[chbot] Just when I thought I had a good soil moisture solution...

[Andy ZL3AG]

Shoot me. Please.


On 18/11/2015, at 2:05 PM, Robin Gilks wrote:

> Well I was going to write something like that - but my ideas just sort of
> dissolved...
> 
> If I keep coming back to this project at the correct Frequency, I'll find
> out if I have the Capacity for it to get finished.
> 
> After all my work, it appears that Resistance is futile...
> 
> 
> 
>> Shouldn't the subj be 'Just when I though I had a Solution for soil
>> Moisture" ? :)
>> 
>> On 18/11/2015 12:40 p.m., Robin Gilks wrote:
>>> ... I discovered that rather than resistive I should be looking at high
>>> frequency capacitive sensors.
>>> 
>>> Commercial ones run at up to 70MHz, this one based on am ATTINY441 AVR
>>> chip runs at the system clock rate of 16MHz and has an I2C interface.
>>> 
>>> https://www.tindie.com/products/miceuz/i2c-soil-moisture-sensor/
>>> 
>>> Very simple mode of operation, its basically using the PCB as the two
>>> plates of a capacitor and as the dielectric constant around it changes
>>> (due to moisture) so does the capacitance.
>>> 
>>> This is measured by driving a high frequency clock to the cap through a
>>> series resistor and measuring the peak voltage swing across the cap with
>>> a
>>> couple of diodes and long(ish) time constant RC network providing a
>>> differential output to the A/D inputs of the micro.
>>> 
>>> Think I'll go this route...
>>> 
> 
> 
> 
> -- 
> Robin Gilks
> 
> 
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