i've been reading up on the 555 timer lately and it might do the trick (i think).

there are two things we could measure, and i don't know which would be the best way to go:

1- the difference in skin resistance to a "fixed" point ("fixed" meaning it can be calibrated) -> 555 timer -> serial port (i don't know much about the serial port, so i'll have to look this up a bit more)
2- the true value of skin resistance (which would directly control the 555 timer... in which case the calibration would be software based)

i think the software based calibration is the better idea (given that we're aiming for as few components as possible to begin with), but i don't know how reliable the hardware will be (given that, depending on the construction and placement of the probes the resistance will be different)

i'll do a bit more research on the 555 timer (i really thought the voltage -> frequency was a good idea, but this seems so much easier...) i know i'm going through ideas and approaches faster than i can actually build any of them, but i think this is promising.

i'll start by building a simple led flasher and i'll play with the capacitor values. the idea is to use my own skin resistance to flash the led (with a fixed 250 kOhm resistor, a 0.1 uF capacitor and a variable skin resistance between 10 kOhm and 500 kOhm, we get a range in frequency from 12 Hz to 65 Hz... a soundcard would not pick that up, most skrew up under 20 hz or so, but for serial port it should be ok... if we need more accuracy (which we probably will), we can boost that up in the kHz so that we get a bigger range...

for testing purposes, i'll try to keep it even lower than 12 Hz so that i can see the LED blink.



if this works, we'll have a very very simple device to build. i don't know if the 555 connects directly to the serial or if it needs some sort of converter (does anyone have a quick answer/schematic that may save up on searching?)

kimpossible, since you used 6 subjects so far, does the resistance level vary a lot across individuals, or is it somewhat similar? also, given your experience in electronics, if you have any comments on what i just said (am i completely off anywhere ?), it would be greately appreciated (actually any kind of help would be appreciated)