Two-wire interface

P

P. Short

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Staff member
Does anyone see any significant advantage in coming up with a two-wire, bi-directional scheme for communication with dimming controllers? Something similar to the Dallas one-wire scheme, but adapted for this type of application. It's not clear to me that there is any big advantage in going from a cat-5 wire scheme down to a simple two-wire scheme (maybe like doorbell wire, or perhaps one twisted pair), but I thought that I would ask. I'm noodling around with some ideas here...

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Phil
 

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I don't really see a problem with using cat 5 currently. It has it's advantages, mostly readily available connectors. But one big advantage to a 2 wire system would be cheaper wire. As long as it would not need to be shielded or twisted pair. One kind of wire that comes to mind is 4 conductor phone/alarm wire. It is alot cheaper then cat 5. The main purpose of cat 5 is noise cancelation for data transmission. Since we are not really transmitting data that requires the twisted pair, the wire really is over kill.

So I say if you think you have a solution that uses only a pair of wires, well you sort of already do with your transformer idea, then it is worth exploring.
 

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If the cabling required for a new design is cheaper than cat 5 then it could have an advantage. If it is less common and more costly cable then there would need to be some other advantage to make up for the extra cost.
 
The two wires that I’ve used in the past, was truly only two wires. Power and ground, where the power line is also used for data communication. If the current needed down the line is low, this can work very well. Its not noise tolerant, so the robustness would need to be added to the protocol.
 
One thing to also consider is that the current renard CAN be done on three wires with RS485. A, B and GND.

You even have a spare wire that could be used for zero cross detection.
 
There still needs to be power...I was thinking of just two wires for power, ground, and bi-directional communications (not just one direction).

Right now I'm considering a current loop setup, with 10 mA representing one level and 20 mA the other level. There could be a number of controllers (up to about 5 or 6, if the current loop generator is capable of supplying up to about 30 V. The controllers would be powered from the line, as well as transmitting and receiving data. This scheme should also be pretty well immune to noise (as compared with a voltage-controlled scheme).

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Phil
 
No...the two wires are just for control and power for the controller. There is only very limited power available over those wires. If you are talking about modulating a control signal on top of low voltage AC, that is a different beast. It's an interesting thought, though.

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Phil
 
The 2 wire system really is worth looking into Phil.Please present your full idea if you can write it as I'm really interested..
 
What about an X10 style controller that sends data along the power lines? Would it be possible to engineer a system that would be fast enough for music synchronization?

-Matt
 
That is going off into an area that I really don't know much about. X10 is too slow, of course, but there may be other, newer technologies that are faster. It may be easier to get a wireless system working than a fast PLC.

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Phil
 
If I lived in Australia (or other places where 24VAC lights are common), I would be very tempted to try and come up with a system for sending the control signals over the same wires as the 24 VAC power. I'm a little bit reluctant to try the same thing over anything higher than about 42VAC, though, and all of the cheap stuff here in the United States is 110 VAC.

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Phil
 
Phil; Sounds a lot like the firing systems we use for fireworks. The field moduals are conecteded using cheep zip cord or any two conductors even two single wires if needed. The best thing about the setup is it can be conected any way you can get the wires to the mods. IE you can branch off one mod and have three sets of wires on it so you can run to another model in a difficult location. They do not need to be in any certain order because thay are individually addressable up to 256 mods with 32 outputs each. We use these systems to choreograph the fireworks to music. The system we use is called Fire One made by Pyrotechnics Management here in Pa. Web site http://www.fireone.com AI
 
Matt,

Yes there is a way to do what you want. I have been working on it as a sideline project for about 5 months. Currently I had to put it aside for a little while to get the other projects ready for christmas. But I hope to have power line data built into my dimmers and other items in time for next years christmas show. I won't claim there are no issues to work out but I can say it is possible at this point. The data rate is fast enought to even support the largest shows using the most complex devices. Like instead of 115Kbs try 7Mbs. If I can get it up and running the others should be able to graph it into the other diy systems with just firmware modifications should they choose to.
 
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