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Subject: Improved Battery Level Calculation w. Remaining Time Estimation (please test it!)
From: Uwe Freese (mail_at_uwe-freese.de)
Date: 2002-10-13


Hello,

The battery level was calculated in a very simple way: linear
interpolation between the BATTERY_EMPTY and BATTERY_FULL voltage, no
matter if the charger (recorder) was on or off.

I made some improvements, now I need some people to test it and your
opinion: Should I continue on this (and will the patch be accepted) or
do you find it useless (and the patch will be rejected). The patch is on
the sourceforge patch tracker:
http://sourceforge.net/tracker/index.php?func=detail&aid=622473&group_id=44306&atid=439120

You can find additional test results and explanations
(voltage graphs etc.) on http://www.uwe-freese.de/rockbox

my improvements in detail:

- The battery level (percentage) is more realistic and considers if the
  charger is on.
- It considers the "lazyness" a battery shows when the charging has just
  turned on or off (see below). But this is not perfect by now.
- The battery level is good enough to estimate the remaining running
  time and the remaining charging time. And so the info screen now shows
  this info.
- The maximum time of a charging cycle is now dynamically calculated out
  of the battery level (percentage) and is not a fixed value.
- A minimum of 60 Minutes is waited after a charging cycle stops
  before another one starts.
- Added another screen in the battery debug screen (press down three
  times).

Note: The charging algorithm (detecting the end of a charging cycle)
considers the raw voltage levels in the power_history-array. This is
left untouched!!
  
implementation:

- Two arrays (of 11 values, showing the voltage at 0%, 10%, ...100%)
  build a realistic voltage curve (avg. of Magnus Holmgrens and my own
  vales) that a NiMh cell shows when decharging and charging. The
  percentage is calculated by linear interpolation between the two
  values that fit most.
- The battery is "lazy". Example: When turning the charger on with 50%
  full batteries, the voltage goes quickly up a little bit, but is lasts
  some minutes to come close to the voltage level the battery would have
  in the mid of the charging cycle when the charging had started with
  empty (0% level) batteries.
  To consider the lazyness, the voltage_to_percent values of both
  arrays are taken and then an average is made. Not in the middle of
  both values, but with an amount that depends on how long the current
  charging/decharging cycle is running. That is implemented with another
  array battery_lazyness.
- The remaining time is calculated out of a battery capacity (constant
  in header file) and a usual decharging current (AJB is playing) or
  usual charging current.

unfinished work:

- For the player (where we don't control charging), the battery level is
  always calculated out of the nocharge-array. Maybe we can detect a
  charging start or stop by simply looking if the voltage goes up or
  down?
- The battery lazyness calculation is not good enough. Is is a first
  approach. But a perfect one would mean no "jumping up and down" in the
  current battery level when starting/stopping charging.
- The battery capacity should be configurable in the menu (1000, 1100,
  ... 2200 mAh).
- Consider if the backlight is on or maybe count how many seconds the
  harddisk was on to make the remaining time est. better.

Now I want to know what you others think of my patch. If it is accepted
(what I hope), I would make it even better and complete the things I
mentioned above.

Please note:

- The patch should be tested with a recorder model to see the behaviour
  when it's charging, but it does compile for the player also.
- The end-of-charging detection is untouched. So if this patch is not
  perfect, this only means the new remaining time estimation is not as
  good as it could be. But there should be no risk for the battery for
  wrong charging. Anyway, test it with caution.

Bye, Uwe.



Page was last modified "Jan 10 2012" The Rockbox Crew
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