Yeah, good luck.  Soil is nasty stuff, full of corrosive and conductive s=
alts, not to mention varying amounts of water.  And live things.

Measureing moisture in soil can be done several ways, the best being elec=
trodes in a block of gypsum.  The trick is, the Gypsum will eventually ab=
sorb 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 t=
rickier than you think. =20

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 reading=
s the same with this apparently blindingly simple method.=20



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

> -----Original Message-----
> From: Mark Hore [mailto:baerwulf@echidna.id.au]
> Sent: Wednesday, September 22, 2004 9:12 AM
> To: Microcontroller discussion list - Public.
> Subject: Re: [PIC]: PH sensor for soil
>=20
> Not really. even with these probes (70 - 100 $US is cheap) measuring pH
> in solids is extremely difficult. The probes will also need to be
> calibrated regularly and cleaned very regularly as they rely upon
> diffusion across a membrane which can become blocked by solids. the
> probes also need to be kept wet or they will fail.
> On Wed, 2004-09-22 at 21:43, Claudio Martin wrote:
> > Hy all:
> > I=B4m looking for a cheap  ph sensor for soil. I=B4m working on a gar=
dening
> project and i need to check temperature, humidity and PH.  These three
> measurements will be interfaced  to a PIC ,after that the PIC will disp=
lay
> the values. I=B4ve seen some PH probes on internet, but they are kind o=
f
> expensive(70-100 U$D) for this project cause i need to place many of th=
em
> in diferent places. Does anybody know if there is other cheaper way to
> mesure PH?. Thanks
> > _______________________________________________
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>=20
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>=20
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