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:

Review of the last 4 years

I was on Google Photos the other day and it highlighted photos from the same dates in previous years and made me realise that I’d been working on the railway now for just over 4 years – the earliest photos I have being from the 2015 Christmas holiday period.  This made me realised just how far it’s come in that time, so I thought it would be a good time to look back, but also high-light some of the more recent work which was not made it to the blog.

2015

2015 saw trains being unpacked and the start of the frame to support the layout.  With very few changes, the frame has been in place ever since. 

2016

The work from over Christmas 2015 continued into the new year to add the surfaces to the layout.  This then allowed the track laying to start, and also the start of some of the scenic work with the engine shed under construction.

2017

Another year and more progress was made on the railway.  This included new additions to enable a future station, the first trains actually being run on the layout which eventually resulted in both loops being usable.  The year also included starting to investigate DCC control and starting to build a viaduct.

2018

This was a very quite year for the layout due to the majority of the year being focused on building a 1:1 scale extension to the house, so very little happened in the loft besides a small amount of cabling work.  This didn’t stop a few new additions to layout

2019

The start of the year continued the quiet spell for the railway as the number of follow up jobs for the extension occupied most of the first half of the year, however the second half of the year has been much more productive with significant progress being made.

This year has seen a number of new additions join the layout including the Dapol Class 68, a Bachmann Class 66, a Hornby Flying Scotsman and the Hattons Railhead Treatment Train.  Interesting to see how the purchases have been split across the different manufacturers rather than just being from a single one.

2019 has also seen significant progress on the wiring front.  Previously only the two main loops were functional, however now there is a control panel and the goods yard is functional allowing trains to traverse the different sidings and on and off the main line.  There’s a blog post here about how the power side of the layout works, and hopefully at some point in the future (no promises on when) there will be one on the point control.

Also moving forward has been the scenic work, mostly in sitting in front of the TV in an evening, however it does allow progress without being in the loft.  This year has seen a large section of retaining wall well on it’s way, the viaduct has gone from a wooden frame to starting to look like a proper railway structure and work as started on something which should become the large station.

2020

Writing the post has made me appreciate how far things have come over the last 4 years, from a concept to a layout which is starting to really take shape one.

Looking ahead to 2020 briefly, I’ll start by making no promises about what and when things will get done as the railway is always one of the lower priority activities, however there are a clear set of next things to do…..

  • Fit the remaining point motors to the points that are currently laid
  • Install the power supplies and relay boards to control the points at the far end of the layout
  • Commission the second half of the control panel
  • Finish the viaduct
  • Landscape around the viaduct area
  • Build the large station platforms
  • Start landscaping the large station and surrounding areas

My aim (as always) is to try and create more blog posts as I go along to show the progress, however please bear with me as time is limited and often blogging time can eat into actually working on the railway.  However this gives me something to look back on next year and see how I did!