What is Command Control?
Using modern electronics, it is possible to use the rails of a model railroad to carry both power AND information at the same time. Using modern digital technology (Ones and Zeroes, as in computers)
a LOT of information can be sent over the rails in a short period. Again using digital technology, small units to pick out (receive) and act upon particular messages can be made affordably.
All together, systems that send power and messages over the rails to receivers in locomotives or other trackside locations are known as carrier control or command control systems.
Various individuals and companies have experimented with these ideas to produce and/or sell command control systems for model trains. However, none of the early developments really worked together;
there was no "common language" for the information messages traveling on the rail.
The National Model Railroad Assn. recently adopted a standard for putting power and information on the rail, providing the "common language" which has been missing. This is called the Digital Command
Control (DCC) Standard.
The standard will allow different manufacturers to now produce command control components that can work well together. Company A's transmitter will correctly control company B, C, and D's receivers
in different locomotives.
In practice, one person's or several people's commands (speed, direction, turnout position, etc.) are electronically combined, and put on the rails all over the railroad. Receivers act only upon the
messages sent to them, using track power to do their jobs. This allows much greater flexibility in the operation of model locomotives, as two or more locomotives can be right next to each other, yet
be controlled by different people, OR, combined together under the control of one person.
With command control, layout wiring can be greatly simplified, since the need for blocks is greatly reduced or eliminated.
David Gibbons
What is command control and how does it work?
You really ought to check out the proposed NMRA standard for Digital Command Control. For a PC and about 30-50 dollars, you have the guts of a CMRI. Some freeware is on the way for the PC, you can
program it yourself or you can purchase one of the excellent programs for $100-$300.
The idea is that the PC can be programmed to send digital command packets out its serial port. It's then sent through a simple amplifier, since most serial ports don't put out the amperage to power a
layout. A freeware program already exists for the Mac; a PC program is forthcoming.
Obviously, the above scenario only allows keyboard control. If you want control panels, walk around throttles and all the other stuff most modelers use, you'll need to do something more. However, if
you're only interested in having a computer control your trains, the above will be more than sufficient.
While most of us look at Digital Command Control as requiring a decoder in every locomotive (expensive) it is not necessary for some operating styles. For instance, a progressive block approach can
be implemented using a decoder in front of a throttle. The command station then controls the DC throttles and they control the trains. Unlike the original Chubb approach that required N (number of
cabs) throttles per block, this technique only require one decoder-cab combination per block.
Switches can be controlled digitally, which provides a method to enter digital computer controlled operations gradually as you budget allows.
Model Railroader recently published an article on using a parallel port to control switch machines. I suspect that it would a cheaper way than having each switch machine equipped with it's own
digital controller, but it will require more wiring.
Decoders are available for all scales (I have installed one in a Microtrain F7 complete with directional lighting)
You can get digital controllers for about $45. Hopefully, this will drop. You presumably have the computer sitting around, being used for other things, so it's practically "free". The only other
thing you need is the program, which will hopefully soon be freeware, and the amplifier, which is about $30. When the price of the controllers drops some, hopefully to ~$20 [I can always hope],
you'll be able to have computer control of 10 independent locomotives for under $250. Used to be the interface to the track from the computer cost more than that....