One diode in series from the battery to Vdd, one resistor from 220VAC
phase to INT (better with an optocoupler).

On 6/26/07, Miguel Reznicek <mreznicek@pretensa.com> wrote:
> Friends:
>
> Does someone know of a PIC chip circuit that will monitor the 220 VAC mains
> and use them to run, but that can automatically switch to a battery power
> when the mains fails?  I need to make an alarm for when the power fails.
>
> Thanks in advance,
>
> Miguel Reznicek
> mreznicek@pretensa.com
>
>
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