DCC Accessory Compatability

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PeterLJ
Posts: 130
Joined: Fri Jul 03, 2009 7:05 pm

DCC Accessory Compatability

Post by PeterLJ » Sat Apr 04, 2015 11:21 am

Hi

Interested in adding signals to modules so need to know what is compatible with what? This is what I think works or does not work:

Lenz will control NCE but not Digitrax accessories.
Digitrax will control Lenz and NCE accessories.
NCE will control Lenz but not Digitrax accessories.

All three feedback systems are incompatible with each other.

Am I right?

Peter L-J

Mike_R
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Joined: Fri Jul 03, 2009 7:05 pm

Re: DCC Accessory Compatability

Post by Mike_R » Sat Apr 04, 2015 11:48 am

Yes if the Digitrax decoders use the Loconet for their commands, but if using the track bus for commands all are compatible.
There are limits on the highest address number that different systems use.

You are correct that the feedback busses are not compatible. Maybe we can standardise on the new NMRA one once stuff is available for it.
Mike Ruby

PeterLJ
Posts: 130
Joined: Fri Jul 03, 2009 7:05 pm

Re: DCC Accessory Compatability

Post by PeterLJ » Sat Apr 04, 2015 6:44 pm

Hi Mike

Thanks I had forgotten Digitrax is either track bus or digitrax throttle bus, and can be set up for both simultaneously. However CML Digitrax accessories appear to be either set up as track bus or (digitrax) throttle bus, not both. Will try and remember to bring the instructions to our next meet and we can have a look.

As you are aware NMRA is ratifying CMRInet as a standard (S-9.10 Draft) but this covers accessories only. The good news is it would not effect effect existing modules in any way (it would involve a 4 wire 485 bus that would just bypass modules which do not want to play). Steve Smith and I are investigating building a technology demonstrator. The bits are ordered.

http://www.nmra.org/sites/default/files ... 0DRAFT.pdf

Bottom of page 4 there is a nice little schematic. There could be one node per module.

See you soon

Peter

Mike_R
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Re: DCC Accessory Compatability

Post by Mike_R » Sat Apr 04, 2015 7:56 pm

Are you sure? S9.10 is not listed.
OpenLCB is S9.7

LCS 9.10 CMRI is layout control for other groups.
Mike Ruby

PeterLJ
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Re: DCC Accessory Compatability

Post by PeterLJ » Sun Apr 05, 2015 8:33 am

Mike_R wrote:Are you sure? S9.10 is not listed.
Hi Mike

It is all a bit confusing, I can find neither at..

http://www.nmra.org/index-nmra-standard ... -practices

But the draft 9.10 is certainly at ...

http://www.nmra.org/sites/default/files ... 0DRAFT.pdf

Peter

Mike_R
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Re: DCC Accessory Compatability

Post by Mike_R » Sun Apr 05, 2015 12:15 pm

The CMRI one is right down the bottom of the page, while the LCB is the last of the standards just before recommended practises.
I thought they were going with the CAN based LCB not RS485 CMRI.
Mike Ruby

geofftiller
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Re: DCC Accessory Compatability

Post by geofftiller » Sun Apr 05, 2015 10:10 pm

Hi Mike

Some recent postings on the JMRI user group suggest there is a drive to get CMRI accepted as a possible standard. This would be in addition to the CAN based system. Personally I am big fan of CAN based systems and am keeping an eye on the MERG CBus system, I've not looked at other hardware yet and Thamesiders are working with DCC accessories and RS feedback on the main EBL layout.

As far as I can see the proposal to create a CMRINet type standard is proposal S9.10, like you I can't find an entry on the NMRA site.

Cheers
Geoff

PeterLJ
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Re: DCC Accessory Compatability

Post by PeterLJ » Wed Apr 08, 2015 8:10 am

geofftiller wrote: I've not looked at other hardware yet and Thamesiders are working with DCC accessories and RS feedback on the main EBL layout.
Hi Geoff

That's really the issue that worries me. We also use Lenz, but I am reluctant to install a system for signalling which will not work with other commend stations.

I know I could turn up to a Digitrax or NCE meet, say, and bring my Lenz command station and use the accessory bus and my own Xpress Net, but thats rather extreme!

