Smallphry - diary of a model railway

Saturday, February 18, 2006

The Basics of DCC: The hardware

There are two major ways to control a layout: DC and DCC.

DC is the traditional method. When you operate the controller any locomotives which are in a ‘live’ section of track will be controlled. This means that if you want to, say, do some shunting in the goods yard while a train runs around the main line you will have to add a second controller and provide some switches to select which sections are operated by which controller. It can get complicated, especially on a large layout.

With DCC the entire layout is live all the time. Each loco has a decoder (or chip) inside with a unique ‘address’. In the handset you select the address of the loco you want to drive. Once you’ve started one loco moving you can select a second loco and drive that while the first one continues on it’s way. You can back a second loco onto the front of the train and easily create a ‘double header’ and it’s especially useful in a locomotive depot setting where many locos can be parked on the same section of track without the need for lots of separate sections.

If you have more than one operator they can each control a train without having to select sections in which to apply power. They can even both drive a train along the same section of track, they just have to be careful not to crash

It’s a simple system but many people are put off using it, probably due to complicated sounding terms such as ‘programming’ and also the process of fitting decoders to the locos.

In this series of articles I will describe the basics, which I hope will give you the courage to take the plunge into DCC.

What do I Need?

Lenz LH100 handset.

There are a wide range of DCC systems available, each with there own features, so what do they all do?

There are four parts to a DCC control system, but many systems combine various parts into a smaller number of boxes:

• A transformer provides low power for the other parts of the system as well as powering accessories such as turnout motors.
• A controller (or handset) is what you actually use to drive the trains. It can use either a traditional knob or a push button interface. Which one you choose will be a matter of personal taste. The controller will also have additional controls for selecting the loco to drive, for switching ‘functions’ on and off (eg for lighting) and for settings the decoders settings (commonly termed programming).
• A command station interprets the commands from controller and turns them into a signal which will be sent to the track.
• A power station amplifies the signals from the command station to sufficient strength to power the trains. You may need additional power stations if you have a large layout.

As I said earlier, most systems combine more than one of these items into one. The entry level systems may even combine all four elements into one box. If you buy a complete system from any of the manufacturers it will include everything you need to get you started.

How do I Choose a System?

The system that best suits you will vary depending on your needs. A basic system may only operate a small number of locos, a top of the range system will allow you to operate the whole layout from a computer.

The chief variations you will find are:

• A simple system may only let you choose from a dozen locos, with each selected by a single button, a full system will let you select locos by number with almost 10,000 loco addresses available. In particular look at whether the system uses four digit loco addresses (loco numbers 1-9999) or two digit addresses (numbers 1-99).
• Most decoders have one or more function outputs used for controlling features such as lights and sound modules. If you want to use functions you’ll need a controller that can control as many functions as you want to use.
• Whichever system you choose must be able to provide enough power. As a rule of thumb an N gauge loco needs about 0.5 amp, an OO/HO loco about 1 amp. Add up the total for the number of locos you want to run at any one time to get the total power rating required. (If you need extra power you can add extra power stations - if your system supports this.
• Can you add extra handsets? If you have friends over to help with running the layout a second (or third) handset will be essential.
• All decoders have features that you can program (an ugly expression that simply means you are setting certain values on the decoder). You’ll want to be able to set the address that the decoder responds to, and all systems will let you do that, but more advanced systems will let you fine tune the performance of the locos motor control, set options for flashing lights, etc. If the advanced stuff interests you choose a system which can do it, and which also makes it easy to do.
• Some systems will allow you to operate two or more locos together in a double header or, using the American expression, a multiple unit.
• If you want to be able to switch turnouts through the controller, then make sure your system can handle it.
• An advanced system will let you add feedback modules. These can report the state of the system to the handset or, via a computer interface, to a computer.
• I mentioned using a computer interface in the above section, and if this is something that interests you, you’ll need a system which can be connected to such an interface.
• Unless you’re very lucky you’ll also need a system which suits your budget. There’s little point buying an all-singing-all-dancing system if your needs can be easily satisfied by a starter system. On the other hand if you aren’t sure exactly what you want it may be worthwhile looking for a system that can be expanded as your experience and needs increase.

Note that any NMRA compatible systems can work together. So a controller from one manufacturer can seamlessly operate a loco using a decoder from a different manufacturer. This means you can easily expand your system and change manufacturers. However, this only applies between the controller and the decoders. You can’t always take, for example, a handset from one system and combine it with a command station from another.

Choosing Decoders

A Lenz Gold Mini decoder, suitable for N gauge.

You will find many people with highly polarised opinions in the DCC world. Some swear by a particular manufacturer and won’t touch anything else, others will try different decoders in a loco until they find the one that gives extra smooth control. In my view that’s a bit like the guy down the street who spends every Sunday afternoon tweaking his car: fiddling under the bonnet, putting on low profile tyres and changing the suspension. The rest of us are perfectly happy with our cars as they left the factory. And it’s the same with DCC, most decoders will provide good performance with most locos. If you want to be a ‘tweaker’ that’s up to you, but you should get on perfectly happily with what comes out of the box.

The chief buying factors for a decoder are:

• The size. What space is available in your loco? A OO gauge diesel will have more space available than an N gauge shunter.
• Make sure the decoder can provide enough power for your loco. Assume you’ll need 0.5 amps for N gauge and 1 amp for OO/HO.
• How many functions can it control? If lighting is important to you you’ll want a decoder with enough outputs.
• Some decoders only allow two digit addresses (addresses 1-99) others allow four digits (addresses 1-9999). Even if you don’t need 100 locos you may find that selecting a number appropriate to the loco is easier with four digit addressing.
• Different decoders can use a different number of speeds. If you use a decoder with only 27 ‘speedsteps’ you may notice less smooth acceleration and deceleration than one which has 256 different speeds.
• And finally price, the smaller a decoder and the more functions it has the more expensive it’s likely to be.

If you have an NMRA compatible control system then you can use any NMRA compatible decoder, whatever the manufacturer.

As ever, if you have any feedback on the above text feel free to click the ‘comments’ link below.

Next time I’ll look at how to wire the track up and how to get your first train running.