The level sensor I built/experimented with was a small piece of
double-sided PCB with one wire attached to each side.  I did not
use the traditional "finger" pattern to help prevent false-shutoffs
due to water spashing and drops sticking between fingers.  I also
completely solder-coated both sides of the PCB (approx 1" sq).

I like the ribbon-cable idea, but oxidation will change the
resistance over time.  And I don't need multiple level sensing
for this.

When I started this project a year ago, I searched and searched
for valves and only came up with industrial units.  Of these, the
only ones that were rated for the pressure and temp of water in
a house were a few hundred dollars each.  Then it hit me -- both
a washing machine and dishwasher control hot & cold water, so
I went to an appliance parts place and picked one up for $26.
Trust me, I'd love to find a low-voltage valve at a low cost.

Right now though, once the water stops, there is not contact path
from the valve to the water in the tub, so the 110VAC there
should not be a concern.  Faults in the circuit that bring that
110VAC back to the water-level sensor is the concern.

Thanks,
-Neil.


----- Original Message -----
From: "Kevin Blain" <kevinb@WOODANDDOUGLAS.CO.UK>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, March 28, 2002 3:36 AM
Subject: Re: [PIC]: Automated whirlpool tub ...


> I once saw a project for a level sensor using a piece of ribbon cable
> with the ends sliced at an angle. When you think about it, this is
> really a very neat solution - Easy to terminate to the board, many
> stages of level sense available, discrete.
>
> My advice to a hobbyist would be use an off the shelf low voltage power
> supply, e.g. a wall wart at say 12V, and try to get some valves that run
> from 12V too. That way, someone else has done the 'scary mains
> isolation' bit for you.
>
> Regards, Kevin
>
> > -----Original Message-----
> > From: pic microcontroller discussion list
> > [mailto:PICLIST@mitvma.mit.edu] On Behalf Of Reginald Neale
> > Sent: 28 March 2002 09:29
> > To: PICLIST@mitvma.mit.edu
> > Subject: Re: [PIC]: Automated whirlpool tub ...
> >
> >
> > Neil:
> >
> > Have you had these suicidal impulses for long? :-)
> >
> > I'm sure you are aware of the huge safety issues. Isolating
> > all your line voltage switching circuitry from the control
> > circuitry is not trivial. Relays are good, but there's
> > creepage, leakage, physical barriers...
> >
> > Even for the level sensing, it's probably not a good idea to
> > get your voltages wet. Aside from the safety issues, output
> > from electrodes in contact with the water/chemical solution
> > may not be stable. For level sensing, GEMS makes some
> > float-type modules that are very reliable and inherently isolated.
> >
> > What does the existing control system use for temperature
> > sensing? You can probably adapt that same sensor to your new circuit.
> >
> > Reg Neale
> >
> > --
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> >
> >
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> >
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