Default pin mode

[alto777]

Well, I painted left to right when I should have gone top to bottom and

learned more than I will ever need to about the DS3231 alarm mechanism only to find

Sadly, the DS3231 does not check alarms when running on battery,

from a search of these fora... so my idea is not workable.

I understand the need to reduce activity for time-keeping by battery. I always thought in normal circumstances that doing any kind of alarm would be easy in my code, so never bothered with the DS3231 build-in alarms.

I am blind combing the data sheet for confirmation, but it fits w/ my observations, which, of course, are subject to any number of flaws starting with not just my eyesight and level of caffeination.

a7

[Smajdalf]

For low power wake ups in the AVR world you may use Timer2 configured as RTC with external watch crystal as the clock source. This way you can get current consumption less than 1 uA and crystal precision of timing.

[srnet]

The Energizer Lithiums (AA and AAA) are well know for their very long shelf life (20years) and ability to operate at -40C.

[alto777]

THX. I'll look. It's not exactly shelf life I'm worrying about, it's the long term effect of dragging just 1 uA out of a battery.

I recently followed the advice of the tech support guy for reviving an instrument with a soft power button running off a 2032, viz:

short the battery for 10 seconds

for some reasoning he gave me which I have forgotten. It was very hard for me to follow that instruction but it did work.

Kinda like how hard it would be to use red wire for ground and black for V+.

a7

[alto777]

@Smajdalf

For low power wake ups in the AVR world you may use Timer2 configured as RTC with external watch crystal as the clock source. This way you can get current consumption less than 1 uA and crystal precision of timing.

Nice idea, I'll keep it handy.

a7

[srnet]

@alto777

THX. I’ll look. It’s not exactly shelf life I’m worrying about, it’s the long term effect of dragging just 1 uA out of a battery.

With batteries like the Energizers it will take several years to find out ..........

[westfw]

@alto777

is there something batteries of that kind do not like about continuous very low current drawn?

I've noticed that that seems to be the case. Devices with "soft" power-on buttons seems to be more prone to battery leakage than devices that fully disconnect the battery.
I don't know why, or whether it's a real problem or just 'seems to', or whether there are any known workarounds.

[Jiggy-Ninja]

@Smajdalf

Unless the pin is used as an interrupt source the digital buffers are disabled in sleep so they do not draw current even in sleep. Worst case current consumption of a floating pin (at room temperature) is 100uA but usually it is much less.
The extra current consumption is not from internal registers changing state but from a “shoot-through” current of the digital buffer when the input voltage is close to its threshold.

They will draw extra current when awake though.