# Pull up resistor

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

1. ### Chris WGuest

Will someone tell me if I am doing this right? I am using the
http://www.interfacebus.com/IC_Output_Input_Pullup_Resistor_Values.html
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.

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Chris W

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3. ### JohnGuest

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

Thanks!

4. ### Rikard BosnjakovicGuest

http://www.seattlerobotics.org/encoder/mar97/basics.html

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Rikard Bosnjakovic http://bos.hack.org/cv/

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5. ### Rikard BosnjakovicGuest

If learning was linear I think that, paradoxally enough, you wouldn't
learn anything.

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6. ### RexGuest

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. ### JohnGuest

it.

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.

Thanks!

8. ### JohnGuest

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
used.

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
term.

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!