max6675 library

Using Arduino Programming Questions
#1

Hey all,

I am currently working on a progam utilizing the max6675 library found here. The problem that I am having is that the functions that return temperature (both Celsius and Fahrenheit) do not work without a delay() command after them.

Is there any way around this? With the my program constantly executing a delay like this there is a noticeable lag in the other inputs ( such as switches) because if they are pressed during the delay they are ignored.

Thanks in advance Mike

#2

You are doing something wrong. Just load the simple example found here: https://github.com/adafruit/MAX6675-library/blob/master/examples/serialthermocouple/serialthermocouple.pde and see that it doesn't have delays after every time it reads the chip.

If you showed us your code (all of it) then maybe I could have told you exactly what it was that you did wrong.

#3

Hey, thanks for the reply. I know there isn't a delay after each function call, but there is a delay before each function is called again. I ran the code you provided without a delay and the function keeps returning the same value no matter what I do to the thermocouple (ie put it in ice water). I also tried with a delay(100) function call at the end which still didn't work, and with a delay(250) call which did work but there was still noticeable lag in my code. I'll post my code below:

#include  //LCD library
#include  //MAX6675 K type thermocouple amp interface library


const int thermo_so_pin  = A1; //naming I/O pin termocouple amp so pin
const int thermo_cs_pin  = A2; //naming I/O pin termocouple amp cs pin
const int thermo_sck_pin = A3; //naming I/O pin termocouple amp sck pin

LiquidCrystal lcd(7, 8, 9, 10, 11, 12); // instance lcd of class LiquidCrystal
MAX6675 thermocouple(thermo_sck_pin, thermo_cs_pin, thermo_so_pin); //instance thermocouple of class MAX6675


void loop ()

int temp;

{
temp = thermocouple.readFahrenheit();
  delay(250);
}


lcd.print(temp);

again, this code works, but it does not work when i remove the "delay(250); function call

#4

Well, you probably have something useful to do during that delay. You obviously don't need to be hammering the poor 6675 thousands of times per second.

void myDelay(unsigned long ms) {
  //delay for ms milliseconds, while checking the inputs and processing them
  unsigned long start = millis();
  while(millis() - start < ms) {
    if(checkSwitches()) return; //leave the delay early if checkSwitches returns true
  }
}
#5

Herein i confirm that even the simplest code reading max6675 doesn't work for me without proper delay between readings. I found delay(200) is minimum to make max6675 work corectly. Apparently max needs some delay between readings to read TC and stabilize reading.

#6 
const unsigned long measurementPeriod = 250;
unsigned long timer;

void setup() {
  timer  = millis();
}

void loop () {
  int temp;
  if (millis() - timer >= measurementPeriod) {
    timer += measurementPeriod;
    temp = thermocouple.readFahrenheit();
    lcd.print(temp);
  }

  // Do useful stuff here with no delay
}