Out of interest here is what some Lenz users in the states did.

http://www.hubdiv.org/docs/signaling/NM ... andout.pdf

Peter L-J

geofftiller
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Re: DCC Accessory Compatability

Post by geofftiller » Wed Apr 08, 2015 10:32 am

Hi Peter

Thanks for the very interesting link.

The issue of compatibility is one that also concerns me, if we were starting entirely from scratch I'm sure things would be different. I would have wanted to go to an layout control bus system such as CBUS or C/MRI but it was a decision made by our technical group and, as always, influenced by multiple factors.

The majority of the modules forming main EBL layout, built to our own legacy standard appear unlikely to be used in our Freemo style meets, and almost all already had accessory decoder driven turnouts.
The layout was already wired to support RS feedback and we have temporarily re-purposed two wires of the control bus to provide an accessory bus, this will later be replaced by an entirely separate accessory bus as per the option in the new specification. This has minimised the modification and disruption to existing modules. Lastly but certainly not least one of our members produces DCC accessory decoders and agreed an advantageous cost with us. Taken together it made the decision to remain with DCC accessories for the main layout easy.

Turnout and signal decoders are driven by a Sprog rather then by the Lenz system making that part independent from the control system and it is possible to use an RS feedback interface independent from the Lenz command station.

Modules built to our branch standard, very similar to the Region specification, are much more likely to be taken to modular meets and these are not included in our signalling project.

For new specification modules I support an entirely agnostic solution, personally I am planning to use accessory decoders on an accessory bus but an not wiring any kind of feedback at present. At the moment I prefer the CAN based technology, the event model used by CBUS and NMRANet seems much more scalable then the polled bus architecture used by C/MRI although I've not looked into either in sufficient depth. If NMRANet actually moves into the mainstream it sounds like it could be very much what we want.

I've also liked the occupancy bus as used by some Free-Mo groups but am not sure it suits our setups, entirely separate from the control system its original form is intended to provide a fully automatic (not PC controlled) ABS system, minimising the work required to get signals on modules working. I believe it has been extended to work with CTC type systems but I've not looked into that development yet. See http://www.free-mo.org/node/94 and http://members.trainorders.com/tracktim ... elines.pdf for more info on that.

regards

Geoff

Mike_R
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Re: DCC Accessory Compatability

Post by Mike_R » Wed Apr 08, 2015 11:07 am

There is the possibility to use the throttle bus 12v, especially if powered outside of the command station, for the feedback / signal two wire bus. That would allow use of the 8 way plugs only.

The advantage of using track bus commanded accessory decoders is that they will work with any system. Even if your module was in a layout with a different or no feedback the signals would still work, in a more limited way.
With more complication, any of the feedback systems could work with each other, but a command station and computer would be needed for each.
Another option a MERG type / hardwired system could use block detectors to make the inputs of the other feedback system's feedback unit. It would require having a feedback unit of each type you are going to connect to. If connected with a plug they could be easily swapped.
Mike Ruby

geofftiller
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Re: DCC Accessory Compatability

Post by geofftiller » Wed Apr 08, 2015 12:18 pm

Hi Mike

I am not sure I understand your suggestion to use the throttle bus 12v for feedback, are you suggesting a data signal modulated on to of the DC?

We have re-purposed the lines used for the booster bus on the basis that those lines only need to be delivered to a small number of point around the layout and the feedback and accessory bus needs to go everywhere it meant the smallest change and least amount of new wiring to get us going. We did have resistance to adding more wiring to modules and this was a way to move forward.

The main reason we went for the Sprog is that the new Lenz interface does not support the extended packet commands so we could not use the accessory decoders in their most efficient way. We do have a couple of the older serial interfaces which do support those commands but wanted the other features of the Ethernet interface. Keeping non track data off the track bus also seemed an advantage. All the boards are wired to allow the accessory to be fed by the accessory bus OR the track bus with simple switching or reconnection. While mostly to help us during the modification phase we're keeping this capability as it ensures all turnouts continue to operate when the computer system is not available.

We are using MERG DTC current detectors and IRDOT infra-red detectors, currently with RS based feedback modules but these could be connected to alternative feedback/input modules in the future.

