MAX6675 with K-Type Thermocouple Control Relay as Thermostat

In this tutorial we learn how to use K-Type Thermonuclear with MAX6675 module to use it as Heater Control or Cooler Control by using a relay. With the provided code, the project can be set to work as Cooler or Heater controller and the temperature value can be set in any unit C, F or K.
Resources for this sketch and video


 
/*
 * Library from : // www.ladyada.net/learn/sensors/thermocouple
 * 
 * This is Arduino code to measure MAX6675 Thermocoupler K-Type sensor
 * and control realy as Heater or cooler
 * 
 * Watch Video instrution for this code: https://youtu.be/dVh77wT-4Ao
 * 
 * Full explanation of this code and wiring diagram is available at
 * my Arduino Course at Udemy.com here: http://robojax.com/L/?id=62

 * Written by Ahmad Shamshiri on May 20, 2020 at in Ajax, Ontario, Canada
 * in Ajax, Ontario, Canada. www.robojax.com
 * 

 * Get this code and other Arduino codes from Robojax.com
Learn Arduino step by step in structured course with all material, wiring diagram and library
all in once place. Purchase My course on Udemy.com http://robojax.com/L/?id=62

If you found this tutorial helpful, please support me so I can continue creating 
content like this. You can support me on Patreon http://robojax.com/L/?id=63

or make donation using PayPal http://robojax.com/L/?id=64
Related videos:
Introduction to MAX6675 K-Type: https://youtu.be/VGqONmUinqA
Using MAX6675 K-Type thermocouple whit LED display: https://youtu.be/cD5oOu4N_AE
Using MAX6675 K-Type thermocouplewith LCD1602-I2C: https://youtu.be/BlhpktgPdKs
Using 2 or more MAX6675 K-Type thermocouple: https://youtu.be/c90NszbNG8c
Using MAX6675 K-Type thermocouple as Heater or Coller controller: [this video]
 *  * This code is "AS IS" without warranty or liability. Free to be used as long as you keep this note intact.* 
 * This code has been download from Robojax.com
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <https://www.gnu.org/licenses/>.


*/


#include "max6675.h"
//Robojax.com heater/cooler with MAX6675 Thermocoupler
int GNDpin = 2;
int VCCpin =3;
int thermoCLK = 4;
int thermoCS = 5;
int thermoDO = 6;
MAX6675 thermocouple(thermoCLK, thermoCS, thermoDO);


const int relayPin =8;
const int relayON = LOW;// do not change
const int relayOFF = HIGH; //do not chage 
int relayState = relayOFF;//initial state of relay

const int TEMPERATURE_UNIT =1;//1=Celsius, 2=Fahrenheit, 3=Keliven
const float START_TEMPERATURE = 80.0;//unit above
const float STOP_TEMPERATURE = 100.0;//unit above
const int CONTROL_TYPE = 1;// 1= heater, 2=cooler
float temperature;

void setup() {
  //Robojax.com heater/cooler with MAX6675 Thermocoupler
  Serial.begin(9600);
  Serial.println("MAX6675 test with relay");
  // use Arduino pins 
  pinMode(relayPin, OUTPUT);//pin for relay
  digitalWrite(relayPin, relayState);
  
  pinMode(VCCpin, OUTPUT);
  digitalWrite(VCCpin, HIGH);

  pinMode(GNDpin, OUTPUT);
  digitalWrite(GNDpin, LOW);

  // wait for MAX chip to stabilize
  delay(500);
//Robojax.com heater/cooler with MAX6675 Thermocoupler  
}

void loop() {
  //Robojax.com heater/cooler with MAX6675 Thermocoupler
   readTemperature();
   printTemperature();
   loadControl(); 
   if(temperature >=89.5)
   {
    ///
   }
   delay(1000);
//Robojax.com heater/cooler with MAX6675 Thermocoupler   
}//loop



/*
 * loadControl()
 * @brief controls the load based 
 * @param state can be either : relayON or relayOFF

