current consumption when 5V apply to input pin of Arduino

Hello, I don't seem to be able to measure the current consumption increase when 5V is apply to the digital input pin 2 (used for interrupt).

I'm trying to make a battery powered Arduino, and I'm using a reed switch that wakes up the Arduino from sleep using the second interrupt pin. There is a little bit of current that flows when the reed switch switches and 5V is applied to the input pin for interrupt. Is the current flow there negligible? I might be able to change the "sense" of the reed switch - make it open most of the time instead of closed most of the time to decrease current drain.

I have a sneaking suspicion this is where internal pull-up or pull-down resistors come into play, but I don't really understand how they work internally.

1) Is current consumption on input pins low enough to ignore? 2) can this current consumption be decreased by doing something with these the internal pull-up or pull-down resistors? If so, does this trick also work on the interrupt pins?

Thanks!

1) yes 2) no

If you don’t enable the internal pull-ups the input current is orders of magnitude less
than you can measure with a multimeter (measured in picoamps).

If an input has its pull-up enabled and you hold it LOW, then it will source between 100 and
250uA

If you try and take an input pin below -0.3V or Vcc+0.3V then it will start
to conduct via the protection diodes which cannot tolerate more than a mA
or so.

arusr: I might be able to change the "sense" of the reed switch - make it open most of the time instead of closed most of the time to decrease current drain.

You should definitely do this.

Shorting a pulled-up pin to ground with a normally closed switch will waste a lot of power.

I'm not sure if I'm "shorting a pull-up pin go ground"?

arusr: I'm not sure if I'm "shorting a pull-up pin go ground"?

Well if you don't know how can we be expected to know, unless you post a schematic of what you propose.

Well, basically I have 5V on the ATMEGA interrupt pin like this. Just wondering if this wastes a lot of power, when the Arduino is in sleep. Wakes up when 5V removed.

I wouldn't have thought so. Have you read:- http://www.gammon.com.au/forum/?id=11497

arusr: Well, basically I have 5V on the ATMEGA interrupt pin like this. Just wondering if this wastes a lot of power, when the Arduino is in sleep.

a) No.

b) You can measure it and find out.