Electronics > Beginners
The energy cost of powering down vs deep sleep
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Peabody:
A timer interrupt would not be appropriate.  An efficient mail carrier might have the mailbox door open for 2-3 seconds once a day, so the timer setting would either waste a lot of effort checking the door sensor every second, or check less frequently at the risk of missing the event entirely.

So I think there would have to be a reset that occurs when the door is opened.   I just haven't looked into how to do that yet.
james_s:
Don't be so sure. It's common to have a timer interrupt wake up a CPU anywhere from 10-100 times a second, run a handful of instructions that takes a tiny amount of time with the CPU running at several MHz and then go back to sleep. What matters is duty cycle, even waking up 100 times a second and polling a pin it could still be sleeping 99.99% of the time.

It's been a while since I've messed with the code but my Moteino based mailbox notifier polls at I think 10Hz and it has been running for months now on a pair of AA cells that are still over 3V.
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