Signals Clinic - Simple signals, Module signals

A look at signaling from a modelling perspective.
I hope to present some different ideas on the subject and inspire some to consider signals as the next project on the layout.
Prototypical, functional or look pretty. How you tackle signaling depends on your layout, the way you operate it and your skills at designing and wiring.
An oval track on a 6 x 3 board will likely have a look pretty system, although you could build a functional system that would automatically power control 2 trains with signaling.

With a large layout where you have ‘nights’ and several operators working, you could use a functional system that must be obeyed. Advising the operators about conditions ahead of them; such as points (turnouts, switches), correct CAB switch settings etc.
If you have modeled a prototype situation you might consider installing working signals in the correct locations as in real life. Of course you have to fudge a little. No fingers could fit into an “N” scale signal box to set the levers, so points and signals would be actuated from toggle switches.

Passage Signaling detects when the train passes the signal and sets it to red. After a time delay the signal returns to yellow then green. If the track power is reversed the signal goes to red. This sort of signal looks very realistic and is most useful for a smallish layout where there is not enough track length to have multiple blocks and a detector system.

In the diagram a simple passage detector is controlling the adjacent signal. A small section of track is isolated and when the loco wheels pass over it the signal action is started. The electronics are on a single board and all you need to do is wire the three track connections and the 12 volt D.C. supply plus the leads to the lamps or LED’s on the signal.

You will notice there are more inputs to the lamp driver, labeled “Y”, “R” etc. When these are switched to ground or the negative supply voltage they hold the aspect and over-ride the time out. This makes the signals more useful in loops, junctions and yards as the points position, next signal ahead or other interlocking conditions can hold the signal aspect until the route is clear.

Approach and Home These signals are interlocking from the points setting. As the train passes the right hand ‘Approach’ signal it goes from green to red and starts timing out. The next (Home) signal will be at green if the route is set to the main line, otherwise will be yellow if the loop is to be taken. As the train passes Home, the signal goes to red and through the ‘red out’ a ground is wired back to the ‘Approach’ signal to hold it at yellow. The distance between the signals needs to be longer than the longest train and the delay time to be about twice the time the train normally takes to pass the signal position.

Block Signals. On a larger layout the signals can be controlled by sensing the presence of the train. The track is divided into blocks (typically twice the length of the longest train you will run) and the signals are controlled through the 3 aspects by the block occupancy detectors. If there is a train in the block ahead of the signal, then it is at red, in the second block ahead the signal will be at yellow.
If none of the two blocks ahead are occupied it will be at green. These aspects can be interlocked also to indicate points positions, CAB coincidence between adjacent blocks, timers and manual switches. Of course the operator must follow the signal indications as he drives through the layout if the full benefit of the signaling is to be obtained.

The diagrams above shows a western approach to the loop. An additional turnout in the loop line is also included to show how you would hold red if the points are set against the approaching train.
Combining these diagrams in both directions gives starter, distant/approach and home signals and would give you a full loop control.

A bi-direction block signaling set-up would be used between loops on a single main line. For Intermediate, distant, advanced signals or APB signaling in American layouts. A further refinement for realism would be a direction detector that would put all opposing signals to red when a train entered the single line section. This is an available option for D.C. controlled trains where the voltage direction indicates which way the train is going. For D.C.C. control 'which way' becomes a little more complicated and would need position sensors to determine which end of the block the train entered from.

Prototype signaling applied to the model world.

This involves far more than I could cover in a clinic but eventually comes back to the simple control principles that I have outlined. In the real world signals have to have input from human beings as well. For example in a single line loop situation, the loco driver has to set the route at the loop, this sets the signal aspects that will allow safe passing of trains. We have to imagine this human’s actions when running on the model.

Signaling terms (USA)

Main Track - occupy with permission only
Siding - use to pass or overtake other trains
Station - authorized stopping place
Switches, Turnouts, Points - allow deviation to another track
Restricted Speed - to stop in half the visible distance
Approach Speed - to stop at the next signal
Permissive Signal - must stop then can proceed with caution
Absolute Signal - stop means stop
Block Signal - controls the following block of track.
Distant Signals - indicate the aspect of the next or home signal
Home Signal - controls a passing loop or station and yards

Junction Signals
At a junction there is the additional need to protect the opposing track where the two cross.
Mainline UP traffic has no problems but UP branch traffic can only proceed when the mainline DOWN traffic has been stopped.

In the prototype situation these signals would all be interlocked and have to be set in the correct order.
Safety is paramount in real life so the sequence is organized so that if at anytime it is stopped there will be no unsafe signalling conditions.

On the model the signals are set by the turnouts and block detectors so both turnouts would be operated together and would set all the appropriate signal arms together. Of course we have to see the junction so that if any trains were around it we would wait.
But what if it were not visible then we would need indication that the blocks were clear (lamps) or to be more sophisticated the points motors could be interlocked by the block detectors so that they did not operate until the blocks were clear. Of course we would also need power control on the blocks to stop trains that were trying to "run the lights"

How do you work it out?

There is only one way and that is to sit (virtually) at each signal position and write down what would need to be told to a train driver as he came to this spot. Turnout switches, block detectors, spot detectors and toggle switches could all be used to activate the correct signaling aspect.

On the diagram are the conditions that would control the various signals at this station/junction.
The Down Starter (D-start) would be Red if linked turnouts 'A' and 'A1' were reversed and Yellow if 'B2' block were occupied. Note though, that if there was no Departure signal at D-depart then block 'B2' occupied would need to make D-start Red as there would be no other place to indicate the condition ahead in the block 'B2'

The logic or wiring needed for the other signals can be worked out just as simply. Turnouts (Points) would also need interlocking so that set B could not be changed while A were at normal.

Although I have used block detectors to control the signals more simple spot detectors and timed delay signals as described earlier would give an almost similar effect and certainly look as realistic to the spectator.

Signaling is easiest done using electronics, but it can be done just using relays and LED's although not with the flexibility of electronics.

wiring diagram

This wiring diagram shows searchlight signals for starter and departure heads using tri-leds, switches actuated by the turnout settings and relays driven by the block detect circuits. The LED's can give three colours red-yellow-green. The voltage (+12volts) comes through the resistors, then the relay and switch contacts to drive the LED's. If you follow the wiring you will see the logic.
S1 - red = TE1 rev or TE1 normal and relay picked (train in the block) ahead
S1 - green = TE1 rev. or TE1 normal and relay normal (Red plus Green gives Yellow if TE1 is reversed)
S1 - yellow = TE1 rev. or TE1 normal and S2 at red (provided the relay is not picked, ie train ahead)

S2 is similar, red if TE2 is reversed or the relay is picked (train ahead) otherwise green.
The turnout at TE2 opposes the train so if reversed it signals red. There is no yellow aspect here.

Finally - What signal to Use. Of course this depends on the prototype generally so here is a selection of signal aspects in the various railway's styles.

signal types