Signalling on the Essex Belt Lines

This article was published in Edition 4 of the OPSIG BR e-News. NMRA British Region members can download the e-newsletter from the OPSIG Newsletters page once logged into the NMRABR website at

Thamesiders’ introductory article for OpSIG BR e-News about wide area CTC on the modular Essex Belt Lines


By Paul Harman

The Essex Belt Lines is a H0 modular layout consisting of two types of module, either Mainline or Branch, built to a module standard that is now over ten years old. The Branch modules depict areas that would have low traffic and be outside of Central Traffic Control (CTC) but the Mainline modules are predominantly single track and experience the level of traffic that would be typical of prototype lines having full CTC. To that end it was thought that, just like the prototype, applying CTC to the main line would have a lot of benefits to operations. Having working signalling would make it easier for train operators by eliminating a lot of the paraphernalia associated with other operation methods making operations more attractive to the novice. Having the branch as well makes operations a multi-disciplinary activity with a different approach being required with trains having to transition between CTC and other methods of control.

A rudimentary system of signalling was implemented on some key modules to allow the regulation of trains but with the aspects having to be set manually by the signaller using redundant loco decoders it was not the most responsive way to regulate trains.

To implement effective automatic CTC like the prototype requires effective feedback of both turnout position and where trains are currently positioned – this is key for both the dispatcher to know where trains are and to the signal control system to set the correct aspects – even on a model it is handy to be able to read the signal aspects to know how far ahead the line is clear to adjust station dwell times and speed as well as being able to check that the route is correctly set (yes, if it is not all red you can go – but you might not want to take the M10000 down the mine branch before querying with the dispatcher!). We are fortunate at Thamesiders in that the module spec allowed for a feedback bus to enable us to easily fit feedback encoders to modules and get occupancy and turnout position information back to the control centre without having to add any extra wiring to intermediate modules. Even if a module does not need to have signals on it there is a need to feed back that it is occupied or that the main line is clear through.

Another feature that is not completely essential but can prove to be a real boon is to use a separate accessory bus. At Thamesiders we use Lenz for our command station, and this is heavily entrenched in the club so moving to a more modern command station for loco control would involve a lot of replacement of hardware with an associated big expense and learning curve for members. While Lenz may not be ideal it does work well for the simple control of locos and turnouts so can be retained for that. In order to not overload the Lenz command station we have added a second more modern command station (a SPROG) to operate accessories from. Again we are fortunate in that the forward thinking of the standards designers had included an extra DCC bus in the module wiring (intended to drive boosters) which we were able to repurpose as an accessory bus and connect the turnout and signal decoders to that. Modules are fitted with a key switch to allow the dispatcher to lock selected main line turnouts to dispatcher only control via the accessory bus or link to the track bus for backwards compatibility. Where modules did not have DCC accessory decoders fitted to operate the turnouts we have fitted servos controlled by Signalist SC2 point decoders to keep costs down. Another cost saving feature has been to use a Raspberry Pi to run the CTC software. The raspberry Pi is small enough to be easily integrated with existing control system under the layout and does not require the space that would be required for a laptop or PC.

A key feature that makes it possible to implement effective CTC on modules is that each module has to be self-contained. This goes against the principle often applied to block working with modules where a signal ‘shim’ board can be inserted between modules to provide an interface between blocks. If a module has a junction on it, it is not reasonable to expect the next module to have to provide a complex junction signal mast, and for a heavily centrally controlled layout a lot of shims would have to be provided and the signals would often be a bit disconnected from the turnouts they are protecting. To this end each module that has signalling implemented has a signal mast to control the access to that module and the mast can be as simple or complex as the module requires. A module that has no signals just becomes a part of the adjacent block by default. This makes it easy to produce self-contained CTC panels for each module that have all of the route and speed information pre-defined as part of the module. As on the prototype it is perfectly feasible to have different block sizes depending on the direction of travel if a signal is only provided facing one way.

