Liquid detecting floor pad

  1. Hey all,

    For a school project, I am trying to design a pad (placed on the floor) which can detect liquid and make a loud buzzing sound immediately upon the detection of the liquids.

    Any ideas?
     
  2. jcsd
  3. If this a school project then what technologies are allowed? Is this a middle school project or a first year EE?

    In middle school use a float switch. 1st year EE, start with a comparator that is balanced by a resistor network (high value resistors) but conductivity of the water sensor pulls one leg up and flips the conspirator. You only need a cheap part like the lm311 and a resistor network. I think the 311 can even directly drive a small LED

    The sensor is just a pair of bare wires.
     
  4. Danger

    Danger 9,878
    Gold Member

    You're making one assumption though; Sapia never stated what the fluid is. It might not be conductive.
    If, on the other hand, it's for the same reason that my neighbour needs such a thing, he can get by with a simple video surveillance system to detect when his dog pulls one leg up.
    I'm thinking that the conductivity issue can be avoided entirely by using some sort of absorbent gel or fabric that will expand when wet, and thus compress some sort of pressure sensor such as a grid of load cells.
     
  5. dlgoff

    dlgoff 3,119
    Science Advisor
    Gold Member
    2014 Award

    I actually installed something like this snake

    [​IMG]

    around the perimeter, under a raised floor like this

    [​IMG]



    It worked. I got a call-in from the maintenance guy informing me the alarm was sounding. He said, "be sure to bring your fishing pole as there are some Smallies under the floor.
     
  6. Danger

    Danger 9,878
    Gold Member

    So... what is that and how does it work?

    :rofl: for the fish joke.
     
  7. dlgoff

    dlgoff 3,119
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    2014 Award

    Conductivity. Once "pure" water penetrates or contacts the concrete floor, it's not "pure" any more and will conduct nicely.
     
  8. Danger

    Danger 9,878
    Gold Member

    Fair enough, but what if the liquid that he wants to detect is alcohol or canola oil?
     
  9. Bobbywhy

    Bobbywhy 1,908
    Gold Member

  10. Danger

    Danger 9,878
    Gold Member

    Ah, yes. And the first line under "Features" specifies "conductive fluid sensing cable". I repeat myself by saying, "What if the fluid that he wants to detect doesn't conduct?"
     
  11. Build in a low wattage constant power heater and a temperature sensor, when the mat gets wet the temperature will fall.
     
  12. For my class project, the liquid that needs to be detected is water. I am hoping to do this as inexpensively as possible (my dad is going to help me pay for the parts so I can build one for presentation). I am hoping to hook the pad up to a buzzer so it makes a loud noise as soon as you spill water on it.
     
  13. Danger

    Danger 9,878
    Gold Member

    I stand corrected. :redface:
    A couple of bare wires and a doorbell will do it.
     
  14. Thanks Danger! Say I buy a cheap buzzer off Amazon (with the two wires exposed, see picture below).

    [​IMG]

    Would I need to add a battery to power it and create the buzz?

    [​IMG]
     
  15. Danger

    Danger 9,878
    Gold Member

    Yes. Pure water doesn't conduct electricity, but it almost always picks up conductive minerals when let loose. Given the items shown in your pictures, just attach the two red wires to each other, then tape or glue the two black ones very close together (maybe 0.5mm).
    Also, smear some sort of grease around the contacts of the battery case just in case the water is conductive enough to short it out.

    edit: And if you have a chance, sneak some salt into the water supply. :devil:
     
    Last edited: May 12, 2013
  16. dlgoff

    dlgoff 3,119
    Science Advisor
    Gold Member
    2014 Award

    Hey sapia,

    Take a look at this technical reference from Omega.

    www.omega.com/techref/pdf/aboutconductivity.pdf

     
  17. berkeman

    Staff: Mentor

    Homework/project thread moved from the EE forum the HH/Engineering forum.

    C'mon guys, please do not do students' homework for them. That's against the PF rules. Please report misplaced posts like this so the Mentors can move the thread to HH and remind the OP that he has to actually show some work and effort on his schoolwork projects.

    sapia, check your PMs.
     
  18. Danger

    Danger 9,878
    Gold Member

    Sorry. I got carried away. :redface:

    (Does it help that I was wrong?)
     
  19. Perhaps capacitance change would work?

    PS Using DC can lead to corrosion/plating problems so using AC might be a better option even if using conductivity.
     
  20. Danger

    Danger 9,878
    Gold Member

    Possibly, but I suspect that the single "AA" battery case that s/he showed might have difficulty providing that.
     
  21. If you are expecting a flood of cooking oil then use a float switch. Only trouble is that you need quite a lot of liquid to turn it on.
    Float Switch
     
    Last edited: May 26, 2013
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