Filtering supply lines

[Oliver Scholz]

> Try grounding the data line to the LCD so it'd just display a blank screen.

That will not be possible since the LCD would stay uninitialized and
the screen would be black, thus concealing all trash pixels.
  
> noise isn't coming in thru your serial line.  Then try connecting your LCD to a 
> battery rather than the car's power supply.  Then try the same thing.  If you

Excellent idea! I will try that. The problem is that the trash pixels
are very random, i.e. I can press the brake pedal 100 times and the next
time the trash appears. I thought I had defeated the problem twice, only
to notice the trash reappearing at random. Very hard to "debug"...
 
> problem with that probably isn't the positive side of the supply.  I'd check 
> your ground.  Being a veteran with car audio I can tell you the horror stories 
> about automotive grounds.  They don't always stay at 0v, EPECIALLY when when 

I tried to eliminate that problem by running all my circuits grounds
to the same point, and connecting *that* point to ground.
That *should* eliminate the problem, right?

If I cant solve the problem in HW, I will fix it in SW by refreshing the
display every once in a while. But I would like to try to really fix it
first...

THanks!

-Oliver