Hello all!
I am using an Arduino UNO to communicate with a GPS and a SIM modul. Arduino UNO is to big for my application, so I want to create my own circuit board with the ATMEGA328P U, where I just use 4 Dig Inputs.
My question now is what to do with the other digital Inputs? Should I connect them with +5V or GND?
Especially the AREF Pin- should I leave it blank or do i have to connect it with +5V or GND?
Thanks for the answers 
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I would appreciate it if you could share your source of information with me, because I have to justify why I did this and I always thought unused I/Os have to get a fixed voltage level from a pull up resistor or have to be connected to GND?
Thanks a lot
Atmel recommends setting unused pins to input with pullups enabled, and not connecting to anything. Though tests of power usage in those conditions that nick gammon conducted seem to imply that this doesn't yield the improvement in sleep power consumption that would be expected
Very useful Information thanks!
But I haven't found the researches of "Nick Gammon" could you pleas send me a Link?
The datasheet of ATMEGA328 also says "If some pins are unused, it is recommended to ensure that these pins have a defined level." & "If low power consumption during reset is important, it is recommended
to use an external pull-up or pull-down."
Do you know what is the usual resistance I should use in this case?
Do I have to define the I/Os as Inputs in the Arduino IDE or whrer should I do this?
Is low power DURING reset required? Usually the chip is in reset for such a short time (the duration that reset is held down) that you don't care about the power usage during reset, and the internal pullups are fine.
Also, do not create multiple threads about the same topic, it is a violation of forum rules because it confuses people answering questions and makes it hard for prospective responders to know the full context of the issue.
Should be fine if I just use the internal pull up.
Two last questions: Do you know how to activate the internal pull up in the IDE?
Where can I find the post of "nick gammon" you talked about in your previous post?
Sorry won't happen again!
pinMode(n,INPUT_PULLUP);