Nope,,, sorry.   You have the chance to do a "squint test" of the 
calibration every so often?  If so perhaps a straight resistance 
value would be useful,,, I just know how much they change with almost 
any of the fertilizers.  You're not using dc on the probe are you?


At 08:02 PM 8/9/2008, you wrote:
>I looked at those. The gypsum block sensors I'm finding are all like
>$20 a pop. Way more than I want to spend for a piece of each sensor.
>
>If you can point me to a supply that is significantly cheaper, please
>let me know!
>
>-Pete
>
>On Aug 9, 2008, at 7:50 AM, Grif w. keith griffith wrote:
>
> >
> > gypsum block sensor.  Change every few years.
> >
> >
> > At 05:16 PM 8/8/2008, you wrote:
> >> Pretty coarse is fine. The intended application is to remain in place
> >> rather than being a portable probe. It is simply to provide some
> >> information back to a sprinkler controller. Target is consumers
> >> rather
> >> than commercial/large ag organizations.
> >>
> >> Basically I need something equivalent to a 10 point scale: bone dry
> >> to
> >> waterlogged.
> >>
> >> -Pete
> >>
> >> On Aug 8, 2008, at 3:51 PM, Grif wrote:
> >>
> >>> resistance/conductivity and moisture content do not track well.  I
> >>> think with what I think I know, simple and cheap go together nicely,
> >>> but reliably and accuracy may be a stretch.  If the soil type can be
> >>> characterised and stays stable,,, (like an orchard or vinyard over
> >>> time), conductivity/resistance may infact work fine.  If it's a
> >>> portable unit, not sure you'll get to what you need.
> >>>
> >>> Units with good resolution seem to be tensioneters, that and his
> >>> hands are all my brother trusts (ag guy).  Not fast if I remember.
> >>> The resistance ones seem to use a gypsum block encased resistance
> >>> element to make sure none of the "other" stuff affects the
> >>> resistance/ph around the sensor.
> >>>
> >>> Seems like the stablization time for any of the commercial ones I'm
> >>> aware of is measured in hours, not seconds and minutes.
> >>>
> >>> What kind of accuracy do you need?
> >>>
> >>> -----Original Message-----
> >>>> From: Peter Loron <peterl@standingwave.org>
> >>>> Sent: Aug 8, 2008 3:19 PM
> >>>> To: "Microcontroller discussion list - Public." <piclist@mit.edu>
> >>>> Subject: [EE] Replacement for L4620
> >>>>
> >>>> Can anybody point me to a replacement for the ST Micro L4620?
> >>>>
> >>>> http://www.allelectronics.com/mas_assets//spec/L4620.pdf
> >>>>
> >>>> I'm looking for a simple, cheap way to reliably measure soil
> >>>> moisture,
> >>>> and am thinking about using an oscillating probe to measure
> >>>> resistance. This chip looks like it has everything I want all in
> >>>> one
> >>>> tidy bundle.
> >>>>
> >>>> Suggestions?
> >>>>
> >>>> Thanks!
> >>>>
> >>>> -Pete
> >>>> --
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> >>>
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> >
> > W. Keith 'Grif'  Griffith
> > N7IVS
> >
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W. Keith 'Grif'  Griffith
N7IVS 

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