How to get raw values from thermistor inputs

Controllers Smoothie
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I would like to know if there is a way to get the actual analog reading value from the thermistor inputs (pins 0.23 - 0.26). I basically just want to bypass the calculated Steinhart Hart curve result as mentioned in the temperature control section of the Smoothieware website.

For context I am not using the smoothieboard for a 3D printer but rather an OpenPnP machine and I want to use the analog inputs for other sensors that provide a linear analog voltage level. I know there are added components on the input pins, but I removed them as I don’t ever plan to use this board to read temperature. If there is a way, it is not clearly documented, but is seems silly to me that this is not possible. Sorry if this is an obvious question, but I have spent hours trying/searching for a solution.

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I wouldn’t be surprised if there was some value for steinhart or for the beta method, that when used, would cause the value to be linear, providing you with the raw value multiplied by a fixed arbitrary ratio.

( I mean by setting some of the beta numbers like r0, r1 etc, to either 0 or 1 each, you likely have a way to make it so the read value isn’t changed by the beta algorythm, but kept untouched, as numbers always are when you add 0 to them and multiply them by 1. You can check out the algorythm here: https://github.com/Smoothieware/Smoothieware/blob/edge/src/modules/tools/temperaturecontrol/Thermistor.cpp#L225 )

Do you think you can figure out those numbers? If not tell me I’ll try to help.

Otherwise, would require a tad bit of coding, just a few lines to change.

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Ahh, yeah thats good advise! Thanks for pointing out the spot in the code. I tried briefly poking around for it last night but my eyes were too tired. I will experiment with suggestions and report back with what I come up with.

Thanks for your help!

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4

I’m working on a similar situation, reading Thermistors from SHH inputs. One workaround is to curve fit the Steinhart Hart equation to the pressure curve based on the sensor you have. I’ve started some work on the OpenPnP forums, but I think it could be as simple as using absolute pressures and characterizing the ADC circuit well enough.

I know Marlin lets you define a lookup table, which is really convenient for a variety of non-thermistor things, but there is a decent linear range for the SHH equation for the quick and dirty route.

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