555 monostable mode

Discussion in 'The Projects Forum' started by Etronic, May 13, 2012.

  1. Etronic

    Thread Starter Active Member

    Oct 7, 2011
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    I build this one shot circuit. But? it dose not work every time i
    push the SW.

    Can somebody tell me what's wrong.

    Also! I would like two use an npn transistor to replace the switch.What parts will i need to include to trigger with the transistor.Once i get the switch to work every time i press it.


    Thanks
     
    Last edited: May 13, 2012
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Last edited: May 13, 2012
  3. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Does that mean it works some of the time you push the switch? See the circuit I posted for a signal conditioner on the trigger circuit.

    What is your power source and what is the voltage?
     
  4. Wendy

    Moderator

    Mar 24, 2008
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  5. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2
    Power source is a 3.6 1cell 2400MAh. I stated the voltage.

    It works but? not every time i press the SW. I already mention this.

    thanks
     
  6. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2

    Can you kindly, tell me what ami missing. Is an input conditioner another
    resistor plus capacitor. If it is where do i connect it.

    The only thing i see on most of these circuits is an cap on pin 2 an a added resistor tied high.

    I stated it dose work. but? Not every time i press the Switch. Please clarify.

    thanks
     
    Last edited: May 13, 2012
  7. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2

    Ok i got it. The only thing i need is the conditioner. As you can see in my circuit the pull up resistor it 20k can i use another 20k an a 1uf or 0.1uf for the conditioner.
    Will this solve the problem of not turning on every time i press the SW.

    Thanks
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    Just curious, did you even try to read the 555 MONOSTABLE MULTIVIBRATOR article?

    It is pretty well spelled out in there, schematic and all. If there is a part that wasn't clear, please refer to it.

    Reading is your friend, always.
     
  9. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2

    Yes i know. But thanks anyways for linking that part.The input needs a shorter lower pulse rate.''conditioner'' This is way it wasn't working every time i press the SW. I will try it with the added parts.

    Thanks Bill
     
  10. tomega3

    New Member

    May 7, 2012
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  11. Burnit0017

    Member

    Feb 15, 2010
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    Hi, de-bounce the switch.
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    You do realize a monostable is a time honored way to debounce a switch?
     
  13. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2

    I did that, with the conditioner.Same thing. Buy adding a cap and resistor to one side of the SW. As tracecom and Bill marsden suggested.


    Thanks for your input. And to everyone who posted in the thread.
     
  14. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2
    The circiut is working. everytime i press the switch the LED comes on for the duration
    time i set it for.

    Next! I need to replace the SW with a npn transistor to trigger the 555 as the SW done. Any suggustions on how to get the transistor to trigger the circuit so the led comes on,Then shuts off for the time i have it set at.
     
  15. Wendy

    Moderator

    Mar 24, 2008
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    Not sure what you mean. You want the LED to be on while timing?

    If so take another look at 555 MONOSTABLE MULTIVIBRATOR , as it does just that, no transistor needed. The chip is rated for 200ma, so it can handle 100ma easily. If you need more power than that I can show you how.
     
  16. sheldons

    Active Member

    Oct 26, 2011
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    you can try this circuit with built in debounce so its triggered every time.....

    [​IMG]
     
  17. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2

    Bill

    I don't want to change the circuit.I want the circuit to function as i have it.But? Have a transistor to trigger pin (2) instead of the SW.
     
  18. BSomer

    Member

    Dec 28, 2011
    433
    106

    Just trying to make this clear. You want to remove the switch and put in a transistor of some kind to trigger the 555 circuit. Is that correct?

    What do you plan on using to trigger the transistor?
     
  19. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2



    BSomer


    That's correct?

    I plan on using positive 1.3Volts to bias the npn transistor.
    how much current will i need to trigger the monostables
    negative pulse so it will start the time duration of the 555.
    the collector connects to pin 2 emitter to ground and positive
    voltage to base. Will this work. Using 2n4401 or a 2n3904
     
  20. Etronic

    Thread Starter Active Member

    Oct 7, 2011
    127
    2
    Can some one tell in my post #19 will work.
     
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