The origins of the Raised Track Signalling System are lost in the mists of time but the people who put the system in, knew exactly what they were doing – ingenious and built to last is the appropriate description!
Unfortunately, the System was showing its age. Nature had taken advantage of the warm, dry cabinets in a way that would delight an Attenborough. Red and Green filters, distorted by the heat from the powerful filament lamps, had begun to melt and the breaks in the track, required to trigger the signals, were interfering with good running. Renewing the track made an upgrade to the signalling system, inevitable.
Cautiously removing the Red and Green plastic filters from the signal and then their reflectors revealed a daunting sight – a rat’s nest of wires. (The Rat had presumably moved out on the grounds that it was too untidy!). It was easy to pick out the two relays wired as a flip-flop but what immediately impressed was the thickness of the incoming wiring. This was Electrical Engineering on a robust scale! It took a while to sort out which wire went where and what it did.
Wildlife Reserve & Rats Nest
Almost by accident, the signal upgrade fell into two phases. In the first phase we replaced the filament lamps with the new generation of ultra-bright LEDs. In the second phase, the triggering system was modernised.
It is only recently that ultra-bright Green LEDs have become available. At this point we worried that even ultra-bright LEDs might not be bright enough in sunlight. In the great tradition of the original engineers, we over-engineered the brightness to the point where there have been comments about the need for sun glasses! Our main headache was that the original filament lamps drew 24 volts from a rough power supply in the bunker – a power supply rough enough to spike at 34 volts at times. To tame this power supply to something more manageable and well-behaved, we had to build a power unit to fit inside the signal cabinet. The LEDs were simply switched by a 24 volt relay connected to the Green Lampholder.
Temporary Circuit Board
Phase two set us worrying about how to trigger the signals. It was clear that the new track would be best unbroken in order to give it maximum strength and integrity. We experimented with a treadle system but unfortunately the front bogie of some of the smaller locomotives, derailed. Salvation came from an unexpected quarter. I was having a roller shutter door fitted to my garage. A light beam is used to stop the door if the threshold is obstructed. It is a robust and reliable system - ideal for detecting trains. The Light Beam System would require power and it was clear that a more robust power supply would be needed than that provided in Phase One.
It was this point that ambition and foolhardiness blossomed. What if we got rid of the relays and the rat’s nest? What if we replaced the relays with an electronic flip-flop?
It took great courage to remove the works from Signal 1. What if we couldn’t sort out the cables? Did we have sufficient understanding of the system? What if….it didn’t work? It was a point of no return.
The Contiboard backing fell to pieces like a degenerate Weetabix. We were left with a heap of relays, wires and lampholders at our feet. We installed the electronics and apprehensively, switched on. It worked! The following week, we installed a new printed circuit board with a few tweaks to make it belt, braces and gaffer-tape reliable. The Light Beam Trigger also worked a treat. If it proves to be as reliable as the original system we will be surprised and delighted.
New printed circuit board
Unfortunately, inside the Signal still looks like a Rat’s nest.
The work was carried out by Dave McKaigue and Peter Watts, with occasional assistance from other members as required.
New Signal Working