Elegant solution. Would I need a computer? Could I just do it with a
multimeter? I love my Raspberry Pis but maybe one isn't required in this
case.
"If I understand the job right, doesn't that mean that you will be doing major
surgery to dry the compartment and solve the water ingress issues?"
Absolutely right.
Thank you,
Peter
On Sun, Jul 7, 2013 at 12:18 PM, Jerry Scharf <
sch...@lagunawayconsulting.com> wrote:
> On 07/06/2013 08:40 AM, Peter Hollenbeck wrote:
> > I am building a 26 foot wood power boat. The bilge below the cabin and
> > afterdeck floor is 7 sealed water tight (hopefully) compartments. I
> > plan no inspection ports but would like a way to detect moisture. If
> > there were an appropriate sensor I could embed one in each compartment
> > and occasionally hook up a Raspberry Pi and check for the presence of
> > water. Cost is a consideration.
> >
> > I would appreciate suggestions.
> > Thanks,
> > Peter
> >
> >
>
> Peter,
>
> If I understand the job right, doesn't that mean that you will be doing
> major surgery to dry the compartment and solve the water ingress issues?
> If so, I think you could just go with a pair of bare copper wires spaced
> 1/2 inch apart near the back bottom part of the compartment (replacing
> the wire is the least of your problems if it gets wet.) (Make sure you
> use separate pieces of tape for the two wires.)
>
> You have one wired to ground and the other that is pulled to a fixed
> voltage with a pair of high resistance resistors (~10^5 range) with one
> to supply voltage and the one to ground. With no conductance, the wire
> will stay at the voltage of the resistor voltage divider, with water in
> the bottom it will drop toward ground. This can be measured with just
> about any of the voltage sensing 1-wire chips. I would have the
> resistors and the sense chip attached to the pi and not to the wires. I
> would just solder the lengths of copper to insulated, waterproof wire
> and bring them to a small dry box. In the box you would tie all the
> grounds together and bring the sense wires to test contacts.
>
> You take a first reading for each sense line and record the voltage.
> When you take follow-on readings, you just need to make sure that the
> bottom of the boat is tilted so that any water sits at the back of each
> compartment (I think this is usually the case in motor boats.) Then you
> connect up a lead, give the sense wire a little while to charge up and
> take the reading. There may be some systemic error do to
> time/temperature variations in the system and resistors, This can be
> factored out by taking a reading with no sense wire attached. It's
> ability to sense moisture is limited, but significant moisture in the
> wood would change the resistance between the wires at least somewhat.
>
> YMMV
>
> jerry
>
>
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