Luyen Tran wrote in HTML:
> I'm going to do a 'Home Automation' project that controls light,
> temperature, yard watering ...

On yard watering, my wife and I were discussing this on the six hour
drive back from our farm on the weekend, and we decided that "time"
isn't good enough as data for deciding when to water, and that
"moisture-level" of the soil should be the determinant.

Then we thought that it should be proportional control, so that the
moisture level determines the duty cycle or ratio of watering/not-
watering periods, so that the plants get to trust their environment and
thrive accordingly.

Then we remembered that the ants tend to crawl up the watering pipes,
and so the volume of water delivered will vary over time.  Sure, the
moisture level feedback would help to fix this, but not rapidly.  I'd
prefer to design the system so that a "volume" of water is delivered
rather than a duty cycle of valve opening.

So does anyone know any water volume measuring techniques suitable for
connection to a PIC microcontroller?  Domestic hobby level stuff, not
industrial control.  Yet.

--
James Cameron                                      (cameron@stl.dec.com)

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