Ground unused pins?

Forum 2005-2010 (read only) Hardware Interfacing
1

Hello, I'm using the Arduino as a prototyping board. Once I get the code and hardware worked out, I plan to build a PCB board for the m168 chip. On this board, should all unused pins be grounded thru a 10K resistor (other value)? OR can they be turned off via software?

My question stems from some reading somewhere, forget where - that unused pins should be grounded... or something. I don't remember the details.

Thanks for any help and info.

Ken H.

2

I think it made a small difference to the current consumption holding the pins low if you are running it on batteries. It doesn't make any odds otherwise.

3

Thanks for the input Pluggy - since I'm not running on battery, power consumption is not an issue - but you're saying it doesn't make any difference?

Thanks for the response.

Ken H.

4

I've got several Arduino projects running full time, all of them with a serious number of unused Pins. I have paid no heed to the unconnected pins, and never had a problem that is related to unconnected pins. Floating pins will give unpredictable results if you read them, you just don't read them........

The only thing I remember reading about floating pins (other than noobs wondering why analogRead doesn't work as expected) is that somebodys Arduino used a couple of milliamps less if he held all the unused pins low. Useful if you want to eke another hour or two from your batteries, otherwise you're not likely to notice.

edit :
I've found the original thread relating to this :

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1243213127/all

Apparently his current consumption dropped 3mA if he used the internal pullup resistors thus holding them high, not low.

5

Thanks for the input and thread Pluggy - I read thru it, then at the bottom there was the following link:

I think that is where I had read before about defining pins as INPUT. From reading there, it does seem like it would be better to define any unused digital pins and set to HIGH - from the link: "Often it is useful to steer an input pin to a known state if no input is present."

BUT if the pins are not read it shouldn't matter - isn't that your experience?

Thank you for the link and info Pluggy - as you can tell, I'm just a baby at this Arduino stuff - programming in any form to be honest.

Ken H>

6

Yep, my experience is that if you don't read the pins, they are quite happy left floating. I suppose internal pullups are cheap enough if you think there may be a problem :slight_smile:

7

i have had issues with floating analog inputs, all I had to do was declare them as inputs and pullup and it was all fine after that

8

FireBall, what type of problems did you have with floating AI pins? did it make the analog pin next to it read funky sometimes?

Thanks to all for the suggestions.

Ken H>

9

incorrect/flaky readings