Push On, Push Off Switch

Discussion in 'The Projects Forum' started by liteace, May 9, 2013.

  1. liteace

    Thread Starter Member

    Mar 7, 2012
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    Hi All, Ive built the little circuit:

    http://forum.allaboutcircuits.com/showthread.php?t=82955

    So 1st have to say a BIG thank you to everyone that helped me with that, its not up and running yet as Ive had no time and am waiting for other parts.
    What I want to do is control this with a push on \ push off 12 volt circuit, so again Im asking for help on building one, 1st question is where do I start, Ive seen 555\6 & transistor circuits for this, whats the best one to go for


    Thanks
     
    Last edited: May 11, 2013
  2. BillB3857

    Senior Member

    Feb 28, 2009
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    liteace likes this.
  3. liteace

    Thread Starter Member

    Mar 7, 2012
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    Thanks for the info, I dont mind building something, give me something to do + it keeps me soldering skills up to scratch
     
  4. elec_mech

    Senior Member

    Nov 12, 2008
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    I would suggest either posting the final schematic you used/made. I went to the link you provided and found a couple of schematics posted by other members, then several pages discussing a circuit, but no schematic of what you built. It makes it much easier to help when we can quickly find and see what you're working with and want to change.

    You can look up 555 toggle circuit. One place shows a few different options here.

    Personally, I like using a CD4013 D-flip flop configured as a T-flip flop. Only requires the IC and two passive parts if memory serves. I can dig up a circuit I've used if you like.

    Either of these options will work fine with 12VDC.
     
    liteace likes this.
  5. Wendy

    Moderator

    Mar 24, 2008
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  6. liteace

    Thread Starter Member

    Mar 7, 2012
    75
    0
    Last edited: May 11, 2013
  7. Wendy

    Moderator

    Mar 24, 2008
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    If you need help learning how to post jpg or png files let us know, for schematics they work better than links.

    So what are you wanting to turn on/off again? The circuit I showed with a simple solid state relay would work, as would a MOSFET.
     
  8. liteace

    Thread Starter Member

    Mar 7, 2012
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    What I want to turn on \ off is a heater controller circuit that is all built, instead of a normal on \ off switch I thought I would like a one touch on and one touch off setup, it's not essential but would be a nice little feature to add

    Thanks
     
  9. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
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    Take a good look at Bill's 555 Bistable Multivibrator - this will achieve what you're looking for. Upon further reflection, I realize the 4013 would have to be fed with a Schmitt trigger, thus requiring two ICs and more board space. Bill's circuit has both a Schmitt trigger (which acts as a debounce for the switch) and the toggle action you want.

    As Bill mentioned, you'll want to connect a MOSFET or similar to the output of the bistable circuit (in place of the LEDs) to control the power feeding your circuit.

    Thus: momentary switch connected to 555 bistable circuit connected to MOSFET which is placed in series with one of the power leads to your circuit (I suggest the positive side). You can add a power-on reset with a capacitor and resistor to pin 4 of the 555 bistable to keep power off when first applied. See here.

    I'd suggest drawing your schematic with the bistable circuit added then posting it here. We can then help verify everything is connected properly and advise on a suitable MOSFET or similar.
     
    liteace likes this.
  10. liteace

    Thread Starter Member

    Mar 7, 2012
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    Thanks, if you could dig out a circuit you've used that would be great, Ive searched for a few 555 toggle circuits but a couple of them say:

    "One disadvantage is the relay may be engaged when power is first applied"

    Thats 1 thing I dont want it to do


    Thanks
     
  11. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
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    Take a look here and look at the section entitled "Power-on reset or trigger". Add a 0.1uF ceramic capacitor and a 10kΩ to pin 4 (reset) as shown and the 555 will stay off (and thus the relay) at power up.
     
  12. liteace

    Thread Starter Member

    Mar 7, 2012
    75
    0
    instead of powering a relay could I use a mosfet, the mosfet would only need to power the heater control circuit as the heater would be on the 40 amp relay, I have here a spare SUP75N08 and also a IRZF44N would any of them work

    something like this:


    [​IMG]


    Thanks
     
    Last edited: Jul 15, 2013
  13. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
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    Could you post a larger picture or an attachment that is bigger when opened? I can't make out the details clearly.

    As a side note, when making schematics you either use arcs to denote when crossing lines are not connected OR use dots to indicate when crossing lines are indeed connected. You do not use both. Personally, I like dots as everything looks cleaner and is easier to read.

    From what I can make out, the heater control is turned on when +12VDC is applied to an input?

    How much current does the controller require? You stated the heater is on a 40A breaker, but I assume the current turning the controller on is much less. We want to ensure the MOSFET is sized properly.
     
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