generic-adc-battery volatge-to-percent formula

generic-adc-battery volatge-to-percent formula

[Belisko Marek]

Hi,

some time ago I did post series which added some conversion table from
voltage to percent for charging and discharging states [1] in
twl4030_madc driver. This approach was not accepted and we still want
to have something like that in kernel. We re-think re-thinking
original idea and also get reference where Pavel point us to formula
which could be used for computing voltage-to-percent conversion [2]

What about adding this formula as a default for the
voltage-to-percent-conversion to
the generic-adc-battery driver (and converting it to DT)? Would that
be a better solution than a table driven and twl4030 only driver?

[1] - http://www.serverphorums.com/read.php?12,1127548
[2] - https://lkml.org/lkml/2015/4/1/557

Many thanks.

BR,

marek

-- 
as simple and primitive as possible
-------------------------------------------------
Marek Belisko - OPEN-NANDRA
Freelance Developer

Ruska Nova Ves 219 | Presov, 08005 Slovak Republic
Tel: +421 915 052 184
skype: marekwhite
twitter: #opennandra
web: http://open-nandra.com

Re: generic-adc-battery volatge-to-percent formula

[Pavel Machek]

Hi!
> 
> some time ago I did post series which added some conversion table from
> voltage to percent for charging and discharging states [1] in
> twl4030_madc driver. This approach was not accepted and we still want
> to have something like that in kernel. We re-think re-thinking
> original idea and also get reference where Pavel point us to formula
> which could be used for computing voltage-to-percent conversion [2]
> 
> What about adding this formula as a default for the
> voltage-to-percent-conversion to
> the generic-adc-battery driver (and converting it to DT)? Would that
> be a better solution than a table driven and twl4030 only driver?

I'd say battery, yes. And maybe even better would be putting it into
lib/ or seaparet driver, as it does not really depend on IIO? You just
supply voltage, current and internal resistance, and it produces number...

I'm using the same conversion tables on n900 (it has battery gauge,
but it is often not calibrated, so fallback method is nice), and it
seems to work quite ok.

Best regards,
									Pavel    
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: generic-adc-battery volatge-to-percent formula

[Belisko Marek]

Hi Pavel,

On Fri, Feb 12, 2016 at 9:51 AM, Pavel Machek <pavel@ucw.cz> wrote:
> Hi!
>>
>> some time ago I did post series which added some conversion table from
>> voltage to percent for charging and discharging states [1] in
>> twl4030_madc driver. This approach was not accepted and we still want
>> to have something like that in kernel. We re-think re-thinking
>> original idea and also get reference where Pavel point us to formula
>> which could be used for computing voltage-to-percent conversion [2]
>>
>> What about adding this formula as a default for the
>> voltage-to-percent-conversion to
>> the generic-adc-battery driver (and converting it to DT)? Would that
>> be a better solution than a table driven and twl4030 only driver?
>
> I'd say battery, yes. And maybe even better would be putting it into
> lib/ or seaparet driver, as it does not really depend on IIO? You just
> supply voltage, current and internal resistance, and it produces number...
Can we put this small helper to some common power header file which
can be then included
to driver which can use this formula. I think it's better way then
adding it to /lib as it won't be used
in whole kernel tree just in power. What do you think? Thanks.
>
> I'm using the same conversion tables on n900 (it has battery gauge,
> but it is often not calibrated, so fallback method is nice), and it
> seems to work quite ok.
+1
>
> Best regards,
>                                                                         Pavel
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

BR,

marek

-- 
as simple and primitive as possible
-------------------------------------------------
Marek Belisko - OPEN-NANDRA
Freelance Developer

Ruska Nova Ves 219 | Presov, 08005 Slovak Republic
Tel: +421 915 052 184
skype: marekwhite
twitter: #opennandra
web: http://open-nandra.com

Re: generic-adc-battery volatge-to-percent formula

[Pavel Machek]

