Sorry - I can help point you in the right direction, but I'm not going to gut my own devices by designing another for you. That'd be kinda silly.

I thought I was giving you some pretty clear pointers, actually...

In order to see enough delta for reasonable self-calibration, I needed to amplify the signal more than thirty-fold. At that kinda SNR, you're going to need something to take the edges off.

Also, what are you looking at for a sample-rate?


As far as asking for my comments: I offered some. The 555 drifts significantly. You pushed that aside "oh, it's working fine for me" but you don't have any measurable data to confirm that. The actual drift is about 1% with another +-1% for the supply. If you figure another few percent for the voltage regulator, you're going to have calibration issues.


Skin resistance varies from person to person. In my tests, I've seen my own vary throughout the night from 1.3MOhm to 105kOhm. The range I've seen on my test subjects is from 52kOhm to 3.3MOhm.