[Solved] Problems reading from MAX81855-K

@timo88 I just did a quick search of the forum and got 7 pages of hits. The search argument is in quotes and is 'K-type ThermoCouple using a Max81855-K'

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Posted by: @timo88

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Can somebody give me a tip what to do fix and or check?

From the README file:

Note that if the read() fails the value of getTemperature() can become incorrect. So it is important to check the return value of read().

I don't see the check in your code.

FWIW, the example sketch only checks for one error. I think the proper check is for read to return OK, else there's an error.

@thank you for your replies. I'll have a look at your suggestions.
I added the read fail check but 99% of the times it still returns 0

Posted by: @zander

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@timo88 I just did a quick search of the forum and got 7 pages of hits. The search argument is in quotes and is 'K-type ThermoCouple using a Max81855-K'

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Thank you. I did search for Max81855-K but it did not return any results, I'll have another look

@timo88 Sorry, I didn't check close enough, even when quoted the search on the long phrase was finding irrelevant words. It looks like you are the first to look into this Max81855-K device.

@timo88 I just did a google search and got only a couple of pages, most from DBWS. Either this is a new device, or it is not used much. The most interesting headline I see in google is from the klipper group (3D printers) mentioning COLD. A bit of a mystery.

Posted by: @zander

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@timo88 I just did a google search and got only a couple of pages, most from DBWS. Either this is a new device, or it is not used much. The most interesting headline I see in google is from the klipper group (3D printers) mentioning COLD. A bit of a mystery.

Oh, I can't change that anymore but it should have been MAX31855-K 🙁

Posted by: @timo88

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I added the read fail check but 99% of the times it still returns 0

I tried to give you a "heads-up" about this. You duplicated the mistake the example makes:

start = micros();
  int status = thermoCouple.read();
  stop = micros();

  if (status == STATUS_NO_COMMUNICATION)

STATUS_COMMUNICATION is just one error code. From the README file

To make a temperature reading call read(). It returns the status of the read which is a value between 0..7

The above is inaccurate. There are 7 distinct return values, but not in the range [0..7]:

The code needs to make sure there's not some other error.

@timo88 I find very little info re this device. What I do see tells me it is a bear to work with. I suggest you change to a more popular device with more support and successful implementations.

Is the thermocouple insulated? If not that is a problem.

@tfmccarthy That is a common hobbyist error. I suspect you like me spent a long professional career filling pages of code with exception checking.

Posted by: @tfmccarthy

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Posted by: @timo88

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I added the read fail check but 99% of the times it still returns 0

I tried to give you a "heads-up" about this. You duplicated the mistake the example makes:

start = micros();
  int status = thermoCouple.read();
  stop = micros();

  if (status == STATUS_NO_COMMUNICATION)

STATUS_COMMUNICATION is just one error code. From the README file

To make a temperature reading call read(). It returns the status of the read which is a value between 0..7

The above is inaccurate. There are 7 distinct return values, but not in the range [0..7]:

value	Description	Action
0	OK
1	Thermocouple open circuit	check wiring
2	Thermocouple short to GND	check wiring
4	Thermocouple short to VCC	check wiring
7	Generic error
128	No read done yet	check wiring
129	No communication	check wiring

The code needs to make sure there's not some other error.

 

Right, that's probably better. I'll have a go at that.

@tfmccarthy  OK even with extra error checking I still get mostly "OK" as a status and 0 value.

Even when I disconnect a data wire, it still reports "OK". 🤣 

I'll take the advise of Ron and look for another chip I guess. @zander

Thank you for your time and help 🙂

I'll try the MAX6675 next I guess