PlantSmart Gardener's Computer

[Garry Boyd]

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Garry Boyd writes:

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I can't see the probe on that one, but normally these use the principle of
dis similar metals. You will see 3 bands of metal seperated by insulators.
The conductivity of the soil changes according to the salts present and
moisture changes. This creates a thermocouple effect generating a small
potential difference between the different metals.
The light measurement is generally a cheap cadmium sulphide or similar cell.
Readings are fairly arbitary depending on soil types. We have sold a more
robust unit to farmers and horticulture people made by Takemura in Japan.
(picture attached. [I have placed this picture on a new page
www.sowacs.com/sensors/bimetal.html  Bruce])

 It is important to keep the electrodes clean, and have a
reasonably large point of contact. Most of the home gardener ones I have
seen are incredibly flimsy.
----- Original Message -----
From: <owner-sowacs@aqua.ccwr.ac.za>
Sent: Tuesday, August 20, 2002 5:43 PM
Subject: PlantSmart Gardener's Computer
>
> One of the sowacs members writes:
> ===8<==============
> Hi Bruce,
>
> some friends and I are studying automatic irrigation systems and  are
> curious about an inexpensive moisture sensor sold by various companies.
It's called
> "PlantSmartô Gardener's Computer" and it retails for $30.  Having looked
at the variety of techniques
> for measuring soil moisture (gypsum blocks, TDR, capacitance,
tensiometers,
> etc.), I am not sure what technique this product uses.  Do you know or can
you
> suggest a method of finding out?  The link to the product is given below:
>
>
http://www.brookstone.com/shop/product.asp?product_code=235416&world_code=3&;
category_code=35&subcategory_code=478&search_type=subcategory
>
> Thanks for your help and for hosting this discussion forum.
>
> [Bruce comments:
> There  are several manufacturers of this type of unit targeted mainly
> at  the  home  market. They magically produce a digital readout of not
> only  soil  dryness or wetness but this model does pH and light levels
> too. They are sold without any explanation of measuring technique, range,
> accuracy  or reliability, all of which we are interested in and need to
> know in order to be able to use with confidence.
> If  anyone  can  shed  any light on how these units work, please share
> with the group.]
>
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>
>
>
>

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