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The DCC Story

Take a seat, and sit back with a coffee....................

Before we start, I'd like to say this:

DCC is not the only kind of control system! There are many thousands of 'traditional' DC layouts in use, and many hobbyists gain great satisfaction from designing and building their own electronic units. Units are available which can provide gradual acceleration and deceleration, automatic stopping, shuttle operations, sound effects, load compensation, and even full computer control. (Features that many people wrongly consider only possible with DCC). Many units of this type are available in our shop, so we fully support this method of control. The majority of exhibition layouts are controlled this way and are an example of what can be achieved, however and needs an electronics knowledge is required, and by their nature, these layouts are unique to the designer.

The main drawback of analogue DC is that the requirements of control grow more complex as a layout grows in size, due to the fact that all loco's on the same track go in the same direction, at the same speed, variations only occurring due to differences in physical characteristics (size, weight, friction etc) To add sophisticated control, requires the need for isolated sections, block control and complicated control panels, and techniques such as CAB control. However, no matter how sophisticated the cab, and how many isolated sections there are, no more than one loco can occupy the same block, this makes supposedly simply operations such as realistic banking, and double heading surprisingly difficult to replicate.

So, DCC is what, exactly?

Not computer control for a start! Computers can be used (and connected a little easier) as they can, and are with conventional control. DCC removes the need for complex wiring, isolated sections and all the associated wiring. No cab control, and no teams of operators using telephones! The layout is just one big single track to the controller, Banking a loco is easy, drive up the the back, push, and drop off at the top of the hill, reverse back down, whilst the express chuffs away into the distance!, queue several locos into the refuelling depot, set up a double header, etc. etc. we're just talking about another, finer control method here. Sure, there are bells and whistles, and we could talk about them all day, in fact we do, and you get a free lunch! - see our training courses for more info.

A short history

With 'traditional', 'conventional', 'analogue' control, all the same - DC control, where an electric model is controlled by applying a varying direct current via the track; changes in direction is achieved by reversing the polarity of current and speed by increasing, or decreasing the voltage. Every modeller and child is familiar with this system which is still used and has been used at every level from the train set oval to the most extensive exhibition layouts.

Many enhancements have been made to this system, some of which have been described above, my personal favourite is inertia control, (simulation) a system which gradually speeds up, and slow down a locomotive, by means of charging and discharging a capacitor, along with various feedback circuits, for the operator this means a throttle and a brake control, - real loco driving! I guess this is where we should introduce the digital revolution....

Digital Command Control (or DCC) has been around for some time now, many believe since the '70s! however, in fact, the concept of a method of controlling locomotives individually began simultaneously with the birth of the model electric locomotive, but the origins of DCC can be found in the 1940s with a two channel system by Lionel Trains using frequency control [An electron tube oscillator generated different frequencies, depending on which button an operator might press. Then a tuned circuit and relay in each engine controlled the direction of the train.] Unfortunately, Lionel’s system was somewhat cumbersome and not always reliable. as it contained glass valves, and would have been susceptible to other frequency sources, and interference.

Then, In the early sixties, GE introduced a five-channel commercial carrier control system designed to control more than one train per block. It was called ASTRAC, which stood for Automatic Simultaneous Train Control. [The system used a silicon controlled rectifier based circuit, which had a receiver in each loco and a transmitter that sent signals through the track]. Later, in the '70s modern transistor technology was used in the Hornby Zero-1 and Airfix MCE systems were the first modern commercial Digital control systems, other systems were being developed in the USA, and Europe. They were functionally restricted (by today's standards), but at the time, represented a massive step forwards in [fairly reliable] locomotive control. Unfortunately, they were handicapped by track conductivity, and proprietary standards. The relatively large size of the decoders also restricted the installation options.

Many forward thinking enthusiast adopted these systems, and Zero-1 still lives on today, as it is still supported by ZTC.

Today's DCC

Today brings us a standardised (more later) system in which, a controller (also called cabs, or throttles) to send information to a command station telling it what you want train X to do which in turn transmits to the loco controller (the decoder) All components are micro-processor controlled miniature electronic circuits for size and reliability reasons.

The decoder, is installed into each locomotive, between the electrical track pickups, and the motor connection. The decoder constantly monitors the track for data, which is encoded into the AC voltage, [usually between 10-16 Volts, depending on the gauge] in a 'data burst' known as a 'packet'. The packet is literally a packet of information, headed by an address. each decoder has a unique address (either 2, or 4 digits) and will ignore packets 'addressed' to anything other than itself. When a packet is recognised as being relevant, the decoder reads the remainder of the data, which contains the instructions issued by the operator and then controls the locomotive as desired.

