I just purchased a manual garden watering valve (no PICs in it). It
is apparently (judging from the label, noises it makes when you
adjust it
and a little deduction) water driven and positive displacement so
that it drives itself off based on true volume of water passed. Such
a valve could probably be persuaded to run continually without
shutting
off and give meter pulses either from the positive displacement rotor
or some other part of the works.

Mine cost is Hozelock (lok?) brand - allegedly UK made - $NZ20 from
"The Warehouse"
so they are probably available cheaply in Oz etc.

Electronic versions are available for 5 times as much and very
possibly contain a PIC.
A home built (PIC based of course) positive displacement meterer
could be built from scratch but at $20 the premade version sounds
like a good starting point. (I could be persuaded to investigate the
intermnals of mine with very little persuasion :-))


regards

    Russell McMahon



-----Original Message-----
From: James Cameron <cameron@STL.DEC.COM>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Monday, January 11, 1999 4:22 PM
Subject: [OT] Re: Home Automation - Water Volume Measurement


>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)
>
>OpenVMS, Linux, Firewalls, Software Engineering, CGI, HTTP, X, C,
FORTH,
>COBOL, BASIC, DCL, csh, bash, ksh, sh, Electronics,
Microcontrollers,
>Disability Engineering, Netrek, Bicycles, Pedant, Farming, Home
Control,
>Remote Area Power, Greek Scholar, Tenor Vocalist, Church Sound,
Husband.
>
>"Specialisation is for insects." -- Robert Heinlein.
>