interrupt timer for long interval - minutes or hours

Is it possible to have a very long interrupt timer such as many minutes or even hours?

Any examples I see using the 16 bit timer1 are on the order of seconds or fractions, and with a prescale of 1024 it looks like 8.3 seconds is the max. I hope I am missing something.

I'm trying to make a very low power moteino project with hardware interrupts. The moteino will sleep most of the time and get interrupted occasionally, but I also want to wake it up every hour or two to check the battery life and send an "I'm still alive" signal to a base station.


The usual method is to use the watchdog timer and wake every 8 seconds just long enough to increment a variable, test it, and go back to sleep. When enough time has passed the variable gets big enough and you wake the rest of the way up and do what you need to do, reset the counter, and go back to sleep. Think of it like hitting the snooze button on the alarm.

If you want to stay down for more than 8 seconds and don't want to do what I just described then you'll need some external circuit to do the timing.

Thanks Much! That kind of a solution was what I was thinking I would have to do. Hopefully that quick wake-up/increment and back to sleep doesn't take much battery juice.

I'm just needing to have a battery life measured in months.

Best tutorial : Gammon Forum : Electronics : Microprocessors : Power saving techniques for microprocessors
Library that I use : Google Code Archive - Long-term storage for Google Code Project Hosting.
I have changed the parameter for narcoleptic to allow a unsigned long for very long sleep time.

The wake-up every 8 seconds is not a problem. It is very short. But the 8 seconds is not accurate.
A ATmeg328P chip with three AAA batteries should run for at least one year.