PID_temperature_control_woLCD.ino

/*    Max6675 Module  ==>   Arduino
 *    CS              ==>     D5
 *    SO              ==>     D6
 *    SCK             ==>     D7
 *    Vcc             ==>     Vcc (5v)
 *    Gnd             ==>     Gnd      */

//LCD config (i2c LCD screen, you need to install the LiquidCrystal_I2C if you don't have it )
//#include <Wire.h> 
//#include <LiquidCrystal_I2C.h>
//LiquidCrystal_I2C lcd(0x3f,20,4);  //sometimes the adress is not 0x3f. Change to 0x27 if it dosn't work.

/*    i2c LCD Module  ==>   Arduino
 *    SCL             ==>     A5
 *    SDA             ==>     A4
 *    Vcc             ==>     Vcc (5v)
 *    Gnd             ==>     Gnd      */

#include <SPI.h>
#include "Adafruit_MAX31855.h"
//We define the SPI pìns
#define MAX31855_CS   5
#define MAX31855_DO   6
#define MAX31855_CLK  7

//Pins
int PWM_pin = 3;


//Variables
float temperature_read = 0.0;
float set_temperature = 100;
float PID_error = 0;
float previous_error = 0;
float elapsedTime, Time, timePrev;
int PID_value = 0;



//PID constants
int kp = 9.1;   int ki = 0.3;   int kd = 1.8;
int PID_p = 0;    int PID_i = 0;    int PID_d = 0;



void setup() {
  pinMode(PWM_pin,OUTPUT);
  TCCR2B = TCCR2B & B11111000 | 0x03;    // pin 3 and 11 PWM frequency of 980.39 Hz
  Time = millis(); 
  Serial.begin(9600);
//  lcd.init();
//  lcd.backlight();
}


void loop() {
 // First we read the real value of temperature
  temperature_read = readThermocouple();
//  if (temperature_read == 0){
//    break;
//   }
  //Next we calculate the error between the setpoint and the real value
  PID_error = set_temperature - temperature_read;
  //Calculate the P value
  PID_p = kp * PID_error;
  //Calculate the I value in a range on +-3
  if(-3 < PID_error <3)
  {
    PID_i = 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 = 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
  analogWrite(PWM_pin,PID_value);
  previous_error = PID_error;     //Remember to store the previous error for next loop.

  delay(300);
  //lcd.clear();

    Serial.println("S:");
    Serial.print(set_temperature,1);
    Serial.print("/t");
    Serial.print("R:");
    Serial.print(temperature_read,1);
//  lcd.setCursor(0,0);
//  lcd.print("PID TEMP control");
//  lcd.setCursor(0,1);
//  lcd.print("S:");
//  lcd.setCursor(2,1);
//  lcd.print(set_temperature,1);
//  lcd.setCursor(9,1);
//  lcd.print("R:");
//  lcd.setCursor(11,1);
//  lcd.print(temperature_read,1);
}

double readThermocouple() {

  uint16_t v;
  pinMode(MAX31855_CS, OUTPUT);
  pinMode(MAX31855_DO, INPUT);
  pinMode(MAX31855_CLK, OUTPUT);
  
  digitalWrite(MAX31855_CS, LOW);
  delay(1); // ms

  // 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(MAX31855_DO, MAX31855_CLK, MSBFIRST);
  v <<= 8;
  v |= shiftIn(MAX31855_DO, MAX31855_CLK, MSBFIRST);
  
  digitalWrite(MAX31855_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;
}