Calibration for dummies

[SCiunczyk]

Using soil_read_loop I got such values:

wet: 3.08;324
dry: 2.97;543

but I have no idea what to type into bparasite_nrf52840_2_0_0.overlay file

soil_calibration_coeffs: soil_calibration_coeffs {
	compatible = "soil-calibration-coeffs";
	dry = <334000 110000 (-15300)>;
	wet = <299000 (-83100) 11200>;
};

I particularly do not get it about negative values. Would anyone be so kind as to orient me in the right direction?

[rbaron]

@SCiunczyk I never got around to document the calibration process, but I explained it a little bit in #79 (comment) and #79 (comment).

What you're seeing there, for example:

• 3.08;324

Means that at 3.08V, the 10-bit adc is reading 324 when fully wet. The point is to collect many of such pairs and fit a 2nd degree poly. This is the "wet" sensor model. The same can be done for the dry model.

I used this spreadsheet for the regression:

You can copy and update it with your own data.

The negative value is just how the 2nd degree poly happened to fit the data. It doesn't mean that the function will evaluate to negative values in the real-world battery range.

[SCiunczyk]

Many thanks. Now my sensors are collected for the winter. So I have time and knowledge to calibrate them.