My sailboat has (or at least had) a battery monitor on it.  You start with
a full battery, and this monitor displayed a number which represented how
many amp hours had been used.  (Usually a negative number, but you could
overcharge the battery and have a positive number).  Alas, my monitor seems
to have been murdered. :-(

The boat took a lightning hit while in the slip, and apparently some of the
electronics in the monitor got zapped.  Although I could buy another one, a
large part of the cost is the shunt, which was not harmed.  They won't sell
the unit without the shunt, so I figure I should be able to use a PIC to
build another monitor.  The shunt is just a resistor, and is described as
follows:
"When current flows through the shunt, a small voltage is developed across
the shunt which is proportional to the current flow. The battery monitor
accurately measures this very low voltage and converts it to the "amps"
reading on the meter. The resistance, which is the ratio between the
voltage across the shunt and the current flowing through it, is a constant
for any particular shunt"
So the PIC would measure the voltage coming from the shunt and use that to
calculate the corresponding current, and use a timer to convert to amp
hours.  The shunt itself is a dual MKB-500/50 (the dead monitor was a Link,
made by Heart Interface).

NOW, please don't flame me for not having a specific, detailed question to
ask!!  I merely want to know if someone on the Piclist might have done
something like this, or have information that would be helpful to me in
designing and building such a critter.  If so, would appreciate such info
-- offline or online, as you choose. :-)

Thanks,
John

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.