semi automatic switch

Discussion in 'General Electronics Chat' started by sureshparanjape, Jun 22, 2013.

  1. sureshparanjape

    Thread Starter Member

    Feb 10, 2012
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    I am working on a small project of water level controller for storage tanks. I have a circuit that works for my requirements with three transistors(547), one relay of 250V/7 amp on 12V supply. The last requirement requires a switch that can be set on manually and shut off when one tank's water level reaches to a certain level.This switch is for the power supply for the circuit.The following figure might give one better idea for what I am looking for.Am I expecting too much?
    Thanking you

    sureshparanjape

    [​IMG]
     
    Last edited by a moderator: Jun 23, 2013
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    No figure attached.

    Ken
     
  3. sureshparanjape

    Thread Starter Member

    Feb 10, 2012
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    Sorry, I thought pasting the picture in the main would be ok. However it appears that it doesn't appear. Here is the attachment.
    sureshparanjape
     
  4. Ramussons

    Active Member

    May 3, 2013
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    sureshparanjape likes this.
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    What you are asking for is known as a 'float switch'.

    It literally floats when the water reaches it. Put the name in Google Images and look at the hundreds of different configurations and you will find one the suits your needs.

    The easiest method will be a 'normally open' switch that is in series with your power supply input voltage. It will be closed and supply voltage to your project until it floats. When it floats it will 'open' and remove power from your project.
     
  6. sureshparanjape

    Thread Starter Member

    Feb 10, 2012
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    Thanks, Mr.Ramesh
    However my intention is to start the switch manually and it should shut off by a signal generated by the project when filling is done.
    sureshparanjape
     
  7. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Your project schematic makes no sense. Maybe you can redraw it.

    Ken
     
  8. sureshparanjape

    Thread Starter Member

    Feb 10, 2012
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    Thanks, Mr. Kermit2
    What I am looking for is circuit equivalent of "float switch",signal generated by the project when water reaches a probe would replace physical action involved in physical float.
    I can visualize a switch when pressed remains pressed till the action of keeping it pressed is released by magnetic force, somewhat like relay magnet action.I have been unable to locate such a switch by Google search.
    sureshparanjape
     
  9. Ramussons

    Active Member

    May 3, 2013
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    I see no need for transistors . . . .
    What you need is a latching relay that powers the pump, and which releases by the water level switch.

    See the schematic. ( may need an explanation :D )

    Maybe you can expand on your requirements.

    Ramesh
     
  10. sureshparanjape

    Thread Starter Member

    Feb 10, 2012
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    Dear Mr.Ramesh,
    Let me see whether I can put it differently and make sense what I want.Project gets power from 12 V source. The project is on/off as power is on/off.Project circuit will do the necessary task of starting the pump whenever needed, stop whenever the task is completed and stop the motor( that is where there is a relay in the project). I do not wish the circuit be on and by the internal(to project) conditions it keeps on/off, making pumping on/off. My circuit is still in experimental stage, working very well on breadboard. My reason for not including the circuit in this correspondence is not because I want to keep it as secret but it is 'half baked"!
    sureshparanjape
     
  11. Ramussons

    Active Member

    May 3, 2013
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    Why not publish the "Half Baked" circuit so all of us here can attempt to "Full Bake" it ? :D

    Ramesh
     
  12. BillB3857

    Senior Member

    Feb 28, 2009
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    It is really hard to help a secret! Besides, Ramussons's solution using one pushbutton and one relay looks like it will do exactly as you wish. Push button to start, float stops unit, unit stays off until button is pushed again.
     
  13. sureshparanjape

    Thread Starter Member

    Feb 10, 2012
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    Dear Mr. Ramesh and Mr.BillB3857,
    I was avoiding to write the thought process in coming up to present form of the circuit, which is attached.Please refer to the circuit.
    The relay part has not been tried and I would be taking professional help for that part since it involves 220 V!
    Problems at this end of world are reliable power and water supply. Hence my requirement of manual starting on the project.I have two tanks, one at lower level and other at the top of the building.My other requirements are pumping should start if (i) water level at the top should be below specified level in the upper tank and (ii) water level in the lower tank should be above a specified level. Hence there are two probes for each tank as shown in the circuit.
    Explanation ?reasons: 615 ohms resister is to limit current in the lower part so that I can use 1/4 watt resistances that I have already with me.Middle transistor part is a NOT gate for the lower tank probe . 1st and third transistor are switches. I have tried this circuit on Breadboard and unless I am making some logical error in the above arrangement the circuit is giving the desired result.
    Pumping would stop when water level reaches U-probe;wouldn't start if L-probe is above water or stop if it goes below lower probe.
    If the circuit is switched on by external switch it would remain on and may start/stop endlessly unless stopped manually.In order to take care of this possibility I wish for a switch that can start manually and stop by the circuit( here by the signal from first transistor.)
    I am sorry to bore you with all these details.
    sureshparanjape
     
  14. Ramussons

    Active Member

    May 3, 2013
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    sureshparanjape,

    From you explanation, I gather:

    1) Water pump must start when

    the top tank has water Below a Set level
    AND
    the water in the lower tank is Above a Set level

    2) The pump must stop when the upper tank fills up Above a Set Level
    OR
    the water in the lower tank is Below a Set Level (this condition is mine, given the above requirement; not yet included in the schematic)

    You don't need Transistors.
    The Relay circuit can run on safe 12 V Car Battery.

    Hope the schematic is not difficult to understand.

    Ramesh

    sorry :mad: small goof in my schematic. pls wait for corrected one.
     
    Last edited: Jun 25, 2013
  15. LDC3

    Active Member

    Apr 27, 2013
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    My first question (since I didn't see it already): what is the signal from the probes for each condition?
    Below low level, between low level and high level, and above high level?
    Second question: Is the "turn on" condition only at the low level of the upper tank and the high level of the lower tank? or can it turn on whenever the low level of the upper tank triggers and the lower tank is not low?
     
  16. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    I'd use a ball float switch as mentioned before. Simple, reliable, cheap. If you want a level use a potentiometer on the float arm, just like a petrol tank.
     
  17. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    From the tone of sureshparanjape's posts, I think he really wants to use his circuit...not the simplest or the best. ;)

    Ken
     
  18. BillB3857

    Senior Member

    Feb 28, 2009
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    Some folks just enjoy having someone help them re-invent the wheel.
     
  19. Ramussons

    Active Member

    May 3, 2013
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    Here's the Schematic with some explanation.

    Ramesh
     
  20. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    PS stick with the float, don't use probes as unless you want to periodically replace them. Plus clean water is a poor conductor, dirty water well that's another story.
     
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