When operating trains on DCC (Digital Command Control) there are two main types of decoders. These decoders interpret the digital signal from the DCC command station to perform a function on the layout. Mobile decoders are used in locomotives and travel around the layout. Stationary decoders are wired directly to the track bus and control stationary functions like switches (turnouts).
Just like there are many different varieties of mobile decoders, there are many stationary decoders to match the accessory and functions you desire. The most common of these are used to control switches (turnouts / points).
Just like the decoders in your locomotives, stationary decoders are programmed to an address. By selecting the address, you can operate the decoder with your DCC throttle just as you would a locomotive. Some decoders will also support a function similar to consisting locomotives. This allows you to program a route into the command station and by pressing the right route address line all of the switches necessary to get to a specific track at once. This can be very useful in yards.
Switch decoders come in many options and you'll want to choose the one that is best for your situation. Because of standards adopted by all manufacturers, you do not have to buy decoders made only by the maker of your DCC system, although the programming and operating steps may be different depending on which system you use. Here are some things to consider when comparing decoders:
- Motor Type: Switch machines / motors come in several varieties. The most common are twin-coil and stall-motor types. These machines draw very different amounts of electrical current, so you'll want to make sure you use a decoder designed for your machine. There are also decoders available for specific manufacturers' track products. Just like you can mix and match switch machines, you can use different types of decoders - just match the decoder with the machine.
- Number of Machines: Some decoders will only control a single machine while others will control multiples. If you are wiring multiple switches in close proximity to each other, it may be cost effective to buy a larger decoder.
- Feedback: Some decoders offer a feedback or transponding function that can report switch position to a computer.
- Additional Options: Many decoders offer additional functions in addition to simply being able to throw the switch. These can include the ability to wire in a manual toggle switch in addition to the address option. Others offer additional terminals to control frog polarity, make switches power-routing or even automatically through a switch with the approach of a train. Each of these functions has a place, but you may not need to spend the extra money for them in every situation.