The Well-Linuxed Car

[Roger Oberholtzer]

On Mon, 2003-12-01 at 18:51, Tony Alfrey wrote:
> On Monday 01 December 2003 07:42 am, David A. Bandel wrote:
> > On Mon, 1 Dec 2003 15:15:30 +0100
> > Roger Oberholtzer <roger at opq.se> wrote:
> >
> > [snip]
> >
> > > Even something as 'innocent' as an RS-232 port takes on new
> > > problems in a vehicle if the equipment at both ends are not sharing
> > > the same ground sense.
> >
> > Boy have you hit a biggie on the head.  And since a vehicle doesn't
> > have a true ground in the full sense of the term, you nailed it with
> > "ground sense".  All equipment _must_ see the same ground from their
> > point of view or you'll get all kinds of strange behavior and odd
> > burnouts.  I see this problem on boats all the time. Aircraft share
> > the same problem.
> >
> > Ciao,
> >
> > David A. Bandel
> 
> "Star" ground.  Each piece of hardware has a ground wire that is run all 
> the way back to some common ground point near the battery (hence the 
> "star") and ideally, each piece of electronics is "floated" wherever it 
> is installed in the car frame.

So be sure your added equipment has a power ground. We have a nice
selection of printers and TFT displays that seem to have left off that
magic third connector on the power connector. In our case (in a vehicle)
this is not optional.

Another fun thing some customers have done is put two UPS in the car and
not connected their grounds properly. Resulting in a 'floating ground'.
That is a fun one.

One more thing re safety: if you put useful voltage in the car BE SURE
TO INSTALL A PROPER POWER BREAKER. Nothing worse than a loose power wire
in the vehicle, all happily working on those lightning proof tyres, when
up comes Joe happily providing that path to the earth. Curly  hair will
be the least of his troubles when he touches anything in the car. In our
systems, death would result. And we really do like most of the crew we
have met.


-- 
Roger Oberholtzer <roger at opq.se>