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How to make flip-flop (frequency-divider) with schmitt inverter?

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by johnyradio, Aug 9, 2017.

  1. johnyradio

    johnyradio New Member

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    Hi

    Ideally, i'm looking for a simple frequency divider that i can feed a square wave, using only schmitt inverters or schmitt NAND (just one if possible). Should work over a wide input-frequency range.

    The posts below provide a schematic for a so-called "flip-flop" (which i think is really a toggle, not a flip-flop) using two schmitt inverters.

    http://www.electro-tech-online.com/threads/electronic-switch.26093/#post-181844
    https://forums.adafruit.com/viewtopic.php?f=8&t=36970&p=607457#p607457
    http://www.learningaboutelectronics.com/Articles/Touch-on-off-circuit-with-a-7414-inverter.php

    The circuit is based on a switch, not a clock, so would not work as-is for my need. But, maybe someone can see a way to make this work as a divider with a clock-input instead of a switch? Or, some alternate flip-flop circuit using schmitts?

    I wired up the above circuit in falstad
    http://tinyurl.com/ya8cz2nm

    Issues:
    • Seems highly sensitive to input on-time.
    • Getting strange oscillations.
    Pressing the switch manually, i sort of get a toggle, sometimes. Seems to depend on how long i hold the switch, and maybe how long i wait between presses, and whether i'm going from low to high or high to low. Also, i seem to get a very high frequency oscillation while holding the switch. Am i doing something wrong?

    Any ideas for a true flip-flop divider based on Schmitts?

    thx
     
  2. crutschow

    crutschow Well-Known Member Most Helpful Member

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    It's difficult to use such a circuit over a wide frequency range since it depends upon RC delays for proper operation..
    Much easier to just us a D-flipflop with the D input connected to the /Q output.
     
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  3. ci139

    ci139 Active Member

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    you could try something alike (but please don't use this simulator for complex circuitry - LT Spice is yet free)
     
  4. dave

    Dave New Member

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  5. johnyradio

    johnyradio New Member

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    Thanks! but It says "convergence failed".
    Where do i connect my square wave source?
    Can you show the scopes? Cannot see the scope for some reason.

    thx!
     
  6. ci139

    ci139 Active Member

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    Attached Files:

    Last edited: Aug 9, 2017
  7. johnyradio

    johnyradio New Member

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    many thanks, ci139
    since no easy, wide-frequency way to do with schmitts, i'll go with a flip-flop chip.

    thx!
     
  8. ci139

    ci139 Active Member

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    you never know until you occasionally somewhere run to it - some setup of T-flop might just do what you need
    [​IMG]
    by Google iS . . . the good question here is where to get the BUTTON with the right "Moment" . . . the 100k somewhat incorporates here . . . donno ← an idea level design (in latch setup the button would be the 3-rd transistor) while the Bjt v. has only 2
    [​IMG]
     
    Last edited: Aug 10, 2017
  9. schmitt trigger

    schmitt trigger Active Member

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    Cross coupled NAND or NOR gates also make a good SR flipflop

    [​IMG]
     
  10. crutschow

    crutschow Well-Known Member Most Helpful Member

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    But not as a toggle flipflop for a frequency divider as the TS wants.
     
  11. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Here is the simplest, "real", divide-by-2 circuit made from gates. It is properly edge-triggered, and changes on rising-edges. It can be built from almost any logic family, provided that the max frequency is consistent with the gate delays.

    49.png
     

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  12. ci139

    ci139 Active Member

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