What is a Digital Decoder?

What is a Digital Decoder?

By Roger Heid


This article addresses all those who are new to digital systems and may not have any clue as to what this is about, what things are called, how they work and how to install them.

Let’s talk about decoders. Here is a little joke, for a starter.

*    *    *    *

Two friends bump into each other and discuss some issue. In parting, one turns around and says:

“Give me a call and tell me what you think.”

“Uh, I don’t have a phone.”

“That doesn’t matter. I got one.”

*    *    *    *

You see, it takes two phones to place and receive a call.

In the world of digital model railroading, there is a very similar situation. A digital command station is one ‘phone’, namely the caller; a decoder is the other ‘phone’, the party being called. A digital locomotive must have a decoder installed to enable a control station to ‘call’ or to address it and to tell it what to do.

Digital control stations and decoders behave just like computers. They communicate with each other using ‘computer language’, something a human cannot understand. There needs to be an ‘interface’ between the human and the machine, a translator of sorts. One interface is a control station which translates your knob twisting and button pushing into ‘cyber language’; the other interface, a decoder, in turn translates the ‘cyber language’ into analog terms like off/on and voltage changes.


Sample of a ESU locomotive decoder


Sample of a locomotive decoder with sound      Decoder for small spaces

In addition to locomotives, there are other devices that can be controlled digitally. Turnout switch motors, de-couplers and signals are samples of items that fit into this category. These decoders are usually not installed in a device directly, but there are some exceptions. One example is a decoder that installs under the roadbed of Maerklin C-track turnouts.


Maerklin C-Track Decoder

Otherwise, these decoders are small boxes, varying in size depending on the manufacturer and features. Decoders are available from several manufacturers.


Samples of Maerklin Decoders


Sample of ESU Decoder

Just like telephones, decoders need to have their own individual ‘phone number’ called an ‘address’ or ‘address code’. The factory pre-sets a given decoder to its ‘default address’ which is reflected in the instruction manual of the decoder. However, the address can be changed by the end user. The manual will tell you how to do this.

Locomotive decoders are more complex because it must be able to perform several functions such as forward and reverse travel directions, maximum speed, lights off and on, volume of sound effects and so on. The number of functions depends on the individual decoder model. Some of the settings can be changed by entering different CV numbers. CV stands for ‘Configuration Value’. Initially, you do not worry about this. You will pick up on that wisdom as you become more experienced. Learn to crawl before you fly.

If you have any questions, please, post them in the Forum under the appropriate topic.

Thank you.

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