biologic sensing/systems research

Several designs were tested based on:

• Voltage divider
  

  The simplest voltage divider circuit as detailed at:

  http://www.schematicsforfree.com/archive/file/Computer/Circuits_using_a_PC/BIOFEEDBACK_MONITOR_PC_BASED.PDF

  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).

Plotted using gnuplot:

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

Also live plots using:

a=0
load "looper"

Entry into minicom and logging to file:

       a=a+1
       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

http://regexp.bjoern.org/archives/000187.html

http://www.sciencetoymaker.org/lieDetec/make.htm

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

http://instruct1.cit.cornell.edu/courses/ece5030/labs/f2009/Plethysmograph.html

http://www.picotech.com/experiments/calculating_heart_rate/

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"

[p107]

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.

[p110]

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

• Elektrometer
  

  Design following Elektor Mai 1977:

  

• Resistance
  

  Measured with a Wheatstone bridge (combined with transistor, and op amp) based on the following design from Peter Lay: Experimente mit paranormalen Phänomenen):

  

  Followed by LM358 inverting op-amp [two 1K resistors into + / - in and 1M poti for feedback/gain]

  See also Psychotron [Elektor, Juli/Aug. 1983]:

  

  

• Impedance
  

  "Impedanzänderungsdetektor", Elektor, Mai 1977, S. 28-30

  Reproduced here: http://www.r-j.de/literatur/elektor.pdf

  Could be constructed using Analog Devices AD5934 or 5933:

  http://www.analog.com/en/rfif-components/direct-digital-synthesis-dds/ad5934/products/product.html

  see also:

  http://instruct1.cit.cornell.edu/courses/eceprojectsland/STUDENTPROJ/2005to2006/yz226/

  • AD5933 Impedance measurement (first tests and design):
    

    

    To be used within plant sensing, soil analysis and bioimpedance measurements.

    • Schematic:

    

    • Board:

    

    • Kicad files:

    http://1010.co.uk/ad5933.zip

    • Arduino C source code:

    http://1010.co.uk/5933.pde

    (based heavily on http://www.mwlyon.com/design_services_pages/arduino.html )

    • Results:

    

    Foil skin electrodes (as used with GSR above) at 10 KHz.