Peter,
KISS says use a multimeter, I started with the 1-wire solution because
that was the thread. This will work fine but I have to admit the sugar
cube seems even nicer. Again, measuring with a multimeter is all it takes.
They make wire that is specifically designed to prevent water ingress
down the length.
jerry
On 07/07/2013 01:05 PM, Peter Hollenbeck wrote:
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
<mailto: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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