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Will the LED be ON or OFF in this circuit?

  1. Nov 29, 2009 #1
    Here is the ciruit. It's a D flip flop
    http://i45.tinypic.com/jtpjfc.jpg

    After reset is applied, will the LED be ON or OFF. Explain your answer.

    The answer is ON but I don't know why.
     
  2. jcsd
  3. Nov 29, 2009 #2

    cepheid

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    Hi physixchic,

    What are those two inputs on the D flip flop that aren't D, Q, Q' or clk? They both have negated inputs.
     
  4. Nov 29, 2009 #3
    i assume SET and RESET.
     
  5. Nov 29, 2009 #4
    Is it because RESET makes everything a 0 which makes Q a 0 and Q' a 1?
     
  6. Nov 29, 2009 #5

    cepheid

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    That's plausible, but I don't know for sure, because the D flip flops I'm familiar with don't have those additional inputs:

    http://hyperphysics.phy-astr.gsu.edu/Hbase/Electronic/Dflipflop.html

    The only thing that I can tell you for sure is that pushing the button pulls the D input low which (after the next rising clock edge) causes the Q output to go low, which causes its complement to go high, which lights up the LED. I have no idea what role the RESET line plays in this circuit.

    By the way, I'm assuming that this is the switch debouncer that you posted in another thread about?
     
  7. Nov 29, 2009 #6

    cepheid

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    Actually...

    Quoted from here:

    http://en.wikipedia.org/wiki/Flip-flop_(electronics)#D_flip-flop
     
  8. Nov 29, 2009 #7
    yes it is. thanks for the help I think i got it now
     
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