Messages in this thread | | | Date | Tue, 11 Apr 2017 19:31:18 +0200 | From | Pavel Machek <> | Subject | Re: generic-adc-battery volatge-to-percent formula |
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On Mon 2016-10-24 15:09:26, H. Nikolaus Schaller wrote: > Hi Pavel, > > > Am 24.10.2016 um 14:34 schrieb Pavel Machek <pavel@ucw.cz>: > > > > Hi! > > > >> On Mon, Feb 22, 2016 at 06:58:13AM +0100, H. Nikolaus Schaller wrote: > >>>>> static inline int fuel_level_LiIon(int mV, int mA, int mOhm) { > >>>>> ... > >>>>> } > >>> > >>> To which header file should this go? > >> > >> I think it should get its own header file in include/linux/power/. > >> Maybe something like "generic-fuel-gauge.h". I'm open to other > >> solutions, though. > > > > I'd like to use use this formula in my own code. Is it somewhere in > > the kernel already? > > Not that I am aware of. Marek is still working on the generic-adc-battery > driver augmented by DT + iio-ADC + formula before publication. > > Here is the latest draft so you can cherry-pick it into your work: > > http://git.goldelico.com/?p=gta04-kernel.git;a=patch;h=22ab047ae296e998379c1aa29fe1210043cfa040 > > But beware: I think it is quite wrong using the sqrt() function above 19.66% > and doing linear interpolation below. > > By using the sqrt() function it has a steepness that goes to infinity when reaching > 19.66% from above. This makes a quite non-realistic curve with a sharp bend at 19.66% > (which is equivalent to 3.756 V). > > No real battery I have seen and measured with a coulomb counter has such a strange > bend at 3.756 V... > > IMHO it would be a better approximation to adjust the factors so that e.g. a realistic > voltage for "empty" (e.g. 3.3 V) is taken as the 0% point where steepness goes through > the roof. > > It should then be something like: > > SOC = sqrt((Volt - 3.3 V) / (4.2 V - 3.3 V)) > > This goes more smoothly between 100% and 0%. > > Or we could even use an exponential function with an exponent different from 1/2 > (1 being linear interpolation): > > SOC = pow((Volt - 3.3 V) / (4.2 V - 3.3 V), factor) > > But this would probably need floating point arithmetic in the kernel or some numeric > approximation algorithm.
Thanks! Pavel
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