Digital Command Control

Part 1..... Getting started with DCC

The purpose of this page is to help anyone interested in starting up with DCC either with a new purpose built layout or converting an existing analogue one.


Many people consider DCC to be a "black art" that needs a knowledge of electronics and technical wizardry to be able to get to grips with. Nothing could be further from the truth and a great deal of "Bunkum" is expounded on the subject that tends to frighten people away. Hopefully I will be able to convince you that it is not a subject to be feared and can be put to use by anyone capable of putting a layout together.

What is it and how does it work.
DCC or Digital Command Control to give it its full title is a method of controlling your layout by sending signals along the track that can be picked up by a locomotive and make that locomotive do just what you want it to. With a standard analogue layout you would control the locomotive by altering the direction and strength of a Direct Current applied to the track to make the the locomotive speed up, slow down or change direction. With DCC there is always a full Alternating Current applied to the track and superimposed on this Alternating Current is another signal that is read by a decoder (chip) placed inside the locomotive.
This "chip" inside the loco is always listening to the signals on the track waiting for one meant especially for that loco and when it recognizes an instruction addressed to itself then it follows the instructions sent by the controller to tell it to speed up, slow down, change direction or indeed other things such as turning lights on or off.
Since each locomotive on the track will only respond to an instruction addressed specifically to itself then it becomes possible to have several locomotives on the same piece of track and all can be independently controlled.

So what do you need to get started.
There are 4 basic parts to a DCC system.
1. A power supply that will deliver enough current to run several locomotives at the same time. Typically between 2 and 5 Amperes.
2. The "Master unit" which is the brains of the system and is basically a small computer that "encodes" the signals from your controller and superimposes them on the continuous AC fed to the track.
3. A control unit (often a hand held or walk-about unit) that may have just buttons or buttons and a knob that lets you control a loco.
4. A decoder (Chip) fitted inside each of your locos that you want to run on the DCC system.

There are several available proprietary units that you can purchase, each containing items 1 to 3 listed above. I am not going to try and recommend any particular brand and will only state that in most cases you get what you pay for. In general the more you pay the more facilities the unit you acquire will have.

OK so you have bought a DCC starter set and are ready to get going. If you have an existing layout that is controlled by analogue then all that you need do to make it work on DCC is simply to replace the DC analogue power supply and controller(s) with your new DCC unit. If you have section switches then just leave them all switched on and that's it, you can now control your chipped locomotives on your layout.
Sound much too simple doesn't it? Well there is just one small problem that will only become apparent if you have locos fitted with either sound or lights. Many layouts use the action of a point to isolate a loco by producing a dead section when the point is switched away from say a siding. If you have a loco that has lights or sound then when that section or siding becomes dead the lights will go out or the sound will stop.
Not a major problem but possibly not what you want to happen.

If you were building from scratch you would simply ensure that all of the track has power to it all of the time and then there would be no danger of having lights or sound going off other than when you you wanted it to happen by using the controller to actually switch them off.

Programing
Many people are put off by thinking that you have to a computer nerd to be able to program your locos but in reality all the work is done for you by the system itself. Most of the units you can buy make it really simple and it is just a matter of pushing a few buttons to set up your loco.
Typically you would want to arrange just a few of things for each loco on your system and these would be :-
1. The loco address, where you would use say the last 4 digits of the loco's running number if your system supports 4 digit numbering. If not then depending on which unit you bought you could be limited to 2 digits or numbers 1 to 9 with the cheapest system.
2. The start voltage that is applied to the loco when you turn the controller to its first step. (typical values here are from 1 to 5)
3. The acceleration rate. A bigger number here makes your loco start picking up speed more slowly and more realistically. (typical values are between 5 and 20)
4. The deceleration rate. Again a bigger number here makes your loco take longer to slow down even if you wind the speed down to zero. (typical values are between 5 and 20)
5. The maximum voltage. A smaller number here will reduce the maximum speed that your loco will reach at full throttle. (maximum value here depends on the make of the decoder)

The only one of the above that is important is No 1 the loco address, as you will need each loco to have its own unique number. Your new chip or ready fitted loco will normally be factory set with an address of 3. All of the others can be left at the default settings that came on the decoder chip and your loco will still work. However you can get a more realistic and to my mind better control by setting the other variable to suit the particular loco.

Cost
How much will it cost to get started with DCC.
At the time of writing this (October 2010) you can get the basic starter set which will allow you to control 9 locos for about £50 and the fully fledged all singing all dancing unit that will allow you to address up to 9999 locos and configure prettywell anything on any loco for £200 with the ability to purchase extra throttles so that more than one person can run trains.
Loco decoders or chips that will suit most 00 locos can be had for as little as £9 each. (miniture ones where space is limited are more expensive at approx. £20) However you will need one chip for each locomotive.

Summary so far
So you have seen how easy it can be to convert an existing layout to DCC but why should you bother going to the trouble and expense of converting?
I will list the Pros and Cons I have found with DCC.

Pros
1. Very much smoother control of your locos especialy with slow running.
2. The ability to have several locos on the same section of track and have individual control of each.
3. There is no need for section switches to isolate locos.
4. If starting a new layout then wiring is greatly reduced.
5. The ability to have lights always on even when trains are stopped.
6. The availability of sound for your engines.
7. Modern locos now come "DCC ready" which means they have a socket inside that you just plug a decoder into.

Cons
1. A momentory short circuit anywhere on the layout will bring everything to a halt.
2. Initial expense of "Chipping" your fleet.
3. Some older locos need to be "Hard Wired" to fit a decoder.

So thats probably as far as I need to go with the basics to give you an idea of what is involved, but if you are like me I was absolutely hooked once I had fitted a chip to a Standard Class 2 Ivatt and found how smoothly it ran.



Part 2 Wiring a DCC layout can be found here

John Essex Heywood Model Railway Group


This page updated 10th October 2010