[last updated: 2025-08-22]
Disclaimers
bioAmp EXG pill
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On This Page:
- Introduction
- Circuit configuration options
- Finger probes
- ...
- Links
- Introduction:
GSR is the resistance of your skin. The actual value of the resistance varies from several megOhms for dry skin, to ??? a few hundreds of kOhms for damp, sweaty skin.
The sweat that affects your skin resistance is much more subtle than what we think of as perspiration or "sweating." It happens almost instantaneously as your mental state changes, and is mostly affected by your stress level.
As such, its two most common usages are
- in biofeedback, to help a person relax,
- and as a lie detector.
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- Circuit configurations:
- Several different circuit configurations/approaches are suggested in different places on the web. Broadly, ...
- Connect GSR resistance probe in series with a fixed resistor to create a voltage divider between +V and gnd,
and then process (amplify and filter) the resulting varying analog voltage in some circuit.
- directly into arduino analog input (after op-amp voltage follower to give the arduino the low input impedance it requires)
- various op amp filter and amplifier circuits...
- Key point:
Some sites used straight analog signal (perhaps amplified and filtered)
while others used the differential, only responding to changes in the signal.
- Use the GSR resistance directly in some circuit, eg. the transistor oscillator (if I can find the link...)
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- Finger probes:
- from instructables link below...
- briefly, a strip of velcro, 3/4" x 4"? long
remove backing to expose the sticky side
strip a lead wire and splay the bare wires and stick them to the sticky side of the velcro
cover all of the sticky side of the velcro including the wire with tin foil, trim to fit.
cut 1/2" x 1/2" piece of velcro "latch" strip and put onto the tin foil side of your strip
instructions said to put it on the opposite end of the strip from the electrodes,
but it made more sense to me to put it on the same end.
done
- Built as such, on index and middle fingers, mine read nom. 400-900k.
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- Differential Input op-amp circuit:
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eof