K-type thermistor on UM2 - New Pin Assignment and code

[dmolina 4]

Hello all,

For a while I've been wanting to have a wider nozzle on my UM2, but a few months ago when I tried to do it I realized that my temp sensor was stuck there. Since I didn't want to be without the printer, I left the idea aside, but yesterday I decided I'd do it, and of course - the thermistor cable ripped and the probe is inside a now unusable nozzle/printer.

So I had ordered some months ago some k-type thermistors from China that fit the nozzle perfectly, but now I can't seem to find a way to make they work on the printer. They have 2 cables instead of the 3 of the UM2. When I connect them to the original cables, they don't work, I still get the message temp sensor problem or whatnot.

I've realized so far that I need a new pin assignment thru pins.h on the Marlin firmware (#define TEMP_0_PIN = 13), but what pin can I use? How do one connects a thermistor, to the 5V and GND?

And above all, where can I find the info on what pins from the EXP1 and EXP2 and so on correspond to what number in the firmware? I've searched for this info in the github and wiki, but couldn't find a definitive answer.

Thanks in advance, all the best,

Diego

[dmolina 4]

Ok, an update: I've tried both sensor that I got around, both have 2 cables, I believe one is a ATC Semitec 104-GT2 thermistor that came with the E3D v6 printhead and the other some generic k-type which I'm not sure.

Anyway, I tested both on the Analog port (it's 82 on the firmware, right?), with and without pull-up resistor, and I can't get a reading. No go at ADCL Analog 0 (97 on the firmware?) either, same results as the analog port.

I'm running out of ideas now...

[dmolina 4]

Ok, an update: I've tried both sensor that I got around, both have 2 cables, I believe one is a ATC Semitec 104-GT2 thermistor that came with the E3D v6 printhead and the other some generic k-type which I'm not sure.

Anyway, I tested both on the Analog port (it's 82 on the firmware, right?), with and without pull-up resistor, and I can't get a reading. No go at ADCL Analog 0 (97 on the firmware?) either, same results as the analog port.

I'm running out of ideas now...

 

Ok, so I figured it out. I´ve connected to ADCL Analog 0, using a 4.7k pull-up resistor, and used TEMP_0_PIN = 0 on the firmware, now I can get a reading just fine.

If anybody hits this, just to clarify ´cause it took me a while to come around this whole thing: you connect a cable to 5V (1st pin on the J26 marked header on the board) and a resistor (4.7k in my case) to this, the resistor goes to one lead of the thermistor, and then to an analog input (1st pin on the J25 marked header on the board) and the other to GND (2nd pin on the J26 marked header on the board). Choose the right thermistor in the Configuration.h and assign TEMP_0_PIN = 0 on pins.h, in the section relative to board 72 (um2), compile, upload and you should be good to go!

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