#include <SPI.h>

//START OF TEMP CONTROL INITIALISE

//#define DBG_SWITCH                // Remove remark slashes to enable extensive debugging


int FanRelais              = 9;     // Define cooling fan relais pin

float Tlow  = 1.0;                 // Temperature the fan should be switched off
float Thigh = 5.0;                 // Temperature the fan should be switched on

boolean pwm = true;                 // True for Pulse Width Modulation, false for on/off control

boolean FanEnabled       = false; // Flag fan to be off

float ST                 = 0.0;
int PW                   = 0;

// START OF SETUP
void setup() {

  Serial.begin (19200);             // Setup the serial port and define communication speed

  pinMode(FanRelais, OUTPUT);       // Define fan relais pin as output
  Serial.println("Fan Off!");
  
  if (!pwm) {
    digitalWrite(FanRelais, LOW);   // Disable Fan relais
    FanEnabled = false;             // Flag fan to be off
  }
  else {
    analogWrite(FanRelais, 0);      // Disable Fan relais
  }
}
// END OF SETUP

float Vin = 5;                    // Voltage fed at the temperature sensor

float Rlow = 12513;                 // Resistance for lowest temperature sensor
float TRlow = 20;                   // Temerature lowest temperature sensor

float Rhigh = 10000;                // Resistance for highest temperature sensor
float TRhigh = 25;                  // Temerature highest temperature sensor

float Tsteps = TRhigh - TRlow;
float st = (Rlow - Rhigh) / Tsteps; // Sensor resistor increase per degree

float Rr = 23500;                   // Value of resistor positioned in serial with the temp sensor

int   Sensor;                       // Sensor valua measured at analoge port
float Vr;                           // Variable for measured voltage on resistor
float I;                            // Current variable
float Rtot;                         // Total resistor value measured
float Rt;                           // Resistance temperature sensor variable
float T;                            // Calculated temperature variable

void loop() {

  // Wait a second
  delay(3000);

  // Measure value at analog input
  Sensor = analogRead(A0);
  //Serial.print("Sensor value: ");
  //Serial.println(Sensor);

  // Calculate the voltage on the resistor
  Vr = Sensor * (5.0 / 1023.0);
  //Serial.print("Voltage 23.5k ohm resistor: ");
  //Serial.println(Vr);

  // Calculate current running throug the resistor
  I = Vr / Rr;
  //Serial.print("Current: ");
  //Serial.println(I);

  // Calculate total resistor (temp resistor + serial resistor)
  Rtot = Vin / I;
  //Serial.print("Rtotaal: ");
  //Serial.println(Rtot);

  // Calculate value of temp. sensor resistor
  Rt = Rtot - Rr;
  //Serial.print("Rt: ");
  //Serial.println(Rt);

  // Calcualte temperature measured
  T = TRhigh - ((Rt - Rhigh) / st);
  Serial.print("Temperature: ");
  Serial.println(T);

  if (!pwm) {
    if (T > Thigh and !FanEnabled) {
      Serial.println("Fan On!");
      digitalWrite(FanRelais, HIGH); // Enable Fan
      FanEnabled = true;
    }

    if (T < Tlow and FanEnabled) {
      Serial.println("Fan Off!");
      digitalWrite(FanRelais, LOW);  // Disable Fan
      FanEnabled = false;
    }
  }
  else {
    ST = 255 / (Thigh - Tlow);
    PW = ST * (T - Tlow);

    if (PW < 0)
      PW = 0;
    else if (PW > 255)
      PW = 255;

    Serial.print("PWM value: ");
    Serial.println(PW);
    analogWrite(FanRelais, PW);
  }
  Serial.println("");
}