Putting AT328 to sleep for small intervals?

I'm going to build a small planter box for some herbs in the kitchen, with a built-in water reservoir/pump and a 1307 RTC that the chip will use to read the time and activate the pump in the morning. I'm debating whether or not to have the AT328 (will probably use an Arduino Pro Mini, with the regulator disabled if I go this route) go to sleep to conserve battery power.

If I put the chip to sleep, I'd have to wake it up using either the 1Hz output from the 1307, or using the watchdog timer every several seconds. I'm wondering if this approach will practically reduce the current consumption enough to make it worthwhile as opposed to just leaving the chip running and scanning the 1307 at all times.

Anybody have any thoughts/comments/advice on this?



Considering that you can scan the clock in a few microseconds, the arduino should be asleep for more than 99.9% of the time if you're waking it at 1Hz from the RTC. So that means you're getting the vast majority of the power savings available.

You could probably slow the clock further using an external counter but my intuition is that the external counter will use as much or more power as you would save in the arduino.

A crazy thought I had is that (I think) any interrupt can be used to wake it. So you could theoretically connect your RTC 1Hz pulse to the T1 input pin and use the timer1 output-compare interrupt to wake the arduino after a specified number of seconds. Have a read of this and the datasheet I guess.