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Subject: Re: How do you calculate the battery status?
From: TP Diffenbach (rockbox_at_diffenbach.org)
Date: 2003-08-13


Quoting Björn Stenberg <bjorn_at_haxx.se>:

> Stoyan Stratev wrote:
> > Hi,
> > I have a JBR 15. I installed the RockBox(nightly build) and I am very happy
> > with it. There is one problem however - the battery status is totally
> wrong.
>
> I posted a message explaining this last week:
>
> http://rockbox.haxx.se/mail/archive/rockbox-archive-2003-08/0202.shtml
 
In which Björn wrote:
2) To avoid wildly fluctuating power levels due to the very varying battery loads
(disk spinup uses 5-8 times normal power), Rockbox implements a limit on how fast
the battery meter is allowed to change.

At least on the fmr, the voltage recovers quite quickly after disk access ceases.
In my extended battery life power monitoring, for each monitoring snapshot, I take
the battery voltage 6 times per minute, at 10 second intervals. Generally, even if
a spin-up has occurred, it will affect the voltage only for one of those
intervals. To be safe, I throw out the the two highest and two lowest volatges,
and average the remaining two. This gives me the "real" voltage with (seemingly)
good accuracy.

In case anyone wants to squint over the real data, here's a sample run, where the
snapshot is taken every two minutes (i.e., every second minute we take 6 data
points every 10 seconds). Snapshot minute is the minute we aim to take the
snapshot, actual minute (decimal minute) is when we really do take the data point,
rank is the order, from 1 (lowest) to 6 (highest) of the voltages in that sample,
and rank "A" is the average of samples 3 and 4, which we use as the "real" data.

Snapshot minute zero is actually immediately after a rolo, beginning at tick 171
(and we do see that the disk is or was recently in use); the second read is at
tick 1172 and is .01 volt below what it might be, but by read three at tick 2173,
we have found a quite reasonable voltage.

(Incidently, at snapshot minute 4 we've begun to play a 320 cbr mpeg, and continue
with 320 cbrs through the end of the run, in case you wonder why the volatge
decreases.)

