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'[ot]: Ground moisture'
2000\12\15@152232 by Peter May

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Hi guys.
I am building a system to keep my worm patch moist (I fish when not playing
with electronics) and want to sense the ground moisture and feed that info
into a pic?

Any ideas?

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2000\12\15@215412 by Dan Michaels

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>Mad Max comes roaring out on a steam powered wooden motorcycle and thows
>nitro at them.
>Everyone at Thunderdome has a giant blow-out and throws another one on the
>barbie.


Poor poor Mad Max. Once he was fighting the Humungous and
wagging his tush at Edward Long[red?]-stockings. Now he's
reduced to eavesdropping into the minds of his girlfriends.
Ya git old, ya git slow, ya git dumb.

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2000\12\15@222426 by severson

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>
> Poor poor Mad Max. Once he was fighting the Humungous and
> wagging his tush at Edward Long[red?]-stockings. Now he's
> reduced to eavesdropping into the minds of his girlfriends.

That'd make him "mad"...


Given the co-star, he's now "Mad About You Max"




I'll stop now...

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2000\12\15@223659 by Dan Michaels

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>> Poor poor Mad Max. Once he was fighting the Humungous and
>> wagging his tush at Edward Long[red?]-stockings. Now he's
>> reduced to eavesdropping into the minds of his girlfriends.
>
>That'd make him "mad"...
>
>Given the co-star, he's now "Mad About You Max"
>
>I'll stop now...
>

..... you win.

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2000\12\15@224021 by David Lions

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Oh well he's still making about $9Million more per job than we do. :)

----- Original Message -----
From: "Dan Michaels" <spam_OUToricomTakeThisOuTspamUSWEST.NET>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Saturday, December 16, 2000 1:54 PM
Subject: Re: [ot]: Ground moisture


> >Mad Max comes roaring out on a steam powered wooden motorcycle and thows
> >nitro at them.
> >Everyone at Thunderdome has a giant blow-out and throws another one on
the
{Quote hidden}

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2000\12\15@232629 by Roman Black

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Brent Brown wrote:
>
> > Hi guys.
> > I am building a system to keep my worm patch moist (I fish when not playing
> > with electronics) and want to sense the ground moisture and feed that info
> > into a pic?
> >
> > Any ideas?
>
> There are sensors you can buy for this, basically just two metallic
> or carbon probes, you drive them with AC and have to measure the
> AC current they draw. However, I am guessing that worms will be
> somewhat sensitive to this so you'll have to keep the current
> extremely low and, only run it for brief periods, to stop the worms
> running away. Ah theres a thought - how about putting 24VAC on
> your probe when your ready to go fishing and the worms will jump
> up into your bucket!

What about weight of the soil?? You could almost do this
mechanically with the container mounted in balancing way with
just a simple microswitch to detect if it has become "too light"
and could trim moisture by adjusting the counterbalance.
I don't think worms would like electricity running through
their wet soil. Wet soil is a couple of times heavier than dry
soil. :o)
-Roman

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2000\12\16@022622 by Peter May

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This is not as dumb as it sounds. I work in Australia for CSIRO
(Commonwealth Scientific and Industrial Research Organisation) and we do
this in 1 TON blocks of soil with our own made balances etc. Problem is with
worms is they actually eat their own weight in food per day so 1 kilo
(couple of thousand worms) add around 1 kilo to the total weight per day
compounding....

{Original Message removed}

2000\12\16@172915 by Peter L. Peres

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I understand that the worms come out when they 'feel' negative ions and a
negative potential of a few kV above the ground. Try an ionizer with a
large flat insulated electrode. Carefully, because this could be
dangerous. To keep humidity constant drive a pipe into the ground and fill
with water once a day (0.75-1 meter pipe bottom end open). This is used to
improve antenna grounds sometimes ;-). No I am not into fishing.

Peter

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2000\12\18@101823 by Lawrence Lile

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When I've played with ground moisture sensors, I've found it very difficult
to get them to be stable over long periods.

First, wet dirt is a really good electrolyte solution.  If you test the
resistance of the dirt with a DC signal, your electrodes will begin to
corrode rapidly, changing their resistance to the soil constantly until it
becomes infinite. Stick your ohmmeter probes in a bucket of dirt and come
back in an hour, you'll have a different reading with virtually no change in
moisture.

So you must have an AC signal on your soil probes.  This could be a simple
as alternately driving them with a pair of ports, and periodically switching
one of these ports to an A/D input to measure resistance.

Another subtler problem exists, though.  Soil resistance changes whenever
any conductive elctrolyte is added.  Fertilizers are usually electrolytes,
and cause large shifts in soil resistance.  Soil is alive with worms and
bugs, which cause their own little disturbances.  Soil resistance is a VERY
unreliable indicator of soil moisture for this reason.

Several of the commercial soil moisture testers use different prinicples
besides soil resistance between metal probes.  Some of them use a wetted
gypsum block buried in the soil, which has a large contact area and less
tendency to corrode.  Thsi is used in soil resistance meters, for more
stability.

Others use a galvanic cell principle.  The cheap meters you buy in a
hardware store for $6US use this principle.  They have a little galvanometer
connected between two dissimilar metals, and use the soil as a battery
electrolyte.  These suffer from long term drift problems as the battery
wears down.

Another principle is that soil capacitance varies more predictably with soil
moisture than soil resistance.  Several patents on this principle are out
there (I didn't hear this was to be commercial so don't worry about the
patents) .  Probably a more solid principle to hang your hat on, if you want
to persue it.

