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:[email protected]] Sent: 18 March 2013 10:29 To: Jong Chern Lim Cc: [email protected] 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: [email protected] [mailto:[email protected]] On Behalf Of Jose F. Mingorance-Puga Sent: 26 February 2013 09:57 To: [email protected] 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 _______________________________________________ Shimmer-users mailing list [email protected] https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users
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