Two switches/one to be replaced

Discussion in 'General Electronics Chat' started by adriadri, Oct 6, 2009.

  1. adriadri

    Thread Starter Member

    Apr 30, 2009
    27
    0
    Hi,
    I have two hard switches A and B that need to be linked in a certain way.

    A is a toggle switch (on / off ) that powers a circuit .
    B is a normally open pushbutton switch.
    B
    must be physically removed and replaced by the following action triggered by A:



    A manually goes from OFF to ON and powers one circuit.

    3 seconds delay..

    And automatically B is briefly closed just to start another circuit (different from the first) and remains open.

    Nothing happens when A manually goes to OFF again.




    I know this could be ridiculously easy to do with timer stuff but I´m on the mechanics side.
    Thanks.
     
    Last edited: Oct 6, 2009
  2. tibbles

    Active Member

    Jun 27, 2008
    249
    3
    HI ADRIADI
    "is briefly closed just to start another circuit"
    do you mean cycle
    could you do us a rough sketch of what you have in mind,
     
  3. adriadri

    Thread Starter Member

    Apr 30, 2009
    27
    0
    Basically A switch triggers a cyle in B pins 3 secs later (b is not there anymore, just two pins)
     
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  4. tibbles

    Active Member

    Jun 27, 2008
    249
    3
    forgive my crude drawing my copiers off at the moment see pic

    just using a relay analogy to start with

    so when you close switch A there is a 3 second delay before the relay operates momentarily sending a pulse to circuit B ?

    are you ok with electronics ?
     
  5. tibbles

    Active Member

    Jun 27, 2008
    249
    3
    adriadri

    i hope were talking low voltage stuff
     
  6. adriadri

    Thread Starter Member

    Apr 30, 2009
    27
    0
    Thank you!
    Yes the analogy is exact. 12 volts is the voltage.I just need a simple circuit to do that .
     
  7. tibbles

    Active Member

    Jun 27, 2008
    249
    3
    something like this
    the output can drive a normally open relay or a power transistor, depends on your circuits really,

    im a bit of a newbie, i was hoping one of the experts would show us the way, they must be all up the pub,
     
  8. tibbles

    Active Member

    Jun 27, 2008
    249
    3
    sorry ,the first input will need a differentiator? to provide the negative trigger pulse,
    sounds complicated but i think its only a diode /resistor

    will get back with this info

    hows your maths?
     
  9. tibbles

    Active Member

    Jun 27, 2008
    249
    3
    if using a relay it will generate a back force on switch off so a diode is needed here to protect the second 555.
     
  10. adriadri

    Thread Starter Member

    Apr 30, 2009
    27
    0
    Thanks for your help Tibbles, I´ll look into this circuit. I´m good in Maths (not counting electrons, but RPM´s)
     
  11. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    A couple of options:

    A positive-edge transistor-triggered 555 monostable: The leading edge of a zero-to-positive pulse on R1 will trigger the 555. Depending on what the input to the B circuit looks like, the 555 output might drive it directly, or through a relay or an opto-coupler.

    A "relay monostable": The ON-period depends on the value of C1 and the resistance of the relay coil. The diode prevents it from being an "edge detector". ;)

    Ken
     
  12. adriadri

    Thread Starter Member

    Apr 30, 2009
    27
    0
    Thanks for your circuits Ken!
    If I´m not wrong the "relay monostable" result is just the relay acting a
    given amount of time "the on-time"?

    If so, I don´t need this.
    What I need is that when I manually move a toggle switch from ON to OFF, (this could be one half of a double toggle switch, the other independent half powers the A circuit that has nothing to do for what I need),
    two pins- absolutely independent from that circuit-are momentarily shorted
    -say the time a PC keyboard key is pressed when you type-.

    The time delay from the toggle switch change till the momentary short occurs, is 3 or 4 seconds.
     
  13. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
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    Oops! missed that. I'll re think this. ;)

    Ken
     
  14. adriadri

    Thread Starter Member

    Apr 30, 2009
    27
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    here´s a pic of what I need.Thanks!
     
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  15. tibbles

    Active Member

    Jun 27, 2008
    249
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    sorry adriadri

    your inititial project shows 2 black boxes, do you need only 1?
     
  16. adriadri

    Thread Starter Member

    Apr 30, 2009
    27
    0
    Yes. In fact the toggle switch is double. So one part triggers the irrelevant (not shown now) first box and the other part is exclusively dedicated to trigger the sequence I need, which means you must see the toggle switch as isolated from everything but the black box of the last attachment.
     
  17. tibbles

    Active Member

    Jun 27, 2008
    249
    3
    im having a discussion on this forum about attaching thumbnails, how do you do it?

    if you still need the delay a similar approach will apply
    as there is no indication of polarity/voltage on the two bottom pins, the relay route would provide isolation
     
  18. tibbles

    Active Member

    Jun 27, 2008
    249
    3
    kens relay circuit looks good, just use the normally open contacts,
    save a lot of electronics,
     
  19. adriadri

    Thread Starter Member

    Apr 30, 2009
    27
    0
    Thanks for your help!
    Well, the thumbnail is uploaded using the "MANAGE ATTACHMENTS" button
    in the additional options dialog.(keep in mind you don´t have to use the "quick reply" option to get this dialog available)
    just use "Post reply".
     
    Last edited: Oct 7, 2009
  20. tibbles

    Active Member

    Jun 27, 2008
    249
    3
    (this could be one half of a double toggle switch, the other independent half powers the )

    if you use a double pole switch double throw switch, you can maintain isolation at this point as well so you can choose your own power supply polarity etc.

    need to look at kens relay circuit to check if the relay is initially closed or initially open, either way just use the relevant contacts.
     
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