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'Help Researching Galvanic Skin Response Circuit D'
1999\06\28@202750 by R. Michael O'Bannon

picon face
>GSR as an absolute measurement IS a difficult measurement... not looking
>for absolute ...
>rather looking for CHANGE in gsr, specifically the change in conductivity
>caused by sweating
>I agree about applying dc currents to body, I didn't suggest in any manner
>that this was the method to make this measurement (although this is the
>classic gsr measurement technique)


Robert,

I've been thinking about your problem for awhile and perhaps I have a useful
idea.  You want to detect sweating, not GSR, and this may be an easier than
it seems.  (I am assuming here that there is actually moisture on the skin
when these symptoms occur.)

Here is a basic design idea:  A small, thin piece of absorbant tissue is be
placed on the surface of the skin, then covered with two contacts etched on
a very small piece of circuit board.  These two layers are securely held
against the body with a bandage or adhesive tape.

If a small direct current is run through the two contacts, there will be
almost no current flow if the tissue is dry.  Sweat would be absorbed into
the tissue and conductivity should increase sharply.  This assumes that
there is enough moisture on the skin to saturate the tissue.  I would guess
it could be made quite sensitive if you place the electrode spacing is close
and the tissue thin.  The circuitry use could be the type used for rain
detectors.  This has been discussed recently on the list.

Perhaps other on the list can clean this idea up a bit.

Best regards,
Michael

R. Michael O'Bannon, Ph.D.
Clinical and Corporate Psychologist
Atlanta, GA

1999\06\28@212019 by tim

flavicon
face
if gsr....... can be described as a moisture change.......sweating     .....
why not try a humidity sensor ?
taped on  as a patch ?          put in different places?
make one as an automatic reference for ambient moisture....auto zeroing the
unit?use a bridge scheme where the resistance  varies and upsets the balance
of things.................now in an controlled setting you could put the two
different sensors in one package for testing purposes........there should be
some relationship or trip point............between the two...........
still thinking and long road ahead...................tim

{Original Message removed}

1999\06\29@065245 by Mark Willis

flavicon
face
R. Michael O'Bannon wrote:
> <snipped>
> Here is a basic design idea:  A small, thin piece of absorbant tissue
> <snipped>
> and the tissue thin.  The circuitry use could be the type used for rain
> detectors.  This has been discussed recently on the list.
>
> Perhaps other on the list can clean this idea up a bit.
>
> Best regards,
> Michael
>
> R. Michael O'Bannon, Ph.D.
> Clinical and Corporate Psychologist
> Atlanta, GA

 I was thinking along the lines of turning an RF transmitter ON when
you detect that there's conductivity between those electrodes, perhaps
instead of a tethered Lead-Acid battery a 9V Ni-Cad on the person in
question would be a good power supply, running the Pic.  Then when you
detect a wheatstone bridge type conductivity change due to sweat, fire
the transmitter.

 Could almost couple a weak AC signal into a "Solar Racer" type
circuit, and when conductivity skyrockets, you know you have lots of
sweat, but ideal rectifiers are not easy to find <G>

 How's THIS for a Totally LOW tech method:  The "Clothespin switch"
method:  If you have a small salt crystal that's held against the paper
that's against the skin, and the salt crystal is holding a microswitch
OPEN, and could basically guarantee that it'd wick up sweat & dissolve
it & close the switch "on cue", you could just use a "Sonalert" and a 9V
battery & a switch.  Might have to run the paper along one or both jaws
of the switch assembly, to make the sweat travel to the crystal properly
- This'd be nice & portable & completely tetherless, and reasonably
cheap, just some labor to make salt crystals.  (Use Rock salt for the
hold-open?  Or a saccharine or "Equal" tabler, or rock candy crystal, or
some other substance that's easy to clean up & doesn't make TOO much of
a mess?)  Clothespin switch with metal on both faces might even just
conduct enough to run the PIC when the salt gets wet enough <G>  I was
thinking of having a sealed microswitch, though, and have the
microswitch allowed to close when the jaws close past a certain point.

 (If your circuit could be small enough, could even *glue* it in place
on an appropriate site - using a Lithium "Pin" type battery or two for
power, perhaps? - and charge a supercap up to speed before inserting the
Pin batteries.  Make the unit look like "Borg jewelry" <G>  Yeah, I'm
modeming WAY too late tonight! <G>)

 Mark

1999\06\30@050632 by Robert K. Johnson

flavicon
face
       The obvious flaw in your hypothesis is that the current flowing through
the 'tissue'
will also flow through the skin as well. Once the tissue becomes conductive
it is a resistance in parallel with the skin it is in contact with... <G>

                       R.K.J.


At 08:32 PM 6/28/99 -0400, you wrote:
{Quote hidden}

1999\06\30@052108 by Robert K. Johnson

flavicon
face
       Hmm... this might work assuming that room humidity affects don't mask th
e
sensor changes... Humidity sensors are not trivial or cheap...  and there
is the challenge of long term exposure to the adhesives used in the tape.
Also it would be an even bet as to how long the subject would be willing to
'tape' himself up every night.

       Now that I have said the obviously nasty stuff <BG> Yours is an
interesting approach
in that you postulate a direct approach to the problem at hand. Clearly you
spent some time
thinking about how to solve the problem. From a technical standpoint yours
was a fresh and valid solution.


