Ye Olde Analogue Control System

[Trofimow]

This post is in response to a request from Kev (SHMD) on my intro in the new members forum for a description of my erstwhile analogue control system. There's nothing particularly special or anything that has not been done before, just the way I did it.

 

My layout is something of an iceberg, in that a very large proportion of it is - well not actually underwater, but certainly below the surface.

 

There are four main sets of storage loops on a lower deck and a few dead end sidings behind the backscene.

 

First designs for the layout were produced in the early 90's (gosh was it really that long ago) and the question was how to control these hidden storage areas.

 

DCC was considered, but ruled out at the time both on grounds of cost and practicality – one would need to know which loco was in each hidden storage location at all times to prevent disasters. So analogue control it had to be.

 

Each set of storage consists of an entry road, a set of parallel loops, a 180 degree return curve, a second set of parallel loops and an exit road. Replicate four times and that adds up to a lot of points and sections to control.

 

I did not want a complex array of switches to operate, so I put the complexity into the system instead and produced a very simple control panel with just two push buttons per loop, one to enter and one to exit.

 

Different controllers were used for incoming and outgoing trains. Only one button push would set the entire route within the hidden storage and power the required track sections from the appropriate controller. This was achieved using diode matrices to control the points, powered by gaugemaster CDU's with additional capacitors added to boost the output to be able to switch up to a dozen points at once.

 

A pair of changeover relays for each track section automatically selected the correct controller according to whether the train was entering or leaving storage. These also used diode switching.

 

Tri colour LED's were used to display the status of each track section, to monitor the progress of trains and to indicate to the operator when to stop the train at the correct position in the loop.

 

Four indications were thus possible for each section.

 

No light – section free

Red – section occupied

Green – section is in selected route and powered from the entry controller but not occupied

Yellow – section is in selected route and powered from the exit controller but not occupied

 

Train detection was by home made track circuit modules based on a circuit in Roger Amos' book on electronics for model railways. The output from the track circuit was fed to a TTL circuit and combined there with signals from the track section relay pairs to drive the LED indications.

 

This all worked satisfactorily for a number of years until I moved to the dark side and replaced it all with DCC, computer control and VDU control panels, but that's another story.

 

 

Alan