Thermocouples on Daughterboard



  • I was stepping through the configuration. I have made a config.g file. I got stopped at Step 7; both temperature sensors are reading 2000. This is documented as a wiring problem. There aren't that many different ways to connect 2 wires on the daughterboard.
    Perhaps, I didn't pick the right options for the reprap firmware generator. How should a thermocouple be treated as opposed to a thermistor? Can you give any tips on this? Or refer me to somewhere this is already discussed?
    Thank you,



  • Just in case it makes any difference...our board is ethernet.




  • administrators

    In particular, make sure you selected the correct type of daughter board in the configurator. Older daughter boards use the MAX31855 chip, newer ones use the MAX31865 chip. This affects the value of the X parameter you need in the M305 commands in config.g.



  • So, the bottom line is that the configurator can't configure thermocouples? I have to put lines of code in manually.


  • administrators

    Yes the configurator can configure thermocouples, but you have to select the correct sort of daughter board in the configurator.



  • Thermocouple Daughterboard

    What does a steady fault light mean vs. a slowly blinking fault light on thermocouple daughterboard?

    Numbering system for heaters
    It is unclear how the numbering system works between the vssa thermistor and the thermocouples.

    Do the heater numbers start at 0 or 1? If I have one vssa thermistor and 2 thermocouples or 2 vssa thermistors, how should the M305 heater number be written in the config file? Are the Vssa thermistors plugged into E0, heater 0?

    VSSA thermistor
    The vssa thermistor is not showing up on the Duet Web Control when power is applied. I see 3 heaters briefly on reboot, but that is it.

    I assume there is no polarity on these thermistors, is this correct?
    The wire supplied with the E3D V6 hot end was not long enough, so we added a short piece which is plugged into the board. Is this a problem with thermistors?

    We confirmed continuity on the new extended wire.



  • Have you read the wiki? This is all well documented there.

    https://duet3d.dozuki.com/Wiki/Temperature_sensors

    Temperature sensors and heaters both start at zero. Bed heaters and thermistors are generally 0, with hotends at 1+.

    There is no such thing as a "VSSA" thermistor, just "thermistor".

    The way M305 is written depends on many things, including what specific thermistor you're using.

    Correct, thermistors do not have polarity.



  • I have read the wiki pages and have seen no indication about how the various sensors are to be numbered in combination. I can not find information about the blinking fault light etc. Thermisters and thermocouples are discussed separately but not in combination.

    They are plugged in different places, do they use a combined numbering system or a separate sequence for each type of sensor. Ie do both thermisters and thermocouples start at 0? So if I have 1 thermister and 2 thermocouples, do I count up to 3 or do i have one 0 for a thermister and one 0 for a thermocouple.

    Temperature sensors and heaters both start at zero. Bed heaters and thermistors are generally 0, with hotends at 1+.

    I have tried various combinations but would prefer to work with known parameters to debug.


  • administrators

    Thermistor sensor numbers start at 0: 0 = bed thermistor connector, 1 = E0 thermistor connector, 2 = E1 thermistor connector.

    As explained in the wiki page on thermocojuples, thermocouple sensor numbers start at either 100 or 150 depending on which daughter board you have. If you have the new one with the FAULT LEDs, they start at 150.

    As explained in the same wiki page, to specify what sensor a particular heater uses, use the X parameter in the M305 command for that heater. Example:

    M305 P1 X150 ; use first thermocouple channel for heater 1 (E0 heater)

    HTH David



  • This is what we mean by "in combination".

    The issue is the P? designation on thermocouples. Is it necessary? Or only ignored and only the X modifier is utilized? In your example above, you used P1. We could not issue a combination of commands which resulted in displays for 1 thermistor and 2 thermocouples in the Web Control interface.

    So if P1 is a thermistor plugged into thermistor1 (E0) on the duet board and we are using 2 thermocouples on the daughterboard, which P designation do we use for the thermocouples? Do we start over with P1 (M305 P1 X150), go back to P0 (M305 P0 X150), or continue to P2 (M305 P2 X150)?

    I also need to know:
    What does a steady fault light mean vs. a slowly blinking fault light on thermocouple daughterboard?

    Should I put this question on a different board on the forum?


  • administrators

    In the M305 command, the P parameter refers to the heater number that is being controlled, e.g. heater 0 = bed heater, heater 1 = E0 heater etc. The X parameter in the command is the sensor channel you want to use to control that heater. If you use the configurator, it will generate the M305 commands for you.

    The fault light can mean a few things:

    • Thermocouple is not connected
    • Thermocouple is shorted to something else. The thermocouple junction must be insulated from the hot end.

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