TWO Max 6675 thermocouple on ramps

Hi repetier
recently i bought a two extruder AHIRO from china with thermocouple max 6675
how can i wire both of them in ramps and how can i setup the firmware ?
i can wire just one of them cause ramps has just one miso and sck in AUX3 . 


  • All spi devices share the same sck/miso pin. They are selected by the CS or slave select pin you define.
  • I wired one max 6675 that has 5 pin to aux 1 d57 and sck /miso from thermocouple board to aux 3 sck / miso and define my thermocouple in repetier firmware ( define pin digital 57 ) and connect another 6675 thermocouple to aux 1 digital pin 1 . But the temp for both extruders are the same as extruder 1 . In another word temp 2 follow temp 1 in changes . Can i define sck and miso in aux 1 pins in pins.h ? I'm confused about wirring them
  • Thermistor pin you define is the slave select pin of the max 6675. sck and miso is the same for all. I don't know pin names/numbers of your board so I can nnot say what belongs where. I even don't have a max 6675:-)
  • Hi,  I am trying the same thing and using the configuration tool you can set the thermocouple pins (which i assume are the CS pins) for each extruder and the heated bed.  I have selected MAX6675 for each extruder and the bed and set the pins to D40, D42 & D44.

    After uploading the configuration Ext0 works using D40 but all the other temperatures are the same as Ext0.  If i try connecting the CS pin to D42 for Ext1 or D44 for the Bed it shows 500 deg (i.e. not working).

    I know when the use of the MAX6675 chip was introduced it was limited to 1 temperature sensor.  Is this still the case?

  • In theory it should work with more since you are right and sensor pin is used as slave select pin and set back to 1 after polling data. Only thing is I still don't have a printer with these chips so it gets only tested by external users.
  • Thanks for teh response.

    I set Ext0 to another type and Ext1 and the Bed to MAX6675 and again the Ext1 and the Bed showed the same temperature even though i only had the MAX6675 connected to Ext1.

    It appears that the code only uses the first MAX6675 and is unable to process the rest.

    I am happy to purchase a couple of these and ship them to you for testing if that will help in the development of this.  I understand the basics of Arduino programming but haven't been able to follow this to see if i can mod the code to get it to work.
  • I see the problem. The MAX6675 is slow and only allows updates every 200ms (here limited to 230). So we buffer the result and only update when enough time is elapsed. Having 2 or more sensors breaks the logic as all use the same variables.

    So while the routine could read from several sensors it would only do it if you have 250ms between calls, and that is not given. So what I need is a array of buffer variables and use extruder index to access right one. Will see how that could be solved, but that is the problem.

  • Ok have written a fix that should work. Please try latest development version.
  • Thanks, I will see if I can try it this afternoon.
  • Hi,

    I have tried the development code, disabling the bed and setting 2 extruders as type 101 with pins 40 & 42.  I never changed any other settings.  It now takes 1 reading from each on start up but then doesn't update the readings again.  

    I restarted the board several times changing the temperature of each probe (holding it between my fingers) and it showed the change of temperature for each sensor on start up but no further updates.  

    I had a similar problem when MAX6675 was first introduced and it conflicted with the SD Card.  In the development version the SD card is disabled so not sure what is causing it to only read once.  
  • My bad. I forgot to set firstRun to false after first run. So it kept asking much too often which is the source of the whole problem. At least that is fixed, so hope it now works.

    Don't think it is a sd issue as it worked before and reading has not changed, just did read to soon again. Please try with updated development version.
  • Yes, that now works with 2 units.  I will add a 3rd soon for the bed and test all 3 running.  

    My MAX6675's are for my new dual extruder and i haven't installed it yet so am currently unable to test them while heating etc.

    Thanks for sorting this out.
  • Hello there guys,

    I'm looking to set up two thermocouples with my MKS board, do I connect two amplifiers: each to the 5v, gnd and signal? then do i change firmware settings? 

    I've seen you have wrote something about development code in order for the readings to be correct for each extruder, what does this mean?

    Oli T
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