Hi, Im trying to monitor plant resistance with as little invasion as possible.
This is normally done with a bridge setup
My present idea is to place two graphite electrodes through opposite sides of a plant pot prior to installing the plant. Ive found that graphite art pencils have low resistance. Metals arent too good here, unless you can afford platinum. These electrodes would be given a bandage of cotton cloth on the inside of the pot, and inside the bandage would be a little slow release fertiliser, the polystyrene bead type.
The plant would be planted, and, hopefully, the root hairs would be attracted to the diffusing fertiliser and surround the electrodes. If one sets up an arduino as a data logger, one would expect over a period of days to weeks that the resistance would decrease to a stable value, providing of course that watering was strictly controlled with deionised water. I would guess that a very small current flow would be least invasive, and probably an AC bridge would be better to cut down on ionic effects. It might be best to have a four electrode setup, with the second set of electrodes not having attraction for the roots.
Does anyone have any ideas about this, or experience in this field??
I’ve tried something similar in a garden, using casting plaster encased bolts; the plaster adopts the surrounding soil humidity and averages nicely. The Arduino has to be electrically isolated from the soil, and the pins are normally held to one state to minimise current. During sampling the pins are held at different states for the same amount of time, to average the current to zero. The idea came from a vineyard, and my addition was the wireless data link.
At the moment I’m using a capacitive sensor instead; Chirp! which has a digital interface. Being a capacitive measurement, you don’t get corrosion and don’t care about the ionic state of the soil.
Thankyou, that helps. Im investigating possible plant/human interactions
(see book “the Secret life of Plants”) and also the crackpot world of
psionics – Im a scientist, and psionic machines cant possibly work.
However, Ive built a couple and they work, on others as well as myself. I
guess they just dont know that they cant work! I will look into the
capacitive sensor.
Thanks. Yes, sometimes crackpot ideas have some parts that can be re-used in science.
My guess with plants, unverified, is that they can participate at some level; because of (a) our neuroplasticity and unconscious neural function, and (b) rhizomes with their fungal and bacterial populations that link plants in a mesh sufficient for resource sharing. No idea how the mechanisms would interact, but it is a field worth studying if only to falsify.
If you get time, do share what you build. 
OK, on the crackpot project, here goes. About fifty years ago, as an
undergraduate, I came across the Heironymus patent for an ore analysis
machine, and the work done by John Campbell, editor of (now) analog
science fact and science fiction magazine…He built the machine according
to the patent information, and he published his work in the magazine.
The device couldnt work according to known science, it did. He or rather
his children found that it worked fine if the valve rf amplifier that
Campbell used wasnt plugged into power. But it wouldnt work if one of the
vacuum tubes was removed. With more work he found that the machine would
work if a drawing of the circuit were substituted for the circuit itself.
That was impossible, but there was no reason to doubt Campbell: he was then
the leading SF editor in the world, his reputation was good…
So later when I had my own lab and some time I built a crude symbolic
machine and tested it on myself, and various members of the community. It
didnt work for the grad students…It worked for the gardeners, the
engineering shop people, and it worked for the cleaners.
Much later, four or five years ago, I designed my own machine, it has
two large coils wound on 6" plastic borepipe (I live in outback Western
Australia) I set up things with two tuners, one potentiometer bank and
one capacitor bank, and I set things up so that I had a small patchboard of
banana plugs, that way I could set up coils, tuners, amplifiers, and
detectors in different ways. My coils have a secondary winding, not
normally used.
I designed as simple as possible twin amplifiers, these were AC coupled,
and they have useful response down to 10 hertz, they were from memory about
150mhz small signal transistors. Each stage of each amplifier had the
bias adjustment by a 10 turn trimpot, so that the the amplifiers could be
matched. Their output went in one case through a second transistor then to
a phase circuit, so that one signal could be reversed with respect to the
other. I found that the machine only worked with the phase switch in one
direction. The summed outputs went to a further amplifier stage, then to
the detector, which as in the case of the original heironymus machine was a
planar coil of insulated wire between two perspex plates, and was a
stiction detector. The amplifiers were built on perspex of about 4 mm
thickness, using circuit board pins epoxied in place. This gave a very
high resistance between parts and avoided any unknown effects from printed
circuit boards. There is an input for plant resistance… It may be the
most advanced research instrument of its kind.
