Digital model railway control systems
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A variety of model train control systems are available to operate locomotives on a model railways. The most popular is Conventional 12v DC, but Digital Command Control is becoming increasingly popular.
Digital Model Railway Control Systems
Modern digital control systems provide the ability to independently control all aspects of operating a model railway using a minimum of wiring; often the rails themselves are the only runs of wiring required. Control is achieved by sending a digital signal down the rails. These digital signals control operation of some, or even all aspects, of the model trains and accessories, including signals, turnouts, level crossings, cranes, turntables, and so forth.
A typical modern system, such as the US NMRA's DCC or Marklin Digital will have the following components:
Throttle
A throttle is a unit which controls operation of a train. Throttles are also known as Cabs, particularly in the US. A throttle can control speed and direction of one train at any time. The throttle also offers some means to select one of many trains which may be operating on a layout.
Central Unit
The central station is the heart of the digital system. The Central Unit receives commands from Throttles (and possibly other sources), and emits the appropriate digital signals onto the track, to implement the commands issued by the throttle or by other sources. Most Central Units include an integrated Booster.
Booster
A Booster amplifies a low-power digital signal produced by the Central Unit, to the power levels needed to operate trains. Boosters are typically limited to a power output of 3 to 4 Amps. With HO or smaller track, currents higher than 4 Amps are high enough that short-circuits caused by a derailment can spot-weld the derailed wheels to the track.
In large layouts, where the total current requirement is higher, the track will be partitioned into multiple segments, and each segment will be powered by its own digital booster. The boosters may receive digital signals via a direct cable from the Central Unit, or simply from the track of an adjacent Booster segment.
Locomotive Decoder
Locomotive decoders are small electronic devices which are fitted inside locomotives. The decoder interprets the digital signal sent from the Digital model railway control systems#Central Unit]] to the rails. When the Central Unit sends commands to change the speed, direction, or other aspects of this locomotive, the decoder alters the electrical feed to the motor accordingly.
Stationary Decoder
Stationary decoders are used to control operating devices which are fixed in position, such as turnouts, (eng.Points) signals, level crossings, and other devices. Since the devices do not move, stationary decoders can be mounted under the layout, and therefore can be significantly larger than locomotive decoders.
Sound and Function Decoders
Basic locomotive decoders provide control of speed and direction, and little else. Supplemental decoders can be placed into a locomotive, to control headlights, ditch lights, or movable non-traction components such as remote-controlled pantographs. These decoders are called Function Decoders.
Sound decoders are, in essence, a miniature PC sound-card with pre-recorded sounds. The sound effects are played in synchronization with the locomotive, so that as a diesel locomotive starts from standstill, the sound decoder plays sounds of a diesel engine starting up. Sound decoders for steam locomotives can play "chuff" sounds in synchrony with rotation of the driving wheels.
Some decoders have all three functions -- locomotive control, sound effects, and function control -- in a single device.
Feedback Bus
To automate a digitally-controlled model railroad, the Central Unit needs to know when trains reach their destination, or when the train reaches a certain point. This information is detected by a sensor, such as an infrared device placed between the tracks, or a device which senses current-draw in a particular section of otherwise-isolated track.
The Feedback Bus is the device which relays an electrical signal -- an "on" condition -- from the sensor hardware back to the digital Central Unit. The Central Unit can then issue commands appropriate for the specific sensor, such as triggering a specific signal, or level crossing.
The advantage of feedback is that each device typically needs only two wires: one to each digital track signal.
Computer Interface
Some Central Units
Digital Command Control
Digital Command Control (DCC) systems are used to operate locomotives on a model railroad (railway). Equipped with DCC, locomotives on the same electrical section of track can be independently controlled. While DCC is only one of several alternative systems for digital model train control, it is often misinterpreted to be a generic term for such systems. Several major manufacturers offer DCC systems.
Digital Command System
| This section contains promotional content. (May 2009) |
Digital Command System (DCS) is an electronic control system for O scale 3-rail and now HO scale model trains and toy trains, developed by MTH Electric Trains as a rival to Lionel's Trainmaster Command Control. It is similar in concept to DCC, the open industry standard used by HO scale and other 2-rail direct current trains.
It permits operation of multiple MTH ProtoSound 2.0 (PS2.0) engines on the same track without complex wiring, and also gives locomotives realistic digitized sounds.
Unlike Lionel, MTH has not licensed its standard to any other company. While MTH's DCS will not operate TMCC locomotives directly and Lionel's TMCC will not unlock all the control features of PS2.0 engines, the two systems will easily operate side by side on the same track. Therefore engines with either system can be operated simultaneously as long as both command control units are installed on the track.
