Need Help Understanding Schematic

Discussion in 'General Electronics Chat' started by StToonz, Dec 2, 2012.

  1. StToonz

    Thread Starter New Member

    Nov 30, 2012
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    hey guys,

    Ok my question is: What is that little bubble on pin 4 (RESET)?

    From what i know about logic gates they sometimes have inversion bubbles on the input or output and occasionally both input and output(the one ive circled). Is this the same thing that is going on here or am i wrong?

    Thanks for you help.

    This is only my second post but this site is very helpful!
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    488
    Yes it's an inversion bubble sign. RESET is low active, i.e. a low on pin pin 4 resets the device.
     
  3. StToonz

    Thread Starter New Member

    Nov 30, 2012
    14
    0
    so for this specific schematic would REST always be triggered connected this way?

    another question i have is, would i have to put the inverting buffer in there myself when the schematic shows this or is it included in the chip?
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    488
    You have to show the whole schematic.

    In a normal schematic, if the buuble is shown, it means it is part of the chip.

    In a draft it could occasionnally be used to indicate that an inverter gate needs to be used.
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    To reset a 555, the voltage on pin 4 needs to be near 0V. Otherwise it needs to be at or near vcc. You don't really need to worry about an inverting buffer, unless the signal you want to use for reset is normally low, and goes high at reset time. Then you would need some sort of inverter.
     
  6. StToonz

    Thread Starter New Member

    Nov 30, 2012
    14
    0
    Thanks for the information it will all collectively help. some of my earlier post had some spelling errors that might have thrown you off but Ron H gave me what i needed.

    I will definitely post a new thread on any issues that i have. because as of now my circuit doesnt work
     
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