Hi Jose,
There is indeed crosstalk. It only occurs when you enable Batt monitoring
because it has an un-buffered moderate to high impedance source. If you need
to sample both the Accel and the battery constantly (and simultaneously) you
can just filter the crosstalk out of the battery readings. In that case the
formula you will need to use is:
VsenseBatt - n * (Zaccel) = VsenseBatt_correct
You are measuring VSenseBatt and Zaccel so you'll know those values. You
will need to calculate 'n', but as this value will not change (as the layout
of the wires is fixed) you will only need to do so once (for each shimmer
rev and each channel combination). So to do this you will need to measure
VSenseBatt when the Accel ADC lines are driven low in GIO mode, and then
again when the Accel is actively sampling.
I apologise for any inconvenience caused.
Best regards,
JC
From: Jose F. Mingorance-Puga [mailto:***@yourehab.com]
Sent: 18 March 2013 10:29
To: Jong Chern Lim
Cc: shimmer-***@eecs.harvard.edu
Subject: Re: [Shimmer-users] Monitoring battery levels
Dear Jong,
Thank you for the information.
I do believe there is a big cross talk between the accelerometer (probably
for axis Z) and the battery readings. Did you ever experience this issue?
How to address it? I was trying to subtract a scaled value of the axis Z to
the battery readings but seems to not to work, i.e. cannot model this cross
talk as linear. Any ideas on it?
Sincerely,
Jose F. Mingorance-Puga
On 27/02/2013 9:03, Jong Chern Lim wrote:
Hi Jose,
You will first need to convert the RAW ADC values. You can use the following
formula to do so
calibratedData=(uncalibratedData-offset)*(((vRefP*1000)/gain)/4095);
where offset = 0, vRefP=3, gain = 1;
VSenseBatt = calibratedData *2; % as the voltage is divided, multiply it by
two
Finally in order to estimate the battery capacity, you can use the following
table, which we've derived from the battery datasheet :-
Remaining Capacity
Voltage
0.0%
3.2
5.9%
3.627
9.8%
3.645
13.8%
3.663
17.7%
3.681
21.6%
3.699
25.6%
3.717
29.5%
3.7314
33.4%
3.735
37.4%
3.7386
41.3%
3.7566
45.2%
3.771
49.2%
3.789
53.1%
3.8034
57.0%
3.8106
61.0%
3.8394
64.9%
3.861
68.9%
3.8826
72.8%
3.9078
76.7%
3.933
80.7%
3.969
84.6%
4.0086
88.5%
4.041
92.5%
4.0734
96.4%
4.113
100.0%
4.167
I hope that helps, please do not hesitate to contact me if you have any
further queries.
Best regards,
JC
-----Original Message-----
From: shimmer-users-***@eecs.harvard.edu
[mailto:shimmer-users-***@eecs.harvard.edu] On Behalf Of Jose F.
Mingorance-Puga
Sent: 26 February 2013 09:57
To: shimmer-***@eecs.harvard.edu
Subject: [Shimmer-users] Monitoring battery levels
Hello,
I am trying to roughly monitor the battery levels of the shimmers,
shimmer2r.
I am reading the values of the analog channel 7 (AnEx7).
A part from the crosstalk and other interferences that might be in, what
are the common ranges of values expected after the AD converter?
I am getting something between 2400 and 2700 out of the AD.
What range should be considered as low charge, high charge?
Sincerely,
Jose F. Mingorance-Puga
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