Now the machine should not have worked. It did work. A particular
sample put in one of the big coils gave a particular reading, either with
the stiction plate or a bit more accurately with a dowsing pendulum over
the stiction plate, which leads to less operator fatigue
. The sample involved gave the same reading, for other people, and in my
own case gave reproducible results from day to day, to about ten percent on
each of the tuning dials. I had four tuning dials on the resistance
tuner, but have found that only the first three give reproducible readings,
the fourth one doesnt seem to give a consistent reading once the first
three are tuned. So its ignored. Most people seem to use three stage
tuners, some use a lot more.
Since then Ive done a great deal of reading, most of it is pure
stupidity and wishful thinking, but there are serious experimenters…
At present I am slowly setting up an experiment with two stevia plants,
one is pretty poorly and will be the subject, the other the control, a
healthier plant. Im making a very simple machine, three pots for the
tuner, a one transistor amplifier, AC coupled. There will be a sample
coil, which Ive built into a large plastic jar for waterproofing in the
garden: it is about 50mm and has a double winding, I guess fifty or sixty
turns, double wound, 1mm encu. That way I can double the inductance or I
can cancel it out – Im like an alchemist, just doing what appears to
work, not really understanding it. That coil has within it three
tablespoons of dry slow release fertiliser. It will be connected to the
amplfier, which I will power with a single cell, and set up for about 50
microamps current or so, thus the cell should work a very long time. The
current will be monitored through a banana jack series connection to the
battery, so that current can be set up, then the meter removed… Now
the circuit output will go to a second coil, which is a degaussing coil
from a ginormous analogue TV. That coil will go around the plant and the
fertiliser coil will be tuned to it, and I will see what if anything
happens. No actual current will flow through the degaussing coil…These
machines work nicely with blocking capacitors and no oscillation in the
circuit. I use a 50mhz digital scope.
Another experiment slowly under way is a psionic amplifier if thats
possible. I have a large quartz crystal, mostly transparent, maybe 200
mm long, double terminated quite thick probably 70mm. This is the kind of
crystal that people call powerful, it gives a definite sensation to some
people who touch or come near it. Ive put two windings on that crystal, a
fifty turn winding closewound, 1mm encu, and a second winding of ten turns
separated by masking tape, and the whole assembly wrapped in duct tape.
These crystals are “cleansed” by leaving them out in sunlight or
moonlight. Ive heard that one experimenter had a similar but smaller wound
crystal and that it seemed to lose efficiency over time. He irradiated it
with UV from I think a 360 nanometer LED, and it again worked ok. I have
some 400 nanometer diodes on order, and will bind these with tape on the
fairly clear termination areas of the crystal, as yet not protected from
light. The idea is that just possibly, passing current from an amplifier
connected to a psionic machine may cause the crystal to store
?something? If that storage is done through the ten turn winding, what
effect would attaching either the ten turn or the fifty turn to a machine
have? Only one way to find out. One has to proceed carefully, it looks
as though psionic machines may be able to kill people, they apparently can
kill caterpillars at an impossible hundred mile plus range, and they can
anecdotally remove life threatening warts from a little girl (Read G. Harry
Stine’s book, its freely downloadable from the Net) Stine was a
scientist, he was so frightened by the results of his machine that
apparently destroyed it, although the circuit and description are in his
book. The worker Heironymus apparently also destroyed his work for the
same reason. He was building mostly machines for health but apparently
died when he was only ninety odd.
I have read that the psionic machines can use skin resistance
measurements as detection. If this is so, then it opens a supermarket full
of tins of worms: if psionic machines can work even as circuit diagrams
(and Ive been there and done that) then it looks as though in some way
patterns on paper can affect the physiology of human beings. If that is
so, then maybe there is more than superstition in the old idea of amulets
and magical drawings forming such amulets…If advertising patterns can
affect your health what then???..
Ive bought some velcro tape this week , and I have 2" wide copper tape
with adhesive backing, and I can make a simple skin resistance setup using
those components for the sensors. I have heard of a psionic machine which
did use skin resistance detection
I think a lot of caution is needed. I can remember the problems the
Curies had, and I can remember as a little boy looking at the bones of my
feet in the x ray machines that shoe shops had in those days…
Good luck with your experiments!