On Tue, 11 Jun 2002 14:15:51 -0500, Adam Smith wrote:
>
>I want the PIC to be asleep when the events are not being=
 fired.
>Also, the times given above (26 and 35 seconds) are just for
>illustration, these will be variable from 1-300 seconds.

>I was thinking of using the WDT with the prescaler and use some
>computations to add a postscaler in accordance to the=
 requirements,
>but given the inaccuracy of the WDT (7-33 ms) it isn't very
>feasible.

>The only reasonable option I've come up with is a 555 timer=
 giving
>me a 1Hz pulse to count off of.  The big downfall here is the=
 power
>consumption.  Not only will this be running off of 4 AA=
 batteries,
>these periodic events will be occurring 24 hours a day.

An LMC555, the CMOS version of the venerable 555 timer, has a=
 typical
current requirement of 0.1 mA @ 5VDC according to National's data=

sheet. It's about 0.05 mA @ 1.5VDC. Also run the PIC as slowly as=

possible for your application.

I've been looking at this for a current project too. In my case I=
 would
like the system to wake up once every 15 minutes, check on=
 things, and
go back to sleep.

Tim

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