Raspberry Pi MAX31855 Thermocouple Circuit Problems.

Discussion in 'Embedded Systems and Microcontrollers' started by Agent Green, Jan 8, 2016.

  1. Agent Green

    Thread Starter New Member

    Nov 13, 2015
    3
    0
    Background - I want to read the temperature from my pottery kiln through a Raspberry Pi. I found the Adafruit breakout boards but they only work with type K chips. Tried to remove the type K and swap it with a type R breaking the board in the process. Their board read my type R but output what type K would be reading.
    Bought some surface mount to breadboard adapters and soldered in the type R chips, found an article here that comes with a circuit. http://www.allaboutcircuits.com/projects/build-a-thermocouple-amplifier-and-custom-kicad-libraries/

    Followed the diagram on my breadboard and tried running it with the Adafruit example program https://github.com/adafruit/Adafruit_Python_MAX31855. This outputs over minus 100c for the reference junction and NAN for thermocouple.

    Tried with another found library which gives me 32 and 32 for the thermocouple and reference junction. https://github.com/Tuckie/max31855

    Tried following the circuit in the data sheet with no luck either, same readings.
    I know very little and battling my way up to something that works so any input would be appreciated.
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,995
    745
    So why did you take the R chip off and not use the K type??
     
  3. Agent Green

    Thread Starter New Member

    Nov 13, 2015
    3
    0
    I took off the K chip to try and use type R. Type R and S are a lot better in pottery kilns up to 1300c and type R is the one I happen to have at hand from an old kiln. I get that the market is in type K thermocouples as they do what most people need so trying to make my own PCB in the end.

    I seem to be missing a few components from the adafruit breakout board but I can't find their circuit. It is just to complicated desoldering an 8 pin chip that small. For me anyway and my crappy iron.
     
  4. Agent Green

    Thread Starter New Member

    Nov 13, 2015
    3
    0
    After working some more on this project I discovered I have been reading my surfacemount to breadboard adapter wrong. It has a 1 next to pin 4 and a circle around pin 1.

    All the programs are now running and type R thermocouple seems to be reading the right temps.

    [​IMG]
     
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