DCC for Railway Modellers (eBook)

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DIGITAL COMMAND CONTROL

What Is Digital Command Control (DCC)?

In a nutshell, digital command control (also sometimes referred to as ‘digital command and control’) is a system, governed by a standard set by the NMRA, which offers the user the capability to run several trains at the same time, with the bonus of more simplified wiring.

As soon as the command station is switched on, the track receives full voltage. Changes to driving speed and direction are made by sending a signal to the decoders in the locomotives, which in turn control the locomotives. The track voltage is effectively AC, so direction is no longer dependent on polarity. Locomotives will respond only to those commands that are directly addressed to them. With DCC, the locomotives are being controlled by the user and not via control of the track voltage (as was the case with analogue control). When using a DCC system, full voltage is supplied all the time the command station is switched on. A controller is used to send information to the command station, telling it what operation a particular locomotive should do. The command station then transforms this information into a stream of digital code and sends it as packets via the track to the decoder, which instructs the locomotive to carry out the instruction as requested. Rather like a digital television, the locomotive will respond only to signals that are addressed directly to it and will ignore all other signals.

The same process applies for accessories, which can also be controlled by a decoder. Accessory decoders can be used to control points, lighting, turntables, servos for crossing gates, and much more.

There are many different terms used in the realm of DCC; a glossary is included at the end of the book to help with understanding.

Choosing a System

When selecting a DCC system, asking a few questions will help you find your way around the range available:

The answers to these questions will point you towards identifying a system that will be the best fit. They can be used as a basis for discussions with a local retailer, who should be able to indicate what options are available, or for an online search. For more details on choosing a DCC system, see Chapter 8.

The Components of DCC

The basic requirements for a DCC system are a command station and handset, together with a suitable power supply. In addition, decoders will be needed for the locomotives. If points and signals are also to be controlled digitally, an accessory decoder will be required (see Chapter 11 for further details).

The choice of systems is wide-ranging, but, despite the many and varied opinions you will encounter among fellow modellers and journalists, there is no such thing as the ‘best’ one. The main advice should be to choose the system that you feel most comfortable with, and always try before you buy. All systems do the same thing, just in a slightly different manner.

As a user, it is essential to be comfortable with how the handset feels in the hand, and with the activation of the buttons, knobs, and so on. Basically, if there is anything about the system that does not feel good, running the layout will not be an enjoyable experience.

A DCC system can be made up of either a desktop command station with a power supply or a command station with a handset and power supply. Desktop units may also have handsets added to them if required.

Command Station

Command stations come in all shapes and sizes, some requiring a handset, some not. Some allow for the use of a smartphone or tablet as the handset.

Handset

Handsets also come in all shapes and sizes and can be added as required, as command stations are able to operate with multiple handsets. The user’s smartphone or tablet may also be used and, in some cases, can operate in conjunction with a DCC handset.

Power Supply

One aspect of a DCC system that is often forgotten is the power supply. It must suit the system purchased and, of course, it needs to be appropriate for the country in which it is to be used. These days, many manufacturers will provide a suitable power supply for their systems. However, if this is not the case, it is essential to have the right information -- the maximum voltage the system will take and whether it will take DC or AC – so that you can choose the correct power supply or transformer for the system.

Boosters

A booster for a DCC system is not a transformer or a power supply, but in principle an amplifier for the DCC signals from the command station. These are then combined with additional power output and the signals and power are sent to the track. Most DCC command stations come with boosters built in, and the total current output will be indicated in the manufacturer’s details. Additional boosters may be required at a later date, depending on a change in the current requirements of the layout. Should the total power required by the layout exceed that of the chosen DCC system, perhaps because the layout has developed and grown, then an additional booster can be added to the layout.

Boosters are responsible for converting the AC or DC power from the power supply into local DC power to the track. They are also responsible for converting the signals from the command station into packets of information to be sent to the locomotives.

Different boosters may offer various features: short-circuit protection, automatic circuit breaker function, regulated voltage provision and auto reversing. These are not essential but can be added bonuses for the layout.

Boosters can be beneficial to a layout if it is some-what more complicated or if it is being used for demonstration purposes, for example, at a club or exhibition. For the average home layout, however, a booster is not necessarily required, especially if best practices are followed for the wiring and the system has sufficient current for its running requirements.

Decoder

The next component required is a decoder for the locomotive, if it is not already fitted with one. Again, there are many makes, with different sizes and capabilities. To decide which is the best one for your requirements, ask yourself the following questions:

Some manufacturers may specify a particular decoder to be used in their locomotives. Although this is useful information for the user, it may be the case that a third-party decoder offers more features.

For more on decoder choices, see Chapter 9.

Accessory Decoder

The final optional component is an accessory decoder, which will allow for the digital operation of points, signals, lights, and much more.

Accessory decoders are normally multi-output units that are mounted under the layout in a stationary position. They can be used to control points/turnouts, structure lights, scene lights, animation, signals, and other items that require an on/off signal. They may or may not provide power to the accessory.

As with everything else, accessory decoders come in a variety of shapes, sizes and outputs. They are usually multifunctional; however, when considering them for control of points, it is very important to know what point motors are being used. There are specific modules for solenoid (snap-action) point motors and for slow-action (stall motor) motors, as well as for servo motors.

Points (also known as turnouts and switches) are movable sections of track that allow a train to move from one line to another, guiding the wheels towards either the straight or the diverging track. In the model railway arena, points are used to change the direction of travel. They are typically made from metal and plastic and can be operated manually or by a point motor. The most important thing to remember when using points is that they must be correctly aligned with the track.

The term ‘turnout’ may be used to describe a point in some instances, but it is actually a combination of a number of components, only one of which is the actual point. The component known as the point is the short section of rail that physically moves to direct the train one way or the other. It is often referred to in model form as the ‘point...