Constant power is supplied to the track and digital signals are sent which require electronic decoders to be fitted to locomotives and other devices to interpret the commands.
Controllers manage operation of locomotives with buttons for additional model features such as lighting and sound.
Accessory decoders are used to control devices which are fixed in position, such as turnouts, signals, and level crossings.
Feedback relays an electrical signal from the sensor hardware back to the digital central unit.
Some central units allow connection to a computer, and a program can then fully automatically control all model train movements and accessories.
Programs have been developed allowing mobile devices to be used as controllers, which also requires the central unit to be connected to a computer.
Digital Command Control (DCC) systems are used to operate locomotives on a model railroad (railway).
[1] Separate sale decoder kits have been offered for installation in all of the above noted scales except H0 and S. DCS is predominantly used in three-rail O gauge.
[2] The principal differences between DCS and DCC transmission technologies include bidirectional communications and the separation of the command signal from track power.
Engines with either system can be operated simultaneously as long as both command control units are installed on the track.
The availability of miniature web server modules in 2014, led to the formation of a DWiC Working group to explore the possibility of using this technology in model railways.
Although it is considerably more complex than any previous model railway control system it largely transparent to the user with tasks such as bi-directional communication being seamless.
DWiC does not use any model rail specific items such as command stations and boosters and so is much lower in cost.
This technology is also useful outside the model rail world as a DWiC controller could open a garage door or remotely turn on sprinklers.
The DWiC controller has a web page loaded on board tailored to the particular "item" - loco, accessory etc.
However, unlike DCC, it uses a 455 kHz radio transmission to carry the command codes separate from track power.
MTH Electric Trains included support to interface and control TMCC with its DCS system.
Both the controller units and the decoder modules required for the locomotives and accessories were expensive, but with a clean track and well-serviced locos the system worked as advertised.
The Zero 1 system supplied the track with a 18 V sinusoidal alternating current at the local mains frequency with a 32-bit control word replacing every third cycle.
The decoder module in the locomotive would switch either the positive or the negative half-cycle of the square wave to the motor according to the desired direction of travel.
Speed control was achieved by pulse-width modulation, varying the width of the portion of the half-cycle, which was switched in 14 steps.
The system is very reliable, the basic 1980s keyboard design being the main problem on older badly stored master control units.
The pre-1981 types were based on a single triac but the square-wave supply and the presence of spikes from the motor and from poor contacts rendered the dV/dt rating of the triac marginal and these units would sometimes self-trigger on the wrong polarity half-cycle, resulting in damage both to the unit itself and to the locomotive motor.
[10] Digitrack 1600 is one of the first generation digital model railway control system developed and marketed by Chuck Balmer and Dick Robbins in 1972.
Introduced in the late 1970s, the RAIL-COMMAND 816 is an eight-channel digital signal system using a constant 12 VDC track voltage.
The application is also compartmentalised into several API layers which makes it easy for third party developers to build derivate works on its foundation.
Although usable with a normal mouse, it has been optimised for touch-screen PCs where you just touch a point, a signal or slide a locomotive throttle.
Rocrail is previously open source, now proprietary software that can control a model train layout from one or more computers.
JMRI is an open source project that can control a model layout including accessories from a computer.
TrainController by Freiwald, also known as Railroad & Co is a high-end proprietary software package which comes in three versions of increasing functionality, Bronze, Silver and Gold.