> i) how were the polynomial weights for the different range selection > resistors derived? measurement vs. precision resistors
> ii) what's the logic of needing the weights? During validation, mapping of data on the analog front end showed that restricting measurement to a proportional region would limit application or introduce additional complexity. The circuit has a really wide measurement range (nearly 4.5 decades). For example, more gain settings could have been used with each in the proportional region, but that choice would have introduced more gain-switching artifacts to application developers. A key simplification was to eliminate the need for a manual or automated "zero" of the tonic by increasing the measurement range. > ii) is there a need/way to calibrate each Shimmer GSR unit in order to > get absolute, rather than relative skin resistance values? I believe the units are absolute within the published specification-- the above weighting was performed against a precision resistor reference. You can calibrate specific units but it is somewhat tedious. For example, if you are only expecting a small range of measurement (say 5k-25k) you can probably calibrate for that range only and end up with a more accurate fit than the multi-decade weighting. While we are on the subject, the GSR board range can be used with other resistive transducers such as stretch or bend sensors. -Ben _______________________________________________ Shimmer-users mailing list [email protected] https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users
