How Holgate Solved Train Detection for DCC-EX Automation

One of the biggest challenges when automating a model railway is not moving the trains. It is knowing where they are.

For Holgate, this became one of the key questions behind the layout's automation:

How can we detect where a locomotive is around the layout so that automation can make safe decisions?

That sounds simple, but on a large club exhibition layout the answer is not quite as straightforward as it first appears. The system needed to know when a train had entered or left a section, whether a route was clear, and whether it was safe to perform actions such as changing signals, resetting points or reserving the next block.

Over time, several different detection methods were considered and tested. Each had advantages, but each also came with practical limitations.

Why RailCom Was Not a Practical Option

The first possible solution was RailCom.

RailCom is designed to allow suitably equipped DCC decoders to communicate information back to the command station. In theory, this could allow the system to identify which locomotive is where on the layout.

For Holgate, however, RailCom was a non-starter.

At the time, RailCom was not supported by DCC-EX. More importantly, many club members' locomotives did not have decoders that supported RailCom either. Asking members to upgrade decoders across privately owned locomotives simply was not realistic.

So although RailCom was interesting in theory, it was not suitable for Holgate in practice.

Testing Hall Effect Sensors

The next option tested was Hall Effect sensors.

These small sensors detect the presence of a magnet. They are discreet and could be placed between or near the sleepers, allowing them to blend into the layout without significantly affecting the visual appearance.

In testing, Hall Effect sensors worked very well.

By fitting a small neodymium magnet underneath a locomotive, the sensor could detect when the locomotive passed over it. This gave a reliable trigger that could then be used by the automation system.

Technically, it was a strong solution.

The problem was not the sensor. The problem was the requirement to fit magnets to locomotives.

Holgate is a club layout and many of the locomotives used on it are privately owned. Some owners were understandably reluctant to attach even a small magnet to the underside of an expensive model. Concerns included possible adhesive residue, the risk of marking the model, and potentially affecting resale value.

In short, the sensors worked. The practicalities of modifying privately owned locomotives were much harder to solve.

Testing Infrared Detection

Infrared detection was then considered as an alternative.

The attraction of infrared was that it did not require a magnet to be fitted to the locomotive. In principle, an infrared emitter and receiver could detect a locomotive as it passed over the sensor.

However, testing revealed several limitations.

Standard infrared detector modules are not normally pulsed, which makes them vulnerable to interference from daylight and exhibition hall lighting. We also found that they could be triggered accidentally by operators placing locomotives or rolling stock onto nearby tracks, simply by waving a hand over the detector.

There was also another issue: colour.

Infrared does not always reflect well from black surfaces. As many locomotive undersides are dark or black, reliable detection could require a small white reflective patch to be fitted underneath the locomotive.

That brought back a similar problem to the Hall Effect sensors. Although it avoided magnets, it still meant attaching something to privately owned locomotives.

Infrared also introduced a visual challenge. Installing detectors around the scenic side of the layout risked damaging or compromising the appearance of the finished scenery. For an exhibition layout, that was not an acceptable trade-off.

The Solution: Current Detection

After testing the alternatives, Holgate ultimately settled on current detection.

Rather than trying to identify the locomotive directly, current detection monitors whether a locomotive is drawing power from a particular section of track.

Short isolated sections of track were created at key locations around the layout. When a locomotive entered or exited one of these sections, the small current draw was detected and used to trigger an opto-isolator.

That pulse was enough to tell the command station and EX-RAIL that a locomotive was in that area.

The system did not need to know the exact identity of the locomotive. It simply needed to know that a train had reached a particular detection point.

From there, EX-RAIL could perform the required action.

This might include:

• Changing a signal aspect.
• Resetting a point after a train had passed.
• Reserving the next block.
• Preventing a conflicting movement.
• Triggering a more complex automation sequence.

For Holgate, current detection provided the best practical balance. It required no magnets, no reflective patches, no modification to club members' locomotives, and no visible sensors on the scenic side of the layout.

Knowing Where a Train Is — Or Where It Was

Current detection did not tell the system exactly which locomotive was present.

It also did not continuously track a locomotive around every inch of the layout. What it did provide was something extremely useful: confirmation that a locomotive had entered or left a known section.

In other words, the system knew where a locomotive was, or at least where it had most recently been detected.

That was enough for EX-RAIL to make intelligent decisions.

Because EX-RAIL already knew what sequence should be taking place, it could use the detector inputs to confirm that events were happening in the expected order. This allowed the automation to become much more advanced than simple timed movements.

Routes could be reserved. Points could be set before a train arrived. Signals could respond to occupancy. Trains could be prevented from entering sections that were already in use.

This was a major step forward for Holgate.

Why This Matters for Automation

Train detection is one of the foundations of reliable model railway automation.

Without feedback from the layout, automation is mostly guesswork. A system can issue commands, but it does not know whether the train has actually reached the expected location.

By adding current detection to Holgate, the automation could respond to what was happening on the railway rather than simply following a fixed script.

This helped reduce operator workload and lowered the risk of accidents, especially in areas where route setting required careful planning. It also made it possible to perform more complex track changes automatically, rather than relying on operators to remember every step.

The result was not simply automation for the sake of automation. It was a practical way to make a busy exhibition layout safer, more consistent and easier to operate.

What Holgate Taught Us

The sensor testing on Holgate showed that there is rarely one perfect answer for every layout.

Hall Effect sensors worked well, but required magnets. Infrared sensors avoided magnets, but introduced issues with lighting, colour, accidental triggering and scenic installation. RailCom was not practical because of support and decoder limitations.

Current detection was not chosen because it was the most advanced technology. It was chosen because it was the most practical solution for Holgate.

It worked with the locomotives already being used. It did not require visible sensors on the scenic side of the layout. It provided reliable feedback to DCC-EX and EX-RAIL. Most importantly, it allowed the automation to make better decisions.

In future articles, we will look more closely at how EX-RAIL used this detection information to reserve blocks, control routes and help prevent trains from being routed into occupied sections.