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Par for Newquay

DCC layout architecture

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Hi Folks

 

Help needed from the DCC gurus please...!

 

*** Newbie alert ***

 

I'm considering how to implement DCC on my first layout in 40 years (OO).  This layout looks great in XTrkCAD although I haven't actually built anything yet.  Still working on the architecture...

 

Here's what I think I want to do:

   Deliver track power and throttle data on one bus, using 3 distinct power districts to get some fault tolerance in

   Deliver power to accessories separately from the track, same reason

 

And here is where I am getting confused;

   How to get the DCC signal to accessories?   I have read about the CAN bus which supposedly can separate both the power and the data for accessories... but...

 i)  Are there any switch decoders out there which can actually use it ... ?

ii)  One of the benefits cited is to "reduce congestion on the throttle bus" by keeping any comms with accessories off it.   Is that a real problem, though - how big does your layout have to be before you notice... what would you notice, if your throttle bus was congested?  And would a DCC control center be clever enough anyway to route instructions down the right bus when it has a choice of two...?

iii)  Another of the benefits cited is that CAN bus is bi-directional, so as well as telling your points and signals what to do they can apparently send information back... When is that useful...?   Anybody doing it?

iv)  If CAN bus is just too difficult, what could I do instead...?

 

Many thanks in advance for your advice.

 

 

 

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Posted (edited)

The pic attached shows the control box I built for Mauch chunk.

49346439618_d19de74950_k.jpg20190316_143208 by Gavin Liddiard, on Flickr

The Lenz LZV100 command station feeds 4 x Tonys train Exchange PSX circuit breakers which in-turn feed the four "power districts" on the layout. These are supplied by the Lenz TR150 5A transformer which handles all track power requirements on the layout (red & black wires).

The PSX breakers trip at a lower current than the command station and we configure them to self reset after the short is cleared.

 

A separate feed is taken from the command station's track bus that is used as a control bus for all the point and signal accessory decoders (orange & purple wires).

Power for all the point motors is supplied by the Lenz TR100 3A transformer, signals are fed from a 12v DC transformer (thick blue & brown wires).

The benefit of this solution is you can still control the points and signals during a shorting event (useful for fixing mistakes).

 

Handsets are connected via a 4 wire control bus  that Lenz call Xpressnet. this is a daisy chained line of 5 pin din sockets dotted around the layout that all handsets and the computer interface connect to. The Xpressnet has bi-directional communication so all handsets have access to the states of all locos and the position of points and signals as set by the command station.

To receive actual feedback from accessories more proprietry electronics are required depending on your system. I have no experience using feedback systems so cannot comment on such.

 

Other manufacturers may do things in different ways but the basic architecture is the same.

 

In General:

Controllers are connected by an independant low power data bus.

 

Track power and control signals are supplied by the command station's main 2 wire track bus.

 

Accessory decoders can take control and power from the track bus, or control from track bus and power from separate transformer.

 

I hope this helps...

Edited by Gavin Liddiard
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Hi P for N.

 

Throttle Data travels down the Track Bus.

 

Track bus goes to your district cut outs for the 3 Power Districts and then from these onto the tracks of each district.

 

If CAN Bus is feeding back info then it's probably for Point indication on a panel or Track occupation etc.

 

I'm sure someone from MERG will soon be on this for you.

 

Dave

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3 hours ago, Par for Newquay said:

Hi Folks

 

Help needed from the DCC gurus please...!

 

*** Newbie alert ***

 

I'm considering how to implement DCC on my first layout in 40 years (OO).  This layout looks great in XTrkCAD although I haven't actually built anything yet.  Still working on the architecture...

 

Here's what I think I want to do:

   Deliver track power and throttle data on one bus, using 3 distinct power districts to get some fault tolerance in

   Deliver power to accessories separately from the track, same reason

 

 

So far, very conventional DCC.    You're delivering DCC to track, and "something" to accessories.   

That accessory signal could be DCC as well, just the same as your track signal, but on a different "power district" so not affected by track issues.

 

 

3 hours ago, Par for Newquay said:

And here is where I am getting confused;

   How to get the DCC signal to accessories?   I have read about the CAN bus which supposedly can separate both the power and the data for accessories... but...

 i)  Are there any switch decoders out there which can actually use it ... ?

ii)  One of the benefits cited is to "reduce congestion on the throttle bus" by keeping any comms with accessories off it.   Is that a real problem, though - how big does your layout have to be before you notice... what would you notice, if your throttle bus was congested?  And would a DCC control center be clever enough anyway to route instructions down the right bus when it has a choice of two...?

iii)  Another of the benefits cited is that CAN bus is bi-directional, so as well as telling your points and signals what to do they can apparently send information back... When is that useful...?   Anybody doing it?

iv)  If CAN bus is just too difficult, what could I do instead...?

 

 

Lets split the options for accessories into three main groupings: 

 

1) - analogue, you just wire switches from a panel to devices on the layout, those can be turnout motors, or any other accessory device.  No electronics, no digital stuff. 

 

2) -  broadcast data only over DCC.   Here you need accessory decoders which read DCC instructions to change turnouts or signals.   The data goes one-way only, from the command station in the middle out to the accessories.    You can still have a real panel to control things, or a software diagram, but that panel has to talk to the command station.  

 

3) -  bi-directional communication with accessories.  Here there is some feedback from the accessories as to their status to your central system.  Has some uses for turnouts and signals, but is necessary if your approach to control needs detection of trains, occupancy of track, etc.. 

Within ( 3 ) there are a lot of options.  There are proprietary bus systems from some makers (eg. Lenz has their system, NCE has a system, etc..).  There is LocoNet, which is also proprietary to Digitrax, but has been licensed to a lot of other makers, so is fairly widely supported on DCC systems, and has a number of third-party manufacturers which offer "clever things" - its probably the most capable of the commercially available bi-directional systems, been around a long time so well tested, and is capable of operating hugely complex layouts (*),  there's also a lot of DIY designs if into building your own electronics modules. 
There are at least two (probably more) CAN options, which are mutually incompatible, so you pick one and use it, you can't mix&match - the most widely used in the UK will be MERG's CBUS  (DIY hobby club supported system), there is another system used by Zimo on their commercially available control systems.    MERG's CBUS can work well, but you do have to be into hobby electronics to at least some extent to build the boards and to get it to work.  

 

 

Addressing your questions on "throttle congestion".  Unless you're running a lot of trains, with a lot of operators, no it will never be a problem.  The problem can exist in layouts with a large number of operators, often controlling multiple locos (eg. US outline "consists" with perhaps 8 locos pulling a train, and using consisting methods which are inefficient in that they duplicate commands to every loco).  

 

No, systems don't route DCC commands to different places (or they don't in normal setups, it would be possible, but people don't).   

 

The big advantage of an independent bi-directional system comes in feedback from the layout, which can be just occupancy (for signalling for example), or it can be tied to automated running.   

 

 

 

So, which to use ?   Depends what you're trying to achieve.  

 

 

 

(* eg. The McKinley Railway, probably the most complex and largest OO model railway in the UK.  Find it on YouTube ).  

 

 

- Nigel

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Pete Waterman’s extremely large O gauge layout is controlled exclusively by MERG CBUS 

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