long countdown timer, how to save power?

[Kamikaze47]

Hi,

Im creating a device that needs to count down a certain period of time which could possibly be weeks, but it will be battery powered, so i'm wondering the best way to do this in order to maximise battery life.

I'm going to have the time remaining displayed on an LCD screen for 5 seconds whenever a button is pressed and this will save power by not powering the LCD all the time, but obviously the PIC needs to be running the whole time in order to keep time.

Does anyone know of any tricks to save power?

Pic i'm working with atm is 18F1320

Cheers

[mackrackit]

Just thoughts...

Run the chip as slow as possible (you know that I am sure).
I can not prove it but it seems the internal OSC uses less power than running an external.

Is there any time when the device will be exposed to light? A solar cell could help, even indoors, to buffer the batteries.

[Kamikaze47]

No sunlight unfortunately.

I've currently got it running off the internal OSC at 4MHz. It can go as low as 125kHz, but I don't know how to tell PBP that its running that slow because DEFINE OSC wont allow to specify 125kHz.

[mackrackit]

Take a look at the OSCCON reg in the data sheet and section 2.5.1 in the PBP manual.
I can not remember what the correct setting is.

[Kamikaze47]

Yeah i looked at that section but couldn't find anything relevant. The closest I can see is the OSCCAL register, but I cant figure out how that would help me tell PBP that i'm using a 125kHz clock.

[mackrackit]

Try???
OSCCON = $16

Section 2.7.1 in the data sheet.