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Part II - How to Control Scale Signaling

By Don Woodwell

(excerpted from Automating Your Model Train Layout, 2nd Edition)

In Part I, creating prototypical signaling for a high rail layout was discussed.

This included both searchlight type and block type signals for NC-Lines and NC-Traction, respectively. Shiloh Signals supplied the scale-sized signals, each of which features long-lasting light emitting diodes (LEDs) rather than light bulbs.

Five signal aspects were illustrated: Clear (allows trains to run at top speed permitted by the road); Stop (any condition that requires a train to stop); Medium Clear (when approaching a diverging route); Slow Clear (when leaving a yard area); and, Approach Slow (when entering a yard or terminal area). Enabling these aspects requires detectors, turnout control, and timers all of which are described below.

Control Alternatives

Detectors – Depending upon where a detector is located, the signal aspect tells an engineer if another train occupies the block and whether he can proceed or not. Changing signal aspects usually only requires one detector. When the locomotive passes the detector the first time the signal is set to Stop. Some detectors hold a circuit to keep the signal aspect fixed until another power drawing car such as a lighted caboose is sensed. When the caboose passes, the aspect is changed to Clear.

Turnout Control – 1:1 scale railroads use signaling to tell an engineer road conditions ahead especially if a train is approaching a diverging track or yard area. Prototypical operations, therefore, require that we provide realistic signal aspects to our “engineers” so they can safely operate their trains. High-rail switching operations can be translated into signal aspects by tapping into turnout voltage outputs.

Detector & Timer Control – A simple detector activates a timer that can change a signal aspect for a select time period. An example is entering and leaving a terminal track area where slow speed is crucial to safety.

Control Connections

Turnout Control – since the position of a turnout indicates whether a train is headed toward a diverging or through route, signals attached to the turnout should also indicate to the engineer the speed at which he can safely proceed. A Medium Clear aspect, for example, permits 30 mph operation on an NC-Lines diverging or merging route over Lionel 0-22 turnouts with a relatively sharp 31” curve.

Lionel four 0-22 turnouts set signal aspects since an AC voltage is always present at two of the three terminals located on the switching housing. The two terminals are the center plus the right or left terminal depending upon the turnout position. The turnout is activated by 20vac that also lights the signal LEDs. In total, twenty 20 signal heads and 30 LEDs show five signal aspects.

Figure 1 is an example of how to wire east- and west-bound signals on the mainline. Shiloh Signals products work on either AC or DC voltage where the 10 to 12 volt range is preferred for long LED life. Burnout at higher 022 switch voltages is prevented with a 470-ohm resistor in series with the signal's common lead.

Figure 1: Lionel 0-22 Turnout Signal Control

An Atlas turnout on NC-Traction's mainline is controlled by a CIRCUITRON Tortoise(R) Switch Machine. The Tortoise's two internal NO (normally open) and NC (normally closed) contacts route 12 volt DC to the signals whose aspects are determined by this turnout's position.

For trolley operation, the Tortoise positions control east- and west-bound signals on the mainline as well as an east-bound signal on a diverging branch (5 heads, 13 LEDs, & 4 aspects). Figure 2 shows these connections.

Figure 2: Tortoise Turnout Control

Detectors & Timers – Two detectors and timers activate back-to-back signals on NC-Traction's mainline just west of the terminal yard. Shiloh makes the timers and supplies a simple yet effective means of detecting the trolley's location -- a bent wire soldered to a small u-shaped bracket. I used epoxy glue to fix the bracket to the track ties so that the bent wire is about 1/16” (16mm) away from the center rail.

As the trolley passes, its pickup roller bridges the gap and triggers the timer whose two intervals may be either 10 or 30 seconds. As a trolley travels toward its terminal track, the normally red eastbound aspect is changed to Approach Slow for ten seconds, sufficient time for trolleys to enter the terminal area. On the reverse side of the mast, the westbound aspect changes from Stop to Clear for ten seconds when the trolley leaves the terminal. See Figure 3 for a diagram of the timer circuits. Sixteen volts from a spare transformer powers the timer which is independent of the applied track voltage.

Figure 3: Timer Control Circuit for Signals


Thesethree control methods work very well on NC-Lines and NC-Traction. As both the short line and interurban operations expand in the next couple of years, the same signaling principles will be applied. Which method you select for your layout signaling depends on your layout plan and operations, and the warnings your engineers require to safely run their trains and the motormen their trolleys.

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