               Robert K. Johnson
               spam_OUTrkj1TakeThisOuTspamix.netcom.com

At 09:21 PM 6/28/99 -0700, you wrote:
>if gsr....... can be described as a moisture change.......sweating     .....
>why not try a humidity sensor ?
> taped on  as a patch ?          put in different places?
>make one as an automatic reference for ambient moisture....auto zeroing the
>unit?use a bridge scheme where the resistance  varies and upsets the balance
>of things.................now in an controlled setting you could put the two
>different sensors in one package for testing purposes........there should be
>some relationship or trip point............between the two...........
>still thinking and long road ahead...................tim
>
>{Original Message removed}

1999\06\30@123449 by Sean Breheny

face picon face
At 01:27 AM 6/30/99 -0700, you wrote:
>        The obvious flaw in your hypothesis is that the current flowing
through
>the 'tissue'
>will also flow through the skin as well. Once the tissue becomes conductive
>it is a resistance in parallel with the skin it is in contact with... <G>
>
>                        R.K.J.
>
>

Well, I think what he was saying is that no current would flow thru the
skin UNTIL the tissue became damp,at which point the alarm would go off
anyway,and we could turn off the current and keep the alarm going until
someone arrived to help the person. This way,there would only be a fraction
of a second exposure to the current, and ONLY when the problem actually
occured.

Sean

|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
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1999\06\30@154829 by Robert K. Johnson

flavicon
face
At 12:32 PM 6/30/99 -0400, you wrote:
>At 01:27 AM 6/30/99 -0700, you wrote:
       Yes that would be the obvious methodology... However that wasn't a part
of
the message.
On further inspection there is 'one' more flaw, The 'tissue' membrane would
require routine maintenance as it WILL collect undesirable elements fron
the skin of the subject... skin oils and skin particles as well as
perspiration residues.

       The point here is that the tissue paper solution was offered as a means
of
avoiding current flow through the  skin of the subject. There are several
methods of solving this problem that minimize or eliminate the current flow
issue.
This part of this thread somehow misses the origional concept, That is that
a current of 5 to 10 µa (being 1 to 5% of the threshold of detection) is
reasonably non intrusive and
not likely to be any kind of health or other physiological issue... IMHO or
as I read this response perhaps not so humble
opinion <BG>

                       Robert K. Johnson
                       rkj1spamKILLspamix.netcom.com

{Quote hidden}


'Help Researching Galvanic Skin Response Circuit D'
1999\07\01@180042 by R. Michael O'Bannon
picon face
>         The obvious flaw in your hypothesis is that the current flowing
through
> the 'tissue'
> will also flow through the skin as well. Once the tissue becomes
conductive
> it is a resistance in parallel with the skin it is in contact with... <G>

There is an obvious flaw in your understanding of the design ;-)

The current does not flow through the skin because the dry tissue insulates
the electrodes from the skin.  The tissue is against the skin and the
electrodes are *on top* of the tissue.  They do not touch the skin.  The
electrodes are measuring the resistance of the tissue only.  The dry
resistance of the tissue will be very high.  The wet resistance of the
tissue, particularly when wet with sweat, will be much, much lower.  The
purpose of the tissue is twofold:  (1) it enhances the difference in
resistance between wet and dry state, and (2) it alleviates the necessity
for current flowing continuously through the skin.

Best regards,
Michael

R. Michael O'Bannon, Ph.D.
Clinical and Corporate Psychologist
Atlanta, GA  30324

1999\07\01@185237 by paulb

flavicon
face
Sean Breheny wrote:

> Well, I think what he was saying is that no current would flow thru
> the skin UNTIL the tissue became damp, at which point the alarm would
> go off anyway,and we could turn off the current and keep the alarm
> going until someone arrived to help the person.

 An interesting point of the "old" relay logic - the "locking" contact
in parallel with the sensor does in general remove the voltage from the
sensor.  Remember the "sequence" doorbells, mains operated with the
light wired across the push?  On simple doorbells, the light goes out
when the button is pressed, but on those, the light went out until the
sequence was finished.

 This is in general *not* the case with an R-S logic latch, but can
most certainly be arranged to be so.

> This way,there would only be a fraction of a second exposure to the
> current, and ONLY when the problem actually occured.

 I can't see that the current is a problem overall.  I *do* assume that
the electrodes are isolated by (polyester, not electrolytic) capacitors
and the monitoring voltage of a couple of volts is constrained to
intermittent pulses at a very low duty cycle.

 Contrary to a previous proposition, ions do *not* take significant
time to accelerate; the conductivity is evident in microsecond pulses.
The principal reason not to use too high a measurement frequency is that
you will spuriously detect the capacitive reactance of your electrodes
and for that matter, body membranes.
--
 Cheers,
       Paul B.

1999\07\05@143134 by Robert K. Johnson

flavicon
face
At 06:05 PM 7/1/99 -0400, you wrote:
>>         The obvious flaw in your hypothesis is that the current flowing
>through
>> the 'tissue'
>> will also flow through the skin as well. Once the tissue becomes
>conductive
>> it is a resistance in parallel with the skin it is in contact with... <G>
This assumption is based on the tissue absorbing moisture from the skin...
not removing moisture from the skin. If the skin is moist enough to supply
moisture to the tissue then BOTH  the skin and the tissue contain moisture
therefore they are two parallel resistors.
As you postulate NO method to keep the skin dry for example a type of
semipermiable membrane. By the postulated defination both the skin and the
tissue are (of necessity I believe for measurement accuracy) at the same
level of moisture content...
Perhaps this will clarify my "understanding of the design" <BG>

{Quote hidden}

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