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Newbie - water detector circuit help please

Discussion in 'Electronic Basics' started by Malcx, Jun 30, 2005.

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  1. Malcx

    Malcx Guest

    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
     
  2. John Fields

    John Fields Guest

     
  3. Malcx

    Malcx Guest

    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
     
  4. Dan Hollands

    Dan Hollands Guest

    There are commercial water detection devices available to warn of water in
    the basement

    I don't know the brand but the plumber installed one when I had a back up
    sump pump installed in the house where I used to live. I made a loud beeping
    sound when it got wet. It ran off a battery

    --

    Dan Hollands
    1120 S Creek Dr
    Webster NY 14580
    585-872-2606

    www.QuickScoreRace.com
     
  5. John Fields

    John Fields Guest

    ---
    Depends. I you're looking for the difference between wet and dry,
    that's probably as good a way to do it as any, but if you want to
    detect 'damp' then something like, say, blotter paper sandwiched
    between two wire grids would be better.

    In either case, though, the circuitry will be the same, so the choice
    of sensor is largely moot.
     
  6. I had a similar problem about 20 years ago. Some time later I wrote an
    elementary article about the resultant project in an electronics
    hobbyist magazine, which you might find useful. My output was a
    miniature loudspeaker, not LEDS, but you may be able to adapt it.

    http://www.terrypin.dial.pipex.com/Images/DampDetect.jpg
    http://www.terrypin.dial.pipex.com/Images/DampDetect.txt
    http://www.terrypin.dial.pipex.com/Images/DampDetector.gif
    http://www.terrypin.dial.pipex.com/Images/DampFigs.gif

    The magazine illustration scan is very poor, but the key schematic is
    shown separately.
     
  7. Malcx

    Malcx Guest

    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
     
  8. One day Malcx got dressed and committed to text
    Not an electronic solution but in our part of the world concealed storage
    tanks are usually installed in a 'tray' fitted with a drain to waste which
    would take care of the floor spoiling effect.
     
  9. Malcx

    Malcx Guest

    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
     
  10. John Fields

    John Fields Guest

    ---
    No, but the probe will be tricky.
    ---
    ---
    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?
     
  11. John

    John Guest

    Not a good idea, since the LED will run down the 9v battery very
    quickly. You probably want an AC powered device, possibly with
    battery backup.

    Some CMOS logic chips or a low power version of the 555 timer chip can
    be used for the latch circuit that stays on after being tripped.

    The most basic wet/dry sensor is a piece of circuit board with the
    copper foil divided in two parts. Board size is dependent on the
    expected size of the wet/damp area (or the drip area, as appropriate).
     
  12. Malcx

    Malcx Guest

    The circuitry's pretty straightforward but, again, the probe will be
    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
     
  13. Have a look at this circuit
    http://www.terrypin.dial.pipex.com/Images/DampDetector.gif
    <Circuit checks "swamp-cooler" water level>
    It is inexpensive and should work quite well. The piezo sounder output

    volume is however a bit low with a 3 volt supply. The 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

    devices are however only spec ed for supply voltages up to 6 volt).



    To accurately measure conductivity an AC voltage should be applied to a

    sensor probe. In this simple moisture probe the current set-up should
    suffice.

    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.



    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 :).



    GvdBerg
     
  14. Previous post now fixed -
    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
     
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