A General Guide to DCC


DCC Digital control can help to bring more realistic operation to a layout. With digital you drive the trains – not the track. The principle is very straight forwards; the track is powered all of the time and the Digital command station sends all of its information down just two wires to the track. All of the decoders will receive the information but will only act on instructions that are addressed specifically to them. On conventional layouts every locomotive that you wish to drive at the same time needs an independent controller and an isolated section to run on – the end result is a lot of wiring and a layout that is fixed and difficult to modify if you want to change how it is operated. Every point and signal needs its own dedicated switch which is also fixed and difficult to modify at a later date.

The idea of these pages is to give a quick guide for beginners and to include some more advanced DCC information that may be useful as you progress - The usual disclaimer applies - this a guide only.

 Figure 1.1 shows a comparison between conventional 12v DC operation and DCC Digital operation.

The major advantage of digital is that the power supply to the track is constant so functions like light and sound remain on even though the locomotive has stopped.  Multiple locomotives can share the same track without complex wiring on the layout. Digital also has the advantage that locomotive speed remains constant even though loads may be changing as the train climbs hill and descends gradients.  With DCC you can also tune a locomotives behavior. Accelleration, deccelleration, Maximum speed and inertia can all be set to give a loco realistic performance. See the section about locomotive decoders.

Digital is known as a "Two wire system" because all control commands can be sent down the same wires.  In conventional 12v DC operation you need a controller for each locomotive that is to be driven, complex isolation for each locomotive that is to remain stationary and, at least, a pair of isolated wires for every switching operation that you wish to control (Points, Signals, lights, etc...).  There is great simplification in layout wiring when using DCC.

Is DCC new?

DCC is now a mature technology with international standards that allow items from all over the world to be compatible.  DCC began in 1991, however Digital control of model railways is much older. Before DCC there was FMZ, Selectrix, Motorola and of course Zero 1. Fleischmann FMZ was introduced in 1985. Selectrix for Trix and Minitrix went on sale in the early 1980s.  Marklin Motorola was announced in 1979, Marklin sensibly took their time to release a finished product and this came in 1985  (As an aside Lenz contracted for this system and used the experience to underpin DCC).  Hornby Zero 1 first appeared in 1979. Each of these digital systems was groundbreaking, however they usually tied you to a single manufacturer.

DCC opened digital to everyone and that is its greatest achievement.  DCC has also benefited from the work put in by the digital pioneers and a great deal of work went into smooth power control for locomotives.

A DCC Layout can be built in stages.

The rate that you convert to DCC is entirely up to you.  The steps below show a possible progression, however it is your choice as to how many of these steps you adopt.

Step 1 
All you need to get running with DCC is a Control System  (DCC Command station) and a loco fitted with a DCC decoder.  More DCC locos may be added over time.

Step 2
You may wish to switch points so you can add point motors and an accessory decoder that gives them an accessory address that can be switched from the DCC Command station.

Step 3
Signals can be switched using DCC accessory addresses. All you need is an accessory decoder that is designed to control the types of signals you choose. Semaphore signals can work like a point motor, colour light signals may need a specific decoder. Some colour light signals now have built in DCC decoders.

Step 4
Layout lighting - Steet lights and buildings may be illuminated and controlled using DCC.  Again there are specific decoders for this job

Step 5
Simple automation - Some DCC systems allow you to control some trains automatically.  Lenz ABC is an example of this. Simple automation is easy to set up and very effective.  The limitations of simple automation are that it cannot control trains operating in different directions on the same line.  It also cannot manage trains crossing over at junctions - for these situations you need computer control. (See Step 7)

Step 6
Train detection.  DCC Feedback modules may be used to detect if tracks are occupied by a train - This can be a great help if you have hidden sidings.  Train detection is a necessary component of Computer controlled automation.

Step 7
Complex Automation.  Some DCC Systems can connect to a Personal Computer.  This allows you to use dedicated software to automate a layout.  The Software drives the layout in a similar way to a person, sending driving commands to the DCC Command station, however it can only 'see' the track plan you give it and the track occupation information that your DCC train detection system provides - Complex automation is very effective and a great part of the fun is designing the layout and its detection system.  Careful planning will bring the greatest satisfaction from Automation.  This has the same challenges as coordinating a group of people to successfully drive a complex layout without incident, only the computer can manage this at a far quicker rate.

