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

Mark Atherton markaren1 at xtra.co.nz
Wed Nov 18 00:15:48 GMT 2015

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...

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