MC14538B as astable ?

Discussion in 'Digital Circuit Design' started by inwo, Aug 9, 2016.

  1. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    I would like to use 1/2 for retrig. monostable and 1/2 for astable if its possible.
    Or find a dual timer that does both. ~12v
    555/556 type isn't a good choice for retriggering. IMO
     
  2. hp1729

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    Nov 23, 2015
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    I don't have an example made up but if you put a power on reset circuit on the reset line and tied the Q0not output to hi trigger input it should go astable but only be in the reset state for about 50 ns. On power on it comes up reset, triggering it. When the timing times out Q-not goes high again, clocking it ...I don't think I ever tried it since I don't have it in a drawing, but in theory it should work.
     
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  3. AnalogKid

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    Aug 1, 2013
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    A CD40106 or CD4093 can do both functions in one chip.
    Does the retriggerable gate the oscillator?
    What is the freq range of the oscillator?

    ak
     
  4. GopherT

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    What is your goal and what are the constraints. Any reason for limiting to a single chip?
     
  5. jpanhalt

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    If you are looking for how to connect the MC14538 as an astable, this might help (you may want the whole application note, see link below):
    upload_2016-8-10_4-13-4.png

    Source: Fairchild AN366 (available here: http://www.scarpaz.com/Documents/AN-366.pdf)

    As just an FYI, MC1xxxx numbers are usually equivalent to NNxxxx . That is, to find circuits for MC14538, try searching on CD4538 or any other chip with just 4538 in its ID.

    John
     
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  6. Alec_t

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    Here's a way you can use 1/2 a CD4538 as an astable :-
    CD4538-as-astable.JPG
     
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  7. GopherT

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    Nice find. Very interesting things in there. I have been looking for the answer to @inwo 's question for a long time and I assumed it couldn't be done.
     
  8. AnalogKid

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    Another option is the dual comparator LM393. Both functions in only 8 pins, 2 V to 36 V power supply range.

    ak
     
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  9. inwo

    Thread Starter Well-Known Member

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    I'll try that.
     
  10. inwo

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    An exercise in kiss.
    Circuit from my other thread works with a retriggerable monostable into an astable 555.

    Making sure I'm not missing a simpler way to do it.

    For those who missed it.
    Project has a signal in from <10 to 500hz.
    Output needs to follow input to ~350hz.
    This is where I'm at so far using TTL.
    Just got in some more parts.
    Over 350hz output = 350 retriggermono123a.png hz.
     
  11. jpanhalt

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    Have you changed your mind? KISS

    John
     
  12. inwo

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    I have 14538 now.
    Quite sure that 1/2 will work as my retrig-mono.
    If the other 1/2 can be a gated astable, I'm in business. One chip solution.........

    If not I'll go back to adding a 555.
     
  13. inwo

    Thread Starter Well-Known Member

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    Is there an easy way to retrigger 555 (1/2-556)without more active components?
    Heck, maybe I can do the whole thing with one 555.
    I'm open to suggestions.
     
  14. inwo

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    14538 same?

    Here is the retrig- mc14538.gif mono 1/2.
     
  15. GopherT

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    Yes, the MC14538 is the same as CD4538 or HEF4538.
     
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  16. Alec_t

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    Use appropriate R and C values; the ones in the sim are merely for proof-of-concept.
     
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  17. jpanhalt

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    Please start by reading post #5.

    John
     
  18. inwo

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    I didn't check the link, as I was aware of that method which requires more gates and both halves.
    I'll check it out.
     
  19. inwo

    Thread Starter Well-Known Member

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    Would you be willing to add a monostable half in the sim? :)
    Oh wait, I have to see if I can gate your astable circuit. :(
     
  20. inwo

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    Last edited: Aug 10, 2016
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