555 Monostable Multivibrator

Discussion in 'General Electronics Chat' started by pedersen, Oct 30, 2014.

  1. pedersen

    Thread Starter New Member

    Oct 25, 2014
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    Hi I looking for a monostable circuit.
    I want it, to complete the time period even if the swicth is hold down constant ..

    I have build a Non-Retriggerable Monoflop, but if I hold the swicth down constant, the LED remain on.

    Hope any boddy can help me with a circuit, or an idea of what to seach for.
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Here you go
    Non-retriggeredMono.gif
     
  3. pedersen

    Thread Starter New Member

    Oct 25, 2014
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    Thanks for reply
    I have build it and test it.. It works :) ..but it seems like it is unstable.. I have to push the swicth 2-3 times before it starts up again.
     
  4. ScottWang

    Moderator

    Aug 23, 2012
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    If your switch is good then change the switch to pin 2 to try and take R1,C1 away .
     
  5. pedersen

    Thread Starter New Member

    Oct 25, 2014
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    The switch is good. I remove R1,C2 ... and it's the same ..
     
  6. ScottWang

    Moderator

    Aug 23, 2012
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    Do you want to using another switch to try or using wire to replace the switch.
     
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Leave R1/C1 as shown; reduce R5 to 1k or less if you need to re-activate the mono quickly.
    The mono pulse width needs to be at least 20mS (which is highly likely if you want to see the LED lit!), to prevent re-triggering by switch-bounce transients.
     
  8. pedersen

    Thread Starter New Member

    Oct 25, 2014
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    R1/C1 is back on. R5 is reduced to 1K ...still the same. We are not talking about quickly re-activate, even if I wait 10 sec. before I pres the swicth again, it behave like that (some time 1 press some time I need to press 3-6 time before it work).
     
  9. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    try a different switch to see if the one you are using is bad.
     
  10. pedersen

    Thread Starter New Member

    Oct 25, 2014
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    Okay I found out why it behave like it did.. now it work like af dream :).. the reason was because I used a cheap wall supply .. I think it was given some kind of spike or so.
    Thanks you all for your help :)
     
  11. ScottWang

    Moderator

    Aug 23, 2012
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    Recheck the wiring and using another 555 to try.
    And how is the voltage of V1?
    I think the 220 Ω for led is designed for V1 power supply.
     
  12. ScottWang

    Moderator

    Aug 23, 2012
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    Because I was used the traditional transformer liner power, so I never happen something like that.

    Two 4 kinds ±5~15V fixed power.
     
  13. pedersen

    Thread Starter New Member

    Oct 25, 2014
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    I just pick one in my pile. I think it original, was from an old tape recorder or similar.
    The circuit will be used in a machine I'm building, so that's why I didn't use my benchtop supply.
    But now I know how important it is to use a good power supply. :)
     
  14. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Good news that you found the culprit and got the mono working.
     
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