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

Robin Gilks robin at gilks.org
Wed Nov 18 01:05:51 GMT 2015

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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