Simply put, The decoder and locomotive do what it is asked to do, leaving the operator free to instruct another locomotive. This tricky to explain, and boring to read but very simple and easy to use system allows you to 'drive' your locomotives independently anywhere on your layout. Hence the well worn phrase - "drive the locomotive, not the track!" - Just like the real thing!

Isn't it expensive though?

Given the fact you may consider I have an axe to grind here, I'll do my best to be neutral! The answer is, it depends on your investment! If you have a fully operational layout, based on traditional control, AND you're perfectly happy with the operation then a definite NO is in order. If you're interested in the concept of close operations between locos (i.e. banking, double heading, refuelling, terminus operation etc. etc. then DCC is worth a good look. If you're considering, or starting a layout build, then you really should take a hard look!

Consider the cost of multiple colours of copper wire, connectors, switches, and isolation sections, add in your precious time designing the wiring plan, plumbing it all in, and then the inevitable trouble shooting and that £200-£300 DCC system starts to seem cheaper.

Consider the other facts outlined here, and in the magazines, shows and clubs, and you'll have the basis for a sound decision.

Yes, but all those decoders....

There is no doubt that the cost of decoders adds up, as you can spend anything between £10 - £30 pounds or upwards of £90-100 for sound! on each loco - another reason to do your research! - don't forget, thanks to NMRA the choice of decoder isn't dictated by your choice of Controller.

Many people buy a controller and 1 or two decoders, often as their first system,[ as it is possible with most systems to operate a single non decoder equipped loco on a DCC layout] and then discover that they don't like the features, or an new controller is announced, and it ends up on Ebay!

I'd rather see people work from the other direction, look at your loco, decide what features you want to control, do you want sound? then get the decoder that provides those functions, install it, and forget. A decoder equipped loco will run on a conventional layout perfectly normally. You can then keep operating your fleet as normal, and only spend a few pounds a go, and then, when the time comes to buy a controller, you can run the entire fleet from day one under DCC this makes that £900 walk about system more achievable.

It's all too easy to get carrier away with features and capabilities - decide what you need first, then look at the gee-whiz stuff.

OK, I'll go with it [for now!], How do I convert?

First, pick your decoder - consider the number of functions, special features (some, only available from certain manufacturers i.e. with the Lenz Gold, it is possible to add a power-1 module, this little widget allows a loco to travel over that dirty piece of track without the lights even flickering, it's not just a battery, it remembers the last set of commands, and so the locomotive continues to behave as commanded) the power your model requires (in Amps) and where you'll put it, if you want sound, where will the speaker go? how big can the speaker be (size DOES matter here!) and how easy is it to wire?

Most newly designed models are advertised as 'DCC Ready' meaning that it can be easily fitted with a decoder unit, normally using standard socket, ('OO' gauge uses a 9-pin NMRA JST plug, 'N' uses 651 plug, and a variety of other systems, the latest being direct connection of the decoder, without any wires.) into which a decoder can be connected in seconds, once you can get the body off the chassis, often the most difficult part of the operation!

Other locos require a little more work, some demand a form of art! - Decoders are available in many sizes and shapes, to fit many circumstances, all decoders and motors must be isolated, this is usually simple, but some models (especially 3 rail, and the old Wrenn locos) need the motor isolating from the chassis, some models need the decoder in the tender, other demand a milling machine! if you're at all bother, either consider our fully insured installation service, or attend one of our courses.

Usually decoders have a unique address on the layout, this can be a 2 digit number (i.e. the last 2 digits of the cab number), or an extended address - 4 digits. There is a [useful] extension to this rule - multiple decoders can have the same address - for example, a modern loco (e.g. class 66 with the older 'BMAC' light clusters) has up to eight lighting configurations, this requires two 4 function decoders( the maximum functions available at the time of writing) both decoders can be programmed to use the same address, simplifying control. This can be extended to multiple units, i.e. put a 4 function decoder with motor control in the driving van of a HST, and a 2 channel decoder in the DVT to control the lights! using this technique it's possible to control many functions within a dedicated set.