We show a huge variety of products on our website - many have specific jobs to do within DCC. All items are designed to be operated by anyone  without specific training.  We endeavour to de-mystify these products with our help videos.
Below is an explanation of the components you may encounter:

DCC System Architecture
This section gives an overview of the DCC components that you may encounter.  Some of these are only needed for specific jobs and may be added at a later date.  Feedback and computer control go hand in hand you need a method of tracking rolling stock if you are to successfully automate a layout.  Feedback information is used by some manufacturers to allow you to build DCC mimic boards. Additional boosters are only necessary if you have a large number of trains running at the same time.

Command Station – The centre of a Digital system, the command station takes your instructions and sends out the correct DCC signal to the model railway layout.  Lenz Command Stations.

Booster – A booster is usually built into the command station and acts like an amplifier in a Hi-Fi system – the booster increases the DCC signal and power so that it may be received cleanly by every DCC decoder and accessory that is connected to the system – Additional boosters are required when the power demands of all your locomotives and digital accessories exceed the power output that you have available. Lenz Booster

Transformer – most systems have separate transformers, allowing you to upgrade the power supply later on.  Check the maximum current that your system can use.   Lenz Transformers

Auxiliary Control Devices – Most DCC systems allow you to plug in additional control handsets so that many people can control different locomotives and accessories on the same layout.  The additional handsets are wired into the systems wiring network (called a ‘Bus’) and suitable sockets can be many meters from the command station allowing operators to move around large layouts and plug into the system at many convenient points.  There are also wireless handsets available using Infrared and Radio to send signals back to the command station.  Importantly the command station has overall control allowing the layout to continue running when auxiliary handsets are disconnected or lose signal.  Lenz Auxiliary Control Devices

Network Buses – these are the wiring networks that manufacturers use to help simplify wiring on large layouts.  Auxiliary control devices, accessory modules and feedback systems can be connected back to the command station using the wiring bus and this avoids sending every instruction through the tracks.  It also avoids having a complex spiders web of wiring beneath the layout radiating from the command station as the Bus system can be daisy chained from one module to another.  Each manufacturer is free to design their own wiring bus system.  

Locomotive decoder – Gives a locomotive a DCC address and allows independent control of the motor and auxiliary functions such as lighting, automatic uncoupling and smoke generators.  A sound decoder or additional sound module allows realistic sound to be generated by the locomotive. Lenz Decoders

Function decoder – Gives an un-motorised piece of rolling stock a DCC address and allows the independent control of functions such as interior lighting, directional lighting or automatic uncoupling. 

Accessory decoder – This is use to drive point motors, uncoupling ramps and signals.  They can also be used to switch layout lighting.  Accessory decoders use Solenoid addresses – these are separate from locomotive addresses on the majority of DCC systems.  A small number of systems use the same addressing for locomotives and accessories – it is worth checking with the manufacturer’s instructions so that you do not have a clash. Lenz, Roco and Uhlenbrock all use separate locomotive, accessory and feedback addressing so you can run loco address 01 over point 01 in feedback section 01 without there being a clash of commands as they all are addressed independently.  Lenz Switching Decoders

Feedback Modules – Status feedback is important for automatic operations and for monitoring hidden sections of the layout.  Feedback allows you to see which sections of rail are occupied and vacant without having to perform a visual check.  See the section on feedback for the relative merits of each feedback detection method.  Some accessory decoders allow the feedback of point and signal positions to the command station so that you can be confidant that a route is set before a train enters it. Lenz Feedback

Track Plan Panels – Mimic boards can simplify complex junctions eliminating the need to remember the number and last setting of a specific point.  Feedback information can also be visually displayed. 

Layout Ambient Effects – Products are available that allow you to bring light and sound to your layout and control it all digitally.  The layout lighting can be tied to a model time clock so that Day and Night can be simulated, streetlights come on as it gets dark, house lights come on in the evening then are extinguished as the night wears on, even thunder storms can punctuate the cycle. These can be controlled automatically by the system or triggered manually by the operator. 

Computer Control – Many systems allow the connection of a PC to the Command Station for updating.  Several systems allow you to use your PC as an auxiliary handset for driving and programming.  Some systems allow partially or fully automatic running of DCC layout using software such as iTrain, WinDigiPet and Railroad & Co.


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