LCC III - Messaging

Back in October I started what I thought would be a relatively easy, if perhaps a bit long, post on messaging in LCC. I was trying to cover it in detail, explaining how the ideal LCC had to be adapted on CAN Bus. That proved distracting and I put that material aside to just focus on the basic messaging capabilities of LCC rather than the implementation on CAN Bus, at least to the extent I could.

In the process of doing this, I've managed to chase myself in circles more than a few times. The LCC standards are very confusing, even by NMRA standards. We're talking about documents written by volunteers rather than professional standards-writers, and generally without a whole lot of editing. I've been reading NMRA standards for more than 25 years and I'm used to having to work at it to puzzle out the actual meaning. But still, the lack of clarity in the LCC documents is exceptional.

I'll detail problem areas throughout this post, but it basically boils down to things either being omitted entirely from the documents or being covered in one of the other technical notes than the one you’d expect. And there's a fair bit of using two different names for the same thing and, conversely, using similar names for two different things.

The revised post is about messaging in LCC and what you can do with it now, and additionally I'm coming at this as a review of the LCC standards, not anything external to them. The OpenLCB team has written a lot of words about OpenLCB, and that’s often helpful, but what matters in a standard is what's actually incorporated in it, either directly or by reference to or citation of an external document.


LCC II - How It Works - Physical

This is the second in a series of posts on the NMRA's new Layout Command Control (LCC) standards. The first post covered the reasons why a control bus, and specifically LCC, were important, as well as providing a fairly high-level view of how LCC works. Today we'll get into some very specific details regarding the physical aspects of the network, specifically the CAN Bus wiring and usage. Next time, I'll cover the actual messaging on the network (i.e., what you can do with it).

LCC I - Layout Command Control

Three years ago, in 2012, the NMRA published their first standard related to a layout control bus, at the time known as NMRAnet. This was standard S-9.7.1 NMRAnet: CAN Physical Layer, which defined the electrical characteristics of the bus (e.g., details of the wire, connectors, bit rate, and voltage levels). Several companies were producing useful circuit boards based on the standard, although their functioning depended on capabilities not adopted at that time.

This standard, and the not-yet-adopted parts used to make the first implementations, were based on something called OpenLCB, which stands for Open Local Control Bus (not "Layout Control Bus"). Open LCB was one of several competing proposals for NMRAnet. The OpenLCB team demonstrated how this would work at the 2010 NMRA convention, and has a page of videos and other information from then. Over the subsequent two years it came out on top as the solution of choice. However, some of the potential demonstrated there does not seem to be fully fleshed-out in even the current standards. We're not done with the development of LCC by any means.

But we have had significant progress this year. Back in February the NMRA adopted 21 additional documents, 10 more Standards and 11 clarifying Technical Notes. They also renumbered them slightly, and changed the name to Layout Command Control, or LCC. These were formally adopted with a six-month comment period that ended on September first. Updates based on those comments are still possible, so the standards aren't quite done yet, but they're probably very close to their final form.

MRC Tech 7 780

DC “Power Packs” for model trains tend to be designed for HO scale trains, at least in North America. There are separate ones for G scale, and some multi-scale packs catering to both HO and larger scales. But those sold for N scale are typically just HO models, with the usual HO “16 volt” or higher output, usually called “Universal” power packs.

Anyone who’s been involved in model railroading for any length of time knows the Model Rectifier Corporation, more commonly just MRC. They’re probably the dominant supplier of DC power packs for HO and N-scale model railroading in North America, aside from those included in starter sets, although Kato’s Unitrack power pack likely gets a fair amount of N-scale market share. But I’ll admit I don’t have hard facts on market share for anyone.

My first power pack, after a cheap Tyco one that came in a starter set, was an MRC Throttlepack 501, circa 1972 (yeah, I’ve been doing this a while, although I took a long break after High School). That 501 still works today, although one of the switches has finally started having problems. But it survived 40 years of damp basements, being thrown in boxes for moves, and running a large variety of trains. That kind of quality leaves a lasting impression. I’d followed it with another MRC, a Control Master II, when I got back into model railroading and needed a second power pack (back around 1992). It too has served well, and still works. But both put out relatively high voltages (19V+), so I’d rather not use them with N-scale trains.

So when I started looking to see what was available in a modern design suited to N-scale, and discovered the MRC Tech 7 line had a model with a rated 14.5 V, 10VA output, it didn’t take me long to decide I wanted to give it a try. It’s a dual-cab power pack, with two independent throttles in one box. But I’m going to use it on a double-track line where I’m normally the only operator, so that’s fine.

DCC Voltage and Cab Lights

’m turning my attention to the cab car decoder install now, and a recent discussion with Don along with a question from a reader had me thinking about potential problems with DCC conversion of N-scale EMU cars with cab lighting. And the one that really worried me was overvoltage from high DCC track voltages, and its harmful (fatal) effect on LEDs. DCC decoders essentially pass track voltage (minus a small bit) through to their function outputs.

NMRAnet - Why You Should Care

In August, the NMRA adopted standard S-9.7.1, NMRAnet Physical Layer, and a short article about it appears in the November issue of the member's magazine. What is this, and why should you care about it?

Well, if you care about Digital Command Control (DCC) for controlling a model railroad, it's an important addition to model railroading that will enhance that. And if you don't care about DCC, it's compatible with other control systems, and you may still want to use it. Read More...

Standards, The NMRA, and Japanese Trains

I recently renewed my NMRA membership, and that set me to thinking about their role in standards-setting, and what it means for the hobby, and about the application of standards to the Japanese-prototype Model Railroading I do today. I’ve been an NMRA member for 20+ years, and the reason I originally joined was to get access to their standards, back when that meant buying a three-ring binder full of paper. Today, those Standards and Recommended Practices are available online, free for anyone to download (the Data Sheets are still members-only, but those are less critical although full of useful information), and I think that’s one of the best things they’ve ever done, even if it does give people one less reason to join.

Track Voltage, Motor Voltage, and DCC

As I’m finishing up the wiring for the two upper-level loops (one of which will be DCC-only, the other will be the switchable DC/DCC line), I’m also getting my DCC electronics set up and ready for use. There are several aspects to this, and I’ll cover others in future musings. But today I’m going to write about track and motor voltage. I could have just used the command station as it came, and it probably would have worked fine. But I like understanding exactly what’s going on under the hood, and so I ran a number of tests and spent some time researching what the track voltage should be, and why, and what that meant for the motor on a train. And if I ever add a booster, it will be important for it and the command station to be set to output the same voltage (this avoids problems when a train bridges between two power districts), so I may as well pick a voltage now.