Marlin: Plot of Thermistor Curves

I made a handy plot of Marlin thermistor curves to help visualize the difference between different types. If there is any interest, send me a line and I will provide you with the code to generate additional curves.

Additionally, I worked out how to compute the curve of an idealized B 3950 thermistor. Mosaic Industries works out the math in more details, and I have summarized it here.

The temperature in function of resistance.
//
// assumes beta 3950
//
celsius_float_t ideal_thermistor_temperature(auto resistance)
{
	float beta = 3950, Rinf = 0.176323;
	float T = beta / log(resistance / Rinf) - 273.15;
	return T;
}

celsius_float_t ideal_thermistor_temperature_from_raw(auto raw)
{
	float resistance = -4700 * (raw) / (raw - 1024);
	return ideal_thermistor_temperature(resistance);
}

Plotting this idealized equation results in a neat curve that follows very closely the value tables from Marlin (here for B=3950 this corresponds to thermistor type 11).

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