> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Olin Lathrop
> Bruce Partridge wrote:
> > The voltage divider is a 59K and a 47K resistor running from the
> > battery.
>
> That is a total of 106Kohms, which will draw 57uA from the 6V battery.
> Also, this presents a 26Kohm impedence to the PIC, which is a lot
> more than
> the 10Kohm maximum recommended by Microchip.  You should reduce
> the voltage
> divider resistors and find a way to switch it on for only a short
> time when
> measuring the battery voltage.  A P channel FET would work fine, or even a
> PNP transistor if accuracy isn't too critical but cost is.
>
> > The pic is powered by a 6V battery which goes through a 4 V voltage
> > regulator.  The regulator powers the PIC, an op amp, and an led.
>
> Is there a reason the opamp needs to be powered from the regulated 4V
> instead of directly from the battery 6V?

I can't think of any.  I'm not sure what the advantage would be from running
it from the battery.  It is a Microchip TC1014, and according to the data
sheet, it draws 50uA regardless of load.  (At least thats how I read it.)

>
> > and the
> > third is the output from the regulator which is being used as VREF.
>
> But the regulator output is also being used as the PIC Vdd, so what's the
> point of using the Vref input?
>

Its actually just a carry over from a previous design the pic ran at 5V and
VREF+ was from a 4V reg that was shut down during sleep.  But is there some
advantage to not having it connected?

Again, I really appreciate all the suggestions.

Bruce
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