--Lawrence Lile


{Original Message removed}

2000\12\18@104340 by Simon Nield

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whilst looking into TDRs a while back I came across a bunch of sites disussing their use to measure
soil moisture. the one that sticks in my mind used a (zig-zag iirc) track on a pcb as the test prod.
no idea how it compares to any other method.

some links:
http://www.google.com/search?q=moisture+tdr
http://www.soilmoisture.com/trase.htm

if you believe the second link then tdr for moisture measurement is 'cutting edge'... oh really? i
am sure their opinion is in no way biased.

if you do head off down this route then do let us know - a pic tdr could be really useful for a lot
of things (like that odd suggestion i came up with for the hospital alarm system)

regards,
Simon

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2000\12\20@162158 by Peter L. Peres

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Afaik reliable moisture measurement w/o dirty contacts etc requires
microwave absorbtion measurement technology. TDR is an option if you use a
bounced beam or a partially buried transmission line, but a crossed beam
or transmissive CW system is simpler, larger, and harder to sell <g> ?
2450MHz strikes me as a *very* appropriate frequency ... Of course this
has nothing at all to do with 'ladder' dipoles aka open folded
transmission line (which sometimes looks like a zigzag, or like a helical
antenna that was run flat by a car <g>), patents, or microwave ovens
choosing that particular frequency for operation after wise physicists
found out that 2450MHz is one of the fundamental resonant frequencies of
the OH- water ion, which occurs mainly in... water (liquid, and slightly
ionized, as in microwaveable food and beverages, and you average garden
soil). Of course they did this at least 40 years ago (I think more), but,
oh my, they did not patent it. I *will* eventually patent my name if this
goes on. Honest. You should too, imho. While you still can.

Peter

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2000\12\20@175425 by Chris Carr

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*** Good Idea but if my memory serves me correct, the idea was to keep the
soil at optimum worm happiness dampness. As worms probably consist mainly of
water, they may not be happy being nuked by 2450MHz.

So, we have eliminated passing an electric current (Good for bringing them
to the surface) and possibly microwave (If I am correct) How about low
frekwency
(sorry about dropping into the "any-spelling-goes-mode (including
Ex-Colonies (i.e. USA) spelling)" now acceptable at UK Skools)

Hey the weather forecast is "No Rain" for the next few days, but in the Vale
of York we can expect Fog, good job I drive a Land Rover 110, I need only
worry about HGV's, anything else I just demolish :-)

But I digress, could LF (i.e. <300kHz ) radiated into the soil offer a
solution. Unfortunately I have lost the URL's but from memory the frequency
and radiation pattern is fairly critical.

Sorry I cannot be more specific

Regards
Chris


Just a thought
{Quote hidden}

***
{Quote hidden}

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2000\12\21@011104 by uter van ooijen & floortje hanneman

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Maybe you can measure the moistureness in a pocket of air, using for
instance a hair-hygrometer (should not be too difficult to couple to a
rotary encoder)? I guess the moisture in the air will have some realtion to
the moisture in the ground, and if you just want to keep the ground moisture
optimal the relation does not need to be linear at all.
Wouter

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2000\12\21@120654 by Ryan Miller

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Another option is a Watermark sensor ( http://www.irrometer.com ). They
are fairly easy to interface to. The sensor changes resistance and
is all self contained, so there is no need to worry about frying
your worms.

Ryan

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2000\12\21@144440 by Chris Carr

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> Another option is a Watermark sensor ( http://www.irrometer.com ). They
> are fairly easy to interface to. The sensor changes resistance and
> is all self contained, so there is no need to worry about frying
> your worms.
>
Ah, now that's a thought, the dew detector recycled from a terminally ill
VCR.

Chris

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2000\12\21@175005 by Peter L. Peres

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>good idea, nuke them with microwaves

I was not suggesting worm wieners. Just a 2450MHz oscillator running 10-50
mW off a regulated PSU and a direct rectifying fieldstrength meter a few
inches away, perhaps with a 1N23 or such, with earth in between... one
could make this differential and have a dried earth probe between the
emitter and another reference detector. This looks like three teflon pipes
stuck about 2" from each other 5" into the ground, in a line. Or at least
I'd try it that way. With a sealed plastic bag or box of dried earth
between 2 of them. I think. ;-)

Peter

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2000\12\23@034817 by Chris Carr

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----- Original Message -----
From: "Chris Carr" <KILLspamnyedKILLspamspambtinternet.com>
To: "Chris Carr" <RemoveMEnyedTakeThisOuTspambtinternet.com>
Sent: Saturday, December 23, 2000 8:47 AM
Subject: Re: [OT]: Ground moisture


> I appologise if this has already been suggested in this thread but,
> why measure the actual moisure content of the soil. Presumably, as the
> purpose of the measurement exercise is to provide optimum conditions for
> worms, the soil is contained within a box and this box is covered, so why
> not measure the humidity of the air above the soil. It would seem
reasonable
> that there is some correlation between the dampness of the soil and the
air
> humidity above it.
>
> Regards
>
> Chris
>
>

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2000\12\25@164514 by Peter L. Peres

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The moisture in the air above the ground is vastly different from that
inside. This has got to do with the vapor pressure of H2O in air (water in
the ground is liquid, in the air it is not). Even 1 cm of spacing will
totally falsify the result.

Even NASA seems to know about two electrodes in a gypsum block for long
therm monitoring. So I'd go and find two larger motor electrodes (I don't
know what you call them - the bronze loaded graphite electrodes that
connect the moving armature of a motor). These come with stranded copper
wire pigtails and screw eye terminals. Paint the non-graphite parts with
roof pitch after connecting wires and make a nice gypsum block of it. That
should be it. Good luck with calibration though <g>.  You will need to
read with an AC bridge (like a portable RLC bridge for starters).

Peter

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