Snapshot Actual Battery
minute rank minute Volatge

0 1 0.03 2.79
0 2 0.20 3.09
0 4 0.36 3.10
0 6 0.53 3.13
0 3 0.70 3.10
0 5 0.86 3.11
0 A 0.53 3.10
                        
2 4 2.03 3.10
2 6 2.20 3.13
2 1 2.36 3.10
2 2 2.53 3.10
2 3 2.70 3.10
2 5 2.86 3.12
2 A 2.36 3.10
                        
4 6 4.03 3.11
4 4 4.20 3.09
4 1 4.36 2.61
4 5 4.53 3.09
4 3 4.70 3.08
4 2 4.86 3.08
4 A 4.45 3.09
                        
6 6 6.03 3.10
6 1 6.20 2.70
6 2 6.36 3.08
6 4 6.53 3.10
6 5 6.70 3.10
6 3 6.86 3.09
6 A 6.70 3.10
                        
8 2 8.03 3.05
8 3 8.20 3.06
8 5 8.36 3.08
8 1 8.53 2.71
8 4 8.70 3.06
8 6 8.86 3.09
8 A 8.45 3.06
                        
10 6 10.03 3.08
10 4 10.20 3.06
10 1 10.37 2.59
10 3 10.53 3.06
10 2 10.70 3.06
10 5 10.87 3.06
10 A 10.36 3.06
                        
12 3 12.03 3.05
12 2 12.20 2.61
12 4 12.37 3.06
12 5 12.53 3.06
12 6 12.70 3.06
12 1 12.87 2.56
12 A 12.20 3.06
                        
14 2 14.03 2.77
14 4 14.20 3.04
14 3 14.36 3.04
14 6 14.53 3.06
14 1 14.70 2.73
14 5 14.87 3.06
14 A 14.28 3.04
                        
16 2 16.03 3.05
16 3 16.20 3.05
16 4 16.36 3.05
16 1 16.53 2.55
16 5 16.70 3.05
16 6 16.87 3.06
16 A 16.28 3.05
                        
18 3 18.03 3.04
18 6 18.20 3.05
18 1 18.36 2.63
18 5 18.53 3.05
18 2 18.70 3.03
18 4 18.87 3.05
18 A 18.45 3.05
                        
20 5 20.03 3.03
20 1 20.20 2.63
20 3 20.37 3.03
20 6 20.53 3.03
20 4 20.70 3.03
20 2 20.87 3.01
20 A 20.53 3.03
                        
22 1 22.03 2.64
22 4 22.20 3.03
22 5 22.37 3.03
22 6 22.53 3.04
22 2 22.70 3.02
22 3 22.87 3.02
22 A 22.53 3.03
                        
24 6 24.03 3.04
24 4 24.20 3.03
24 5 24.37 3.03
24 2 24.53 3.01
24 3 24.70 3.01
24 1 24.87 3.00
24 A 24.45 3.02
                        
26 5 26.03 3.00
26 3 26.20 3.00
26 4 26.37 3.00
26 6 26.53 3.01
26 2 26.70 3.00
26 1 26.87 2.55
26 A 26.28 3.00
                        
28 5 28.03 3.01
28 3 28.20 3.00
28 4 28.37 3.01
28 6 28.53 3.02
28 1 28.70 2.71
28 2 28.87 2.99
28 A 28.28 3.01
                        
30 5 30.03 3.01
30 2 30.20 2.99
30 3 30.37 2.99
30 1 30.53 2.95
30 6 30.70 3.01
30 4 30.87 3.01
30 A 30.62 3.00
                        
32 6 32.03 3.03
32 5 32.20 3.01
32 2 32.37 2.98
32 3 32.53 2.98
32 4 32.70 2.99
32 1 32.87 2.67
32 A 32.62 2.99
                        
34 5 34.03 3.00
34 2 34.20 2.97
34 3 34.37 2.97
34 6 34.53 3.01
34 1 34.70 2.65
34 4 34.87 2.99
34 A 34.62 2.98
                        
36 2 36.03 2.95
36 6 36.20 3.01
36 5 36.37 3.00
36 1 36.53 2.61
36 3 36.70 2.97
36 4 36.87 2.98
36 A 36.78 2.98
                        
38 3 38.03 2.99
38 4 38.20 2.99
38 1 38.37 2.71
38 6 38.54 3.01
38 5 38.70 2.99
38 2 38.87 2.98
38 A 38.12 2.99
                        
40 5 40.03 2.99
40 1 40.20 2.55
40 4 40.37 2.98
40 6 40.53 2.99
40 3 40.70 2.97
40 2 40.87 2.93
40 A 40.53 2.98
                        
42 1 42.03 2.67
42 5 42.20 2.98
42 6 42.37 2.99
42 4 42.53 2.97
42 2 42.70 2.95
42 3 42.87 2.96
42 A 42.70 2.97
                        
44 6 44.03 2.98
44 5 44.20 2.97
44 1 44.37 2.58
44 4 44.53 2.97
44 3 44.70 2.97
44 2 44.87 2.95
44 A 44.62 2.97
                        
46 3 46.03 2.96
46 6 46.20 2.99
46 4 46.37 2.97
46 5 46.53 2.97
46 2 46.70 2.95
46 1 46.87 2.58
46 A 46.20 2.97
                        
48 5 48.03 2.97
48 3 48.20 2.96
48 4 48.37 2.97
48 6 48.53 2.97
48 1 48.70 2.66
48 2 48.87 2.93
48 A 48.28 2.97
                        
50 4 50.03 2.96
50 2 50.20 2.95
50 6 50.37 2.98
50 1 50.53 2.67
50 3 50.70 2.96
50 5 50.87 2.98
50 A 50.37 2.96
                        
52 4 52.03 2.95
52 6 52.20 2.97
52 2 52.37 2.92
52 5 52.53 2.95
52 3 52.70 2.94
52 1 52.87 2.56
52 A 52.37 2.95
                        

-- 
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