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The purpose of this article is to help you decide if you should use DCC as the means of controlling your model railroad. First I will present a brief overview of what DCC is, how it works, and how it differs from standard layout control systems. Next I'll answer the question "Why use DCC?" Then I will review the various components that comprise a DCC system (including some items the DCC vendors won't tell you about.) I'll also give you some idea of costs and what it is like to operate a DCC controlled model railroad.
Be forewarned that I have built both standard and DCC layouts, and I am a total convert to DCC. Consequently, this article is definitely slanted in favor of DCC. Also, this article is based on the HO scale, where locomotives are powered by 12V DC motors. Some differences may apply to using DCC in other scales.
What is DCC?
DCC stands for Digital Command and Control. This means that instead of controlling locomotives by continuously varying the voltage of the current the locomotive's motor receives, you instead send each locomotive a coded digital signal that the locomotive uses to control its speed and direction. In a DCC layout, each loco has a unique digital address, and each loco only responds to signals sent to that address.
What this means, in operational terms, is that you can control each locomotive individually, no matter where it is on your layout. Since each loco is uniquely identified, you can simultaneously run as many locos as you want, and you can do so from a single controller by simply selecting the identifying number of the loco you want to control at the moment.
With DCC there is no need for electrically isolated blocks of track, or block control switches and indicator lights. Moreover, you need not have separate controllers for each loco you are running: a single DCC controller can run all your locos at once. You can, of course, have multiple controllers is you want to have several people operating locos at one time.
Also, as I will explain later, you need not have any physical switches for controlling turnouts, nor do you need a physical control panel, indicator lights, or any of the wiring all that requires.
How does DCC work?
In a standard HO layout the rails carry plain DC current. The polarity of the current determines the direction of the loco, and the voltage determines its speed. Because of this, if you put two locos on the same section of track, they will run in the same direction at the same speed because they both "see" the same polarity and voltage on the rails.
In a DCC system the power on the rails is not standard DC current. Instead, the DCC controller breaks the continuous DC voltage up into a series of pulses, and it puts these pulses of DC power on the rails. The DCC controller also has the ability to generate pulses of different frequencies, and it can put multiple frequencies on the rails at the same time.
In a DCC system, each loco is equipped with a small circuit card called a decoder. Each decoder has a unique identifying number that is keyed to one of the power frequencies generated by the DCC controller. Consequently, each loco picks up only one of the power frequencies sent out by the DCC controller. This is what allows each loco to be controlled individually: you simply tell the DCC controller which loco you want to control, and then you vary the power (speed) and direction for only that loco, even while other locos continue running at their previous settings.
Why use DCC?
The answer is simple: a DCC controlled layout allows you to operate your trains in a way that is much more like operating a prototype railroad. Specifically, you can run as many locomotives as you like, wherever you like, with no concern for block controls or any other issues related specifically to model railroads. You can control each loco individually, and you can use one, or multiple, controllers at the same time.
Even though this sounds like hyperbole, the truth is that DCC is the single biggest improvement in model railroading since the invention of electricity. Of course, the only people who believe that are the ones who are currently running a DCC layout. If you are serious about model railroading, you should be one of them.
How does DCC work?
There are really two types of components in a DCC system: the ones you have to have, and the ones that are nice to have.
First you must have a DCC power supply. Unlike standard Power Packs, a DCC system uses a separate power supply that you must purchase as an individual item. The DCC power supply is really nothing more than a transformer, circuit breaker (to cut off power in the event of a short on your layout), and an on/off switch. DCC power supplies cost about $40.
Next is the main DCC unit itself. This is the "brains" of the system and is often called the Command Station or Booster. This unit has two functions: (1) it converts the AC input from the power supply to DC, and (2) it converts the continuous DC power to pulses of various frequencies, where each frequency will be sensed by an individual loco.