Data on same pair supplying power?

[Ausman]

Hi all,

I have been asked to do a small job (which is actually big when you get into it) where there is only one pair of wires to a location, and no means of adding more.  Grrrrr!  They want to put a "trendy thermostat" there that does simple switching on a number of poles.  The operations are not complex, just continuous on or offs according to what the t/stat demands, and I have been tossing up ways to do this.  Have considered a tiny 6 channel wireless transmitter/receiver system which will work but is a little cumbersome to fit and needs a tiny control addition at the receiver end to work properly.

Preferably..... has anyone found and used a small gizmo that multiplexes such simple data onto a 24DC/AC power line?  This is a very common but very proprietary practice in HVAC land where you have wall mounted controls talking to their A/C unit via their own bus protocol on top of the power to run the remote, but I have never done it from scratch.  A bit of googling reveals most stuff to be "development kits" and I want something proven and off the shelf.  Speed can be be really slow due to the simple and slow changing actions.  The main thing is proven and reliable.  The distance will only be 4 to 5 metres at most.  Ideally the sending "box" will have terminated inputs that react at the receiver end as terminated matching outputs.  I know I'm not asking much!

I'm not going to get into the reason for replacing a dedicated controller that works well, with a "trendy" one that will work worse and take lots of $s and fiddle farting around!  Ohhhh......in saying that I guess I have!

cheers,

Aus

[Joe Tauser]

I've used I/O repeaters before, but none of them are physically small.  Here's an example:

http://www.dutec.net/dsrepeater.htm

 

Then I Googled "trendy thermostat".  This is one of the images that came up:

 

Hope that doesn't happen.  

Joe T.

[hotwires]

I recall the old simplex school clocks synchonizing from a master clock that sent out a 19kHz signal over the AC building wiring.  It controlled the bells also. Maybe some BASIC STAMPS and DTMF codes (master send, slaves selectivly or collectively receiving). would be easier if devices were DC powered, a bias tee to inject signalling AC. Just thinking cheap.  Not off the shelf  

there are protocols out there for such: https://en.m.wikipedia.org/wiki/Power-line_communication however unknown on compact, low cost hardware.

Sounds like something an audrino, raspberry pi, or parallax basic stamp could be programmed to do. I generally loath anything that is "trendy". 

[Ausman]

Thanks guys, I don't think either of these is going to be suitable for me.   Joe's too big (and does it work on top of power over just the one pair?  Couldn't find that?) and hot's me essentially making something which might not be durable.

Although thermostats control heat and cool, I don't like the idea of uncontrolled fire either!

cheers,

Aus