 * @return returns none
 * Written by Ahmad Shamshiri for robojax.com
 * on May 20, 2020 at 15:23 in Ajax, Ontario, Canada
 */
void loadControl()
{
//Robojax.com heater/cooler with MAX6675 Thermocoupler  
     // Serial.print("Start: ");
     // Serial.print(START_TEMPERATURE);
     // Serial.print(" Stop: ");
      //Serial.println(STOP_TEMPERATURE);      
  if(CONTROL_TYPE ==1)
  {
    if(START_TEMPERATURE >= temperature && STOP_TEMPERATURE >=temperature)
    {
      relayControl(relayON);
    }
    if(STOP_TEMPERATURE <=temperature)
    {
      relayControl(relayOFF);
    }
  }else{
    if(START_TEMPERATURE >= temperature && STOP_TEMPERATURE >=temperature)
    {
      relayControl(relayOFF);
    }
    if(STOP_TEMPERATURE <=temperature)
    {
      relayControl(relayON);
    }
  }
    
//Robojax.com heater/cooler with MAX6675 Thermocoupler
}//loadControl()


/*
 * relayControl(int state))
 * @brief turns the relay ON or OFF
 * @param state is "relayON" or "relayOFF" defined at the top of code
 * @return returns none
 * Written by Ahmad Shamshiri for robojax.com
 * on May 20, 2020 at 15:23 in Ajax, Ontario, Canada
 */
void relayControl(int state)
{
  //Robojax.com heater/cooler with MAX6675 Thermocoupler
  if(state ==relayON)
  {
    digitalWrite(relayPin, relayON);
    Serial.println("Relay ON");   
  }else{
   digitalWrite(relayPin, relayOFF);    
    Serial.println("Relay OFF");   
  }
  //Robojax.com heater/cooler with MAX6675 Thermocoupler  

}//relayControl()


/*
 *  readTemperature()
 * @brief reads the temperature based on the TEMPERATURE_UNIT
 * @param average temperature

 * @return returns one of the values above
 * Written by Ahmad Shamshiri for robojax.com
 * on May 20, 2020 at 15:23 in Ajax, Ontario, Canada
 */
void readTemperature()
{
 //Robojax.com heater/cooler with MAX6675 Thermocoupler 

  if(TEMPERATURE_UNIT ==2)
   {
   temperature = thermocouple.readFahrenheit();//convert to Fahrenheit 
   }else if(TEMPERATURE_UNIT ==3)
   {
    temperature = thermocouple.readCelsius() + 273.15;//convert to Kelvin
   }else{
    temperature = thermocouple.readCelsius();// return Celsius
   }    
 //Robojax.com heater/cooler with MAX6675 Thermocoupler 
}// readTemperature()

/*
 * printTemperature()
 * @brief prints  temperature on serial monitor
 * @param charact type
 * @param "type" is character
 *     C = Celsius
 *     K = Keliven
 *     F = Fahrenheit
 * @return none
 * Written by Ahmad Shamshiri for robojax.com
 * on May 08, 2020 at 02:45 in Ajax, Ontario, Canada
 */
void printTemperature()
{
//Robojax.com heater/cooler with MAX6675 Thermocoupler
   Serial.print(temperature);
    printDegree();    
  if(TEMPERATURE_UNIT ==2)
   {
     Serial.print("F");
    }else if(TEMPERATURE_UNIT ==3)
   {
     Serial.print("K");
   }else{
     Serial.print("C");
   }    
  Serial.println();
//Robojax.com heater/cooler with MAX6675 Thermocoupler  
}//printTemperature()

/*
 * @brief prints degree symbol on serial monitor
 * @param none
 * @return returns nothing
 * Written by Ahmad Shamshiri on July 13, 2019
 * for Robojax Tutorial Robojax.com
 */
void printDegree()
{
    Serial.print("\xC2"); 
    Serial.print("\xB0");  
}