Jattie van der Linde wrote:

> > Several years ago we demonstrated a bus (built as described above)
> > operating quite happily at 230K baud while a 60W 110V light bulb
> > operated from a dimmer over the two bus lines. (Not recommended in
> > actual practice.)
> >
> > -- Tom Rogers  VP - R&D  Time Tech Inc.
>
> Why not. ?

Sorry about the delay; I've been busy at being busy...

The why not is this: I don't want to ever have people connecting
equipment I've designed to a live power circuit except under very
special circumstances. The fact that you can specify standard power
connectors and such in no way should lure you into disrespect for the
qualitative properties of this stuff: at the very least if something
disasterous happens you can assume the comforting mantle of common
practice. In most cases, if you stick to approved connectors and
assembly practices you can be assured of good legal standing when the
sparks fly.

So: when you want to connect your com line to a hot circuit, the
following dilemma arises: if you use approved connectors, you end up
with something people will plug into the wall by accident; if you use
any other connectors, you get live voltages on connectors not meant for
them, and in unusual places (like on what looks like a com line.. )

This problem is really the biggie when it comes to the question of
sharing power lines with data. In the case of the rs-485 stuff, there's
the additional problem of needing to use proper twisted pair for any
high speed communication. The appropriate cable isn't rated for
delivering power.

It always seems to come back to some vaguely legal consideration when
you intend to sell something, doesn't it? Oh, well.

--TR