SR flip-flop

Discussion in 'General Electronics Chat' started by GTeclips, Mar 14, 2012.

  1. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    Hey guys, sorry to bug you with yet another probably simple question.

    I have a little breadboard project I'm working on, and I need just one SR flip-flop. I searched Radio Shack, but all I found were Dual-D flip-flops and more complex IC's. Does anyone know of any good, reliable Single SR flip-flops dip IC's that would be relatively inexpensive and easy to obtain?

    Again, sorry to bother you guys with this simple question, Thanks for the view!
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    For a simple S-R flip-flop you can use two NAND gates or two NOR gates, and you will have two spare gates.
     
  3. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    I suppose that would work. If this was to be the case, I would need to know of a dual nand dip IC (I already know of quad nand dip IC, but my circuits is low on space and I need as many open grooves as possible). Thank you for the idea!
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    They don't come in duals AFAIK. Typically quads, and now a days singles in microscopically small SMD packages.

    RS may well have them.
     
  5. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    So, the only way to make a single SR would be to use a quad nand? They don't have prepackaged SR's?
     
  6. MrChips

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    Are you looking for TTL or CMOS? TTL 74LS74 is pretty much standard.
     
  7. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    Okay, thank you. I personally prefer TTL over CMOS. Another question I was wondering, (sorry if you already answered this) instead of using 2 nand gates to make an SR, could you just use 2 not gates?

    EDIT: And could you also use 3 not gates to make a pulse generator?
     
  8. MrChips

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    1) It is possible to use two NOT gates to make an S-R flip-flop, depending on what you are using to generate the S and R. You will have to show your circuit.

    2) You can use three NOT gates to make an oscillator. You can also do it with a single Schmitt trigger NOT gate. You can substitute a 74LS14 hex Schmitt trigger inverters for regular 74LS04 inverters.
     
  9. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    74LS279 is a quad SR latch, with negative true inputs. 74HC279 is also available.
     
  10. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    Thanks for the chip number Ron!

    MrChip, I'm trying to upload my diagram, but I'm having trouble uploading it my usual way (photo bucket). Are there any other ways?
     
  11. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    Sorry that this isn't a real diagramming software, its a logic simulator, but its the best I have.

    TOP: SR flip-flop
    BOTTOM: Oscillator

    [​IMG]
     
  12. MrChips

    Moderator

    Oct 2, 2009
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    If you just wish to demonstrate an S-R flip-flop using NOT gates, here is a simple circuit:

    [​IMG]
     
  13. MrChips

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    Here is a simple oscillator using a single 74LS14 Schmitt trigger inverter.
    I will provide component values later after I get a chance to test it on a breadboard.


    [​IMG]
     
  14. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    Thank you MrChips, I'm trying to make an SR flip-flop using a NTE 74C04 TTL 14 dip hex inverter IC, but I believe I am wiring it incorrectly because it will not function properly.
     
  15. MrChips

    Moderator

    Oct 2, 2009
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    Try 74LS04 instead.
     
  16. MrChips

    Moderator

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    Here is a working circuit for an oscillator from a single 74LS14 inverter.
    The second inverter is there only to drive the LED.
    The RC values will give a frequency that is visible on the LED. You may change R and C to suit. Typical range for R is 100 to 4700 ohms.

    [​IMG]
     
  17. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    I see how that works, but I'm a little frustrated that it won't work with the 74C04, what is the major diffrence bettween the 74C04 and the 74LS04, because I already have a 74C04, and I only want to get additional chips if necessary? (BTW I'm talking about the SR flip-flop.)
     
  18. MrChips

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    Oct 2, 2009
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    When one push button is pressed and held pressed, does the corresponding LED come on?

    What happens when you release the push button?
     
  19. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    Wait, do you mean a button conected to the IC, the connected to a led, or just a button conected to a led?
     
  20. MrChips

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    Oct 2, 2009
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    Now I have no idea what you are talking about.
    Maybe you should post a photograph of your setup.
     
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