Multiple MAX31855 Instances in an array

[wesg]

I'm looking to have multiple MAX31855 sensors in my project, and that means reading them all efficiently. I understand that the chips can already share DO and CS pins, so I'm trying to code up a foundation that makes it really easy to add more sensors.

How can I go about adding multiple objects to a single array and referencing them?

Currently I create the array like this:

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Adafruit_MAX31855 * thermocouples[1];

(I'm only using 1 sensor at the moment)

Then add objects in a loop like this:

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for (int i = 0; i < NUMBER_OF_THERMOCOUPLES; i++) {
    Adafruit_MAX31855 thermocouple(thermoCLKs[i], sharedThermoPins[1], sharedThermoPins[0]);
    thermocouples[i] = thermocouple;  
  }

And finally I try to reference them this way:

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Adafruit_MAX31855 * thermocouple = thermocouples[0];
  Serial.println(thermocouple.readCelsius());

but unfortunately it's not going quite so well.

[adafruit_support_rick]

Try this:

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#include "Adafruit_MAX31855.h"

int thermoDO = 3;
int thermoCS = 4;
int thermoCLK = 5;

#define NUMBER_OF_THERMOCOUPLES 2
int sharedThermoPins[] = {thermoDO, thermoCS}; 
int thermoCLKs[NUMBER_OF_THERMOCOUPLES] = {thermoCLK, thermoCLK+1};
Adafruit_MAX31855  *thermocouples[NUMBER_OF_THERMOCOUPLES];
  
void setup() {
  Serial.begin(9600);
  
  Serial.println("MAX31855 array test");
  // wait for MAX chip to stabilize
  delay(500);
  
  for (int i = 0; i < NUMBER_OF_THERMOCOUPLES; i++) {
    thermocouples[i] = new Adafruit_MAX31855(thermoCLKs[i], sharedThermoPins[1], sharedThermoPins[0]);  
  }
}

void loop() {
  // basic readout test, just print the current temp
    for (int i = 0; i < NUMBER_OF_THERMOCOUPLES; i++) {
      Serial.print("Internal Temp "); Serial.print(i); Serial.print(" = ");
      Serial.println(thermocouples[i]->readInternal());

      double c = thermocouples[i]->readCelsius();
      if (isnan(c)) {
        Serial.print("Something wrong with thermocouple");Serial.print(i); Serial.println("!");
      }else {
        Serial.print("C ");Serial.print(i); Serial.print(" = "); 
        Serial.println(c);
      }
      //Serial.print("F ");Serial.print(i); Serial.print(" = ");
      //Serial.println(thermocouples[i].readFarenheit());
   }
   delay(1000);
}

[wesg]

Thanks, Driver, that looks good. It seems, though, that Arduino does not support the "new" keyword, so I haven't yet added the thermocouples to the array.

[mtbf0]

I understand that the chips can already share DO and CS pins

should that not be DO and CLK? though it seems as if you could just pull CS low on every board, share the data line and strobe individual clocks per chip.

... unless i didn't read far enough into the product description to see that there's a good reason one might want to deselect all of one's MAX31855s. noise maybe...

look at me! i still haven't learned to just shut up when i know not whereof i speak, but i, at least, am now capable of thinking of reasons why i should.

[wesg]

I understand that the chips can already share DO and CS pins

should that not be DO and CLK? though it seems as if you could just pull CS low on every board, share the data line and strobe individual clocks per chip.

You're right about that, my mistake! This thread has the answer, which means I need to readjust my pin assignments.

