On Thu, 3 Jun 1999, 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?

I haven't tried this, but it should work... You could have a 'high pass'
filter in parallel with a 'low pass' filter on both the transmit and
recieve sides of your 2-wire interface. The dc would flow through the low
pass filter while the communication signal, which is ac, would pass
through the high pass filter.

The filters do not need to be too sophisticated. The high pass filter
could be just a capacitor while the low pass filter could be just an
inductor.  The inductor needs to be chosen such that a) it doesn't
saturate when the full DC current pass through it b) the inductance is
large enough to keep the AC signal from being shorted. The capacitor is
less critical - the bigger the better (though I'd personally try to use a
ceramic cap [e.g. 0.1uF] and just look for the rising/falling edges
[assuming your transmitter is from a pic I/O pin]).