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measuring relative light level with a CdS cell, logarithmic calculation?

I

ITSME.ULTIMATE

Ok, I put together a simple sensor circuit consisting of a resistive
divider and a CdS. Since CdS have a negative resistance characteristic
with input and I want positive output with input, I put the resistive
divider between the ground and sensor so that output increase with
light.


http://img518.imageshack.us/my.php?image=cdscalculation9bq.png
This is what my circuit looks like and I measured the Vo four times a
minute for a few hours and I have the data in form of voltage as a
function of time.

The chart is a CdS light input vs resistance chart. I'm not sure what
kind of CdS cell it is from, but it is logarithmic. Assuming my CdS
follows a similar characteristic, how should I process my output voltage
so I can get a graph of relative light input that is roughly linear to
level of light?
 
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