Hi!
> 
> On Fri, Feb 12, 2016 at 9:51 AM, Pavel Machek <pavel@ucw.cz> wrote:
> > Hi!
> >>
> >> some time ago I did post series which added some conversion table from
> >> voltage to percent for charging and discharging states [1] in
> >> twl4030_madc driver. This approach was not accepted and we still want
> >> to have something like that in kernel. We re-think re-thinking
> >> original idea and also get reference where Pavel point us to formula
> >> which could be used for computing voltage-to-percent conversion [2]
> >>
> >> What about adding this formula as a default for the
> >> voltage-to-percent-conversion to
> >> the generic-adc-battery driver (and converting it to DT)? Would that
> >> be a better solution than a table driven and twl4030 only driver?
> >
> > I'd say battery, yes. And maybe even better would be putting it into
> > lib/ or seaparet driver, as it does not really depend on IIO? You just
> > supply voltage, current and internal resistance, and it produces number...
> Can we put this small helper to some common power header file which
> can be then included
> to driver which can use this formula. I think it's better way then
> adding it to /lib as it won't be used
> in whole kernel tree just in power. What do you think? Thanks.

Sounds good to me.

Thanks,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: generic-adc-battery volatge-to-percent formula

[Sebastian Reichel]

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Hi,

On Mon, Feb 15, 2016 at 12:53:04PM +0100, Pavel Machek wrote:
> > >> some time ago I did post series which added some conversion table from
> > >> voltage to percent for charging and discharging states [1] in
> > >> twl4030_madc driver. This approach was not accepted and we still want
> > >> to have something like that in kernel. We re-think re-thinking
> > >> original idea and also get reference where Pavel point us to formula
> > >> which could be used for computing voltage-to-percent conversion [2]
> > >>
> > >> What about adding this formula as a default for the
> > >> voltage-to-percent-conversion to the generic-adc-battery
> > >> driver (and converting it to DT)? Would that be a better
> > >> solution than a table driven and twl4030 only driver?
> > >
> > > I'd say battery, yes. And maybe even better would be putting it into
> > > lib/ or seaparet driver, as it does not really depend on IIO? You just
> > > supply voltage, current and internal resistance, and it produces number...
> > >
> > Can we put this small helper to some common power header file
> > which can be then included to driver which can use this formula.
> > I think it's better way then adding it to /lib as it won't be
> > used in whole kernel tree just in power. What do you think?
> > Thanks.
> 
> Sounds good to me.

Sounds fine for me, too.

-- Sebastian

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Re: generic-adc-battery volatge-to-percent formula

[H. Nikolaus Schaller]

Hi,

Am 21.02.2016 um 21:06 schrieb Sebastian Reichel <sre@kernel.org>:

> Hi,
> 
> On Mon, Feb 15, 2016 at 12:53:04PM +0100, Pavel Machek wrote:
>>>>> some time ago I did post series which added some conversion table from
>>>>> voltage to percent for charging and discharging states [1] in
>>>>> twl4030_madc driver. This approach was not accepted and we still want
>>>>> to have something like that in kernel. We re-think re-thinking
>>>>> original idea and also get reference where Pavel point us to formula
>>>>> which could be used for computing voltage-to-percent conversion [2]
>>>>> 
>>>>> What about adding this formula as a default for the
>>>>> voltage-to-percent-conversion to the generic-adc-battery
>>>>> driver (and converting it to DT)? Would that be a better
>>>>> solution than a table driven and twl4030 only driver?
>>>> 
>>>> I'd say battery, yes. And maybe even better would be putting it into
>>>> lib/ or seaparet driver, as it does not really depend on IIO? You just
>>>> supply voltage, current and internal resistance, and it produces number...

it could be something similar to (I might have made a mistake when applying scaling):

/* calculate remaining fuel level (in %) of a LiIon battery assuming
* a standard chemistry model
*    http://cseweb.ucsd.edu/~trosing/lectures/battery.pdf
*
* @mV: voltage measured outside the battery
* @mA: current flowing out of the battery
* @mOhm: assumed series resitance of the battery
*
* returns value between 0 and 100
*/

static inline int fuel_level_LiIon(int mV, int mA, int mOhm) {
	int u;
	/* internal battery voltage is higher than measured */
	mV += (mOhm * mA) /1000;

	/* apply formula */
 	u = 3870000 - (14523 * (37835 - 10 * mV));
	if (u < 0)
		return ((mV - 3300) * ((3756 - 3300) * 1966)) / 100000;
	return (1966 + sqrt(u))/100;
}

>>>> 
>>> Can we put this small helper to some common power header file
>>> which can be then included to driver which can use this formula.
>>> I think it's better way then adding it to /lib as it won't be
>>> used in whole kernel tree just in power. What do you think?
>>> Thanks.
>> 
>> Sounds good to me.
> 
> Sounds fine for me, too.

