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Decoders receive commands from throttles or other devices and are responsible for controlling the motor and/or performing certain functions.

[edit] Types Of Decoders

Decoders can be grouped into two main categories. The first type, Mobile Decoders, are typically installed into locomotives or other rolling stock that moves along the rails. The second type of decoder is a stationary decoder, which is normally mounted under the benchwork in a "stationary" position.

[edit] Mobile Decoders

Digitrax Plug N Play decoder.

Mobile decoders are typically installed in locomotives, but can also be installed into cars to control lights, animation,sound or even uncoupling devices.

[edit] How they work

An explanation of how a decoder converts DCC power to DC power, and delivers it to the engine is discussed at the DCC Power article.

[edit] Selecting a decoder

The decoder size will be dictated by the amount of room inside the engine or tender as well as the amount of current that is needed by the motor. Before starting, it's best to measure the stall current on your particular locomotive. One decoder can drive multiple motors, provided the sum of the stall currents doesn't exceed the decoder's current rating.

We have also started a mobile decoder comparison guide to get you started on selecting a mobile decoder.

[edit] Features

Mobile decoders have a number of possible features and functions that vary with the manufacturer, and even the specific decoder model. Don't be alarmed by the large list of features listed. Usually, the defaults that come with today's decoders work well. If the decoder you have has a feature you don't need or want, you simple ignore it and don't use it. We've broken the list down to a few basic areas:

Movement and speed

• Back EMF - Keeps engines running at a constant speed, regardless of train length, weight, or track grade.
• Decoder-Assisted Consisting (DAC) - Provide an optional way to do MU consisting
  • DAC - Function control - Allows you to specify which on-board functions operate while consisted
  • DAC - Momentum trim - Adjust trim momentum differently when MUed.
• Dither - Significantly help locos run smoothly at very slow speeds.
• High-Frequency Decoders - AKA: "Quiet Drive", "Silent Running", "SuperSonic Drive".
  • Helps quiet the motor hum/buzz by increasing the pulse frequency
• Kick Start - Gives a "quick kick in the pants" to a locomotive to get it started at low speed.
• Loco Momentum - Simulates a loaded train - affects acceleration and deceleration.
• Loco Trim - Forward and reverse. Allows fine-tuning speed individually in either direction.
• MU consisting - Decoder assisted consisting.
• Speed Steps - 14, 28, or 128 speed step - how much resolution of the speed control available.
• Speed Table - 28 values, for more resolution. Can be used to set maximum speed, match throttle readout to scale MPH, or speed
• Switching Speed - Halves the speed of the motor throughout the full speed range, gives much better low speed control.
  • Enabled by turned on Function 6 for decoders that have this option.
• Three Step Speed Table -- AKA - V-Start, V-Mid, and V-Max

match different locomotives very precisely.

Programming and addressing

• Addressing: Two and Four Digits - Decoder address length - two modes
• CV Reset - Resets all decoder settings to factory defaults
• Decoder Programming
  • Paged Mode
  • Direct Bit Mode
  • Direct Byte Mode
  • Operations Mode
• Decoder Programming Lock - Helps protect against decoder settings from being accidentally changed.
• Decoder user values - User defined space - IE: loco owner ID. Entering values here doesn't make the decoder operate any differently, but it does make it possible to tell two identical locomotives apart.

Lighting and effects (functions)

• Directional Lighting - also usually provides individual control of headlights.
• Function Re-mapping - changes what function button a function responds to.
• FX Lighting - Special lighting modes - requires programming CVs greater than 100. Exact effects differ from one manufacturer to another. See your specific decoder specifications.
• Master Light Switch - Turn all functions off with one operation.

Misc

• Short-Circuit Protection (decoder)|Short-Circuit Protection]] - Protects the decoder against incorrect wiring when first turn on
• Thermal Protection - Protects the decoder against heat damage if it's decoder is overloaded or over heated
• Transponding - Only Digitrax (????)

[edit] Functions

Functions are solid state control circuits on decoders that can control nearly anything you can think of - lights, sounds, smoke, animation, uncoupling devices, etc. Many are not limited to simple on/off functions - for example lighting functions are capable of imitating MARS lights, Gyralights, Rule 17 dimming, single or double flashing strobes, ditch lights, and other effects. Output is generally 12 volts DC - if you want to use LEDs or low-voltage lights, you'll need to use a resistor as well.

There are currently 13 functions, F0-F12, however there is a proposal to extend this to 19 functions F0-F18.

[edit] Decoder Installation

Main article: Decoder installation

All mobile decoder installations include the following steps:

1. Select a decoder that fits inside the body shell
2. Has the required current rating
3. Isolate the motor from the track pickups
4. Install the decoder along with wiring for any extra effects
5. Test the completed installation.

[edit] Testers

There are various testers by various manufacturers and even vendors.

[edit] Digitrax LT1

The LT1 is included with all Digitrax Starter Sets. It consists of a harness with 6 conductor Telco type wire and a male plug, a tester with a female 6 conductor jack and a protection resistor.

The LT1 can be used to test LocoNet cables, as well as mobile decoders.

[edit] Loy's Decoder Tester

The Loy's Decoder Teste includes clips to quickly connect decoder wires NMRA socket to test decoders with an NMRA plug. LEDs are used to indicate speed, direction, and function status. This device is assembled and ready to use - not a kit

[edit] Stationary Decoders

NCE Stationary Decoder - this one is for switches

Stationary decoders can be used to control railway switches, structure lights, scene lighting, animation, and signaling.

[edit] Avoid connecting to rails

Most stationary decoders can been connected directly to the track for both rail power, and to receive DCC commands (tell them what to to do). However:

• It should be noted that it's recommended to to not connect stationary decoders directly to the rails if your DCC system allows for another method. The reasoning being this is that the decoders will draw power that could other wise be used for locomotives and other rolling stock. DCC power is very expensive when compared to a traditional power supply. An even more important reason for not connecting stationary decoders to track power is that in the event of a short on the line (often the result of running a turnout set against you) you will have no power to the decoders controlling the turnout, and therefore you will have to move the locomotive by hand.

• If your system allows for an external power source, other than the rails, you should utilize this. If your system and stationary decoder allows for an external method of receiving commands, this should be utilized as well. For example, a Digitrax stationary decoder can receive it's commands, and send decoder status information back to the command station, through the throttle network (or LocoNet in Digitrax's case).

If you simply _must_ use track power style power distribution with your stationary decoders, at least use some kind of power managing device to isolate the stationary decoder power from the track power

...someone needs to add more...

[edit] Decoder FAQ

[edit] What conditions can cause a decoder to fail?

1. Overvoltage on input (from track)
2. Current draw exceeds decoder ratings (wiring short or other overload condition)
   1. Be carefull when first testing a decoder installation. Put the DCC device on a test track (programming track or section with a 100-ohm series resistor) instead of the main line for testing. If all functions work, and it can move (assuming motor output drive from decoder) at low speed steps, then you should be relatively safe to place it on the main. As always, follow the manufacturer's instructions for testing in addition to the above.
3. Overheating
   1. Imagine running a black loco in direct sunlight and hauling a heavy load at nearly the limit of the current output of the decoder. Now imagine the decoder only having current limits, and not thermal limits built in. The scenario can also happen if the decoder is installed in an area with little air space. Consider the heat is the only suggestion so far...

[edit] See Also

• Decoder installation - How to install mobile decoders
• Installing LEDs with DCC Decoders
• Throttles
• Configuration variable
• Category:Throttle Network
• Decoder Features
• Category:Sound