My O Gauge Journal on
 Modelling the GWR

A personal Journey

Colour light signalling

Problem: how to control two turnouts with a 3 junction colour light signal.

First I needed to put together a 3 light signal and as Hornby never built one I constructed one out of two signals as shown here:

Next how to switch the signals to create the right combination. For this I think a rotary switch will serve the purpose. Here is a diagram of its makeup:

Click on any image for a larger view.

The rotary switch is a 4 pole 3 position switch. The difficulty now comes in controlling the points. The switch will not be momentary so some circuitry will be necessary. I currently think a delay circuit might fit the bill.

But a far simpler solution is to include push button switches on the points side of the switch as shown here:-

I've added a CDU to fire the points. The arrangement will work as follows:

move the rotary knob to the required setting, (this sets the lights), then press the adjoining push button to set the points correctly. This is what the control panel should look like:-

One thing I learned about rotary switches. The poles are fixed but the positions are set by a washer close to the body. It has a lug that sets how many positions the spindle can turn. I'm not sure what this means but when the right hole is located by the washer it is indeed a 3 position switch. How the other options work I'm not too clear about.

Here is the control box with the switch installed. Waiting for the press switches to arrive.

Here is a video of the work completed so far:


The next step is to develop the circuit to control the two points using the push buttons in conjunction with the rotary switch. My aim is to keep it simple, I know there are several other ways to do this but my choice is always keep it simple! Here is the updated diagram with help and grateful; thanks to the guys at MERG.

Finally the wiring is completed as per the diagram above and here is the video showing the outcome:-


I now have a further project to signal a 4 section siding at the other end of the layout. Click Here to see how that progresses.


Logic principles

2 turnouts offer 2 states each

3 way colour light signals offer 2 states each

Turnouts are arranged in series