Fine for me as well.

And the generic-adc-battery can use it as a default translation function
when initialized by device tree (which provides the mOhm value as well).

-- hns

Re: generic-adc-battery volatge-to-percent formula

[Pavel Machek]

Hi!

> 
> it could be something similar to (I might have made a mistake when applying scaling):
> 
> /* calculate remaining fuel level (in %) of a LiIon battery assuming
> * a standard chemistry model
> *    http://cseweb.ucsd.edu/~trosing/lectures/battery.pdf
> *
> * @mV: voltage measured outside the battery
> * @mA: current flowing out of the battery
> * @mOhm: assumed series resitance of the battery
> *
> * returns value between 0 and 100
> */
> 
> static inline int fuel_level_LiIon(int mV, int mA, int mOhm) {
> 	int u;
> 	/* internal battery voltage is higher than measured */

add " when discharging".

> 	mV += (mOhm * mA) /1000;
> 
> 	/* apply formula */
>  	u = 3870000 - (14523 * (37835 - 10 * mV));

	/* linear approximation between 3.756V */

> 	if (u < 0)
> 		return ((mV - 3300) * ((3756 - 3300) * 1966)) / 100000;
> 	return (1966 + sqrt(u))/100;
> }
>

Thanks,
									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: generic-adc-battery volatge-to-percent formula

[H. Nikolaus Schaller]

Hi,

Am 21.02.2016 um 22:12 schrieb Pavel Machek <pavel@ucw.cz>:

> Hi!
> 
>> 
>> it could be something similar to (I might have made a mistake when applying scaling):
>> 
>> /* calculate remaining fuel level (in %) of a LiIon battery assuming
>> * a standard chemistry model
>> *    http://cseweb.ucsd.edu/~trosing/lectures/battery.pdf
>> *
>> * @mV: voltage measured outside the battery
>> * @mA: current flowing out of the battery
>> * @mOhm: assumed series resitance of the battery
>> *
>> * returns value between 0 and 100
>> */
>> 
>> static inline int fuel_level_LiIon(int mV, int mA, int mOhm) {
>> 	int u;
>> 	/* internal battery voltage is higher than measured */
> 
> add " when discharging".
> 
>> 	mV += (mOhm * mA) /1000;
>> 
>> 	/* apply formula */
>> 	u = 3870000 - (14523 * (37835 - 10 * mV));
> 
> 	/* linear approximation between 3.756V */

/* use linear approx. below 3.756V / 19.66% assuming 3.3V / 0% */

> 
>> 	if (u < 0)

I just recognised that we should for a really robust formula
also limit the linear approx. to 0 if someone measures <3300 mV.

>> 		return ((mV - 3300) * ((3756 - 3300) * 1966)) / 100000;

		return max(((mV - 3300) * ((3756 - 3300) * 1966)) / 100000, 0);


>> 	return (1966 + sqrt(u))/100;

and this should be limited to 100.

return min((1966 + int_sqrt(u))/100, 100);

>> }
>> 

To which header file should this go?

-- hns

Re: generic-adc-battery volatge-to-percent formula

[Sebastian Reichel]

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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.

-- Sebastian

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Re: generic-adc-battery volatge-to-percent formula

[Pavel Machek]

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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?

Thanks,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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Re: generic-adc-battery volatge-to-percent formula

[H. Nikolaus Schaller]

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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.

BR,
Nikolaus


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Re: generic-adc-battery volatge-to-percent formula

[Pavel Machek]

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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



-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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