Märklin Digital
Märklin Digital was one of the first digital model railway control systems. It consisted of a full system including locomotive decoders (based on a Motorola chip), central control, a computer interface, turnout decoders, digital relays and s88 feedback modules.
Rocrail
Rocrail is an Open Source Project that can control a model train layout from one or more computers. You can run trains directly from your computer, and you can have the computer run trains automatically for you. You can even have some of the trains on your layout running automatically while you control others by hand.
Selectrix
Selectrix is a digital model train command control system developed by German company Döhler & Haas for model railway manufacturer Trix in early 1980s. Selectrix is based on data communication protocol developed by Siemens for communication between mainframe computers. Döhler & Haas offered their system to several model railway manufacturers in the 1980s. Only manufacturer interested in the system was Trix and this resulted in exclusive licensing agreement between the two companies giving. In 1999 the two companies mutually agreed to terminate their exclusive licensing agreement. Since then, Selectrix has become a widely recognized open standard and is supported by several equipment manufacturers in Europe. European Model Train Association, MOROP has covered Selectrix partially in their NEM standards.
Selectrix bus
Selectrix is based on the principle of using one single data bus for controlling everything in a model railway layout including rolling stock, accessories and also feedback from various system components. Data bus is bi-directional and synchronized. This makes it possible to integrate many types of automatic functions in a model railway without a separate control computer and software using only a Selectrix central unit.
Bi-directional data bus signal is available in SX-bus. Standard connectors of SX bus are 5 pin DIN 45500 plugs and sockets. The topology of bus connections is free and Selectrix accessories can be connected together in closed circle, chained or daisy chain style. SX bus accepts any type of Selectrix accessories apart from system boosters. For connecting boosters to the central unit or to each other Selectrix systems have a dedicated PX-bus available. SX-bus signal is available in the track also and connected through two cables directly from central unit (or booster) to the track. Track signal is unidirectional only.
Data signal of SX bus consists of the contents of all bus memory addresses transmitted sequentially and repeated 13 times per second. SX bus has 128 addresses numbered from 0 to 127 and each consisting of eight bits. The first 112 addresses (0-111) are normally available for controlling the model railway. The remaining 15 addresses (112-127) are reserved for system's internal use.
Controlling a Selectrix locomotive decoder requires one SX address with its' eight bits. Therefore one Selectrix bus can control maximum 112 locomotives simultaneously. If the system central unit is equipped with more than one SX-bus, only the first one (SX 0) is connected to the track and can be used to control locomotives.
If a Selectrix bus address is used to control turnouts, signals or other accessories one SX bus address can control maximum 8 items. In this case one bit with its two values (0 and 1) in a SX address can correspond to two turnout positions.
For feedback an occupancy detector based on current consumption on track or a decoder detecting a closed contact can be connected to SX bus. Because system decoders can share bus addresses thus allowing decoders to control each other directly, it is, for instance, quite possible to use an occupancy detector to switch a signal to stop position automatically when there is a train in track block protected by the signal.
Locomotive decoders
Selectrix locomotive decoders have traditionally been quite small in comparison to decoders used in competing systems. For this reason Selectrix has been a very popular choise in smaller N- and Z-scale model railways. A locomotive decoder has 5 bits reserved for controlling the locomotive speed. This gives 32 speed steps in both directions. Internally most Selectrix decoders use 128 speed steps though. In addition to speed control a Selectrix decoder provides control for locomotive head and rear lights and one additional function. If more functionality is required, there are Selectrix decoders equipped with SUSI-bus for an additional sound decoder or similar.
Selectrix decoders have an automatic brake function which is activated when a decoder detects an asymmetrical track SX signal (this can be accomplished with a single diode used as a rectifier). This feature can be used to stop trains in front of a red signal automatically, for instance.
Modern Selectrix decoders have transponding capability where the decoder ID of a locomotive found in certain track block is reported back to the system. Using transponding function requires Selectrix occupancy detectors with transponder capability in track.
Manufacturers
The most important manufacturers of Selectrix equipment are Rautenhaus, Müt-Digirail and MTTM. Selectrix components from various manufacturers are compatible at all levels and can be freely combined in real-world Selectrix control solutions.
Trainmaster Command Control
Trainmaster Command Control (TMCC) is Lionel's electronic control system for O scale 3-rail model trains and toy trains. Conceptually it is similar to Digital Command Control (DCC), the industry's open standard used by HO scale and other 2-rail DC trains. It has one advantage over DCC, in that TMCC-equipped locomotives can run simultaneously with non-TMCC locomotives.[1]
References
External Links
- DCCWiki - Community DCC site for model railroad.