555 output

Discussion in 'General Electronics Chat' started by rasheed_it, May 16, 2011.

  1. rasheed_it

    Thread Starter New Member

    Mar 26, 2011
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    How can I generate this output directly from the 555 timer without using an inverter.

    I need the output to be low for a predefined time and then it should go high, and once the reset pin is grounded the output will go low.

    Image attached.. Please help!!! 75_1160365057.jpg
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    [​IMG]

    This is a retriggerable version.

    For a nonretriggerable version make a standard 555 monostable with a signal conditioner and use a transistor inverter.

    555 Monostable

    Are you wanting to have them time out together? You image is not clear on that point.

    Since the standard monostable triggers on the negitive edge some sort of inverter is required, though it can be a transistorized version.
     
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  3. rasheed_it

    Thread Starter New Member

    Mar 26, 2011
    12
    0
    Thank you so much... Just another clarification.... wether this will trigger from low to high or from high to low?

    I need to trigger it from low to high..
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    With the transistor in front to be an inverter it will be from low to high. However, as long as the circuit is held high it is not timing. This is the definition of a retriggerable monostable.

    If you want it to act like a standard 555 monostable then you have to add an inverter (which can be a simple transistor circuit) in front of a standard 555 circuit, such as the link I gave you.
     
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