Howdy,

 > What I need help with is the external aspect of my project, specifically,
 > interfacing my PIC board to my Orbit sprinkler valve.

You might want to check out my sprinkler controller project at www.rgbled.org

You can build it for 1 to 27 zones and while a request can be sent for up to 
254 minutes at a time, you can queue multiple requests  for the same valve so 
that staying open many hours is not a problem.  However, it is not a "time of 
day" unit -- it's meant to be commanded by something else (like a computer, HA 
controller, etc).  It purpose is to allow control to be put at the point where 
the valve wiring is and to insure that valves are turned on and insure they 
get turned off again.

It has 8 queues, so you can have a long running cycle like you describe in one 
queue and put other watering commands into other queues so they run in parallel.

For example, I have on long running cycle for a soaker hose that is on for 
about 4 hours in one queue while my regular lawn and flower watering is done 
in another queue to run in parallel.  If you have the water flow rate, you can 
also use multiple queues to allow multiple valves to be open at the same time.

All the firmware, docs, schematics, etc are available for download for free 
non-commercial use.  Even if you can't use it as is, you may find some aspects 
you can reuse for your project.

Gerry
-- 
Gerry Duprey
Ann Arbor, MI 48103
http://www.cdp1802.org
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