Time and again we get asked the question on how one can stop a locomotive in front of a signal displaying a red light (Stop aspect). Every model train enthusiast must find an answer to this question if he or she wants to construct a prototypical layout.
Unfortunately there is no simple answer that is valid for all different scenarios. There are several different solution approaches that differ considerably in terms of their cost and compatibility.
Here we would like to present a solution approach that can be realised without special software on your computer. This solution can be realized with ESU standard components at a reasonable cost.
Of course, this solution also works only when certain ancillary conditions are met.
It is quickly explained:
- You only use decoders that support the Lenz ABC braking method. Besides the latest generation of Lenz decoders all ESU decoders LokPilot V4.0 and also all ESU LokSound V4.0 decoders support this technology.
- You use an ESU ECoS or a Märklin® Central Station Reloaded as your command station: the boosters of the command station must provide an absolutely clean, symmetrical digital track voltage. This must also be true for all external boosters. Older booster models (e.g.: Märklin®6017) are designed with so called half bridges and provide a distorted track voltage that prevents the proper functioning of the ABC braking method.
The basic idea of this solution is to split the layout into several sectors. Just like with the prototype these so called blocks must be long enough to hold the longest train. Ideally each block will have some extra length to cater for the braking distance of the train. The blocks are electrically separated (only one rail) from the rest of the layout.
Each block will be equipped with a so called block signal. If this block signal displays “red”, then the train must stop. If it shows “green”, then the train may continue onwards. In order to assure that the train stops, the braking sector will be powered either by the digital track voltage or a special signal for braking. The block signal is controlled directly by an ESU SwitchPilot decoder. This – in conjunction with the SwitchPilot Extension Module facilitates the generation and supply of the braking signal.
The actual brake signal is a modified DCC signal: The track signal provided by the ECoS is routed via 4 silicon diodes. At each of these diodes a voltage drop occurs resulting in one half wave of the DCC signal now being 1.5V to 2V lower than the other half wave. All decoders supporting the ABC braking method detect this voltage difference and commence the braking action as a consequence.
If you combine the ABC braking method with the constant braking distance (which can be accomplished with all ESU V4 decoders), it is possible to achieve precise braking even if the locomotives approach the red signal at different speeds.
We are showing the wiring both for the 2-rail system as well as for the 3-rail system in the adjacent pdf document. Please make sure that you wire this circuit exactly as it is shown and also make sure that the insulation gaps on the layout provide a reliable separation between the adjacent track sectors. There is no need to create transition sectors or similar: with this method nothing untoward can happen when a train enters the braking sector even if a train erroneously should bridge both sectors.
You should use ultra fast, sufficiently dimensioned silicon diodes for generating the braking signal. We have found the type UF5404 to be well suited that can be ordered from Reichelt (part No. UF 5405) or Conrad (part No. 162400) amongst others at a reasonable price.
If the locomotives are supposed to enter and pass through the sector, then the relay output of the SwitchPilot Extension module bridges the four diodes of the diode cascade. Please make sure that you wire the block signal to the correct terminals of the relay module.
It is particularly useful to employ track occupancy detectors for sectors that cannot easily be seen (e.g.: in the storage yard under the layout). You may use an ECoSDetector module for this purpose. It is suitable for both – two rail and three rail systems – and can monitor up to 16 track sectors and even detect the identity of the locomotives in four sectors. In order to facilitate this, the decoder must support RailCom®. All ESU LokPilot V4.0 and LokSound V4.0 decoders support RailCom®.
The occupancy status of the track and the address of the locomotive (on four tracks) can be displayed on the touch screen of your ECoS command station.
The ESU V4 decoders perfectly manage ABC braking; however, ex works this feature is turned off. All braking modes are controlled in CV 27. Please also observe the relevant remarks in the LokSound V4.0 respectively LokPilot V4.0 manuals. The necessary settings are described in greater detail in chapter 10.5. We recommend to only activate ABC braking.
- Write the value 3 into CV 27 if you want to stop the locomotive – both in three rail and in two rail systems – under all circumstances regardless of the direction of travel.
- If you want to stop the locomotive only if the DCC signal on the right hand track is higher than on the left hand one in a two rail system, then write the value 1 into CV 27.
- If you only want to stop the locomotive if the DCC signal on the left hand track is higher than on the right hand one in a two rail system, then write the value 2 into CV 27.
The owners of an ESU LokProgrammer can adjust all these settings comfortably by clicking the appropriate entry fields on the computer monitor.