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QUOTE (Rail-Rider @ 18 Jan 2006, 13:58)THE Bus?
Here we hit maybe THE fundamental problem for beginners!
Mention of busses immediately makes it apparent that DCC may not be as simple as just buying a digital controller, a chipped loco or two, plug in and go. Sure, it CAN be, but the sheer volume of enquiries about busses and wiring is a dead giveaway that it is not really that simple in practice. If it were really that simple, those bus and wiring queries would have no need to exist!

To which, I must add and heavily emphasize that this topic is not aimed at someone making a fresh start with a clean slate (though it might be useful anyway), but is squarely aimed at modellers with well-established layouts who are contemplating its conversion to digital.

For these people, and there are probably thousands of them, it looks more and more certain that a simple 'two wire' setup just won't be adequate.

How to convert an existing DC layout to DCC;
1. Disconnect DC controller
2. Connect DCC system to wher you just removed the DC controller from
3. Turn all isolation sections so that all of the track is live
4. Turn on power
5. run trains

I could probably include a step 2a. Install decoders in your loco's, but as you don't have to do this with all your loco's before using them on DCC (with most systems) I left it out.

We were told, "all you need is two wires to the track", so why all this talk about 'busses' and wiring? Should we now forget the idealised 'TWO WIRE' principle as being far too simplistic for anything but the simplest layouts and therefore inadequate for converting anything more complex? You can forget it if you like, but there are only 2 wires from the system to the track no matter how big or small a layout is.

What, exactly, is a bus?A BUS (note capitalised) is any wire or multiple wires which has multiple connection points along its/their length. Think of a water pipe with several taps along it, that's a pretty fair representation of what a BUS is.

HOW MANY buses are needed?In DCC terms there are 2 BUSes, the track BUS, and the communications BUS.
What are the differences between busses? Why is a bus needed - what is it used for?
1.The track BUS - this is the 2 wires that come from the digital system and connect to the track at various places. This BUS is made up of 2 wires, one for each rail, as there is only 2 rails on a length of railway track you only need 2 wires for this BUS.
2. The communications BUS (Com BUS)- this BUS is made up of 4-8 wires and is what the throttles are connected to. This BUS allows the throttles and other devices (such as accessory decoders and block detectors) to communicate with the Command Station so that they are not only receiving commands but can also send back messages to the rest of the system. You can even eradicate this BUS almost completely if you use a system with wireless throttles.

Unfortunately it's not quite that simple, XpressNET isn't capable of handling all the device on your layout, so any system which uses XpressNET (Hornby, Lenz, Roco, ZTC) also has a 3rd BUS (the feedback BUS), this additional 2 wire BUS makes up for the missing functionality of XpressNET. There are also some systems which have the same problem as XpressNET systems, however instead of adding a 3rd BUS they simply don't have full functionality, have a look at the DCC systems Comparison Table and you will see these systems marked with a 'No' in the feedback column.

How do we know which bus people are talking about?In general when people are talking about 'the BUS' they are refering to the track BUS.

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That would explain why the LS150 is so cheap then!

BUS -a BUS (note capitalised) is any wire or multiple wires which has multiple connection points along its/their length.

You just need to give it a name like Accessory Power BUS?

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QUOTE (Doug @ 18 Jan 2006, 20:39)I honestly don't know if these terms are 100% right. There is no DCC dictionary. Don't get any ideas Lisa
I was actually thinking of doing that.

QUOTE (ChrisE @ 18 Jan 2006, 23:27)Let me tell you that as someone looking to start in DCC I thought that I had the bus issues sorted before I read this thread but now I am mightily confused.
Don't worry, they've almost confused me too.

QUOTE 1. I hope we would all agree that I need a track power bus and that this is 2 wires of different colours to aid identity that are connected regularly to the track so that one rail is always connected to one wire & the other colour wire to the other rail. Basically the connections from this bus to the rail should ideally be such that there is a connection to each rail between every rail joiner - eg onto every piece of track. I have learnt that the bus should not be a ring circuit but needs to terminate. I guess that in a tailchase layout for that to mean anything the track must not be a ring circuit either and must thus have insulated joiners that correspond with the break in the power bus.
OK, you've got this mostly worked out, however there is no reason why you can't have aring circuit, the need to terminate this BUS is an age old myth which comes up from time to time, ignore it and build a ring main like the rest of us.

QUOTE 2. Now it gets complicated. Some of you are telling me that I can take power for accessories from the track & some of you say not & thus that I nees a separate bus. I am totally at a loss to know whether the control signal for these accessories comes down the track bus or down the accessory bus or whether I really need one. 2 more wires.
It would seem that some of the cheaper accessory decoders need a seperate power supply rather than using the track power, avoid these decoders and you won't need this extra BUS.

QUOTE 3. I now come to the feedback bus the necessity for which seems to depend on the brand of DCC that I buy. Lenz & its cronies need such a bus whilst Digitrax does not. As I haven't decided which system to buy yet & I may change my mind that is 2 more wires. I assume that this bus needs connecting to something but I am nor sure what. If guess it is just accessories rather than the track & I am sure that I will need to make it easily accessible for that extra accessory I will buy that they haven't even invented yet.
You can avoid this extra BUS by buying a system from CVP, Digitrax, NCE, or Zimo, these are all top notch systems which you pretty much can't go wrong with. If you want to complicate matters then buy an XpressNet system (Hornby, Lenz, Roco, ZTC) and add 2 more wires to your list.

Come to think of it, I don't think ZTC has a feedback BUS, it's just missing a chunk of functionality.

QUOTE 4. As I might like to do something else on my layout like put lighting into buildings I need a separate power supply for that as well. 12v & 2 more wires & again easy access to put extras onto it in the future.
You can run your lights from track power, I do.

QUOTE The way I count this I need to run 4 buses and thus have 8 wires. There may be others that I haven't thought of yet. When I started this I would never have imagined that I would need more colours that my electrical wholesaler can supply but it appears that I do.
How am I doing?
Actually by your reckoning you need 5 BUSes, you missed out the Com BUS which the throttles plug into. However DCC only requires 2 BUSes;
The Track BUS
The Com BUS
Extra BUSes are only required to make up for a deficiency in either the system or the accessories you connect to it. This all comes down to which system you buy, and which accessories you buy, you pays your money and you makes your choice. However you definitely don't need more than 2 BUSes on a well designed DCC system.
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