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Author Topic: Pull-up and pull-down resistors  (Read 602 times)
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Durham UK
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Hi,

can anyone direct me to a user friendly tutorial / help on these? How do I choose between the two types and what sizes of ohms etc..
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Craig Turner, blog: http://gampageek.blogspot.co.uk/ It helps with my learning if I write things down, esp. for others to follow (constructive comments welcomed to improve)

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No need,

I found one here when looking at a previous reply on a different subject:



http://www.thebox.myzen.co.uk/Tutorial/Inputs.html
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Craig Turner, blog: http://gampageek.blogspot.co.uk/ It helps with my learning if I write things down, esp. for others to follow (constructive comments welcomed to improve)

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Here are 3 really good articles:

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


by far the best overall description I've seen.

http://www.sparkfun.com/tutorials/218

Good description of how to determine exact value for pull-up resistor

http://www.arduino.cc/en/Tutorial/DigitalPins

Good info on Arduino internal pull-ups
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Thanks that's really helpful!

Just out of curiosity, why don't we use diodes instead?

I tried these pull-up / pull-down cicuits on a simulator with 10Meg resistors and they still work. So then I thought a diode could replace the large resistor and
it still worked.

mmm....?


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Craig Turner, blog: http://gampageek.blogspot.co.uk/ It helps with my learning if I write things down, esp. for others to follow (constructive comments welcomed to improve)

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Simulators usually do not handle shorts and opens very well. 

A diode is (effectively) a short or open depending on the forward voltage.  The resistor allows current to flow regardless of the voltage applied, which is why it "pulls-up/down."
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Thanks,

I understand better now.

I'll use 4.7 or 10k resistors on my buttons unless directed otherwise by designs or datasheets.
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Craig Turner, blog: http://gampageek.blogspot.co.uk/ It helps with my learning if I write things down, esp. for others to follow (constructive comments welcomed to improve)

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