Resettable circuit

Discussion in 'The Projects Forum' started by TitaniuIVI, Apr 19, 2011.

  1. TitaniuIVI

    Thread Starter New Member

    Apr 15, 2011
    2
    0
    I currently have a sensor which controls a relay. When the sensor is open it powers the coils on the relay and turns a pump on. When the sensor is closed, that means something happened the the pump shuts off. What I want to add to this is that once the sensor is closed, the pump will turn off, and stay off even if the sensor goes back to open. I would then have to hit a reset button in order for the pump to turn back on. I've been looking around and can't really find any specific information about this, but I'm probably not looking for the right thing. From what I did find, it seems like I would need a MOSFET, but I've never worked with these, so not sure if that is what I need. Could someone point me in the right direction on what I would need to get this setup?
     
  2. JDT

    Well-Known Member

    Feb 12, 2009
    658
    85
    I had to think about how this could be done with relays (no horrible electronics). Think I have come up with a circuit. You will need to add two small (and fast) relays. These will control your larger and slower pump relay. The pump relay will need an extra N.C. contact.

    This circuit relies on the fact that the operation of the pump relay is delayed compared with the sensor relay. See the timing diagram attached.

    RL2 is reset by pressing the button. It holds itself energised when the button is released with its own contact.

    RL2 remains energised if the sensor relay (RL1) energises before the pump relay (green line).

    RL2 de-energises when the sensor relay (RL1) switches off before the pump relay (red line).

    When RL2 is de-energised the pump cannot run even if the sensor is on.
     
  3. TitaniuIVI

    Thread Starter New Member

    Apr 15, 2011
    2
    0
    That's a pretty cool idea, but I was looking for something a bit less complicated. The logic you apply there seems like it could be done with and AND gate. Can anyone that has used AND gates shed some light on this? I get the part where it won't send out a signal through Y unless A AND B have a signal, but how do I make it keep a signal on the side with the momentary push button when it should be on, and stopped until I push the button?
     
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