555 timer settings

Discussion in 'The Projects Forum' started by Hipervids, Mar 23, 2009.

  1. Hipervids

    Thread Starter Member

    Sep 28, 2008
    14
    0
    Hi
    Does anyone have a good site I can go to for some monostable one shots from a 555 timer IC?
    I need a one shot that will create a 1ms pulse or even 2ms from a 5ms input pulse.

    The main thing here is that the input pulse is actually longer than the output pulse.

    Ive seen plenty of oneshots that can make smaller pulses than the input but none that make longer ones than the input and that can be retriggered as much as i want.

    Ideally the input pulse to the 555 is simply a pulse that can vary from 1 to 10 ms, like a pushbutton switch pressed fast but I need a accurate 1ms pulse to come out of it that will be 1ms even if I have the trigger pulse held on all day.

    Say I press a pushbutton switch as the trigger for as short of time as I could, i need a 1ms pulse to be generated from that but the 1ms pulse has to be generated as fast as I can press the button but if I hold the button down, still only a 1ms pulse will come out.
    Do you know what I mean??


    Is this easy to do from a 555 or do I need a different IC?

    I dont have any simulation software so the circuits I have been trying have been all hardware.
    Could someone simulate something similar for me and show me the results?
    Ive tried about 5 different circuits but none do what I need.


    Thanks alot.
     
    Last edited: Mar 23, 2009
  2. gotumal

    Active Member

    Mar 24, 2008
    99
    0
    This link might be useful.
    http://home.cogeco.ca/~rpaisley4/LM555.html#2


    It's a usual application.

    Circuit should be positive edge triggered, with appropriate RC (debounce)

    555 could be used.
     
  3. Hipervids

    Thread Starter Member

    Sep 28, 2008
    14
    0
    Excellent site thanks alot just what I was looking for.

    I made a mistake above and said the input pulse was shorter than the output pulse but its actually longer.
    Ive edited my post.
    Thanks again
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,170
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    Have you tried to differentiate input sig.? One side of PB, NO to ground, other to .o1 μF and 47kΩ ,other end of R to +. Open end of cap to P 2 and a 10kΩ , other end ofR to +. Should have something like a 100 μs - pulse.A diode, from P 3 to top of SW keeps 555 from retriggering on bounces. Adj. R4 for 1ms, R3 for about 10 ms, or as long as you need between pulses. Not bread-boarded or simulated except from top of my bald head.
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    I had crow for supper, better remove diode from P 3 or re trigger difficult[ imposible] but need to prevent SW bounce from triggering. Maybe arother 555?
     
  6. Hipervids

    Thread Starter Member

    Sep 28, 2008
    14
    0
    I'm gonna try it.
    Thanks alot.
     
  7. Wendy

    Moderator

    Mar 24, 2008
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  8. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,170
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    Wheew.. you've got lots of reading to do. Going back to my not so pretty drawing, change 47k to something like 1 to 2 MΩ, to overlap any SW bounce.P 7 not used & I believe you can fill in the remaining pins.
     
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Bread boarded hard-wired simulation. One ms pulse, no SW bounce, 20 pps rep. rate. Tried Rs From 10k to 20M; ocasional extraneous pulses at 10k, missing pulses at 20M[ 10 pps]. Trigger always wins over threshhold so it's no advantage to stretch off time, rely on Rs for bounce protection.
     
  10. Hipervids

    Thread Starter Member

    Sep 28, 2008
    14
    0
    Thanks mate it works great.
    Sorry for delay ive been away.
     
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