Use a DS1302.  Plus you get a clock for free (almost).


At 12:14 AM 6/30/98 -0400, you wrote:
>Hi,
>
>I plan on using the DS1233 (or variant) as a brownout detection to reste
>MCLR on a PIC project i have using a 16C73 as Myke Predko explained).  I
>remember others on the list having problems with the PIC brwonout circuits,
>so this seems like a good method.  However, I wanted to add a battery
>backup to the PIC, as this chip will normally be powered by a 9V DC power
>supply that is connected to AC.  The 9V will go through a 5V fixed
>regulator before the PIC of course.  My question is, what kind of circuit
>can I build that would switch in or out a 9v battery as a backup?  I was
>thinking a switched MOSFET, except that depending on how variable the 9Vdc
>was, the MOSFET might go into the active region and get pretty hot if it
>dropped to lets say 8Vdc.
>
>ALso, there aren't any chips similiar to the Dallas brownout chip that have
>the battery backup?  I've looked, but the onew with battery backup seem
>rather complicated.
>
>Thanks for any thoughts or suggestions!
>
>Rob
>
>
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Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
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