IC possibly malfunctioning

Discussion in 'General Electronics Chat' started by GTeclips, Mar 1, 2013.

  1. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    Hi all,

    I'm working on a small little circuit, and I'm confident the logic is correct, and I believe the wiring is also correct. But it is not working, and I believe the IC I am using is to blame.

    I'm using the NTE74C04 (http://www.nteinc.com/specs/7400to7499/pdf/nte74C00_20.pdf) which is a hex inverter. I have each input wired to the negative buss with a 10k Ω resistor, and I gave it a 9v power supply. The problem I am having is I can get three of the NOT gates to work, but when I set the input of a forth one to high, in output remains high. So basically only half of the chip can work at one time.

    Can anyone explain this?

    Thank you!
     
  2. ScottWang

    Moderator

    Aug 23, 2012
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    You better attach your circuit.
     
  3. tshuck

    Well-Known Member

    Oct 18, 2012
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    A schematic, and even a picture of your setup will help narrow the solutions.
     
  4. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    Okay. I'm not good at diagramming the circuits, so I will just post post a picture of the logic diagram an what I want it to do, and a picture of the circuit I currently have. I don't know when I will post it, but I will try to be quick with it.
     
  5. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
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    Verify your chip pinout. Inputs to the chip should be on pins 1, 3, 5, 9, 11 or 13 as shown on page three of your linked datasheet.
     
  6. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    I know this image is hard to follow, but it is the best I could do.

    [​IMG]

    When switches 1, 2, 4, 5, 8 are high, and 3, 6, 7 are low, the LED will light, and only when these are in the correct combination.

    I had a logic diagram, but photo bucket wasn't liking it, so this picture is the best I can do.

    *EDIT* Oh yeah, I have the buses reverse of what you are supposed to (I think), upper is positive, lower is negative.
     
  7. tshuck

    Well-Known Member

    Oct 18, 2012
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    You can upload images in your post using the paperclip icon above the text box.

    I'm not following what you have done? You have one output, yet expect other outputs to affect the LED? The way you have it hooked up, if switches 1,2,4,5,or 8 are closed, the LED will light.

    Your output is only dependent on 1A, and the output is 1Y....

    ...it also looks like you have two outputs tied together! BIG no-no....
     
  8. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
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    Have you tied all of the outputs of the inverters together? That can only be done on a "open collector" output logic gate. What are you trying to do with this circuit?
     
  9. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    Okay, I think I properly attached the diagram of what I hope to accomplish.
     
  10. MrChips

    Moderator

    Oct 2, 2009
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    Mistake #1. Don't use the same color wires for Vcc and GND.
    It confuses the electrons.
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    Mistake #2. You cannot wire the outputs of logic gates together.
    Gates don't like to play tug o' war.
     
  12. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    Oops, how could I have forgotten. XD
     
  13. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    Why can't that be done?

    *EDIT* And how might I fix it?
     
  14. MrChips

    Moderator

    Oct 2, 2009
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    Because when one gate is high and the other is low who wins?
     
  15. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    Obviously high. But that is what I want.
     
  16. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Mistake #2. Don't connect multiple outputs together.
    It lets all the magic smoke out of the ICs.
     
  17. tshuck

    Well-Known Member

    Oct 18, 2012
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    You need some additional logic chips, open-collector, or tristate inverters to do what you are trying.


    The poor little inverters are attempting to drive the logic HI while some others are attempting to drive it LO. Which one wins out depends on the device...if it doesn't die first....
     
  18. MrChips

    Moderator

    Oct 2, 2009
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    Obviously that's wrong!
     
  19. GTeclips

    Thread Starter Member

    Feb 18, 2012
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    Wait, aren't all the logic gates in the IC all separate and individual?
     
  20. MrChips

    Moderator

    Oct 2, 2009
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    Has nothing to do with Mistake #2.
    One gate is pulling one way and the other the other way.
    This is a short circuit across the power supply.
     
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