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DCC - 101

(Digital Command Control)

"DCC Advanced" gives a more detailed insight into DCC as well as a comparison of different systems.

With Digital Command Control (DCC) you can run your model railway without the constant switching of toggle switches for throttle and/or block selection. All you have to do is control the speed and direction of the locomotive.

HOW IT WORKS

Simple schematics of DC and DCC systems are show below. Click on either one to enlarge it.

DC Schematic DCC Schematic

Click on an image to enlarge

This circuit board is called a decoder and the following points should be noted.

WHAT YOU NEED

The basic components necessary to run a DCC railway are:

The last two items are often combined in a single unit, or if not, are usually purchased together when you buy your DCC system.

If it's not included in the base package, you can purchase the proper power supply from the same manufacturer as the throttle and command station, or you can source your own. The throttle is an item that must be purchased – you cannot make your own as you may have done in DC days – and it must be from the same manufacturer as the command station.

The command station is the intelligence of the system. Its job is to route the orders from the throttle to the decoder in locomotive(s). It does this via a very high frequency square wave signal that travels through the track with, but independently of, the AC power supply.

You assign every decoder on your railway with a unique address. Most modellers use either the last two or last four digits of the locomotive in which it’s installed.

When you, via the throttle, issue the command for locomotive #1234 to move at, say, one quarter of full speed in a reverse direction, the command station writes a data packet that is addressed to, and only read by, the decoder in locomotive #1234. All other decoders on the layout ignore the signal because it is not addressed to them. In simple terms, the signal will tell the decoder to provide the power to rotate the motor in the locomotive at 25% maximum speed, in whatever direction it turns to make the locomotive move backwards.

The decoder can not only tell the motor which way to rotate and how fast, but also turn the headlights and ditch lights on or off as well as sound a horn and/or bell, squeal the brakes, 'hiss' the steam etc. if a speaker is installed.

Once the instructions have been received by the decoder it will blindly follow them until told to do otherwise. This means that even if you unplug the throttle the locomotive will keep on obeying its last instruction.  To the DCC novice this can be a bit unnerving – it probably feels like cruise-control to the learner driver - but as you gain experience you realize the benefits.

Modern DCC systems can be operated with both tethered (plug-in) and wireless throttles. The Nottawasaga Model Railway uses both, and you may have noticed that some of us have to plug our throttles in to one of a number of communications ports situated around the layout while others don’t have to plug in at all. The latter are operating wireless throttles. Most plug-in throttles can be modified by the manufacturer to wireless.

WIRING

A lot simpler than DC, but good electrical connections are an absolute must with DCC. This is because not only is power being carried through the wires and track but also a high-frequency communications signal. It’s recommended that you solder the connectors to the rails at every second joint in the track, leaving alternate joints unsoldered to allow for expansion. It's also recommendation that the feeder wires from the bus be soldered to the track every six feet. However, if you look closely at the Nottawasaga Model Railway you’ll see that we cannot install permanent feeder wires to those 6” sections of track we use to connect the rails between modules. These sections have 14ga solid wire soldered at each end and this wire fits snugly against the permanently fixed track on the module. However, every section of permanent track on every module does have a feed from the bus.

If operators are going to move around your layout with a tethered throttle, a communication cable (usually, but not always a six-wire telephone cord) is required with any number of inexpensive plug-in ports sited where convenient. Wireless throttles need neither the communication cable nor the ports.

Top-of-the-line DCC systems can be operated with up to 120 throttles.

Loconet Port

A Digitrax Loconet ™ Port

You can probably reckon on spending between $175 for a basic DCC system to over $500 for a top-of-the-line wireless system. The less expensive system will, for most model railways, likely be adequate. You can spend more by purchasing a wireless system, one with a higher amperage rating (which lets you run more locomotives at the same time) as well as a throttle that is, to some extent, two throttles in one in that it provides two speed knobs, two forward/reverse buttons etc. Most, although not all, low end systems can be added to, to make them equal to their high-end brothers. You'll find more details on costs and capabilities etc. in the DCC - The Technical Description" page which provides much more detail on costs and how DCC works.

Tablets and smartphones are now ubiquitious and, thanks to inexpensive apps, can be programmed to operate as throttles. Tablets are especially popular because their size allows you, if you have the dexterity of a one-armed paper hanger and the reactions of an F1 racing car driver, to run up to four locomotives at the same time from a switch list that's also being displayed. But that's another facet of the hobby altogether and club member Bill Hambly has a description on his web page at http://www.model-railroad-infoguy.com/model-train-control.html

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