Disfunctional IC?

Discussion in 'General Electronics Chat' started by LaserPhile, Apr 30, 2015.

  1. LaserPhile

    Thread Starter New Member

    Apr 24, 2015
    7
    0
    Hello,

    I am trying to build a 3-bit full adder for a class on some breadboard. I am using a TI CD74HCT08E integrated circuit (it's just 4 AND gates) and for some reason that I cannot figure out, no matter what it is outputting power. How can I fix this? Any input is appreciated.
     
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,127
    266
    Post your schematic please.
     
  3. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,780
    1,219
    Please be advised that the 'low' output state is not zero volts...

    If the outputs are indeed above 'High' threshold inappropriately, please rule-out open 'ground' and floating inputs --- Also, although 'latch up' is unlikely with the cited series, it is not entirely imposable...

    Best regards and good luck!
    HP
     
    Last edited: Apr 30, 2015
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,516
    1,246
    You can't make a full adder with nothing but AND gates.

    ak
     
  5. dl324

    Distinguished Member

    Mar 30, 2015
    3,235
    619
    If this is homework, it should be posted in the Homework Help Forum so anyone who tries to help doesn't just give you the answer.
    Help us help you. Post a schematic.
     
  6. LaserPhile

    Thread Starter New Member

    Apr 24, 2015
    7
    0
    I figured out the problem. The issue was with grounding. Newbie mistake I suppose. I was using a 9v supply through a 5v (7805) regulator, that was jumped through several switches and connected to my gates. After the gate structure of the adder, there was a 16 pin DIP LED followed by several resistors. The problem was that I was not grounding the switches, so the charge deposited on the gates by the voltage was staying there, causing unexpected issues with the gate. I solved the problem by adding a SIP resistor after the switches, and jumping them to ground. The project is now working perfectly.

    Sorry for the lack of information guys, I'm new here so I'm still learning the best way to make a thread.

    dl324, thanks for letting me know to post in the homework help forum. I wasn't aware there was one. I will use it from now on.
     
  7. dl324

    Distinguished Member

    Mar 30, 2015
    3,235
    619
    No problem; I'm new too, but long past the need to do homework.

    Apparently instructor have been known to catch a student cheating. Being guided to a solution seems to be allowed.
     
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