RHJ Rail

TECHNICAL - Page 8

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Signals

RHJ Rail recently (2020) implemented a signal system for both main lines on the layout. As is the usual practice, it was decided to design the entire system rather than purchasing a commercial product. The reasons for this were to figure out how to do this (a common goal for the railroad) and, perhaps more importantly, to make it compatible with the other components of the Automated Operations Control Centre (AOCC).

The new semi-prototypical signal system monitors trains and adjusts the signals around the layout. The signal system is controlled by the AOCC which runs on a Windows computer using JMRI, a model railroad computer interface. Details of how this works are presented below for those with a technical interest.

Signal masts (see below and at bottom) were purchased on-line. The ones used were of a single-target design similar to the one shown below. Each target has three LEDs (light-emitting diodes) contained in the signal head with separate wires for each colour and a common ground. These can be easily operated on 12 volts DC with an appropriate resistor for current-limiting purposes.

Each separate signal has four aspects, as used on RHJ Rail: Green, Yellow, Red and Dark (no colour displayed)

The matter of how to control and operate the signals was examined and it was determined that the current draw for each LED was about 25 mA, an appropriate match for the lighting outputs of a DCC decoder.

Signal control boards were constructed as shown at the bottom of this page. Each board controls two separate signals. There are 20 signals on the two main lines, 10 on each, designed for directional right-hand running. Additionally, two more signals were added at intermediate points to control train access in the middle of blocks.

Each signal control board contains one 6-function DCC mobile decoder. Three functions control one signal and the other three control another signal. The mobile decoder is just the same as would typically be put in a locomotive but instead it is mounted on a board as shown below and connected to the DCC control bus.

This means that a DCC throttle can address the decoder and set any of its six functions to True (on) or False (off). With RHJ Rail, the throttles are actually included in JMRI scripts. A sub-system has been designed to address and set any signal head (actually a DCC throttle and a specific function) to any of the four possible aspects.

This sub-system, integrated with the AOCC, can change any signal to any aspect when requested from any JMRI script. A call to the script for the signal sub-system provides the necessary information to select a specific signal and set its aspect as required.

Importantly, such calls not only specify which signal is to be set to which aspect but also to set trailing signals in the same subscript call.

Thus, when a train passes a given location on the layout (as detected by the AOCC system), the signal beside the lead locomotive of a consist can be set to Red, and signals behind that set to the appropriate aspect.

Typically when a locomotive passes a signal, that signal will be set to Red and the signals immediately behind set to (for example) Red, Yellow, Green.

This, of course depends upon several factors, the most important of which are the train length and the block length. If a train is longer than the current block, then the sequence of signals would be RRYG. If the train is longer that two blocks (rarely, but it does happen), then the sequence of signals could be RRRYG. Up to seven signals are allowed for in the programming for the AOCC system. Since there are only 10 signals on each main line, this was considered a reasonable number but it could be adjusted if necessary.

Occasionally, these standards don't apply exactly as described. For example, if a train is backing up, then the signals may be set to indicate that the block BEHIND the train is Red and the blocks behind that are set appropriately.

Another example is the track-cleaning train which traverses the entire layout multiple times, regardless of right-hand running, signal status, and the like. In this instance, that train is considered to be running in "Dark" territory and the signal system is turned off (all signals are set to Dark). The train uses a "track warrant" to grant it authority to occupy any main track on the layout as long as it is not occupied. This process takes about 15 minutes of real time and after it is finished the train returns to its "home" location and then the signal system is activated again, ready for any scheduled run.

Those familiar with DCC programming will recognize that, "out of the box", DCC mobile decoders will not likely use functions (F1 - F6 for example) to do precisely what is required for this system to work. What is needed is that each of the six functions of the DCC mobile decoder must respond independently, that is F0 must not be dependent on the direction travel (Fwd or Rev) and F2 (normally the horn or whistle) must "latch", that is stay active as long as the function remains on.

In order for the signals to work independently of direction-of-travel or key press remaining ON, a few CVs (control variables) need to be re-programmed.

RHJ Rail decided to use Digitrax DH 166 decoders as they were readily available and several were already on-hand. Any six-function decoder will do but the following programming sequence is specific to that decoder. The goal is to set each of the six outputs so they can be independently controlled and do not depend on direction-of-travel, non-latching (horn or whistle) or anything else.

CV 35 - 1
CV 36 - 2
CV 37 - 4

CV 38 - 1
CV 39 - 4
CV 40 - 2

(CV 38, 39, 40 could be set to 1, 2, 4 as are CV 35, 36, 37 if the wiring were changed a bit)

Typical Signal Mast with 3-LEDs

Signal Decoder Board for controlling two signal masts, with three colours each, using a Digitrax DH 166 mobile decoder. Each signal mast consists of R-Y-G-B wires corresponding to the colour of the target and a ground wire (black).

The label on the board shows (l - r) the signal number, the decoder/throttle address, and the segment of the signal on the decoder (i.e. A = 1 - 3 for the first signal and B = 4 - 6 for the second signal).

Although electricity is colour-blind, four-conductor (RYGB) telco wire makes it much easier to keep track of the wiring from the Signal Decoder Board to each signal.

And, yes, it all works according to plan.

More details on any of the above can, of course, be obtained by contacting RHJ Rail.

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