Occupancy detection: S88 vs. Loconet

If you start using DCC, someday you may feel the need to go further than just controlling trains. There are numerous options today: smart touch screen command centers, PC control… But the prerequisite for automating a layout is to implement basic train detection: modules that will monitor your track sections and tell your DCC system whether or not a train is there.
Here is a quick introduction of 2 popular systems used for train detection: S88 and Loconet.

Overview of both buses:

S88, the mother of all detection

One of the oldest – and still popular – detection bus is called S88. It was created by/for Märklin more than 15 years ago. It is simple, and most of all cheap now that it is in the public domain.

S88 is a “serial” bus: all modules are connected in a chain, one after the other. There is no “adressing” per say, each feedback address depends on the position of the module in the chain, and how many feedback addresses the module has (8 or 16 in most cases):

Basic principle of the S88 bus

The modules are connected via a standard 6-pin cable from a module to another, and finally to the control station (or PC interface).

S88 cable

There is however an alternative to this flat cable (prone to interferences in some cases): the use of standard computer network cables as a replacement. There is a semi-official norm for this new S88 connection, called S88-N. This standard is now being adopted by many manufacturers (mostly German), who integrate network (RJ45) plugs directly in their modules.
Just a common sense piece of advice: using Network cables to connect your S88 modules does NOT mean you can plug your module to a computer network; it simply means the cables are shielded, and will be less prone to interference than the legacy flat cables of the S88 norm.

A module from LittfinskiDatenTechnik ©
Equipped with both standard (S88) and RJ45 (S88-N) connectors

Loconet, the allrounder

Loconet was developed by the US-based company Digitrax. It is semi-open, as the company allows other companies to distribute product based on the technology, and publishes extensive documentation.

It differs a great deal from S88, for 2 mains reasons:

  1. It is not only an occupancy detection bus
    There is a wide variety of  Loconet modules, the network is not limited to occupancy detection. There are DCC switching modules, sound modules…
  2. The network topography is pretty much up to you
    As opposed to S88, Loconet can be arranged the way you want. As long as you don’t make a loop, you can do anything you want (tree branches, simple chain…). It is in fact very similar to a computer network.
    A nice consequence of this, is that you attribute addresses to the module, wherever they are on the network: you can add a module in a chain or a branch without having to change the addresses of any other module.

Example of Loconet networks (Source: http://en.wikipedia.org/wiki/Network_topology)

 

Loconet connections are based on RJ-12 cables, which is a standard phone connector in the US, that Europeans are used to seing on devices such as computer or DSL modems. One should note however, that RJ12 uses 6 cables, instead of the 4 cables present in the standard RJ11 phone plugs (in other words, don’t use phone cables for Loconet).

Loconet cable with RJ12 plugs

Which one do I need?

Well, it all depends on what you want to achieve. In my case, I started with S88. There are many people complaining about S88 reliability (interferences on large layouts). These reports are surely true. But if you have a reasonably sized layout, and use the RJ45 S88-N connectors instead of the flat 6 pin S88 cables, you have little chances of encountering reliability issues.

Loconet may seem a bit more complex, but is allows much more. In my case, I ended up converting to Loconet after deciding to build a modular layout. What this means for me is that I can add a new module in the middle of my layout without having to reconfigure all feedback addresses numbers.

Of course, all this depends on which central station you are using. Here is a – far from exhaustive – list of S88 or Loconet capable interfaces:

Command station
 
S88
Loconet
Uhlenbrock - Intellibox 1
Uhlenbrock - Intellibox Basic
Uhlenbrock - Intellibox II
Uhlenbrock - IB-Com
* S88 only in most recent models.
Both the old and the new model have the
same reference, so be careful.
*
ESU - ECOS I
ESU - ECOS II
Digitrax - DCS51

More about the modules will be discussed later in this blog. I hope this introduction helped those some of you, who are starting to feel the need to know where your trains are!

What is your preference, do you favor another bus type (XpressNet…)? Don’t hesitate to comment.