NMRA DCC, some history and thoughts

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The system adopted by the NMRA as a standard for digital command control is originally developed by Lenz from Germany, it became available in 1989 as a DCC system from Märklin, but suited for 2-rail layouts, instead of Märklin's own 3-rail stud-contact system. An 'n-scale' version, i.e. lower output voltage of this system was offered by Arnold, an n-scale pioneer from Germany. Design was similar to the equipment used for Märklin's own system and some devices were exchangable, for others special DCC versions were made. All this equipment was developed by the small electronics comapny of Lenz, from Giessen, Germany. A few years later, Märklin stopped the DCC range of products, while Lenz took over marketing and production, as well as introducing new features. In 1990, the NMRA of the USA, choose the Lenz format as a standard for digital command control. This means that other manufacturers can make compatible equipment that should work with each other within given criteria. A few things are NOT compatible with each other.

Over the years a few generations of DCC equipment have been developed, the difference is in the adress range and number of speed steps, newer loco decoders may have more features like a programmable 'speed curve'.

1st generation: 99 loco addresses, 256 accessory addresses, 14/27 speed steps.

2nd generation: 99 loco addresses, 256 accessory addresses, 28 speed steps.

3rd generation: 10,000 loco addresses, 2,000 accessory addresses, 128 speed steps.

4th generation: 10,000 loco adresses, 2,000 accessory adresses, 128 speed steps, with improved user interface, wireless connections to base unit etc. etc.

Some equipment is somewhere between these generations, like the Lenz LE030 and LE040 loco decoders, which have a 10,000 address capacity, but have only 28 speed steps. All equipment offered today is of the 2nd or 3rd generation. Starter systems are mostly of the 2nd generation, high-end systems are always of the 3rd generation, sometimes with added features, like transponding.

In the NMRA standard the following should work with each other:

- Loco decoders and accessory decoders should work with all DCC systems, an exclusion is made for simple 'starter kits', differences in the various generations of equipment should be noticed.

- New decoders should work on older systems, but sometimes with limited functionality.

- Old decoders should work with newer systems, these new systems should have a 'backward compatibilty'.

The following are not included in the standard:

System archtecture; any system that has the proper output and functionality can achieve a 'conformance warrant', whatever there is inside. Manufacturers are allowed to use their own control bus system, the same applies for a feedback system, when you use track circuits, the output of these may be fed back to the command station for further processing. Latest featurer is transponding, where adapted track circuits can read the output of transponding devices, buikt into your trains. The outputs of the transponding receivers can be used for further processing.

Over the years, at least 5 different 'cab bus' systems have been developed, each manuafcturer is allowed to create its own cab bus system. The 'cab bus' is the wiring to which your loco controllers connect with the command station and possibly other devices around the layout. A short list of cab bus system is shown below:

Choosing the right DCC system

Choosing the system that is right for you can be a difficult task, but depends on the following:

- Your demands, what capacity and features should your system have? How many trains do you want to run at the same time? Large layouts need a high-capacity system, smaller layouts can do with a simpler system. Do want to use your computer to control your layout? If so, there should be an RS-232, USB 2.0 or network interface available, some systems have included this in their command station. (Uhlenbrock, Fleischmann, CT-Elektronik, CVP's EasyDCC, NCE)

- Your budget. Very important, as a DCC system will cost you a lot of money, so making the right choice is critical. Do not forget the cost of loco decoders, which will probably be more than you will spend on the rest of your DCC system. Extra transformers for boosters are also a hidden cost.

- Personal preferences. Do you like a system for its design, functionality or whatever. Remember that you should handle the controllers easily and without making too many mistakes. All systems have a 'learning curve', but IMHO this should be as short as possible.

- Technical specifications: for N-scale a system with an adjustable and stabilised output voltage is preferred. The output voltage should be a controlled 12 Volts or slightly less or more. This limits your choice to Lenz, CT-Elektronik, Digitrax, Zimo or Easy DCC with 5 Amp booster units, as only these have a stabilied output. The output voltage of a Lenz system is set by jumpers inside the booster units or is programmable from the handheld controller, Digitrax has a switch on the booster/command station and the output of a Zimo system can be programmed into the command station / booster unit.

Latest trends

DCC technology is always developing and there are a few trends in DCC. First there's a trend towards more user-friendly high-end systems, at a price of about € 450.- and upwards. ESU and Viessmann have introduced such systems, Trix will follow later. Another trend is the growing acceptance of radio links between central station and hand-held controller. Bachmann will inrtoduce a system named 'Dynamis' that is based on 2-way infra-red wireless technology. Finally, Zimo is developing software that will run on a modern hand-held PC that turns the handheld computer into the ultimate model train controller. This project is named 'Ultramobile' and uses wireless PC network technology. Zimo is working on the use of Lenz 'Railcom' sensors in a Zimo DCC system. Technology is developing at a very fast rate, watch this space!

The Apple iPhone with it's WiFi access has inspired software developers to use this handy device as a model railway controller.

ultramobile Zimo's 'Ultramobile' running on a Samsung Q1 handheld PC (photo: Zimo)

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> Some backgrounds on Digital Command Control

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