Up until quite recently it was considered unthinkable to apply full CTC with prototype signalling to a modular setup because of the planning that would be required in creating the signal logic for anything other than very basic signalling, and the time that would be required to rework any plan to incorporate late changes. Two things have changed that, the first is Signalmast Logic in JMRI which almost completely eliminates any need to understand signal logic when setting up signals, and the second is in JMRI panel connectors which enable you to create separate panels for each module and just tack them together at time of setup to join all the logic together. To this end I consider JMRI to be a great enabler for CTC on modules and I would recommend anyone interested in CTC to download JMRI and have a look at what Signalmast Logic can do (don’t worry JMRI is completely free). If you have looked at JMRI before and found it all a bit baffling it is worth having another look because things are much easier now, there has been a step change in functionality and usability over the last few years.

Signals are a very visual part of CTC and often the only bit that is seen. At Thamesiders we have decided to make the signals plug in and removable to ensure that they do not suffer damage during set-up and transportation. We wanted a standard interface, and with some masts requiring up to ten wires we decided to use our own 10-pin signal interface which is more or less compatible with similar 10-pin signal interfaces from Digitrax (and now Signalist). We created our own 3D printed plug in base which fits neatly in to a 14mm hole drilled in the baseboard with the cable run made in ribbon cable to Signalist SC1 signal mast decoders. As well as being convenient to connect up easily it has been modelled to look like the prototype mast base including the cast base and concrete slab.

For simplicity we have chosen to control the turnouts and signals from a representation of a US&S CTC panel created in JMRI. It takes a little bit of work in JMRI to link the layout to the CTC panel, but it is worth the effort. With a track diagram, a row of turnout switches, and a row of signal switches the basics are very easy to grasp. With feedback of turnout position, and block occupancy shown, just like on the prototype the dispatcher should not even need to be in the same room as the layout.

A selection of Thamesiders’ club and member’s modules in Layout editor panels


Individual layout editor panels are produced for each module. The panels are linked together using the edge connector feature and the signalmast logic is autodiscovered. The layout editor panels show the signal aspects which can be handy of there is a sighting problem on the physical mast.

The Panel editor US&S CTC panels which are associated with the above panels


The white lamps on the track diagram show occupancy.

The top row of switches operate the turnouts. The switches have odd numbers that correspond with the turnouts on the track diagram. Green lamps (main line turnouts) or white lamps (yard turnouts) indicate the turnout is in its ‘Normal’ state. Yellow lamps (main line turnouts) or red lamps (yard turnouts) indicate the turnout is in the ‘Reverse’ state.

The next row of switches (even numbers) operate the signals. Move the switch left clears the signals for trains to go left (westbound) and moving the switch right clears the signals for trains to go right (Eastbound). A green light indicates that a signal has successfully cleared, while the red lamp indicates that all signals are at stop.

The bottom row of switches allow extra control of the signals to reduce dispatcher workload:-

‘Switch Out’ – Releases hold on all the signal masts so that they operate as automatic absolute block signals. Handy when a control point is not in use.

‘Convoy’ – Prevents trains passing through a control point from returning the signals to held so that following trains will automatically get the same route.

‘Local’ – Enables the local control of main line turnouts by the train crew (for switching etc.)

Local panel for TBR module built by Mike Meadows


The local panel is used by crews to operate the local turnouts when switching, or by a local dispatcher in an emergency. This panel is based on a Lenz LW150 module which plugs in to the XpressNet with a 5-pin DIN plug for quick setup.

We are now in the final stages of testing the signal system ready for exhibition at Alexandra Palace in the spring when the Essex Belt Lines modules will be linked up to some Freemo modules to fully exercise the signalling system.

Further information on the core components of the system can be found on these sites:

Harman DCC (Signalist) decoders:

Harman DCC signal parts :


WiThrottle :

Engine Driver :

Sprog :

Lenz DCC : and


Paco RS8 :


Heathcote Electronics :