You could try two opto-isolators in a bridge. Turn one on with the
3-30V and the other one on with your PIC circuit. When the bridge is
balanced, the current through both diodes should be about the same.

Obviously the accuracy will depend on how similar the optos are.

John

>
> I need to measure a voltage 3-30VDC using a PIC, but the PIC has a totally
> different ground reference than the voltage I'm supposed to be measuring
> (the two circuits _are_ connected, but I have no way of knowing how because
> each install will probably be different).
>
> I was thinking that this is an ideal situation for using an opto-isolator,
> and was wondering if anybody knew in a practical way if this would provide
> reasonable accuracy with varied temps, etc.
>
> Anybody have any other suggestions?
>
> Thanks!
>
> Andy
>
> ==================================================================
>                      Andy Kunz - Montana Design
>           Go fast, turn right, and keep the wet side down!
> ==================================================================
>
>
>