AVR-Chat

Hello again,
   
   
  For my project,  I need low accuracy. 
  I just want to know when my little apple tree or plants that I have  in the house need water.
  Just one type of soil.
   
   FTDI USB to serial converter  sounds very cool.
  


Zack Widup <w9sz@prairienet.org> wrote:
          
I haven't spoken out about this yet but I thought I'd throw in a few 
words. I work for a geotechnical engineering firm that has a soils 
testing lab. I spend quite a bit of time doing all sorts of soil and rock 
tests, including moisture contents.

I never saw it mentioned exactly why the electronic means of measuring 
soil moisture content was needed or what kind of accuracy was desired. 
But I can tell you this - there are so many different kinds of soils which 
all have different characteristics and read differently that you just 
can't do it with much accuracy.

I've worked with silts, clays, silty clays, clayey silts, clays with 
little to some sand, etc. - I've seen everything you will find on the 
Burmister and Unified Soil Classification charts. I once had the idea 
that we might be able to measure moisture content electronically. After 
spending some time at it, I concluded it wouldn't work. If it did, ASTM 
would have a techniquue outlined for it. They don't.

You might be able to calibrate ONE sample of ONE type of soil for 
electronic moisture content measurement, but take some soils from a few 
feet away and it will be dfferent. The only way to accurately get a 
measurement of moistuire content is to apply the ASTM standards, which 
involve weighing the soil with moisture, baking the water out of it and 
reweighing.

I hate to be the bearer of bad news but I do this profesionally and I've 
been there, done that.

Zack

On Thu, 18 Oct 2007, Thomas Keller wrote:

> Show me soil with pure, distilled water in it.
>
> Look, I am just telling you what will work. There is no way for a simple
> test unit with a probe to tell the difference between water or high metallic
> content in the soil. I can tell you that dry soil, regardless of
> mineral makeup
> will have a MUCH higher resistance than wet soil.
>
> Ralph Hilton wrote:
>>
>> On Thu, 18 Oct 2007 16:16:18 -0500 you (Thomas Keller
>> <tjkeller1@alltel.net <mailto:tjkeller1%40alltel.net>>)
>> wrote:
>>
>>> Basicly, the resistance of soil is based on moisture content, because it
>>> is the moisture
>>> that provides the conductivity from particle to particle, not the
>>> mineral or other
>>> dry content of the soil.
>>>
>>
>> I'd suggest testing it in practice. It doesn't work that way. Pure
>> distilled
>> water has a very low conductivity. The dissolved salts in the water
>> bring about
>> the conductivity. That's the principle on which a TDS meter is based.
>> (total
>> dissolved solids).
>>
>>> avrFreak
>>>
>>> Ralph Hilton wrote:
>>>>
>>>> On Thu, 18 Oct 2007 12:27:59 -0500 you (Thomas Keller
>>>> <tjkeller1@alltel.net <mailto:tjkeller1%40alltel.net>
>> <mailto:tjkeller1%40alltel.net>>)
>>>> wrote:
>>>>
>>>> I was wondering how a simple resistance measurement could
>>>> differentiate between
>>>> a moist soil with low nutrient content and a drier soil containing a
>>>> lot of
>>>> soluble nutrients.
>>>>
>>
>> --
>> Ralph Hilton
>> http://www.ralphhilton.org <http://www.ralphhilton.org>
>> C-Meter: http://www.cmeter.org <http://www.cmeter.org>
>> FZAOINT http://www.fzaoint.net <http://www.fzaoint.net>
>>
>>
>
>


                         

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