DCC Tutorial (Basic System)

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This article is part
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DCC compared to computers
Basic System
Power
Starter Sets

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Welcome to the DCC Tutorial (Basic System). This article will try to get your DCC Starter Set out of the box and get your trains running.

We're trying to make this as basic as possible. DCC is a bit more complicated if you get into the nuts and bolts, but setting up a basic system takes just a few more steps than setting up a traditional Analog power pack.

The nuts and bolts of DCC do get rather technical-- after all, you're dealing with a computer network! Fortunately, you don't need to understand computers to make DCC work for you!.

Don't worry if you don't understand it right away, we'll present the same material several different ways in hopes that you'll understand one of them.

Contents

A quick comparison between Analog and DCC

An analog control system permits only one train per cab/block at any one time. A Digital Command Control system, however, can be all one electrical block - but many locos can be individually operated simultaneously! One person can run several locomotives at once, several people can each run one locomotive at a time, or several people can each run several locomotives at a time.

The key advantage of DCC over the traditional analog direct current systems is the elimination of separate blocks for train control. With DCC, many trains can be controlled independently within the same electrical block. Before DCC, control of speed and direction was related to the voltage and polarity present on the track, which was controlled by the operator using a potentiometer (or rheostat) and a direction switch. (The reason it is called analog is that the speed and direction of the locomotive is directly related to the amount of voltage and its polarity.)

If you already have a layout wired with block control and want to switch to DCC, you can make the change. Please refer to the article on track wiring for details.


Cab Control system panel. This example dates back to the 1960s (50 years.)
What lurks beneath... This took not only a lot of time to design, note the craftsmanship in the wiring. The transistors are 2N555 Germanium devices. Germanium was a common semiconductor material in the 1950s and 60s, giving way to silicon during the 60s.


Looking at the above pictures, do you still think DCC is complicated?

What DCC is

Digital Command Control (DCC) is a scheme for controlling locomotives on a model railroad layout. It allows more than one locomotive to occupy the same electrical section of track. It allows for multiple operators to control multiple locomotives simultaneously, even in the same block (electrical division), which in analog (or DC power) is difficult at best, if not impossible.

If you only have the single DCC equipped locomotive that came with your starter set, you can run a single non-DCC (analog) locomotive along with your DCC locomotives. If you want to know how this works, check out the section on zero stretching. Not all systems can do this, but many can.

DCC Components

Let's give you the terms so you'll get familiar with them. The most basic Digital Command Control (DCC) system consists of several parts: a throttle, a command station, a booster, a decoder, and a power supply to run it all. Most systems also use a throttle network which allows multiple throttles to talk to the command station. Confused? Don't worry - it won't last!

Let's break this down a little.
Simple DCC system diagram.
  1. You use a throttle as an input to tell the system what you want a locomotive to do.
    • The throttle sends your request over a throttle network to the command station.
  2. The command station creates a digital packet and forwards it to the booster.
    • Some systems combine a command station and a booster into a single unit.
  3. The booster combines the power from the power supply with the digital data packet from the command station and puts it out on your railroad layout using your track wiring to the rails.
  4. A DCC-equipped Locomotive has a decoder inside. Every decoder is programmed with a unique address. The decoder listens to each digital packet as it goes past. It checks if the packet is valid (i.e. not corrupt), and if the address of the packet matches that of the decoder. If the decoder finds a valid data packet addressed to itself, the decoder performs the requested action. If the two addresses don't match, or if the packet isn't valid, the decoder ignores the packet and continues whatever it was doing.
    • Don't worry if the decoder ignores the first attempt, since the command station continuously repeats all current data packets in case any decoder did not receive it. This is one way that DCC is reliable - error checking and ways for recovery. We'll cover this in more detail later.

More details

The following sections are optional to understanding DCC. You are welcome to skip this section and go onto the DCC power section of this tutorial.

The following sections are summaries of devices. See the main articles for further details.

Throttle

Main article: Throttle

The throttle is the box with the knob you turn or lever you move or the buttons you push to tell your engine what to do: speed up, slow down, stop, brake, turn the lights on/off, ring the bell, blow the whistle. There are various types of throttles- from a simple knob and a few buttons, to a NASA-style control panel that will scare you senseless!

Another term is "Cab". Because all the controls are in your hand (whistle/horn, throttle, brake, direction and sound effects), it is the equivalent of sitting in the cab. Cab and throttle are essentially the same thing.

Power Supply

Main article: Power supply

The power supply is a device which supplies low-voltage AC or DC to the Command Station and Booster. Depending on the scale you are operating, you'll need a power supply with various voltages (covered later). For now, just think of the power supply as a device that converts the voltage supplied by the utility to a lower voltage required by the booster.

Command Station

Main article: Command station

The command station is the real intelligence of the DCC system. Typically, the command station is combined with the booster into a single device; however you can buy additional booster-only units for larger layouts that need more power to run more trains. The command station contains a microcontroller (computer) and is responsible for all communication between the throttles and the decoders. The command station communicates with decoders by transmitting packets of data to them through the rails. Each digital packet tells a train how to run: fast, slow, forwards, backwards, or to turn lights, sound, and other effects on and off.

Booster

Main article: Booster

The booster is sometimes referred to as a the "Power Station" and is responsible for combining the intelligence from the command station with the power of the power supply. Typically, a booster is combined with your first command station. More boosters can be added to the layout as demand for power increases.

Decoder

Main article: Decoder

While the Command Station is the intelligence of the layout, decoders are the "brains" of the locomotive. Each decoder is programmed with a unique address. The decoder monitors the DCC data and listens for commands with its address. All power in the locomotive flows from the rails, to the decoder, and then on to the motor, lights, and sound. These tiny special purpose computers rectify (change) the current to DC and vary the voltage and polarity to provide the motor control, as well as creating any lighting or sound effects they may be capable of performing.

The decoders are programmable, allowing you to change the address, motor performance, and lighting and sound effects. The programming is stored in semi-permanent (non-volatile) memory that saves the information when there's no power to the decoder. They can be re-programmed with new information any time you like, and some functions can even be programmed while the train is running, see Decoder Programming for details.

Did you catch the fact that even the "unique address" can be changed? If you have a train with more than one engine, you can program them all to the same address and control them with a single throttle. If you accidentally program 2 engines with the same address, interesting accidents can occur.

Each decoder is different. There are certain standard functions that they are required to have, but most of the things that make brands and models of decoder different are optional - particularly when it comes to various light and sound effects and fine tuning motor control functions they offer. Check your decoder's capabilities before you buy them!

Some decoders are unique to a certain brand and model of locomotive-- they're built in strange shapes to fit the odd nooks and crannies inside the locomotive. Check with various manufacturers to see if there's a special decoder for your engine.

Confused?

If not, skip this section as the article listed below may confuse you. Use the following article only if you still don't know what's going on.

If you are confused or would like to see DCC explained by using modern day computers and networks as comparisons, please read this article. Please note, this article may make DCC seem more complex than it really is. Think of this as the nerd's comparison between computers and DCC.

What's Next

Now that you have an understanding of the most basic DCC system, let's continue on to explain DCC power

Also see the article on Starter Sets here.

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