[geeks] 9v battery meter

[Dave Kimmel]

On Fri, 10 Jan 2003, Dave McGuire wrote:

> >   So to read a 9v battery, I should power
> > it with a 9v battery?
>
>    It's been probably fifteen years since I played with one of those,
> but that sounds about right.  Ideally the supply voltage should be a
> tad higher than the highest voltage you want to measure but I'm not
> sure what the input margins are like on the LM3914.

What if you used a 9V battery plus 7805 regulator to power the circuit and
used a voltage divider (say a pair of 500 ohm resistors, which also give
you a load for the battery being tested) to bring the battery voltage down
to the range of the circuit?  Then you get a reference voltage that's .5V
higher than the maximum voltage you'll measure and enough of a margin that
a 10V source could be applied without damaging things.

-- Dave Kimmel
   crisco_kid at shaw.ca