One more thing to watch out for.  A dead Lead Acid battery is not 0V.  =
It's 12.00V or so.  Each cell is about  2.0 to 2.2 volts....6 cells and =
it's 13.2 for fully charged and 12.0 for empty. =20

And I'm with the group on this one....a resister division network and a =
PIC with A/D is the way to go....

Tim

>>> olin_piclist@EMBEDINC.COM 12/02/03 06:39AM >>>
Matt Redmond wrote:
> Basically I care about only three states:  A total lack of
> power (e.g., V-no_battery =3D 0V), the engine is not running
> (V-battery =3D about 12V) and the engine is running
> (V-alternator =3D about 13-14V).
>
> Any way I can do this by using just two inputs on my PIC?
>  I'd like to avoid a chip that has an a/d converter if
> possible.

Why?  Two resistors and a capacitor tied to an A/D input seems like the
obvious and simple answer.  Many PICs have a built in A/D, and there is
usually at least one in a subfamily.

You could do this with a couple of opamps or comparators.  Since you don't
need high accuracy, you could use bipolar transistors instead as
comparators.

Another option is use a 12F675 to look at the voltage with its A/D, then
output the two digital signals you want.


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