Just think for a moment - when have you seen a loco hauling a train, that has it's rear lights on? Whilst on the subject of lighting, one disadvantage of DCC is that a non-decoder equipped loco with directional lighting will run with all lights on, continuously. Another reason to equip with decoders first!

The primary job of a decoder is motor control, this can be simple faster-slower STOP!, plus all stops in between. This is the basic out of the box settings, but there are many other possibilities - we all have the loco that's a bit 'sticky' the one that needs the knob turning up before the train jolts forward, and takes off like a hare! Many controllers can be programmed with a start-up jolt, so when you start a loco, the motor is given a fraction of a second at a higher power to overcome the initial 'stiction' of the motor and drive train, the decoder then returns power to the instructed setting, the result is a good start, with no skid marks!

It's possible to program a top speed, so your '08 shunter doesn't overtake your Eurostar, [Interestingly this doesn't just 'cap' the top speed, it makes control 'finer' across the whole range of the controller, so you get better control of the loco!] Prototypical power and braking curves can be programmed, giving realistic acceleration and deceleration, this can include inertia as well. Incidentally, we offer a full programming service for a small additional charge, just let us know your needs in the notes section of the order, and we'll come back to you. Another benefit is that the method of driving the motor is different, instead of a DC voltage, a pulsed DC voltage is used, this often results in a quieter running loco.

As referred to above, many decoders have function outputs that can be used to control lights independently of the locomotive speed or direction, and as, with DCC the track is always live, so lights will stay on just as brightly when the train is at a halt. This can be extended to operate many other loco mounted accessories: smoke generators, uncoupling devices, even operation of cranes and the like.

About Standards

The issues caused by differing proprietary standards were a trigger factor in the NMRA's (National Model Railroad Association) standard for DCC, Lenz originally proposed the core set of commands and the encoding process which had a number of advantages over competing systems. The standard was made 'open' and is now used by all manufacturers ensuring different manufacturers DCC equipment will work together. The terms NMRA standard, NMRA plug, etc. are commonly found on DCC equipment, a guarantee that the protocols and certain hardware aspects (e.g. wiring colour code) conform to standards and will work with all other NMRA standards compliant devices. There are two commonly seen logos, which indicate DCC compliance status:

As a result of NMRA conformance standards, a digital signal from a controller can be received by any commercially available decoders. This allows the 'Hi-Fi' approach of best of breed to be used.

Other, incompatible, systems can also be described as DCC such as the Marklin/Motorola System (although some of the more advanced NMRA-DCC systems can support this system as well (such as ZIMO)

What else is possible?

Many things, Static, or accessory decoders permit trackside items to be controller, from point and signals, to trucks and gantry cranes. Route setting can be programmed in, changing many points, and releasing signals with one command. Sound can provide synchronised locomotive effects, even to the sounds of the fireman shovelling!

Wireless walk-around controllers (great for garden railways) Add on controllers, permitting multiple operators, Block control, automatic braking, loco id & feedback, the list goes on, and more is released each week!

In summary:

Operation is far more realistic with each independent train control. Double heading, banking and stabling is possible, and with a little programming speeds of locomotives from different manufacturers can be matched. You can program realistic acceleration and deceleration rates, or limit the top speed of a locomotive.

Everyone from the beginner to the advanced modeller and every layout from the smallest to the largest can benifit. Once you have the basic system you can decide what parts of the functionality you want to use and simply expand as your layout grows. The basic equipment you already have forms the basis as more features are added. The decoders you buy will remaine compatible even if you upgrade to a top of the range controller Add sound or computer control: Your railway can be as simple or complicated as you wish.

A few Cautions and warnings!

Don't forget, DCC is not a panacea, it won't take a problem layout and make it trouble free, "if it don't work DC, it won't work DCC!"

Though fault tracing is simplified, due to the reduced wiring requirements, everyday issues on a DC system have implications with DCC.

A short circuit is a momentary problem with DC, DCC however has higher voltages, and higher current provision, it therefore has sensitive current limiting devices, and when these cut the power, the whole layout stops. This can be limited by introducing power districts, dividing the layout into areas controlled by individual trips.

DCC won't make a bad runner into a good one! If a locomotive runs badly using DC it'll do the same with DCC.

Track: Dirty or poorly maintained rails won't run well. With DCC the track has a constant voltage, but good connectivity is just as important. Live frogs still work best as well!

Oh yes, with up to 99 locos on the track at a time, you'll need a lot of coffee to stop your attention from lapsing!