Robin Sundt Echini

I have built a large double track loop that runs from the northern end of Shalford round to the southern end of Havant so that I can run trains round the loop in both directions. In the middle I built an equivalent of Guildford Station with four tracks so that I can run express trains through with another train stopped at the platform.

Having built the signal box for Hayling Island where the signals are manually controlled through the levers, I thought it would be fun to build automatic signals to react to trains approaching Guildford. The way the signals operate is determined by the setting of the points into and out of the station. One half of the tracks through Guildford looks like this:
Auto-signalTrack Plan.jpg 
A train entering Block A will trigger the signals. There are four possible combinations of the two points and the position of the points will dictate the signal pattern.

1). If both points are set to normal for an express train then, when a train enters Block A, the Distant and Junction Main will go to clear and the Junction Branch and Platform Starter will be at Danger. The Starter will stay at danger even if there is a train in the station waiting to leave in Block B.

2). If Point 1 is reversed for a train going into the platform then, when the train enters Block A, the Distant and Junction Main will be at Danger and the Junction Branch will show clear. Point 2 must be at Normal to stop the train in the station.

3). If Point 1 is set to normal but Point 2 is reversed, then the Distant and both Junction signals will remain at danger and the approaching train in Block A will stop when it hits Block C just before the Junction signal. When the track is clear (point 2 is reset to normal) then power will return to Block C and the Junction signal will display the safe road depending upon the position of Point 1.

4). If there is a train in Block B and Point 2 is reversed then the Starter will show clear so that the train can leave the Platform and return to the main line and all the other signals will be at danger. There will be no power in Block C, so any approaching train will stop before the Junction signal.

When a train leaves Block C then the Distant and Junction signals will revert to danger, same with a train leaving Block B.

The above describes the Down Line and the system will need to be duplicated (eventually) for the Up Line, which is logically identical.

I am not much good with electronics but quite happy with electrics, relays and switching. I am sure that there will be a sophisticated electronic way of doing this but I decided to try to do it the old fashioned way. The four signals are driven by servos that are in turn driven by a Megapoints 4R servo board. The servos are triggered by shorting the appropriate terminal to ground on the board. I also decided to use two DCC Concepts Rex boards one connected to each IP Digital point motor. The Rex boards have four L-C-R terminals, one is used to control the “stop” section before each point that stops an engine running into a point that is set against it. That leaves three terminal sets on each Rex board. The Block detectors are BD40s, one for both Block A and C and the other for Block B.

I sketched out the boards and started to work out the wiring that I needed to create the correct signal movements for each combination. I ended up with a rough drawing like this:
Auto Signal Draft01.jpg 
Once I think that I may have something that works, I photocopy the drawing four times (once for each possible combination of the two points) and, with each switch in the appropriate position, trace the electricity with a red pen to see if it goes where I want it and not where I don’t. The above drawing shows the flow with both points set to normal and the result is that the Distant and Junction Main signals operate to show clear for an express.

Later, I introduced Block C so that if the Junction signals are at Danger, the engine will stop before the signal but once the line is clear, power will be returned to Block C, the signals will reset and the engine will move off. The Block A BD40 also covers the Block C section by wrapping the feed wires for both Block A and Block C through the BD40.

The next step was to draw a schematic to position the two Rex boards, the Magapoints board and the necessary connectors. Each of the terminals could then be numbered to show the appropriate connections as a guide to installing the wiring. This schematic at full size was laminated and mounted on a piece of plywood that could be installed under the layout.
Auto Signal Schematic.jpg 
Finally, the two Rex units and the Servo Controller were mounted on the board, the wiring was installed and the whole setup tested to make sure that it was working correctly before it was installed on the layout and connected to the power supply, block detectors, signals, signal lamps and point motors.

Wired Board.jpg 
The Distant signal and the Platform Starter signal are both installed but there is still work to do to complete the Junction signal similar to the one I made for Hayling, except in this case the Branch signal is shorter than the Main line signal.

