At 01:51 10/02/99 -0600, you wrote:
>Hello,
>I'm finishing up my first (?real?) PIC project. A chess clock. I'd like
>to power it with either a 9V battery or a little wall transformer.
>
>I'm guessing there is an IC out there to switch between supplies. Or
>maybe there is some other trivial way to do this.

Assuming there's a regulator on the PIC circuit, use a 9V battery and a 12V
supply, with a diode in series with each.  Then if the 12V drops below 9V,
the battery will take over supply.  Quick and dirty, and usually works just
fine ;-)

Nigel