Hi all,

Now that I know a few things about PIC's, I thought I'd redesign the =
control
circuit for my automated whirlpool tub.  In a nutshell, the current =
system
allows me to start filling the whirlpool tub via phone control, so I =
have nice
hot water when I get home.  (See what stressful customers can lead a
person to do? :-).  Currently, the system is switched on via X10, using =
an
X10 phone interface, and this turns on 2 valves (a dual valve from a
washing machine) to start the flow of water.  Shutoff is timed, but it's =
not
great since the timer is very innacurate, it wastes water, and it wastes
hot water to the point that on occassion I do not have enough left to =
get
the tub warm enough.

The new system will have:
 - 2 water level sensors -- one f/normal shutoff, other on floor f/alarm =
(??)
 - Temp control
 - 2-button / 3-LED display interface to set the desired temp.
 - PIC timer as a last-resort shutoff.

The circuit's mostly designed, but a few thoughts/questions are open =
still:

(1) Which (submersible) water-temp sensor do I use?  Suggestions?

(2) I want to isolate all 110V circuitry from the water-level sensors, =
so I
   thought I'd run the PIC on batteries (4.5V?).  I have not calculated =
the
   power draw yet, but my guess is that it will not be good, cause I'm
   using relays to control the (110V) water valves.  Other option is to
   just run the PIC off of a 5V power supply derived from the 110V line.
   Should I worry then about the lack of isolation?

(3) I built a water-level sensor by experimenting with a transistor =
switch
   circuit and some resistor values.  Got it working, but I noticed that
   the dry and wet voltage levels weren't always consistent.  So I
   thought I could add this neat feature where an A/D in the PIC would
   take a snapshot of the water detector voltage level at startup (which
   should be dry) and add a small voltage amount to that for use as
   the trigger-level.  Should I bother?  Or is there a standard =
water-level
   circuit somewhere that would give me better consistency.  (Not much
   luck with web-search).  For simplicity, I'm avoiding using additional
   chips such as schmitt triggers, etc. However, space is not an issue
   with this circuit, and the cost difference is minimal, so I'd still =
like to
   hear any suggestions.

Here's a schematic (untested, and missing drivers for LED commons)
for the interested/curious ...
         http://www.avn-tech.com/stuff/whirlpool_control_v2.jpg

Yes, I will document/post the project (including plumbing) when all =
done.

Thanks much,
-Neil.

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