It must be 15 years since I started adding detection sensors to the railway, and little has changed. Commercially available detectors fall into two camps:
- Electrical block detectors: these give a yes/no indication about whether a train is present in a block, but no information about where the train is in the block. This is a good technology to indicate that a block is occupied, and therefore another train should not enter it. By default, locomotives are detected because the prove=ide a current load to the track. Resistor wheelsets are needed for other rolling stock (wagons, carriages...) to they can also be detected.Â
- Infra-Red detectors: these are OK to provide an indication that "there is something a this position" but they do not signal that a track section is occupied. Plastic bodies of modern modes are not very IR reflective, but sticky tape can resolve that. They are prone to being operated by human hands passing over them, and by background lighting.
Block detectors are great for indicating occupancy. Identifying train position within a block remains an unsolved problem. There are at least a few ideas around for alternative solutions, and Hans Tanner in his excellent "Internet of Toy Trains" work has identified most of these and investigated some.
- Hans Tanner has investigated Lidar sensors. These indicate the distance of an object from the sensor, using a fairly narrow optical beam. They give an analogue readout of distance, which would need an extension to LocoNet messaging or a different message transport (eg MQTT). In principle this technology could be really good for stopping a train at a particular spot on a platform, for example: short trains could be stopped further up the track so the passengers can be near the entry and exit. A potential issue is that they probably lack the ability to discriminate between two adjacent tracks at longer distances. This is OK if the relevant track can be deduced from context. Traincontroller could make that distinction, because it knows which block to expect moving trains in, but it would need new code to do that and it is closed source. Possibly qualifying the sensor report with the "most recently occupied" status of the two tracks from block detectors could help.
- "Train side" sensors could work well, but that would need new electronics an new communication from the rail mounted vehicles. Viable for larger scales but probably not for N/TT/Z scales.
- Camera based detection has been proposed (and I think Hans Tanner mentions this in an interview). Prone to interruption by humans leaning over, and by lighting conditions that may change during the day. Given the very low cost of modern cameras and processing, this must be a technology to be considered at some point.Â
- Could acoustic detection and triangulation using several microphones be relevant?
- ... no doubt there are other possible technologies!
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