I read with great interest John Hobden’s article in the Gazette, Vol 20 No 2, and his account of setting up a block signalling arrangement on his railway. His words confirmed that I was on the right track, but I wanted to have block signalling units that included signal operation as well. So I initially searched the internet for a ‘model specific’ answer to this to see if there was anything on the market and came up with the name ‘Triang’. Figure 1 shows the Triang set, minus the cables and battery pack etc. There is one indicator, a switch and a tapper for a bell in each box. It was designed for single line working over two sections and I believe the bells were of differing sounds. The commutator on one worked the indicator on the other as did the tappers and bells. Figure 1

Having found, but just missed, one of Triang’s single line block systems for sale on eBay, I then spent some time looking into how it could be brought up to date. I realised how much I didn’t know myself about signal control, and that little had been done to promote it in the model railway world.

So could I build an up to date version of the Triang system that wouldn’t run into hundreds or even thousands of pounds, wouldn’t be over complicated electronically or be elitist in the sense that it used a collection of original signal box equipment? Thus began the usual thought processes.

Unlike John’s system, I wanted to try to retain the original feel of the communication system and began by looking to see if the solenoid indicators used in signal boxes could be replaced by servos. Could the three position commutators which appeared to have been gravity activated in some way, and as such always appeared in the vertical plane, be replaced by three position rotary switches and servos, and could I integrate this, and a simple bell system giving a single ring at the touch of a button, all in one control box?

Of course, the answer had to be a yes, so I started looking at how this might be achieved.

To use servos, I would need a PCB board of some sort to control them. I’m no electronics expert, but I thought that commercially produced boards out there that controlled semaphore signals might be developed to offer three positions instead of the usual two. To make this possible, I would have to encourage someone to make a change, to alter their board design to allow for this. If this could be done, the next step would be to identify what kind of circuit would be needed to allow a simple rotary switch to change two servos simultaneously acting as indicator, one a home and one on a distant control panel, to any one of its three pre-set positions?

A couple of companies I contacted could see it as a possibility but for them it was not going to be priority. But, I have to say that when I finally contacted GF Controls they could see a relatively easy solution and came to my aid with a rewrite of their chip ‘software’ as used on their control board, and the three position control of a servo suddenly became a reality.

There were also design implications as to what all this might look like if built as a single control panel for each block. It had to house everything necessary, replacing the traditional ‘shelf’ festooned with all the expensive paraphernalia found in real signal boxes. Figure 2 was my initial ‘mock-up’ design for a through section of the railway, although the indicators would need rearranging. It shows the two sets of indicators and buttons and the signal control levers would be Cobalt S-switches. The bells will fit on the sides of the control box. Figure 2

My railway has four boxes. Representing four signal boxes, the working procedure assumes that each Box controls the entrance of locomotives to its section only. To accomplish this as described in John’s article, Figure 3 illustrates how the indicators would be connected to particular switches in each box. As my railway has two terminus stations and two through stations, I needed two types of control boxes, set up as shown in Figure 3. Figure 3

Figure 4 The connections for the bells in each box are shown in Figure 4. In total there will be three different types of circuits controlling my signals and occupancy of the roads. A separate circuit is necessary for the indicators as described previously, and a further one that controls the position of the signals in each section is also needed. At this stage, I’m not looking to interlock signals with points.

Figure 5

A word here about modifying the bells’ strike. I rearranged the wiring as shown in Figure 5. This cancelled out the make and break ac tion of the solenoids. It was then necessary to adjust the striker slightly until it gave a single laudable ‘ding’ from a single instantaneous press of the bell button. The bells were very cheap and obtained from a scientific supplies company.

Figure 6 below, shows a completed control box for a terminus box. One set of indicators, one three way switch, one bell push, one bell and a set of signal switches. I chose Cobalt-S switches as they are in fact three switches in one and will allow me to control a point, a signal and an LED on a routing control panel. An added bonus for this kind of design is that it is not scale or gauge dependant. Figure 6

Figure 7 shows the layout for a through box containing two sets of indicators, two 3 way switches, two bell pushes, two bells and a set of signal switches. Figure 7

For more detail on how these control boxes were built and how the components in them were put together, read on.

The control boxes are standard Camden Boss, 8000series, plastic enclosures, measuring 187 x 243 x 103mm. They come with an aluminium face but I chose to replace it with a white plastic face for aesthetic and practical reasons. I set out the positions of the components to be attached to the face of the control boxes, as shown in Figure 8. Figure 8

All the required measurements are given. As my railway is arranged in a giant horse shoe shape, the first and last boxes were made left and right handed using only half of the measurements shown, Figure 6 shows the left 3-way switches and the servos for the indicators. Watkins and Doncaster supplied small plastic boxes with clear covers for the indicator enclosures. ISG (International Scientific Group Ltd), supplied the bells.

The control PCBs, modified for the indicators’ three positions, came from GF Controls. Signal and point controls on my railway are on separate circuits, but the PCBs controlling them are also found in the control boxes and were purchased from Heathcote Electronics. Finally the Cobalt-S lever switches were obtained from Hattons. Figure 9

Having marked out the holes on the replacement plastic fascias, the correct size holes were drilled to allow for the fitting of the servos as shown in Figure 10. These were secured using countersunk screws and nuts. The 3-way switches and push button switches were also fixed in place at the same time. Figure 10

The plastic box bases were drilled out and stuck over the holes where the servo spindles appeared. This step can be seen in Figure 11 and this shows one of the single setups for a terminus signal box. The space on the right is where the Cobalt S-lever switches will go.

A through control box looks like the version in Figure 12. The bells are fixed to the side of the control box and it makes for a neat and compact system. Inserts for the indicators were printed using glossy photo paper as shown in Figure 12. Figure 11 Figure 12 Figure 13

The white plastic servo arms were covered with a black strip of card to represent a pointer. The finished assemblies are shown in Figures 6 and 7. Tuning the indicators turned out to be as straight forward as Figure 12 setting semaphore signal positions.

These boxes come into their own where space is at a premium. They add a touch of realism to the railway and add to its control and interest. Extending the servo cables can be problematic but I used terminal adapters cut into threes and good servo wire, 22awg Futaba quality.

The final view, Figure 14, shows the inside of a control box, with everything installed in position. Figure 14

More details and videos can be found on my website at: www.bpodmore.co.uk Look in the projects section for links, or use the search facility in the menu and look for Block signalling.