DCC - Digital Command Control - is a control system for model railways where a micro processor 'decoder' carried in the locomotives is used to provide control of speed and direction of the motor. Instructions are passed from the controller to the decoder by means of digital signals superimposed over a constant track voltage. Put simply, you control the locomotive and not the track, so every locomotive will operate independantly of any other locomotive, according to the instructions given to the decoder.
As each locomotive is under the separate, independant control of its' own decoder the need for separate power and isolating sections to keep a train stopped in eliminated. This greatly simplifys the wiring of a large or growing layout, tracks are simply wired in parallel, with insulation only needed where opposite rails meet, like at the V or frog of a point. Simple electrical circuitry to connect red and black wires to each track with no need for complex control systems.
Once the whole layout is live you set your route and drive the train. Stop trains where you want, put two trains into a platform at the station and buffer up engines in a line in the engine shed.
As well as output to power the motor, many decoders also have a number of auxiliary outputs that can power other functions, eg lights and with a constant track voltage power is available all of the time, not just when the train is moving. Locomotive directional lights will automatically change and will remain lit when the engine stops, plus train carriage lighting will remain lit. Many more models are now available with realistic recorded sound systems also controlled by the DCC decoder and automatically adjusting sounds with the speed of the train.
More advanced DCC controllers offer more features and options like :
The ability to control 'static' decoders that operating points and signals from the same handset as is used to run the locomotives.
Double heading of trains running two engines together, adding a pilot or banking engine or joining multiple units.
Most locomotives and multiple unit trains designed since 2000 have been equiped with a socket for the quick fitting of a decoder. Often one version of a new model is offered with DCC already fitted and the range of ready-to-run DCC sound fitted locomotives is growing.
DCC Ready - A socket is provided for the quick installation of a decoder. Check the number of pins, 6, 8 or 21 used to find the correct decoders.
DCC OnBoard - A model with a factory fitted DCC decoder, ready for service!
DCC Sound - A locomotive fitted with a DCC controller and sound system.