Model railway wiring part 2 – point control

In the previous update I started writing about how the wiring of the layout works and focused mainly on the power to the track and control of the actual trains would be handled.  This is fine for running trains up and down a single line or loop, however the interesting piece comes when trains can change their routes and for that you need to be able to control the points.

At the heart of the functionality is the point motor.  For this I’m using the Gaugemaster PM-1 which handles both the switching, but also has an accessory switch that I’m using to drive the electro frog of the point.  For more information about how to wire this section up then I’d suggest reading the excellent guides from Brian Lambert on this topic.  The piece that is more interesting for me is how to control and trigger the point motor to actually switch, and again the discussion of DC or DCC control comes up again.

At the most basic level the point motor needs around 16V applied to one side of the coil or the other to switch.  In a classic analog layout then this is usually through the form of momentary switches or touching contacts to make it switch.  However in a DCC layout this is an accessory decoder which picks up the commands from the DCC data stream and then triggers the switch.

When I started thinking about the layout I did some looking at DCC accessory decoders and discovered that there are ways of building a simple and cost effective decoder using an Arduino.  This would take the DCC signal, decode it and then provide GPI outputs to control the points.  Since this is low voltage (5V) and not enough to drive the points directly then this will require a relay board to switch the 16V.  So invested in some 16 way boards similar to this one on ebay.

Over time the reality of my DCC knowledge and trying to get a functioning layout working as meant that I’ve limited my ambition, so the point control using the relay boards needed for the long term DCC control, however in the short (and probably medium) team they will be triggered from simple momentary switches on the control panels.

The final addition was a Capacitor Discharge Unit (CDU) to assist with the drive of the motors.  Since most of the points on the layout work as pairs where both need to be set correctly for the route to work then I’ve wired them together so there is no chance of one being set and not the other.  This means that a fair current is needed in that moment to drive them both.  The CDU uses the capacitors to store the charge and as the name suggests discharges is quickly to drive the motors.  The design is the basic CDU with additional capacitor taken from Brian Lambert’s website referenced earlier, fed from an old laptop power supply.

So once this is all put together you end up with something that looks like this:

And finally, some photos of what this actually looks like on the layout itself:

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