OR-gate clarification please

Discussion in 'Digital Circuit Design' started by Joel Hopper, Jun 24, 2016.

  1. Joel Hopper

    Thread Starter New Member

    Jun 24, 2016
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    So, this is from memory, and I don't have a schematic, but it's simple enough to describe.

    How can I easily get inputs for a 4071/4072 to be low, with a pushbutton making high, one input? I'm still very new to electronic design, and I'm not sure how to do this. I want 2 buttons, each to make only 1 input of a dual input OR gate high, but without pushing the button they need to be low. How can I efficiently accommodate that? I tried just a regular SPST pushbutton wired to +5, but the input is technically not low at that point. So I'm just a bit confused...

    Thanks for any assistance.

    Doc
     
  2. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    What you are looking for is called a pull down resistor! I'm on my phone, so I can only describe the configuration.

    You need a resistor. The recommended value depends on the type of OR gate you have, but I'll assume CMOS 4071 OR gate. I'd use a pair of 4.7 kohm resistors.

    Connect one end of your pushbutton to 5v. Connect the other end to a resistor AND the OR gate input. On the resistor, connect it's other end to ground. The resistor pulls the input low to ground when the button is not pressed. When you press the button, the 5v brings the input high.

    If I get a chance, I'll post a schematic soon.
     
    Last edited: Jun 24, 2016
  3. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    PullDown.png
     
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  4. Joel Hopper

    Thread Starter New Member

    Jun 24, 2016
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    Oh. All right. I'll give that a try. Thanks a ton!! I've heard that term, but was not aware it worked like that for pushbuttons too.
     
  5. DocHopper

    New Member

    Apr 13, 2012
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    Just tried it. Works like a champ!!! Thanks again!
     
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  6. EM Fields

    Member

    Jun 8, 2016
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  7. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Oops, thanks for the catch! I missed that. Was a slip of the mouse click!
     
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  8. eetech00

    Active Member

    Jun 8, 2013
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    Hmm...must be some good push buttons...
     
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