/*    Max6675 Module  ==>   Arduino
 *    CS              ==>     D10
 *    SO              ==>     D12
 *    SCK             ==>     D13
 *    Vcc             ==>     Vcc (5v)
 *    Gnd             ==>     Gnd      */
#include <SPI.h>
String recieved_data;

// I/O
int PWM_pin = 3; // Pin for PWM signal to the MOSFET driver (the BJT npn with pullup)

// Variables
float set_temperature = 100; // Default temperature setpoint. Leave it 0 and control it with rotary encoder

float temperature_read = 0.0;
float PID_error = 0;
float previous_error = 0;
float elapsedTime, Time, timePrev;
float PID_value = 0;
float last_set_temperature = 0;

// PID constants
//////////////////////////////////////////////////////////
int kp = 5;
int ki = 2;
int kd = 1;
//////////////////////////////////////////////////////////

int PID_p = 0;
int PID_i = 0;
int PID_d = 0;
float last_kp = 0;
float last_ki = 0;
float last_kd = 0;

// Pins for the SPI with MAX6675
#define MAX6675_CS 10
#define MAX6675_SO 12
#define MAX6675_SCK 13

void setup()
{
  Serial.begin(9600);
  pinMode(PWM_pin, OUTPUT);
  TCCR2B = TCCR2B & B11111000 | 0x03; // pin 3 and 11 PWM frequency of 928.5 Hz
  Time = millis();

  pinMode(11, INPUT);
}

void loop()
{
  if (Serial.available() > 0)
  {
    recieved_data = (Serial.readString());
    
  }


  // First we read the real value of temperature
  temperature_read = readThermocouple();
  // Next we calculate the error between the setpoint and the real value
  PID_error = set_temperature - temperature_read + 3;
  // Calculate the P value
  PID_p = 0.01 * kp * PID_error;
  // Calculate the I value in a range on +-3
  PID_i = 0.01 * PID_i + (ki * PID_error);

  // For derivative we need real time to calculate speed change rate
  timePrev = Time; // the previous time is stored before the actual time read
  Time = millis(); // actual time read
  elapsedTime = (Time - timePrev) / 1000;
  // Now we can calculate the D calue
  PID_d = 0.01 * kd * ((PID_error - previous_error) / elapsedTime);
  // Final total PID value is the sum of P + I + D
  PID_value = PID_p + PID_i + PID_d;

  // We define PWM range between 0 and 255
  if (PID_value < 0)
  {
    PID_value = 0;
  }
  if (PID_value > 255)
  {
    PID_value = 255;
  }
  // Now we can write the PWM signal to the mosfet on digital pin D3
  // Since we activate the MOSFET with a 0 to the base of the BJT, we write 255-PID value (inverted)
  analogWrite(PWM_pin, 255 - PID_value);
  previous_error = PID_error; // Remember to store the previous error for next loop.
  
  
  Serial.print("Okunan Isı");
  Serial.println(temperature_read);

  Serial.print("PID value");
  Serial.println(PID_value);

  delay(250); // Refresh rate
} // Loop end

// The function that reads the SPI data from MAX6675
double readThermocouple()
{

  uint16_t v;
  pinMode(MAX6675_CS, OUTPUT);
  pinMode(MAX6675_SO, INPUT);
  pinMode(MAX6675_SCK, OUTPUT);

  digitalWrite(MAX6675_CS, LOW);
  delay(1);

  // Read in 16 bits,
  //  15    = 0 always
  //  14..2 = 0.25 degree counts MSB First
  //  2     = 1 if thermocouple is open circuit
  //  1..0  = uninteresting status

  v = shiftIn(MAX6675_SO, MAX6675_SCK, MSBFIRST);
  v <<= 8;
  v |= shiftIn(MAX6675_SO, MAX6675_SCK, MSBFIRST);

  digitalWrite(MAX6675_CS, HIGH);
  if (v & 0x4)
  {
    // Bit 2 indicates if the thermocouple is disconnected
    return NAN;
  }

  // The lower three bits (0,1,2) are discarded status bits
  v >>= 3;

  // The remaining bits are the number of 0.25 degree (C) counts
  return v * 0.25;
}