[Shimmer-users] [Shimmer GSR sensor reading] Which set of linear coefficient to use (or which way to Rome?)

Niamh O'Mahony

2013-05-03 15:10:37 UTC

Hi Ha,

You should use the linear conversion from the documentation to convert ADC
values to skin conductance. This linear conversion replaces the previous
polynomial conversion from ADC to resistance (remember to calculate the
inverse of the conductance if resistance is what you are interested in
measuring) and provides a more accurate conversion.

The code for the new linear conversion will be released to the github
repository in the coming weeks.

Best regards,

Niamh

From: shimmer-users-***@eecs.harvard.edu
[mailto:shimmer-users-***@eecs.harvard.edu] On Behalf Of Dang Thi Hai Ha
Sent: 03 May 2013 15:45
To: shimmer-***@eecs.harvard.edu
Subject: [Shimmer-users] [Shimmer GSR sensor reading] Which set of linear
coefficient to use (or which way to Rome?)

Hi all,

I'm using a Shimmer2r GSR Sensor to monitor user's Skin Resistance. I
installed the tinyos apps example SimpleGSR (from here
http://tinyos.cvs.sourceforge.net/viewvc/tinyos/tinyos-2.x-contrib/shimmer/a
pps/SimpleGSR/).

The confusion appears when I read the instruction in the Shimmer's
documentation about how to calculate GSR from ADC value:

- In the documentation, it says that the GSR can be calculated by using a
linear function with TWO coefficients, also given in the documentation.

- Whereas, in the file
/opt/tinyos-2.1.1/tos/platforms/shimmer/chips/gsr/GsrP.c which is used by
the SimpleGSR app, I found that the GSR value is calculated by using a
linear function with FIVE coefficients. Moreover, these FIVE coefficients
seem to have nothing in common with the other TWO coefficients given in the
Shimmer's documentation.

So, my question is: which set of coefficients should I use to calculate the
GSR value?

Thank you very much for your reply.

Have a nice weekend to all !!! :-D

Cheers,

Ha.