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

[Charles Manning]

I wonder whether one of those CapSense things might work
http://www.cypress.com/products/capsense-controllers

Another approach might be running the capacitor as part of an RC oscillator
and measuring the frequency.

On Wed, Nov 18, 2015 at 2:05 PM, Robin Gilks <robin at gilks.org> 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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