);
  delay(100);
}

double readTemp() {
 int tempM = analogRead(tempPin);
 double tempD = (double) tempM;
 tempD = tempD * (5.0 / 1023.0) * 1000.0 * (1 / 10.0);
 return tempD;
}