Michael,

If its low voltage motor/lamp control you need and the power line can
be about 16v AC then I have an abstract solution. The NMRA have a
standard for the control of model railways using DCC (Digital
Command Control). The idea is each motor (loco) has a assigned address
and packet data is sent down the AC line which is collected and decoded
by a MPU within the loco body. The AC supply therefore comes the data
carrier and motor drive current.

An overview and the spec info can be found at

http://users.vnet.net/paulrver/dccbasic.html

I have some URLs for PIC code (not mine) to do both the base station
and motor ends of this, drop me a mail if needed. As I say it is using
this system 'out of context' but the way the data packets are delivered
to the motors can be using in any application, you just redefine the
packet content to fit you need.

        Paul Fletcher.

Michael Shiloh wrote:
>
> I've toyed with this idea and I don't know if it's practical.
> Neither RF nor power transmission is my area of expertise, so
> forgive me if I am asking stupid questions.
>
> Suppose I have a situation where I want to send power and control
> signals to a device. Suppose too that I want to do this all with
> 2 wires (power and return). Is it at all feasible to send the data
> on top of the power line, and have it separated at the destination?
>
> Kinda like X10 but this is DC.
>
> Any other ideas along these lines?
>
> Michael