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'[PIC]: PH sensor for soil'
2004\09\22@094344 by Claudio Martin

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Hy all:
I´m looking for a cheap  ph sensor for soil. I´m working on a gardening project and i need to check temperature, humidity and PH.  These three measurements will be interfaced  to a PIC ,after that the PIC will display the values. I´ve seen some PH probes on internet, but they are kind of expensive(70-100 U$D) for this project cause i need to place many of them in diferent places. Does anybody know if there is other cheaper way to mesure PH?. Thanks _______________________________________________
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2004\09\22@111603 by Mark Hore

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part 1 1539 bytes content-type:multipart/signed; micalg=pgp-sha1; (decoded quoted-printable)


-- 2004\09\22@111622 by Mark Hore
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part 1 1539 bytes content-type:multipart/signed; micalg=pgp-sha1; (decoded quoted-printable)


-- 2004\09\22@182035 by Lawrence Lile
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Yeah, good luck.  Soil is nasty stuff, full of corrosive and conductive salts, not to mention varying amounts of water.  And live things.

Measureing moisture in soil can be done several ways, the best being electrodes in a block of gypsum.  The trick is, the Gypsum will eventually absorb water but keep out some of the fertilizer that the gardener dumps on the ground, which is mostly conductive salts that send your measurements haywire.

PH I don't know about.  I do know that the soil moisture measurement is trickier than you think.  
Stick your meter electrodes in some soil, read resistance, and come back in a few hours and see how it has drifted.  I could never get two readings the same with this apparently blindingly simple method.


-- Lawrence Lile, P.E.
Electrical and Electronic Solutions
Project Solutions Companies
http://www.projsolco.com
573-443-7100 ext 221

> {Original Message removed}

2004\09\23@091051 by Morgan Olsson

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(Resending from correct personality...)

pH probes are expensive and chemically and mechanically (and electrically) fragile.  I guess the best method is to mix a little distilled water with the soil, then filter out just the water and measure that.

/Morgan
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Morgan Olsson, Kivik, Sweden

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2004\09\23@112146 by Richard Zinn

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I read about this ISFET-sensor bias in the EDN magazine a few months
back and thought of using it for a similar purpose.  What do you think
of it?  Is it also as delicate?  It doesn't appear to be as
expensive...
http://www.reed-electronics.com/ednmag/article/CA421506?text=isfet


On Thu, 23 Sep 2004 15:10:02 +0200, Morgan Olsson
<spam_OUTdlistTakeThisOuTspammorgansreglerteknik.se> wrote:
{Quote hidden}

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2004\09\24@023609 by hilip Stortz

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actually, many of them are very cheap (well under $50 ea.), and very
robust chemically and mechanically, and i've never seen one that wasn't
electrically robust.  see <http://www.omega.com> for lots of info on ph sensors
in general and models that might be good in a soil enviroment.  i'd
think you'd want one of the fet based probes for soil ph, but i could
easilly be wrong.  if the omega site doesn't mention soil ph, ask them,
they probably know or can find out for you.

Morgan Olsson wrote:
>
> (Resending from correct personality...)
>
> pH probes are expensive and chemically and mechanically (and electrically) fragile.  I guess the best method is to mix a little distilled water with the soil, then filter out just the water and measure that.
--------

-- Philip Stortz--"In Germany they came first for the Communists, and I
didn't speak up because I wasn't a Communist. Then they came for the Jews, and I didn't speak up because I wasn't a
Jew. Then they came for the trade unionists, and I didn't speak up because I
wasn't a trade unionist. Then they came for the Catholics, and I didn't speak up because I was a
Protestant. Then they came for me, and by that time no one was left to speak up."
-- Martin Niemöller, 1892-1984 (German Lutheran Pastor), on the Nazi
Holocaust, Congressional Record 14th October 1968 p31636.



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