biologic sensing/systems research

Table of Contents



Galvanic Skin Response (also for plant sensing):


Several designs were tested based on:

  • Voltage divider

    The simplest voltage divider circuit as detailed at:


    was also tested and gave poorer results when compared to more complex Wheatstone bridge style detailed below.

  • Wheatstone bridge


    A design using OPA336 and following http://courses.cit.cornell.edu/ee476/FinalProjects/s2006/hmm32_pjw32/index.html was constructed. At first it appeared to give good results but when tested after six months the results were very flat. This could have been due to oxidation of copper tape electrodes and the design should be retested


    In the meantime, a new design based on: http://web.media.mit.edu/~msung/VitaMon/vitamonschematics.htm but using an op07 op-amp was tested with silver foil electrodes (below). After minor adjustment of the offset potentiometer, the GSR seems to work well, responding to changes in breathing, relaxation and excitement. The signal from this GSR is fed to the input of Arduino/ATmega8 ADC - we record 20 samples 1 ms apart and average these.

    Question: why is the offset adjustment always necessary? Without adjustment the GSR plot/values remain very flat

    Further notes (8.3.2011): adjustment seems at first sight to be necessary because of changes in placement of electrodes and perhaps changes in environmental/skin conditions. A short series of tests was made with the clothespeg electrodes (below) which did not need any adjustment between cold starts of apparatus seperated by say 10 minutes. Values around 500-600 were displayed with sharp variations visible a few seconds after deep in-breath. Offset resistance measured as 6K to +5v connection. Later tests (say half an hour) needed more adjustment (as did the velcro), and even then results were not so clear? The clothes-peg arrangement with this circuit seems the most solid (to test with different op-amps, think on new electrode possibilities).



Constructed with copper tape, velcro and aluminium cooking foil after: http://extremenxt.com/gsr.htm



Copper tape with conductive adhesive is stuck to folded strips of tinfoil. Wire is soldered and taped to the copper tape backing of these new foil strips. These are then stuck on the adhesive side of the velcro as shown above. The electrodes are placed on the tips of the 1st and 2nd fingers.

Tests were also made with two paper clips on the ends of fingers (painful) and clothes-pegs with foil (too tight but working well).

Some results


Plotted using gnuplot:

set term png
set output "midnight.png"
plot "/root/projects/biologic/skin/gsr_files/midnight2" with lines

Also live plots using:

load "looper"

Entry into minicom and logging to file:

       plot [0:][400:600]"/root/test2" with lines
#       plot "/root/test2" with lines
       pause 0.1
       if(a<50000) reread


See below under plant sensing…


Lie detector from Elektor (date?):



Links and overview: http://www.chris3000.com/archive/galvanic-skin-response/

Simple lie detector: http://www.hackcanada.com/ice3/wetware/lie_detector_circuit_2.html



Forensic psychophysiology using the polygraph: scientific truth verification, lie detection. James Allan Matté



Measuring changes in blood volume within the finger/on the earlobe (the beating of the heart). The clothes-pegged infrared LED/phototransistor (SFH487-2 and SFH309 (FA would make more sense) from reichelt) duo was implemented following the links below. Note that the anode (to 100 Ohm resistor and thence to +5v) of the SFH487-2 infrared emitter/photodiode is the shorter of the two leads. The filter/amplifier circuit was constructed following the first of the links below, but leaving aside the diode offset. A short arduino software reads values from the amplifier every 10 mS, and prints these to serial port, allowing for easy plotting with gnuplot scripts (see above).




Plant sensing

With reference also to: http://lib.fo.am/plant_sensing

Electricity in plants

Scott, Bruce I. H., "Electricity in Plants", Scientific American, Oct. 1962, S. 107-115

at: http://www.r-j.de/literatur/electricity.pdf

"Electrical disturbances similar to the nerve impulse are associated with a number of plant life processes. It seems likely that these currents and fields somehow influence plant growth and development"


The root of a bean shoot growing a weakly conductive medium, for example, is found to act as an electric generator sending tiny current into the medium and back through the root […]

The instrumentation must be highly sensitive, because only about a hunderdth of a microampere flows across a square millimeter of root surface […]

Without any stimulation the potential near the root starts to oscillate in a rhythmic fashion, the oscillations continuing for perhaps several hours […] The periods of oscillation for the roots we have studied are about five minutes.


Note also: solutions of potassium chloride or sodium chloride

Karlsson, L., "Instrumentation for Measuring Biolectrical Signals in Plants", The Review of Scientific Instruments, Vol. 43, Nr. 3, March 1972, S. 458-463

at: http://www.r-j.de/literatur/karlsson1.pdf

Remote Biodynamic Sensing and the "Biogram" by Michael Theroux

at: http://www.borderlands.com/newstuff/research/rbs.htm

Detecting Biodynamic Signals by Michael Theroux

[referring to the work of L. George Lawrence inc. schematics]

at: http://www.borderlands.com/archives/arch/detectin.htm

L.George Lawrence: More Experiments in Electroculture

at: http://www.swtpc.com/mholley/PopularElectronics/Jun1971/PE_Jun1971.htm

Further general links

Author: root <m@1010.co.uk>

Date: 2013-03-28 15:56:32 GMT

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