[mtbf0]

so how about

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#include "Adafruit_MAX31855.h"

int thermoDO = 3;
int thermoCS = 4;
int thermoCLK = 5;

#define NUMBER_OF_THERMOCOUPLES 3

Adafruit_MAX31855 tc0 (thermoCLK, 3, thermoCLK);
Adafruit_MAX31855 tc1 (thermoCLK, 6, thermoCLK);
Adafruit_MAX31855 tc2 (thermoCLK, 7, thermoCLK);

Adafruit_MAX31855  *thermocouples = {tc0, tc1, tc2};

void setup() {
  Serial.begin(9600);
  Serial.println("MAX31855 array test");
// wait for MAX chip to stabilize
  delay(500);
}

void loop() {
  // basic readout test, just print the current temp
    for (int i = 0; i < NUMBER_OF_THERMOCOUPLES; i++) {
      Serial.print("Internal Temp "); Serial.print(i); Serial.print(" = ");
      Serial.println(thermocouples[i]->readInternal());
      double c = thermocouples[i]->readCelsius();
      if (isnan(c)) {
        Serial.print("Something wrong with thermocouple");
        Serial.print(i); Serial.println("!");
      }else {
        Serial.print("C ");Serial.print(i); Serial.print(" = ");
        Serial.println(c);
      }
      //Serial.print("F ");Serial.print(i); Serial.print(" = ");
      //Serial.println(thermocouples[i].readFarenheit());
   }
   delay(1000);
}

[wesg]

Thanks to this Arduino.cc thread I've figured it out using a dynamic MALLOC call.

For future reference, I'll try to outline the different components I used to make this work, using the MAX31855 library.

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// declare a dynamic array variable above setup()
Adafruit_MAX31855 * thermocouples;

// create the thermocouple objects you want (inside the setup() function). The variables should be self explanatory
void createThermocouples() {
  thermocouples = (Adafruit_MAX31855 *) malloc(sizeof(Adafruit_MAX31855) * NUMBER_OF_THERMOCOUPLES);
  for (int i = 0; i < NUMBER_OF_THERMOCOUPLES; i++) {
    Adafruit_MAX31855 thermocouple(sharedThermoPins[1], thermoCSs[i], sharedThermoPins[0]);
    thermocouples[i] = thermocouple;
  }
}

// read a thermocouple inside loop(). Use an array to print them all
 double reading = thermocouples[0].readCelsius();

I can provide my full code if necessary. The array used in declaring the objects is just my way of enclosing the different sensors.

[mtbf0]

if you know the number of sensors at compile time, i'd think it would be better to stay away from malloc, which could lead to tears in case you ever get memory constrained.

[adafruit_support_rick]

It seems, though, that Arduino does not support the "new" keyword

Well, I compiled and ran that code with Arduino 1.0.1. It didn't complain about 'new'.

[jpwerner1505]

Thanks to this Arduino.cc thread I've figured it out using a dynamic MALLOC call.

For future reference, I'll try to outline the different components I used to make this work, using the MAX31855 library.

Code: Select all

// declare a dynamic array variable above setup()
Adafruit_MAX31855 * thermocouples;

// create the thermocouple objects you want (inside the setup() function). The variables should be self explanatory
void createThermocouples() {
  thermocouples = (Adafruit_MAX31855 *) malloc(sizeof(Adafruit_MAX31855) * NUMBER_OF_THERMOCOUPLES);
  for (int i = 0; i < NUMBER_OF_THERMOCOUPLES; i++) {
    Adafruit_MAX31855 thermocouple(sharedThermoPins[1], thermoCSs[i], sharedThermoPins[0]);
    thermocouples[i] = thermocouple;
  }
}

// read a thermocouple inside loop(). Use an array to print them all
 double reading = thermocouples[0].readCelsius();

I can provide my full code if necessary. The array used in declaring the objects is just my way of enclosing the different sensors.

If you wouldn't mind posting the code, it would be of great help to those of us just getting started Thanks!

[eltron247]

I apologize ahead of time as I realize this post is old, however, I second that request. The code would be very helpful to us beginners if you would be so kind as to post it.

[Wbru]

I am new on this forum
I am Wim (Bill) Brussee
I com from the netherlands (and my englisch is not so good)
I am working on a sketch for a speksteen stove
I have a sketch for one max31855 and this works good but the sketch for two max31855 is a problem
I hope you can help me with the full code for two max31855 for the arduino pro mini i use the Arduino IDE 1.8.7

Greatings,