Dual water level

Discussion in 'The Projects Forum' started by susannah, Mar 10, 2014.

  1. susannah

    Thread Starter Active Member

    Feb 14, 2010
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    I have 12V solenoid valve and 12V water pump.

    I need to monitor water level in tub:

    -turn valve open when less water than 10 inch
    -turn valve close when more than 20 inch water

    -when less water than 1 inch then turn pump off
    -when more water than 5 inch then turn pump on

    Thanks
     
  2. inwo

    Well-Known Member

    Nov 7, 2013
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    I like to use probes suspended in the water.

    The commercial level sensing relays aren't too high priced.

    I believe it can be done with logic chips or even fet/bjt.

    What do you want to work with?
     
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  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I have used the GEM line of float Switches, they are similar to this ebay listing 251241767990
    Max.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    Is this basically fresh tap water in an open tub? Not salt water, not a closed vessel? Not distilled water?
     
  5. inwo

    Well-Known Member

    Nov 7, 2013
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  6. susannah

    Thread Starter Active Member

    Feb 14, 2010
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    I think i want to use transistors if possible. I currently have only these transistors and logic gates if it helps:
    S8050/S8550/S9012/S9013/S9014/S9015/S9018/2N5551/2N5401/A1015/C1815
    74HC00, 74HC02, 74H04, 74HC08, 74HC32, 74HC86 logic chips

    "Is this basically fresh tap water in an open tub? Not salt water, not a closed vessel? Not distilled water?"

    Yes, fresh tap water, no salt, not closed, not distilled.
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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  8. inwo

    Well-Known Member

    Nov 7, 2013
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    Here is something from the web.

    Use one to latch relay. Another to unlatch.
     
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  9. susannah

    Thread Starter Active Member

    Feb 14, 2010
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    Does this work with 12V? I'm really newbie in these things.
     
  10. inwo

    Well-Known Member

    Nov 7, 2013
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    Here's one for 12v.
    Again, just from the web.[​IMG]
     
  11. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    DC biasing in inow's circuits (schematics) will cause the continuously submerged electrodes to corrode. His Floatless Relay uses AC on the electrodes to prevent this.

    Ken
     
  12. inwo

    Well-Known Member

    Nov 7, 2013
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    True, there will be some corrosion issues.

    I thought I would get time to draw a more appropriate design, but this is a start.

    Still needs a relay/solenoid inverted driver.

    Might just be better to buy a "level relay"
     
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  13. inwo

    Well-Known Member

    Nov 7, 2013
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    This one may be more correct function.
    Drives relay or small solenoid.
     
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  14. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Why not just use a toilet float valve.
    No 12 volt needed.
     
  15. susannah

    Thread Starter Active Member

    Feb 14, 2010
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  16. inwo

    Well-Known Member

    Nov 7, 2013
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    Possibly, the solution suggested in #13 requires 12vdc supply and 12vdc relay .

    I'm not up to re-testing the circuit today.
     
  17. wayneh

    Expert

    Sep 9, 2010
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    My first approach might be to use 4 standard float switches since these are off-the-shelf.

    My next approach would be to use an external sight tube, possibly containing a float, and 4 LED break-beam pairs to sense the 4 specified levels. The water level in the attached, clear tube would be the same as in the tank, since both vent to atmospheric.

    I would then use comparators (eg. LM339) to react to the water level or the presence of the float within the beam. Each comparator would use an adjustable reference voltage on one input pin, so that the sensitivity can be adjusted as needed.

    I haven't worked out the logic tree (I can't quite follow your control scheme) but I think you might want to "OR" together 2 or more comparators to define the various states of the valve and pump.

    The comparators will control 2 MOSFETs that are appropriate for the two loads.
     
  18. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    One problem with the float in the sight tube is that beam break has at latch that reading. The float will not continue to block a level sensor as it rises or falls past the sensor.

    Not a big logic problem, but must be considered.

    Ken
     
  19. wayneh

    Expert

    Sep 9, 2010
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    Yes, I think sensing the water itself might be better than trying to catch the float as it passes by. I believe a standard IR pair would be fine for detecting water but you'd have to be sure the clear tube itself doesn't absorb too much.
     
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