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Logic gates + noise

Discussion in 'Electronic Design' started by Jon Slaughter, Aug 25, 2008.

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  1. I was playing around with some logic gates and they seem to be extremely

    If I take an AND gate and breadboard it, and put both it's inputs to high(by
    a jumper wire of about 1.5in), and touch the jumper wire which is sheilded,
    the output fluxuates ;/ I could understand leaving the input floating but
    when it's directly jumped to high? Is this normal or something else going
  2. Potentially... I didn't think that maybe there would be minute vibrations
    that would be enough to cause contact issues... thats the best explination
    at least
  3. Something else is going on.
    Likeliest culprit is a bad connection on the input. Measure the
    voltage directly on the chips input pin and see if it really is logic
    Check your ground and power connections on the actual chip pins too,
    they could be making bad contact.
    Try the other AND gates in the package.
    Some trickier culprits will depend upon what logic family you are

  4. Also make sure that the original poster is grounded, to eliminate static.

    Dirk - Transcendence UK - A UK political party - Our podcasts on weird stuff
  5. Try powering the chip through Vcc... ;)

    Sometimes cmos chips will power up through the inputs, and seem like
    they work, but it'll lead to strange results. Make sure you have Vcc
    firmly tied to your 5V rail.

    Bob Monsen
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