At 02:25 PM 7/26/99 , you wrote:
>In a discussion with someone else, I was asked if all a car's
>"auxiliary" lighting could be replaced with LEDs, and/or how to monitor
>existing bulbs with a PIC (so you can tell when a turn signal bulb burns
>out, etc.)

One feature of incandescent bulbs that you can exploit is that when off, an
incandescent filament is very low resistance- much lower than when it is
glowing.  You can trickle a small (fractions of a milliamp) current through
the bulb- if there is current flow, the bulb is good, none, the bulb is
burnt out.  This method can only tell you the health of the bulb when the
bulb is off.  Make the current small enough not to light the bulb.  I can't
remember the issue, but this was detailed in one of the "design ideas"
columns in EDN or Electronic Design a few years back.

Matt Bennett