Geoff

Mike_R
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Re: DCC Accessory Compatability

Post by Mike_R » Wed Apr 08, 2015 12:30 pm

I mean that you don't necessarily need another power bus for a separate feedback bus, but could use the cab bus for the same power. Most systems use two wires for communications and two for power, The 8 wire bus doesn't have enough, using the throttle power means that it will fit on the 8 wire bus.
This would mean checking that the common of the throttle power and feedback power can be connected together.
Lenz and Digitrax, not sure of the others, can use external power to maintain the voltage and current capacity.
Mike Ruby

signalist
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Re: DCC Accessory Compatability

Post by signalist » Wed Apr 08, 2015 2:39 pm

Hi Peter

I have been working with Geoff on the Thamesiders' signalling team

There are two main things to consider when putting in signalling:-

1. How to send commands to the signals.

2. How to get feedback of the state of the track.

Both have existing NMRA standards for implementation, and there are a lot of proprietary methods too.

The existing NMRA standard for controlling signals is using accessory decoders that take the DCC track signal and use either the standard accessory packet format (really only suitable for 2-aspect signals) or the extended accessory packet format (suitable for up to 32-aspect signals). Although new methods are being proposed this method is perfectly adequate (especially using the extended accessory packets) and is likely to remain the simplest and most cost effective method of controlling signals whether connected to the track bus or connected to a separate accessory bus. Proprietery methods of control are only available from a limited range of manufacturers such as Digitrax and MERG and using any of these is going to limit your choice of accessory decoders and restrict you to a command station, while both Digitrax and MERG support use of the NMRA standard track-fed accessory decoders as well anyway.

As for feedback the existing NMRA ratified method is using Lenz Railcom. This has a huge advantage of working over the track bus and therefore not requiring any new wiring for the feedback bus - but has the huge downside that there is very limited supply (if any) of feedback encoders to support using it. This really means that using a feedback method that is readily available has to be the way to go in the short term.

The Lenz RS bus wins out currently for modular operations in my book for several reasons:-

A. Every feedback encoder is individually addressed so that it does not matter how modules are connected together - they will always have the same address and can be easily identified by the control system. HSI-88 bus for example falls down on this point because the address of a module will change on every setup depending on the position of the modules.

B. The RS bus is a 2-wire interface so not too much wiring to do. Two circuits can be much more easily found in inter-module connectors than the four circuits of NCE, or the six circuits of Digitrax loconet, MERG CBUS and HSI-88.

C. There are some nice feedback encoders available from 3rd party suppliers such as LDT (RS-16-O) and Paco (RS8) as well as the Lenz modules giving you some choice.

D. 3rd party RS bus interfaces are available so that you are not tied to a Lenz command station. There are serial, USB and Ethernet interfaces available.

If you use the LDT RS-16-O or Paco RS8 RS bus feedback modules these can easily be replaced with others at a later date if you choose to change to a different feedback bus so most of your investment in occupancy detectors such as MERG DTC or IRDOTs will be future proof, and of course the signals and accessory decoders will be suitable regardless of which command station is in use. Just keep the track bus, accessory bus, feedback bus and cab bus separate and it will always be possible to mix and match to get the best solution from what is available.

The original Thamesiders spec was very forward thinking in mandating the RS feedback bus to all main line modules and that has allowed the signalling project to proceed without having to touch any modules except the ones that are involved with the signalling directly. If you do not have any through wiring in place you will just have to add a 4-wire bus with the accessory bus (2-wires) and RS feedback bus (2-wires) to all modules before you get going.

Paul

Mike_R
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Re: DCC Accessory Compatability

Post by Mike_R » Wed Apr 08, 2015 6:07 pm

We copied the Thamesiders 8 wire control bus and all our new single track modules have it along with the separate accessory bus. Currently it is all Lenz, but as you say that can be changed.
Mike Ruby

PeterLJ
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Re: DCC Accessory Compatability

Post by PeterLJ » Thu Apr 09, 2015 10:28 am

Hi

Wish we had a white board, make it easier to follow. But having read all this assuming we have JMRI have we a problem (I thought we had, but am not so sure now).

If Lenz modules appear at a meet where the command station is Digitrax or NCE they need to provide a "R,S" bus and connect that to the JMRI Master Computer via a Lenz Command Station and Computer Interface. Digitrax Modules are different, they need only provide the Loconet Buss and the computer interface. Have not used NCE accessories so do not know what happens with them.

Then we let the JMRI computer take the strain. At WU we have run Digitrax and Lenz simultaneously from one computer.

But am still studying previous posts.

Peter

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