Arduino nano, max6675 and triac soldering station

Projects General Guidance
1

I decided to built the the project from the link below, and I need to know if the function that blocks the program is correct (it was wrote by me) and I also need to know if the function is correctly called in that line of code - in the setup part of the program, right after reading the temperature.

void errorFunction () {
realTemperature = thermocouple.readCelsius();
if (isnan(realTemperature) or realTemperature >= 432){
   while(true){
   digitalWrite(triac, low);
   digitalWrite(relay,low); // the relay will disconnect the power to the soldering iron heating element
    // here I will add the code to display the error
    // for example: "ERROR !!!"
   }
}
}

The project:

"triac" is the pin of the triac
"relay " is the pin that controls a relay that cuts off the power to the heating element when a error is detected.

I need some advice, or some code that could help me in solving this problem.

2

I had expected that the errorFunction() returns a value indicating whether everything is fine. Then your main program can handle normal and error states differently.

Where do you want to display the error message?

3

The error messages will be displayed on a 5110 LCD for tests. The final version will use a 1602 LCD.

I have re-wrote the function:

byte errorFunction () {
  realTemperature = thermocouple.readCelsius();
  if (isnan(realTemperature) or realTemperature >= 432) {
    while (true) {
      digitalWrite(triac, LOW);
      digitalWrite(relay, LOW); // the relay will disconnect the power to the soldering iron heating element
      lcd.setCursor(0, 0);
      lcd.print("ERROR !!!");
      delay(200);
    }
  } else {
    return 1;
  }
}

Should I add in the main program a condition that updates the display and call the attachinterrupt function when there is no overheating and no wires are disconnected from the thermocouple ?

4

Here is the code that I modified in order to display a error message on the lcd when the temp goes above 432 C or when the TC gets disconnected:

#include <PCD8544.h>
#include <SPI.h>
#include <Wire.h>
#include <max6675.h>

#define thermoDO 11
#define thermoCS 12
#define thermoCLK 13
#define potentiometer A0
#define zerocrossing 2
#define triac 7
#define relay 9

float temperature, realTemperature;
int pottemperature;
int counter;

MAX6675 thermocouple(thermoCLK, thermoCS, thermoDO);

PCD8544 lcd;

void setup() {
  lcd.begin(84, 48);
  pinMode(potentiometer, INPUT);
  pinMode(zerocrossing, INPUT_PULLUP);
  pinMode(triac, OUTPUT);
  digitalWrite(triac, LOW);
  counter = 0;
  realTemperature = thermocouple.readCelsius();
  temperature = 0.779828 * realTemperature - 10.3427;
  updatedisplay();
  attachInterrupt(0, zero, RISING);
}

void loop() {
}

void zero() {
  counter++;
  if (counter < 40) {
    if (temperature <= pottemperature) {
      digitalWrite(triac, HIGH);
    }
    else {
      digitalWrite(triac, LOW);
    }
  }

  if (counter == 40) {
    digitalWrite(triac, LOW);
    detachInterrupt(0);
    realTemperature = thermocouple.readCelsius();
    temperature = 0.779828 * realTemperature - 10.3427;
    updatedisplay();
    counter = 0;
    attachInterrupt(0, zero, RISING);
  }
}

void updatedisplay() {
  pottemperature = analogRead(potentiometer);
  pottemperature = map(pottemperature, 0, 1023, 0, 400);
  checkForErrors();
  lcd.setCursor(0, 0);
  lcd.print("SET= ");
  lcd.print(5, 0);
  lcd.print(pottemperature);
  lcd.setCursor(0, 1);
  lcd.print("READ= ");
  lcd.setCursor(7, 1);
  lcd.print((int)temperature);
  delay(200);

}

void checkForErrors() {
  realTemperature = thermocouple.readCelsius();
  if (isnan(realTemperature) or realTemperature >= 432) {
    while (true) {
      detachInterrupt(0);
      digitalWrite(triac, LOW);
      digitalWrite(relay, LOW); // the relay will disconnect the power to the soldering iron heating element
      lcd.clear();
      lcd.setCursor(0, 0);
      lcd.print("Error !");
      delay(500);
    }
  }
}
5

Hello, I would like to built the project from this web site:

Please let me know if the circuit will work the same if I will use standard connection ( https://www.arduino.cc/en/Tutorial/HelloWorld ) for the 1602 LCD display instead of i2c ?

6

At least you'll have to call the lcd.begin() version for the parallel interface.