Measuring Skin Response

[Johnny101]

Hi everyone!

I am trying to measure the skin conductance, for that I found this circuit online.
[url]http://obrazki.elektroda.pl/1838370700_1446817605.png[/url]
So from it what I have understood so far:

- There is a low pass active filter at first stage with cut off of 1.6 Hz and variable gain.
- The second stage is also a filter with unity gain and is biased at half the voltage supply and the first stage is biased at the output of second.

What I don't understand:

- Why is the gain variable at first stage as the Rskin chages the gain would change?
- Isn't the first stage enough?
- Can't understand the biasing of the op-amps as well.

[pebe]

It's difficult to understand the operation of the circuit without knowing what the symbols Vco, Vo, Vd and Vcc refer to in this context. Does the 'obrazki' site give any more information?

[bwetman]

Hi,
It's very difficult to understand, if any one know please tell me.