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CMOS gate not working?

Discussion in 'General Electronics Discussion' started by javawizkid, Oct 21, 2011.

  1. javawizkid

    javawizkid

    3
    0
    Oct 21, 2011
    Hey,
    New to this forum :)

    I'm beginning out with electronics and I've got myself a few different types of gates to play around with.

    I connected up an AND gate but doesn't output as it should. I've looked at the documentation where etch inputs and outputs are. I've also connected the DC supply to the correct pin and the ground to the correct pin.

    I've noticed when I turn on the supply, my LED lights up even though both inputs are OFF. When I turn the inputs on the LED just gets brighter. No idea what is up.

    Thanks!
     
  2. BobK

    BobK

    7,626
    1,654
    Jan 5, 2010
    You cannot just leave the inputs unconnected, they must be connected to either a low or high signal at all times. Try connecting the two inputs to ground and see if the LED goes off.

    Bob
     
  3. javawizkid

    javawizkid

    3
    0
    Oct 21, 2011
    They are connected but switched off with a switch, I suppose thats the same as not being connected to the 0v though?
     
  4. BobK

    BobK

    7,626
    1,654
    Jan 5, 2010
    Yep, no connection is not the same as 0V.

    Bob
     
  5. javawizkid

    javawizkid

    3
    0
    Oct 21, 2011
    Do all of the other unused pins have to be connected to 0v or can they float?

    Just found out for myself, the answer seems to be no.

    How could I utilise a physical switch button to determine the AND inputs?

    Figured that out too, thanks :)
     
    Last edited: Oct 21, 2011
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