Two Button On Off Latching Circuit

Discussion in 'The Projects Forum' started by Jasonh74, Sep 7, 2015.

  1. Jasonh74

    Thread Starter New Member

    May 18, 2015
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    I want to be able to control a 12V water pump for filling a surge tank when required.
    When the water level drops to a certain low point, I want the pump to turn on and when the water level reaches a certain high point, I want to turn the pump off.

    Ideally this will be a 12V circuit. I can find lots of circuits that use a single push button to turn the pump on and off but I want to use two. One micro switch will be at the low point and one will be at the high point.

    Can anyone point me in the direction of a circuit that will achieve this.

    Thanks in advance.

    Jason
     
  2. pwdixon

    Member

    Oct 11, 2012
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    You could use a flip-flop set by one switch and reset by the other, obviously you'd also need a driver circuit to drive the pump too.
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Get a float switch. They are designed for this.
     
  4. pwdixon

    Member

    Oct 11, 2012
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    But with only one switch won't the pump just top up the tank? The OP wanted to cycle the tank between a low level and a high level.
     
  5. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    No, there are two contacts on the float (low and high) with a dead zone between.

    Several options are possible
    1) A simple 555 timer can be used in a monostable mode one low level is detected. The 555 runs until the high level switch is contacted and that pulls the 555 reset pin low.

    2) turn on a mosfet base (through a diode) to keep it on through the dead zone and, one the high limit is reached, a second mosfet is triggered that drains the base voltage latch on the base of the first mosfet.

    Any combination (including an arduino or PIC) that he would have used with micro switches and high/low limits.

    Or a 555 flip-flop circuit. Instead of the LED, drive a relay that starts the pump...

    image.jpg
     
    Last edited: Sep 7, 2015
  6. blocco a spirale

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    Jun 18, 2008
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    Last edited: Sep 7, 2015
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Simplest circuit using two float switches. Make-on-empty float switch has be be rated for the pump starting current. If not, use two relays, one for the latch, the other rated to switch the pump. Or use a two-pole relay, using the second pole to switch the pump.

    float.gif
     
    Last edited: Sep 7, 2015
  8. ScottWang

    Moderator

    Aug 23, 2012
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    The first circuit could be have the problem of key bounce.
     
  9. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    This is the circuit I was referring to, I don't see a bounce issue:
    [​IMG]
     
  10. Lestraveled

    Well-Known Member

    May 19, 2014
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    They make sump pump float switches that are designed for this application. They are ingeniously simple. A single toggle switch with an extended toggle arm connected to a light weight vertical shaft. There is a float that slides up and down the shaft. When the water level drops the float drops until it hits a bottom stop on the shaft and pulls the toggle switch into the down position. The water rises, the float slides up the shaft until it hits the upper stop and pushes the toggle switch into the upper position.

    [​IMG]
     
    blocco a spirale likes this.
  11. ScottWang

    Moderator

    Aug 23, 2012
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    For a relay probably it works for less than 10hz, and the key bounce maybe 30hz, so the key bounce won't affecting the relay, the relay circuit you attached that it was similar with Mike, that is used the easy way to reach the purpose.
     
  12. jayanthd

    Member

    Jul 4, 2015
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    I made this circuit but I have not calculated the resistor values. It is only a rough circuit. SCR used is C106D or C106M/1. If LEDs are needed to indicate manual ON/OFF and Tank High/Low then it can be easily added using additional BC337 transistors and LEDs.

    On pressing the ON button or if the Tank Low sensor closes then SCR turns ON and motor turns ON. If manually OFF button is pressed then transistor turns OFF and hence SCR current falls below holding current and hence motor turns OFF. Same happens if Tank High Sensor closes.

    Alternately a relay can be used which in turn drives the 12V motor.

    Auto ON OFF for Pump.png
     
  13. jayanthd

    Member

    Jul 4, 2015
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    Well I use US020 ultrasonic sensor to detect the level of water and then a TFT graphically displays the level of water in sump and overhead tanks. I used Arduino Mega2560.
     
  14. TheButtonThief

    Active Member

    Feb 26, 2011
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    With the exception of Mr. spirale, you're all completely over complicating this with electronic schematics. The solution is electrical, not electronic and as far as electrical design goes, it's the most simple:

    pump.jpg

    When the water level is high and S01 and S02 are floating, Their NC contacts are open and so the pump is not on. When the water level falls below S02 (High Level), S02's NC contact closes but the circuit is still open as the water level continues to drop. When the water level drops below S01, it's NC contact closes and activates the contactor/relay (K01) to turn on the pump. A NO auxiliary on K01 keeps the supply to K01 high while the water level rises (S01's contact opens but the circuit stays complete). When the water level reaches the top, S02's contact opens and so K01 un latches and turns off, the motor stops until the water level drops below S01 once again.
     
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