long countdown timer, how to save power?

[skimask]

Open a new page in PBP and write only Define OSC 4, save it and compile.......................Anyway . . . just an idea.

Wayyyyyy to many macro's to mess with to get that too work! But, it is an idea...if a guy has that sort of time!
Power saving...there is an internal 31-ish khz backup to the backup to the backup oscillator (I think, don't have datasheets on hand, not ambitious enough to look them up).
But it's not accurate enough to keep any time.
Easiest thing in my mind is to get an 8pin RTC, DS1602 type and use that. Then you can put the PIC to sleep and have it wake itself up every roughly XX number of seconds using the WDT timer and the WDT prescaler.

Internal oscillator does saves power, for comparisons sake, 2x the power.
Running slowly saves power, say 4x the power.
Putting it to sleep saves LOADS of power, say 1000x the power when compared to the other methods.
In the circuit I'm playing with at the house: PIC18F4685 @ 40Mhz (10Mhz external plus 4xPLL) = about 45mA, like the datasheet says. Running it at 8Mhz internal OSC = about 20mA (little high, but close enough to the datasheet), run it on the 31Khz backup oscillator = roughly 5mA with nothing else going on (tight loop only)...
BUT...put it to sleep and the mA doesn't even read. It bounces back and forth between zero and one mA.