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:
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:
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.
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.
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.