AND GAte problem

Discussion in 'General Electronics Chat' started by Hassaan Aslam, May 3, 2013.

  1. Hassaan Aslam

    Thread Starter New Member

    Apr 20, 2013
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    hi!!! i am a beginner, when i use and gate i get '1' output even if my inputs are '0'. i have tried two ic's 7408 and 4081 but i am getting same problem with both of them. can any one guide me hoe to use these ic's correctly.... :confused: :( :confused:
     
    Last edited by a moderator: May 4, 2013
  2. MrChips

    Moderator

    Oct 2, 2009
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    Did you remember to connect Vcc and GND correctly?
     
  3. Hassaan Aslam

    Thread Starter New Member

    Apr 20, 2013
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    yes i had connected Vcc and ground....
     
  4. MrChips

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    Next step is to post a photograph of your setup.
     
  5. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    did you connect the inputs to ground, or are you simply assuming that unconnected means logic 0?
     
    MrChips likes this.
  6. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Another question is what are you using for power? The 7408 is only designed for 5 volts on Vcc. If you connected a higher voltage, you've likely damaged the chip.

    Also, what are you using to drive the inputs?
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    Yeah, I forgot about that one too.
     
  8. Hassaan Aslam

    Thread Starter New Member

    Apr 20, 2013
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    i am currently using 4081 i am using 5 volt input but i have not connected inputs to ground.
     
  9. Hassaan Aslam

    Thread Starter New Member

    Apr 20, 2013
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    if the inputs are connected to ground then how will i apply "1" inputs to the input terminals???
     
  10. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    You need to have ALL inputs connected to either supply voltage or ground or output of another gate. Without that the inputs will act like antenna and will have any value.
     
  11. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    You connect them to either ground of supply voltage. You can also connect them through a resistor to ground, for example 10k.
     
  12. Hassaan Aslam

    Thread Starter New Member

    Apr 20, 2013
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    okay thanks all of you i will try this
     
  13. Ramussons

    Active Member

    May 3, 2013
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    In Logic Gates, an Open Input is as good as 1, or Logic Hi.

    Ramesh
     
  14. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Only with TTL chips, and still it is a very bad practice to leave it unconnected.
     
  15. Ramussons

    Active Member

    May 3, 2013
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    I would Never, Never design a circuit without following this fundamental rule!

    Ramesh
     
    Last edited: May 6, 2013
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