Miguel Reznicek 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
>
>
>   
Monitoring of 220VAC mains is best done with an optocoupler in series 
with several high-ohmage resistors.
Normally 1M ohm is enough, but in actual operation, the 220VAC will jump 
over the resistive material, so
several at 470K in series will then work properly.

A simple diode can allow a battery to take over when power fails. Don't 
make this more complicated than it needs to be.

--Bob A

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