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Pull up resistor

Discussion in 'Electronic Basics' started by Chris W, Mar 28, 2005.

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  1. Chris W

    Chris W Guest

    Will someone tell me if I am doing this right? I am using the
    calculations on this page
    for a 74HCT74. The data sheet doesn't list an Iih, just Ii of +/- 1uA
    so I guess that is all the current I need to make an input go high? Vcc
    [min] is 4.5V Vih is listed as 2v min so I will use 2.5v for a margin.
    Solving the formula on that page in step 5 for R, I get . . .

    R = (Vcc[min] - Vih)/Ii or
    R = (4.5 - 2.5)/.000001 = 2,000,000

    So I can use as a 2m ohm resistor to pull up an input high, right? What
    kind of current draw might there be if there were no resistor, just a
    direct connection to Vcc? Finally what if I want to pull up 8 inputs on
    2 different 74HCT74s do I just use 2,000,000/8 or 250,000 ohms? Right
    now I have a 100k ohm resistor pulling up all 8 inputs and it seems to
    work fine.

    Chris W

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  2. John Fields

    John Fields Guest

  3. John

    John Guest

    Why is it called a pull-up resistor and what are its uses? I'm sorry to
    hijack the thread.


  4. You can read about it here:

    Rikard Bosnjakovic

    Anyone sending unwanted advertising e-mail to my address will be
    charged $250 for network traffic and computing time. By extracting
    address from this message or its header, you agree to these terms.
  5. If learning was linear I think that, paradoxally enough, you wouldn't
    learn anything.

    Rikard Bosnjakovic

    Anyone sending unwanted advertising e-mail to my address will be
    charged $250 for network traffic and computing time. By extracting
    address from this message or its header, you agree to these terms.
  6. Rex

    Rex Guest

    Sounds like mosaic ala Marshall McLuhan.
    Possibly. Pattern recognition based on language skills is (I think) the
    basis of all rational thought and therefore learning. I think you can
    learn linearly if the pattern is linear or an extrapolation of previous
    linear patterns.
  7. John

    John Guest

    Yeah, I just found this article and was about to let you know that I found

    It's still not basic enough for a beginner but it's good enough (high
    impedance and all that) but then again learning is not linear so you gotta
    jump here and there and come back to previous material until you get it.

  8. John

    John Guest

    Language skills are not required for learning. You DO learn through language
    skills faster but it requires you to relate to the vocabulary that's being

    It's like building a house. You stop from bottom and you build to top. At
    the lowest level are all your experiences/observations. As you go to the
    top, things start getting more language specific and abstract. At the top
    levels you don't need as much experience since you have founding experiences
    to build on.

    Anyway... since I'm still in school, I'd like to say that best teachers are
    those who relate topics to real world experiences, not those who can say 10
    technical terms in a minute. The technical terms won't make sense to those
    who don't know those terms (haven't related it to their knowledge...they
    know the same thing you do but they haven't put a label to their knowledge).

    So when you teach you explain in terms that can easily be picked up from
    experience (known as layman's terms) so that people can relate their
    knowledge/experiences/observations to yours and finally you put a label to
    those things so that they know exactly what you mean next time you say that

    I hate teachers who think they are the shit when they speak in a formal
    manner all the time with a bunch of buzz words when they are trying to teach
    me something because they're not there to teach me but instead to stroke
    their own egos or they are ignorant to how the brain works (which I think is
    important to know when you become a teacher if you're to be successful).

    Abstract concepts are easier learned by yourself and not at school. Unless
    you have a lot of experience using/dealing with highly technical terms you
    won't get much from listening to someone say it (you have to go at your own
    pace until you assimilate the word...sometimes it's hard to assimilate
    because you haven't been told the whole story).

    Anyway, I can go on forever like this, I can even write a whole book based
    on learning and other related topics but then again, I have better things to
    do with my time, like learn electronics and create some sweet gadgets :)

    Thanks listening to my rant!
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