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If you've been around Digital Command Control (DCC) for any length of time, you're already familiar with mobile decoders, the type you put in locomotives. Another type of decoder is the stationary or accessory decoder. This is typically much larger than the mobile decoder and is used to control layout accessories such as switch machines, signals, and other electrically operated devices.
One of the most common uses for stationary decoders is to control switch machines and switch motors. Switch machines includetwin-coil solonoids, such as Atlas and N.J. International. and bipolar solonoids, such as Kato and LGB. Examples of switch motors include Switch Master and Tortoise, which use a DC motor to set points.
Each type of switch machine/motor has its own unique power requirements. Some decoders are capable of controlling multiple types of turnout motors with special wiring or programming. Others are made to be used with just one type of solon0id or motor. Some stationary decoders can also provide feedback to your personal computer for signal control.
Power. Stationary decoders get their power directly from the track bus, the same way moble decoders do, which enables them to receive and send signals to the DCC system. Power for the turnout motors that the decoders control can come from the DCC system or a separate power supply, depending upon the design of the decoder.
Powering stationary decoders directly from the track bus has the advantage of requiring less wiring. The disadvantage of this method is that should a short circuit occur due to someone running through an open turnout, track power will automatically be shut off by the DCC booster, including the stationary decoder as well. This makes it difficult to clear the problem by relining the switch points. To avoid the pronblem, my stationary decoders are on a separate power district to maintain DCC control regardless of what happens on the rails above.
Control. Most, but not all, DCC throttles have stationary decoder controls. Selecting a stationary decoder isn't much different than selecting a moble decoder in a locomotive. Typically it involves pressing a selection key and entering the stationary decoder's address to operate it.
From there, most throttles will offer you the option for setting the decoder in one direction or another, such as lining a turnout for the main or siding. Common control symbols for this can be ""N" and "R", for normal and reversed (following the protype0, or "C" and "T" for closed and thrown. I've also seen "+" and "-" used as well as as "on" and "off", which is useful if the control is for something other than a turnout.
Some DCC systems also allow for a computer interface with the command station, which allows computer software to activate stationary decoders.
Route Control. Most DCC systems allow you to control multiple stationary decoders at the same time. This is very useful for locations such as a yard throat or staging yard. With one command, you can line all turnouts necessary to run your train to a specific track. In addition some decoders, such as such as DCC Specialties' Wabbit and Team Digital's SMC4 and SMD82, have route control built directly into the decoder. This allows DCC systems that don't have route control to do the same thing.
Signals. A more recent development in stationary decoders is the signal decoder. Digitrax has the SE8C, which controls up to 32 signal heads or 8 slow motion turnout motors. It's a little different than other decoders as it takes its command from the cab bus (in the case of Digitrax's Loco Net). Either a computer or a Digitrax DCC system can supply LocoNet commands: You can use software running on a computer to control the signal system for you, or you can mannually operate the signals with a Digitrax throttle.
Programming. Most stationary decoders have configuration variables (CVs), which can be programmed by connecting the decoder to a standard proramming track. Moving the decoder to the programming track when you wish to make changes isn't always convenient, especially if it is mounted permanently under your layout. For this reason, some brands of stationary decoders can be programmed via the track bus.
Several companies make stationary decoders that are designed to control turnout motors. Following is a sampling of some of the decoders that are available in North America. It's always best to do some investigating when buying decoders, since some may be better suited to your application's requirements than others.
* CVP (EasyDCC) makes the AD4MC for switch motors and bipolar switch machines and the AD4HC for the twin coil machines. Each CVP stationary decoder is designed to control up to four turnout motors.
* DCC Specialties makes the Hare, specifically to plug directly on a Tortoise switch motor. It also makes the Wabbit, designed to control two switch motors, the WabbitFB, which also provides feedback, and the PSX-ARFB, which both a stationary and a DCC circuit breaker with auto-reversing capabilities. The PSX-ARF can be set to completely automate reverse loops.
* Digitrax has five stationary decoders for turnouts. The DS44 controls four switch motors. THE DS51K1 controls one bipolar machine, while the DS61K1 is designed to snap directly into Kato turnouts, which use bipolar machines. The DS52 controls tow turnout mechanisms of any type. and the DS64 controls four.
* Lenz has two stationary decoders. The LS100/110 is a general purpose decoder designed to control turnouts, signals, uncoupling ramps, and other devices. It has four outputs. The LS150 can control up to six turnout mechanisms of any type.
* Model Rectifier Corp. (MRC) makes the 1628 multi-purpose decoder that can control four turnout mechanisms. Each of its four outputs can be programmed independently to operate either motors or solenoids. It can also be used to light signals.
* NCE has four stationary decoders for turnouts. The Switch It is designed to control two switch motors, while the Switch 8 controls eight. The Snap It is designed to control wo twin-coil switch machines, the Switch Kat is designed to control bipolar switch machines.
* Team Digital offers two stationary decoders. The SMC4 is suited to drive switch motors or servo motors for semaphores. It has four outputs. The SMD82 is designed for turnout mechanisms of all types and has eight outputs.
* Hrbrid. A notable addition to the family of stationary decoders is the Smail. Offered by Circuitron, the Smail is a Tortoise switch motor with built-in DCC stationary decoder. The Smail connects directly to the track bus, which powers the decoder and motor.
The above is a Model Railroader article, April 2008
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