Eric Borcherding wrote:

> RS485 drivers run at 5V and do not require the pump caps.
> It is also a differential mode multi point connection, twisted
> pairs can be used as well.  See MAXim site and MAX485

  I would have made the suggestion; use RS485, with twin pair (common
telephone strip cable) and the crimp-on "RJ" connectors.  If you don't
need power on the cable, use the other pair for grounding (first pair is
centre pair, so this would form a shield of sorts).

  The notion here is; look at what is current in network cabling.  Co-ax
(10Base-2) is still fine and note that on network cards, the cable
sheath is *not* grounded, but is isolated using a DC-DC converter and a
(multiple) pulse transformer.

  10Base-T (ribbon cable) is isolated at the other end (the hub) also by
pulse transformers.

  For your application, you want the isolation, so either isolate the
power supply at the display end (plug-pack/ Wall Wart; based on the
notion that the display is only a display, has no other connections), or
you must provide a DC-DC isolation converter (a standard item) and an
optocoupler for the slower (than Ethernet) data.

  Use of an NRZI protocol (quite manageable with raw PICs instead of
UARTs) facilitates polarity independence on the link using "twisted
pair".
--
  Cheers,
        Paul B.