Help with non standard temperature sensor config



  • G'day Folks,

    I am interfacing a Duet expansion connector to pre-existing printer hardware and need some help with the temperature sensors.

    Specifically, the hardware uses thermocouples and has its own signal conditioning which presents the Duet temperature pin with 6.6mV / degree C.

    I'm not sure how to set up the G code to make it work. I also need to figure out how to reassign the temperature pins from the expansion connector to be read as E0, E1 and bed temperature sensors.

    I am currently running RRF3 firmware.

    Any help greatly appreciated.

    Pete


  • administrators

    @Pete_A said in Help with non standard temperature sensor config:

    Specifically, the hardware uses thermocouples and has its own signal conditioning which presents the Duet temperature pin with 6.6mV / degree C

    The easiest way will probably to use the themocouple daughter-board:
    https://www.duet3d.com/TC_K_DaughterBoard

    In RRF 3 you would reference the pins as described here:
    https://duet3d.dozuki.com/Wiki/RepRapFirmware_3_overview#Section_M308_Create_or_modify_sensor_or_report_sensor_parameters, e.g:

    M308 S2 P"spi.cs1" Y"thermocouple-max31856"; define temperature sensor number 2 as a default, K Type thermocouple on the first port of a temperature daugher board plugged into the Duet 2.
    

    Alternatively you might be able to get get away with the "linear-analog sensor type with the existing thermocouple interface, I have never tried that.



  • @T3P3Tony Thanks Tony, I appreciate your taking the time.

    I had started looking a the analog-linear G-Code and I suspect this is the way I will need to go.

    Achieving a direct connection between the existing thermocouples and the Duet thermocouple daughter board isn't going to be achievable; one of my design constraints is I must be plug compatible with the existing chassis and I can not make any permanent modifications.

    Once I assign a non standard ADC pin as a particular temperature input, do I need to 'un-assign' the default input pin for that input somehow ? Or does the firmware accept only the most recently assigned input pin ?

    I will report back on any success using analog-linear

    Regards,
    Pete



  • TL:DR success using analog-linear.

    I have one (of three) thermocouples working using analog-linear, so the software handles the ADC correctly. The other two thermocouples have a different signal path and I need to figure out what is different in how the chassis handles them.

    I also need to work out the exact scaling factor for the thermocouple I can read but that should just be a case of looking at the configuration around the signal conditioning IC (ran out of time today).


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