Newbie - water detector circuit help please

[Malcx]

Hi all,


I've not dabled with any electronics since High school (about 10 years)
and have a fairly specific requirement for a detector that I want/need
to put together....

Background:
My storage tank leaked and ruined the flooring - the plumber couldnt
find anything obviously wrong with the tank but replaced the pieces
that showed signs of wear and we've had no obvious leakage since...

Now before the floor is re-laid I want to be doublly sure there no slow
leak going on...

As the storage tank gets warm, any surface (i.e. detectable) water will
evaporate pretty quickly while other moisture will seep out of sight
and do damage...

Specification:
I envisgae all being contained in a small box with probes coming out on
lengthy wires.

The box will have an LED that is permenantly on when the battery has
power (I'd envisage a 9v cell...)

There would need to be 2 or 3 moisture detection probes, when any 1
probe registers moisture another led on the box will be lit. This led
remains lit even after the probe dries. Only 1 led will be needed for
all of the probes - i.e. there does not need to be an led for each
probe.

A reset button will be required to reset the state of the device back
to "power led on only" mode.

(Ideally the sensitivity of the probes would be adjustable)

Can anyone help me with this seemingly simple circuit design? (I can
fit it all together, pcb design etc once I've the circuit diagram)

Thanks for your help in advance!

Mal

 

[Malcx]

Initially I was just thinking of just using etched copper board as we
used to in school - is there a better/more reliable alternative?

Thanks,

Mal

 

[Malcx]

Yeah Just wet vs dry is enough for me - mearly knowing that water has
been present since I last checked is enough to tell me there is a
problem that I'll need to call the plumber back for.

As water's not pouring out I'm in favor of an LED warninfg rather than
buzzer as being woken at 2 in the morning wouldnt be appreciated by the
girlfriend ;-)

Having said all that I'm looking at this as a learning excercise as
well and like the thought of damp detection with wire grids/blotter
paper - would it be a massive undertaking to do an LED scale (say 1-5)
measuring how damp it had been?
(i.e. if it is just damp 1 LED lights, under water = all 5 light with
the display "locking" at the highest level recorded since last reset? -
this is beyond what I need to do but if still fairly straightforward
would be more fun!)

Thanks again for your help!

Mal

 

[Malcx]

The tank itself is stood in a tray, but it's seems the leak was (is?)
from a connecting pipe - the leak would have only be sporadic (pressure
too high - cold/warm pipes - something else) and must have run down the
pipe beyond the tray...

Thanks anyway!

Mal

 

[Malcx]

The circuitry's pretty straightforward but, again, the probe will be
tricky, so, first things first and I'll generate something for you for
the wet/dry unit.

BTW, how long do the cables have to be and what kind of a power supply
do you want to use to run the thing?

Cable length would need to be varying length depending on where I place
the unit - but none would need to be more that 750mm (shortest -
probably about 150mm)

I was planning on using a 9v battery, but other posts here suggest that
it'd wear down pretty quickly if an led is on permenantly to indicate
power.

I dont really have access to a wall socket here so it will need to be
battery powered - is there another/better/less energy hungry way of
indicating there is still enough juice?

Cheers,

Mal

 

[Gerhard v d Berg]

Previous post now fixed -
"Terry Pinnell" <terrypinDELETE@THESEdial.pipex.com> wrote in message
news:7e5jc153lfd031m6s9h0irc1uv550isti4@4ax.com...

Have a look at this circuit
http://www.terrypin.dial.pipex.com/Images/DampDetector.gif

I don't think he's interested - I suggested that (with full details)
up-thread about 5 days ago!

--
Terry Pinnell
Hobbyist, West Sussex, UK

Thanks Terry -- for being diplomatic -- I had your URL -- My horrible post
is hopefulle now fixed with the correct URL - maybe it could help someone
else .

Have a look at this circuit
http://www.edn.com/article/CA253786.html?spacedesc=designideas
or the .pdf version
http://a330.g.akamai.net/7/330/2540/20021024153820/www.edn.com/contents/imag
es/103102di.pdf
Circuit checks "swamp-cooler" water level - form EDN Magazine 2002-10-31

It is an inexpensive circuit and should work quite well. The piezo sounder
output
volume is however a bit low with the 3 volt supply. The 4093 circuit will
however
accommodate supplies up to 15volt. I would recommend a 6volt or 9volt
supply for better sensor sensitivity and operation (74HC93 or 74HC132
'equivalent' devices are however only speced for supply voltages up to 6
volt).

To accurately measure conductivity, an AC voltage should be applied to a
sensor probe using chemically inert electrodes. (By applying a DC voltage,
in a damp environment, to probe metals such as copper and tin, can grow
all sorts of low impedance current paths). You could try stainless steel as
a probe material. Soldering stainless requires special solders, so it might
be better to crimp the probe leads to the stainless electrodes. Remember
to keep the crimps dry by covering them with a dab of silicon (bath)
sealant.
(screw terminals for joining wires can be used, if you do not have crimp
tools)

Advice by other members in the group on how to construct a moisture probe
might result in a good enough sensor for the job.

It would be better to have short leads for the probe and extend the
leads of the piezo sounder to locate it at a convenient site where it
would be noticed.

As a challenge add a latching circuit, with a manual reset, that beeps only
once a minute and a battery low detect Another 4093 and a simple
voltage detect circuit should be able to do it, else remember to replace
the batteries every year or two.

As for waking the girlfriend - add a kill switch to the piezo.
She should be pleased that your gadget managed to save the ceiling and
carpets .

I hope you don't get to many false alarms.
(Watch out for ceiling rats and bats - they can foul moisture probes

Gerhard