On Sun, 16 Sep 2012 11:53:22 +0200, you wrote:

>=20
>Hi,
>
>thanks for all the input!
>
>The proposal to let float the cold end of the voltage divider by simply
>connecting it to a PIC input port appears as a rather dirty solution to me=
,
>for due to the protection diodes an undefined current flow "to somewhere"
>can happen. (I once operated a 628A by simply connecting a RS232 Rx line t=
o
>constant +5V (idle state) via a 1k resistor!)
>
>The proposal with the MOSFET to apply the battery voltage to the divider i=
s
>surely professional, but I like most the solution with the PNP transistor
>which base is "triggered" via the capacitor! This solution surely consumes
>nothing but the base-collector current plus the leakage current through th=
e
>capacitor which both are way lower than those 2=B5A of my 1702. May be the=
 PNP
>can be replaced by a Mosfet.

Yes you could use a fet, and it would be slightly more accurate.=20
The base current is not an issue as it's nly drawn for a short time when yo=
u read the battery=20
voltage. Leakage on a ceramic cap is negligible, probably not even measurab=
le.=20

Incidentally the IO line used to switch the divider can often be shared wit=
h something else if pins
are in short supply.=20


--=20
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