I’m trying to replace the control board from my old Dremel 3d20 printer. I’m unable to configure the thermistor, it keeps giving me temperatures that are out of range. That is while the heater is at room temperature.
I could find no documentation of what kind of thermistor is in the printer. After trying for some time, I’ve decided that I’ll measure its resistance using a multimeter. From my measurements, it seems to be a very unusual type of thermistor: PTC that is around 3 ohms at room temperature (2 ohms at 0C, 2.7 ohms at 20C and 5.3 ohms at 100C). Is there a way to use this thermistor?
The attached klipper log has a few trials. Including some junk when I renamed the sensor to check whether klipper is trying to load it or not. But ultimately, when I’m using the actual numbers, it’s saying it’s using “beta” thermistor, without saying why.
At this point, I feel like I should probably by another thermistor. Even if I can somehow configure it, I suspect that with such a low resistance, it wouldn’t give me too inaccurate readings anyway. But regardless, I’d like to know if there’s a way to do this.
I’m pretty sure it isn’t an NTC thermistor. I think it is a K type thermocouple. There is support in my repo for this but I’m not sure what kind of ADC is on your new board that will support this.
There has been some success running klipper on the existing control board.
@pierre286 I’m interested in trying to add support for the original printerboard to my repo. Let me know if you want to sell me the original board. thanks!
absolutely correct - and STS’s instructions reference my repo for ADS1118 and k-type thermocouple support in Klipper. The easiest path forward for the OP is to replace the thermocouple with an NTC thermistor. Trying to support a thermocouple on a board with no hardware support for it will be challenging.
It’s not a case of enough pins. It’s that thermocouples can produce very small and only slightly voltage differences. Therefore they need an amplifier.
Hi guys, I have never seen a 3D20 motherboard. On the 3D40 motherboard the ADS1118 is present.
My instructions have pictures of the 3D40 motherboard. Does the one on the 3D20 look very similar or different.
Here a picture on the 3D40. It is U302 placed above the ribbon cable to the print head.
actually just searched through my computer and found some data that I had collected at that time. Someone had done a Marlin configuration file for the 3D20 and it lists the ADS1118. It also lists all the pins, so you have a way simpler job than I had all needed info.txt (18.2 KB)
It’s more than that too - you also need a cold juntion temperature reading. Much simpler to change to a thermistor for a board that doesn’t support thermocouples.
I was referring to a thermistor! It’s just possible to connect the thermistor to the original printer board, if there is an ADC pin available. That’s why I proposed
This may seem a bit blunt advice, as you cannot just connect a thermistor to a free MCU pin without the hardware to support it, e.g. the necessary voltage divider etc.