Recent National developments and building the folding baseboard for my grandsons have delayed things a bit but I hope to have the system running sometime soon and I will put up a video once it is complete.

Keep safe


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Absolutely stunning Robin, your application to signals and interlocking is in a league of its own.  I feel quite pleased with myself for having a loop that works and a single independent semaphore!  Interlocking is on another planet for me.  I can't wait for the video to see this system in operation. 

At least we are both putting our isolation to good use!
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Extremely well done Robin i can see you have spent a lot of time designing and producing the system. I am implementing interlocking and block signalling but my approach is different as i use software the Itrain program  linked through my ecos which has LDT signalling controll units which control all of aspect signals. all the points are controlled through either Lenz ls 150 units or Dcc concepts ad8fx . You are using semaphore signals but i think i could do the same but using servo control units. I suppose the only advantage with using the software version is for example i have 4 aspect signalling so the software creates the reservations and interlocking and number of blocks ahead. I assume you could do that your way but the wiring would become quite complex.

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Nive work and a neat and logical layout that will be easy to maintain in the future. (Something often forgotten when we create all that colourful wiring "spagetti" under the baseboard).

Sharing successful application of electronics is an aim of this forum, so its great to see your post.

Even though we produce hundreds of "How to" diagrams for users there is always yet another question - and even though we know just how versatile the things we create can be, it needs many minds thinking about it to explore the limits. It is amazing what can be achieved,

regards, Ahjay
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Excellent Robin

I have DCC and use the ADS 2SX points decoders. This is because they have extra outputs for frogs, and contacts for things like signals. I have one set of points where the two signals guarding the points are controlled by one ADS with the led output feeding green on one and red on the other and vice versa.  With DCC using one of these to drive a signal guarding points is fine if only using a Command Station, but can cause complications if using a system like iTrain, because ideally you would expect signals to be at danger if a train occupies the next block or if the points are set against your road.

If using DC control, I believe the decoders can be used by connecting a switch to the control inputs.

A very useful piece of kit in my opinion.

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I can see your point there Chris with Itrain or Railroad &co if the block was occupied the previous signal protecting the next block would be set to red plus if more than 2 aspect the blocks before that would have yellow warnings.

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I'm afraid my knowledge of electrics is far more basic - you lost me at the first wiring sketch!! My simpler (and far less sophisticated) solution to having semaphore signals synchronise with the points was via 2 Alpha Central panels, IP digital point motors and TrainTech / Dapol signal controllers. The only downside is, due to the strange design of Dapol semaphore signals, that some of the signals sometimes go out of sequence with the points - a quick crawl under the layout and a reset on the signal controllers rectifies this.
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Robin Sundt Echini

I finally managed to finish the junction signal and wire up and test the automatic signal system that I have built for the approach to the Guildford Down line.

The automatic signalling is controlled by the combinations of the two points leading into and out of the station platform. The layout is as follows:
Auto-signalTrack Plan.jpg 

I created videos to illustrate the possible combinations, starting with a stopping train going into the platform, so Point 1 is reversed and Point 2 is normal, which will stop the engine in Block B. The Distant signal stays at Caution while the Branch signal on the Junction signals is set, both set by the engine running in Block A and Block C.

By the way, don’t be surprised if the North Downs over Guildford look like shelves as the layout has rather overflowed into that part of the cellar! Also Guildford Station is still work in progress.

As the first train waits in the station, an Express train comes through on the fast line. As both points are set for it, the express engine triggers the Distant signal and the Main signal on the Junction signal as it runs across Block A and Block C.

With the first train still in the station, another express (suspiciously like the first one) arrives into Block A but Point 2 has been set to allow the first train to leave the platform. As a result, both the Distant signal and the Junction signals remain at danger and the express train stops. If it ran on, it would be stopped by Block C, which has no power. With Point 2 reversed, putting power into Block B, the Starter signal is set and the train can leave the platform. When the train has departed and Point 2 is set to normal, the Main Junction signal is set, power is restored to Block C and the express can proceed.

