push button to control reverse current momentary switches

Discussion in 'The Projects Forum' started by Marcusone, Apr 25, 2015.

  1. Marcusone

    Thread Starter New Member

    Apr 25, 2015
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    I'm looking to create a circuit that has a single push button, that when pressed will cause a momentary pulse connection (12v) to a connected device, then on the next push, a -12v pulse, then +12, -12, etc etc.

    It should not draw any power when "idle".

    the device typically will draw 100mA when connected momentarily.

    I have no real experience with creating circuits, but can follow and put together most diagrams.

    I would guess i need some kind of latchine SPDT relay, connected to 2 DPDT relays... but how do i get the pulse (momentary) portion?

    Diagrams/solutions very welcome!

    Thank you,
     
  2. GopherT

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    Nov 23, 2012
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    @Marcusone
    Your description is confusing. Do you want a momentary power pulse when the button is pushed or latching power when pushed?

    Also, do you have your heart set on push buttons (requires programming, Microcontroller and bridge of transistors to get the reversing function) - difficult
    Or is a toggle switch (on - off - on format) feasible - this would be easy, easy, easy
     
  3. Marcusone

    Thread Starter New Member

    Apr 25, 2015
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    The toggle switch is what I will likely use as you can get a DPDT (on)-off-(on) as i'm sure your well aware.

    I would love to do a single push button with it toggling between + and - pulses. my design skills are rather lacking for that :(
     
  4. Alec_t

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    The toggle switch is undoubtedly the simplest solution, but the single-button method could be made to work with a handful of components (including a CMOS IC or two). Is the device a purely resistive load, or does it have an inductive nature (e.g. relay, motor)?
     
  5. Marcusone

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    Apr 25, 2015
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    Its for a latching solenoid valve (no manual, far as i can find on the internet, they usually have very little draw).
     
  6. MaxHeadRoom

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    So the solenoid itself is already magnetically latched?
    Or does it use power in one position?
    Max.
     
  7. Marcusone

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    Apr 25, 2015
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    the latching solenoid only uses power to switch from open-close, or close-open positions.
     
  8. MaxHeadRoom

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    Then surely two momentary switches will do it? If necessary a N.O. and N.C. contact on each, the N.C. would serve as an interlock to prevent opposite polarity simultaneously being supplied.
    Max.
     
  9. GopherT

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    Nov 23, 2012
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    @Marcusone
    Here. One momentary push button activates a D_type flip flop (cd4013) and each button push-and-release cause Q outputs to toggle on or off.

    The Q output and Q-bar are each connected to a mosfet (2n7000).

    The drain of each mosfet is connected to its own 555 timer. The 555 is configured to stay on for 200 mSec. Adjust as needed with your solenoid.

    The 555 will sink or source as appropriate - up to 250 mA as a bridge in this case.

    image.jpg

    image.jpg
     
    Last edited: Apr 27, 2015
  10. MaxHeadRoom

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    Unless I am missing something, a device such as a latching solenoid is not critical of pulse length, is any electronics really necessary?o_O
    Especially as the requirement is not to draw any power between activation.
    Max.
     
  11. GopherT

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    With a toggle switch, no. With a single momentary push-button, yes. The OP was hoping to use a single momentary push button.

    The Datasheet of one latching relay I found (I did not look for more) said they needed a minimum of 100 mSec pulse to latch/unlatch.

    The pulses shown above correspond to each button push and no current is drawn between button pushes (0V).
     
  12. BillB3857

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  13. MaxHeadRoom

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    The normal human response to a P.B. is most likely more than 100msec.
    The OP mentions "It should not draw any power when "idle".
    The circuit is drawing power when the solenoid is not in use if the above refers to the whole circuit.
    P&B/Tyco . make magnetic latch/unlatch relay, which also requires no power when non-activated
    Max.
     
  14. Reloadron

    Active Member

    Jan 15, 2015
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    Looking at what the OP has mentioned to date:

    The actual device:

    Latching solenoid valves like this come in a few flavors but if we assume a single coil latching solenoid valve most require one polarity to open and reversing polarity to close. Much like the output of an H Bridge to reverse a DC motor's direction. In post #3 where the OP mentions the use of a DPDT switch he also shows the switch as (ON)-OFF-(ON) where the use of the brackets implies the (ON) as momentary with a center OFF position which would be simple and work fine as long as the momentary were held long enough for the solenoid to latch on or off. Just about all of the solenoids like this I have worked with were typically a 100 mSec pulse to change states. Not very long at all.

    If a single push button is really that necessary or needed I like GopherT's suggested circuit. A D flip flop driving a pair of one shots. With any circuit like this there will be minor current draw but pretty much insignificant. The only way around that is the DPDT switch as I see it. Obviously the switch is plain and simple and requires beside nothing to put together.

    Ron
     
  15. GopherT

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    I agree that a PB is likely longer than 100 mSec but I don't have another solution that cycles a SINGLE pushbutton to alternately cycle a +12 with one press and -12V pulse with the next press. Do you have another solution to a SINGLE push button that would not require a timing element like an RC or 555?

    I think the "draws no power" has to be elaborated on by the OP. I tend to screen what OPs says with a common sense filter to and offer reasonable alternatives to their requests. I think the OP may have meant "not powering my coil all the time", and a few mA of quiescent current of two mono-stables and a flip-flop may be acceptable to him. I will wait for his response to see if this works for him or not.

    I know, that is where I got the 100 mSec pulse requirement. Note that the circuit I proposed only powers the solenoid for 100 mSec after the switch is pressed, and then nothing (except the quiescent current of the 555s and flip-flop. Again, do you have an option for a push button that could work with no power? I agree (and stated in POST 2 of this thread) that an on-off-on momentary toggle switch would be "easy, easy, easy."
     
    Reloadron likes this.
  16. Kermit2

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    This can be done with relays only, but only toggle latching relays would provide the " no idle current" requirement. If OP desires I could provide a wiring diagram and probably part numbers.
     
  17. Alec_t

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    Gopher, you might want to add switch debounce to your circuit. Power-on reset, too (if the start-up state is important to the OP)? Will a 555 provide enough current for driving a solenoid valve?
     
  18. MaxHeadRoom

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    Another simple method of essential one button without the need for interlock is the panel mount centre off and momentary left and right.
    ebay 270877685430 .
    Max.
     
  19. GopherT

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    Good points. Let's wait for the OP to get back and offer some feedback before I do any more on it. I was actually hoping to convince home how easy the momentary toggle switch (on-off-on) that I mentioned in Post 2 would be instead of this.
     
  20. MaxHeadRoom

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    Agree!
    A $3.00 fix.
    [​IMG]
    Momentary L&R.
    Max.
     
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