Re: electrical problems with Galvanic Skin Response circuit ( GSR SCL )

Hi Stefan


> Looking at your scope screenshot, I can see that the period matches your
> mains (assuming that the timebase is indeed what you specify), but it
> doesn't look like simple hum.  You don't run a phase-controlled dimmer in
> close proximity?  Any other electric machine?

You were right, the problem was a massage chair with a heating in the 
seat, that stood beside me. It wasn't powered on, but the 12V power 
supply seems to be connected with the seat.
Now there is only a little noise, which i will try to filter next week 
with your suggestion.

Only one problem is left. The amplification of the AD623 doesn't match 
my calculations. With a 900k resistor (this is equal to my skin 
resistance) and R25=25k --> Gain=5, i get an output voltage of 2,35V. 
(attachment measurement.png)
This is to less, with a gain of 101, it should be about 11V, 
respectively 5V, because this is the supply-voltage.

Besides i see no way to get an output voltage between 0,5 and 5V, if the 
Skin resistance is alternating between 700 and 800Kohm. I tried many 
values of R25 and R24, but always the change of the output value is little.

	
> Regarding your resistor value query; I only work with SMT components.  A
> resistor marked 1003 means 100_plus_3_zeros, i.e. 100 000 ohms.  Similarly
> you would have the following values:
> 2702 = 27K
> 222   = 2K2
> 101   = 100
> 100   =   10         ( ! )
> 1804 = 1M8

Thanks for the explanations.

Regard Steffen



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