Hi Everyone,

I have an application that I'd like to use standard 3 core power extension
leads (different connectors) for powering and sending data to many external
units - I want to use these cables for cost and durability reasons.
Unfortunately I can't really be too explicit about the actual application
(it is commercial), but the units are spread over a large area (say up to
200 metres) from the controller).

I was thinking of an arrangement similar to television receiver "mast-head
amps" where DC current is feed to the remote amp via the same line as the
signal. Capacitors at each end are used to allow the video signal to share
the DC line.

In my case I'd like to use something like a RS485 network (at say 19200
baud). The remote units have to be able to transmit, but I was going for
half-duplex. The power will be about 24 volts DC.

The DC power going to the unit can and will have some current pulses as
things activate.

I was thinking of having a Ground (0v) wire then the remaining two wires
would deliver the DC current and form the "loop" for the RS485.

Am I insane? :) Has anyone done something like this or could offer some
advise?

Is there any other way? Can I use a single wire + ground (leaving the other
to supply power) to get reliable data rates of at least 19200 baud over
these distances? I may be able to arrange the system into a "tree" structure
where the nodes of the trees are "repeaters". There is one "master" on the
network, and the remote nodes only reply to messages after they have been
directly addressed. Perhaps a "current loop" system like MIDI?

Thanks for any suggestions you can give.
Ash.

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