The camera that I am using, a NIYPS Mini Camera from Amazon, does not focus well below about a foot so the engine is rather out of focus. I modified a small truck to hold the camera with a cut-out of a carriage, which is completely out of focus. The camera is at an angle, as perversely the image is not square to the camera base.

Not the best camera work and  there is too much cellar and not enough layout but that is a function of trying to get a quart into a pint pot! There is a topic on the forum about small cameras for filming model railways, so I will post one of these videos there too and would love to find something that works better.

Keep safe and keep modelling.


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Absolutely stunning Robin.  Completely mind blowing to a simple modeller such as me.  If my Dapol semaphore works when I press the button I'm happy, that's as far as my signalling goes!

Great job.
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Just a basic point of information for anyone interested.
A semaphore Distant signal can display yellow aspect “on” or caution, and green aspect “off” or clear. It may be passed in either position, in the “on” position be prepared to stop at next signal, in “off” position all stop signals to which it applies on the line ahead worked by the same signal box have also been cleared.
A semaphore stop signal can display red aspect “on” or danger and green aspect “off” or clear. A stop signal may not be passed at “danger” except in cases of failure or where authorised by controlling signal box or in local appendix.

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Robin Sundt Echini

Train Detection and Signals

I have been working on more automatic signals that are triggered by an approaching train and set by the way that the points, that the locomotive is approaching, are set.

If the points are facing, then the point position decides which junction signal operates. If the points are trailing, then the signals will stay at danger until the points are set for the oncoming train. Using the IP Digital motor and a DCC Concepts Rex extender, there is also a “dead” piece of track that will stop the locomotive before the home signal.

A while ago, I acquired a number of BD20 occupancy detectors and I have been using those to detect the locomotives. A typical trailing point setup looks like this:
Double BD20 Wiring.jpg 

Two wires are wound through the BD20, one connected to Block A and the Bus and the other to Block B but switched through the IP Digital Point motor (or Rex). This means that there is always power in Block A but there will only be power in Block B if the point is set for the oncoming train.

As the locomotive enters Block A, the BD20 will be triggered but, if the point is against the oncoming train, the Rex will interrupt the circuit and the signals will not be activated. There will be no power in Block B, so the locomotive will stop short of the home signal, which will remain at danger.

If the point is set for the oncoming train, the locomotive entering Block A will trigger both the home and distant signals. The signals will stay at safe when the locomotive enters Block B and then the signals will revert to danger once the locomotive is clear of Block B.

Running two sets of wires through the BD20 works well, although it is important that the track feeds enter the BD20 the same way around or the two circuits, circulating in opposite directions, can cancel each other out and the BD20 will not work.

The BD20s seem increasingly difficult to get hold of and the price seems to have gone up a lot so I have also been experimenting with the Megapoints Block Detector, which is easily available and less than half the price.

In this case, the two boards are wired to their respective blocks and the two  ground terminals on each board and the two logic/signal terminals on each board are each joined together to activate the signal servo.
Double MegapointsWiring.jpg 

Two Megapoints boards wired like this work very well and are still much cheaper than one BD20 (and a lot easier to come by these days).

Just completing the signals and control board for the Down Distant, Down Home, Up Platform and Sidings Ground signal for Havant with one BD20 on the Down line, one on the Up Platform and one on the sidings. The Up Platform Starter at Havant had a route indicator that showed "W" for Waterloo, "C" for Chichester or "H" for Hayling. I've included the route indicator but have not yet made a working one! (That is a challenge!)
Havant Board.jpg 

This is probably the last time that I will use BD20s as I have now run out of my supply. The next signal controller will use the Magapoints board.

So far there are 19 working signals on the layout including two junction signals and three disc ground signals. I'll have to do another video soon. Still more to do.

Happy modelling and keep safe.


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Absolutely brilliant Robin, and in a league way above me!  I can't wait to see it all working in the video.
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