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Using a Thermocouple with Repetier

Legion23Legion23
in Extruder & Bed
Dear Community

I want to use a Thermocouple instead of a thermistor for my hotend.
I´m using a RADDS v1.2 board with an Arduino Due.

In the configurator, I can already choose a thermocouple amplifier:

image
This  breakout board generates a voltage of 0 - 3,3 V for -250°C to 410 °C.

My first question is the resolution: Does the Repetier firmware read the analog voltage with 10 bits resolution (resulting in 0,64°C steps) or with 12 bit resolution (the DUE has 12 bit ADCs,  older boards have 10bit ADCs).

Second question: Can I wire the voltage output of the breakout board to the thermistor pins or do I have to use the spare analog inputs of the RADDS?
image

When I have a look at the diagram that´s shown in the configuration tool, the thermistor input is directly wired to the analog input an GND, but can the voltage be pulled up by Vref?

The alternativ would be to use the analog input on the RADDS
image
But which Pin is it in the firmware?

Or can I wire the Thermocouple to the RADDS without any additional electronics?

Comments

  • RepetierRepetier
    You need a special thermocouple electronic like Adafruit AD8495 breakout board.

    Pin is this:

    #define THERMOCOUPLE_0_PIN  2   // Dua analog pin #59 = A5 -> AD 2

  • lazy_mosquitolazy_mosquito
    I followed your suggestion and installed the AD8495. i connected it to the aux adc.

    And wrote in the configurationfile:

    #define MOTHERBOARD 402
    #define EXT0_TEMPSENSOR_TYPE 61
    #define EXT0_TEMPSENSOR_PIN THERMOCOUPLE_0_PIN

    and in the pins.h

    i find:

    #if MOTHERBOARD == 402
    ........
    ........
    #define THERMOCOUPLE_0_PIN  2   // Dua analog pin #59 = A5 -> AD 2

    As far as i can see everything is alright, and when i measure the thermocouple it changes values with changing temperature, but the adc doesn't give 3,3V which could explain why the readings don't work.
    I then tried to connect the thermocouple to the x-min endstop and changed it accordingly in the configurationfile. The x-min endstop gets 3,3V but in the readings of repetierserver i get a fixed -250V. Is the x-min endstop a pullup? Is there another pin i could use on the RADDS as thermocouple pin? 


  • napiermnapierm
    Hello,

    I would like to do the same thing.  RADDS board and thermocouple input for higher hot end temp.

    Has anyone gotten this to work?

    Thanks,

    Mark Napier

  • RepetierRepetier
    I have tested teh adafruit breakout successfully. Make sure to select thermocouple pin 0 and AD8495 with 1.25V offset as the adafruit board does. It has a special switch to adapt for 3,3v in temp. computation.

    You can only select analog pins as input so x min might not be correct. And you need the analog channel for the pin. Not sure if any othe rpin has the requirement, but that is not importnant as all would behave the same.
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