[chbot] Just when I thought I had a good soil moisture solution...
cdhmanning at gmail.com
Wed Nov 18 03:03:50 GMT 2015
I wonder whether one of those CapSense things might work
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
> 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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