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Topic: [SORTED] - Internal Pull-up resistor - still need external resistor? (Read 502 times) previous topic - next topic

Inprogress

Mar 10, 2012, 09:34 pm Last Edit: Mar 12, 2012, 10:05 am by Inprogress Reason: 1
I've been trying to confirm this but thus far in vain. When I use the internal pull up resistor, and I connect to ground, specifically the Ground pin (not some external ground), do I also need a resistor in to ensure no damage to my Arduino board? I think I do not need a resistor before GND, but I am just a tad apprehensive since I don't want to damage my board with full pin output into GND.

Also, it might be the time of night though...will I damage my board if I enable say 5 pins' internal pull-up resistor all to the GND pin? I've just gotten it in my head for some weird reason, that if I push all 5 buttons, the GND will receive 25 volts? But that doesn't make sense either. I am very sure I have just over thinked this  :~ :~ :~ :~ :~ :~ :~ :~

"The really amazing thing is how many people are successful with their Arduino projects considering the fact that so many of them do not have a technical background.  A lot of them seem to try, and succeed with, projects that no sane engineer would even attempt." - floresta commenting on the proper use of LCD displays

retrolefty


I've been trying to confirm this but thus far in vain. When I use the internal pull up resistor, and I connect to ground, specifically the Ground pin (not some external ground), do I also need a resistor in to ensure no damage to my Arduino board? I think I do not need a resistor before GND, but I am just a tad apprehensive since I don't want to damage my board with full pin output into GND.

No, when the pin is configured as an input pin and then the internal pull-up option is enable, it is prefectly safe to ground the input pin. The risk with direct grounding of a I/O pin is that if it happens to be set as a output pin and set HIGH (either by user error or software bug, same thing really) then there will be pin damage as that is a direct short circuit from Vcc to ground through the pin.

Also, it might be the time of night though...will I damage my board if I enable say 5 pins' internal pull-up resistor all to the GND pin? I've just gotten it in my head for some weird reason, that if I push all 5 buttons, the GND will receive 25 volts? But that doesn't make sense either. I am very sure I have just over thinked this  :~ :~ :~ :~ :~ :~ :~ :~

No, you need more sleep. ;) Doesn't matter how many INPUT pins you short to ground there can be no damage. Only when pins are set to ouput mode do you need to concern yourself and understand about current flow and current limits.

MarkT

The internal pull-ups are spec'd as "20k to 50k" so each will allow at most 250uA to flow if the pin is shorted to ground.  250uA is a small current, no bad thing is going to happen!
[ I won't respond to messages, use the forum please ]

Inprogress

HAHAHAH, thanks to all. I did get some sleep.

I wish you all a wonderful week!
"The really amazing thing is how many people are successful with their Arduino projects considering the fact that so many of them do not have a technical background.  A lot of them seem to try, and succeed with, projects that no sane engineer would even attempt." - floresta commenting on the proper use of LCD displays

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