pulse output

Discussion in 'The Projects Forum' started by Brian Krupicka, Sep 8, 2017.

  1. Brian Krupicka

    Thread Starter New Member

    Nov 1, 2014
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    I need some help….Thank you

    When a ground (input) is applied (via a switch) monetarily or indefinitely, I need the output to provide a single output pulse of ½ second (or so). The output can be either positive or negative. Once the switch opens the cycle will repeat itself.

    This may be simple to most of you but this old man needs some help.
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    You need what is known as a monostable multivibrator.
    You can do this with any one of these TLC555, 74HC123, CD4538 or similar devices.
     
  3. crutschow

    Expert

    Mar 14, 2008
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    What supply and signal voltages do you have?
     
  4. Brian Krupicka

    Thread Starter New Member

    Nov 1, 2014
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    5V supply
     
  5. crutschow

    Expert

    Mar 14, 2008
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    Below is the LTspice simulation of a typical 555 one-shot circuit.
    It generates a ≈0.5s output positive pulse for any length trigger from the switch.
    Any 555 type IC will work (they come with several different prefixes such as uA, LM and NE but they are all the same.

    upload_2017-9-8_13-33-17.png
     
  6. Brian Krupicka

    Thread Starter New Member

    Nov 1, 2014
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    Thank you for your quick response.
    I will build it and post my results.
    Brian K
     
  7. wayneh

    Expert

    Sep 9, 2010
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    A one-shot won't give you a second pulse when the trigger is removed. It only generates a pulse when the trigger is pulled low (when the green trace goes high in the simulation above). I think this can be solved simply if you really need that pulse when the switch opens as well as when it closes.
     
  8. Brian Krupicka

    Thread Starter New Member

    Nov 1, 2014
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    I bread boarded the circuit “CRUTSCHOW” detailed above. It works as detailed.
    However, I need to apology to all. The requirement is to provide a 0.5 sec. output pulse when the switch opens (ground is removed).

    Brian K
     
    Last edited: Sep 10, 2017
  9. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    So, is that an output pulse *both* when the switch closes and opens, or only when the switch opens?

    ak
     
  10. Brian Krupicka

    Thread Starter New Member

    Nov 1, 2014
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    When the trigger switch opens (ground is removed), the output is a one pulse of 0.5 seconds.

    Brian K
     
  11. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    Here is a quickie, 1-transistor circuit. The trailing edge of the output pulse will not be nanoseconds-fast, more like milliseconds.

    ak
    upload_2017-9-10_18-51-25.png
     
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