On Sun, May 19, 2013 3:42 am, David wrote:
> All,
>
> I have written a simple article which might be of use to some people,
> measuring the PIC Vdd using no external components.
>
> This builds on an older Microchip application note designed for outdated
> parts, so it isn't a new idea. However it works well enough for simple
> battery monitoring and can be added to any project on a supported PIC.
>
> You can find it here: http://edeca.net/wp/electronics/measurin
> g-pic-vdd-with-no-external-components-using-the-fvr/
c

Unfortunately, there is a very good reason why you don't see this very
often- the FVR isn't very 'F' - it can vary by as much as 5% on the PIC18
you mention, and by -8 to +6% on the 12LF1840- and these aren't errata-
these are the published and tested specs- they aren't very good
references- you would need to take into account the amount the reference
can vary over temperature and voltage.  I don't believe that the chart you
posted takes the variance into account

It is great to get a rough estimate, ... you may be able to calibrate each
part- if you want any kind of precision, you'll need to use an external
FVR.



Matt Bennett
Just outside of Austin, TX
30.51,-97.91

The views I express are my own, not that of my employer, a large
multinational corporation that you are familiar with.
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