Well, if you're using the power straight off the battery to run the PIC,
then it's tough to use the internal reference since your ADC reading is
gonna be 100% every time, but if you're regulating that voltage to
something like 5V, then you can usually do a precision voltage divider
to get the unregulated battery voltage down to a safe level and read it
using the internal reference if you aren't wholly concerned with
super-uber crazy accuracy.  I've had really good results doing just
that, once you have a calibrated value it worked quite well.

If you are just running off the battery directly, you could use an
external reference chip, or a zener-diode type reference, and run the
PIC ADC off an external reference.

Nick Veys | nick@veys.com

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Denny Esterline
> Sent: Saturday, August 09, 2003 4:58 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [PIC]: monitoring battery voltage with 16F676 A/D converter
>
>
> Has anyone had any experience using a PIC's internal A/D to
> monitor its own battery supply?
>
> My application will use one of the little PICs 12F675 or
> 16f676, but information about others would be useful.
>
> The part I'm having a hard time wrapping my noodle around is,
> what do I use for a reference voltage?
>
> This could be a high volume device, so cost is a concern. But
> I don't need a high degree of precision, 4 or 5 bits would be
> fine. I just need an approximation of battery health.
>
>  Thanks
>  Denny
>
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