Model railway hobbyists who want to trigger train-controlled switching operations depending on the direction of travel often have things easy with systems such as Märklin HO or Miniclub Z gauge, since the corresponding switching track sections can be actuated individually in both directions. Things are different with other systems, such as the Märklin Maxi/1 gauge. Here it’s necessary to use selective switching hardware for this purpose. A popular approach is to use reed switches together with permanent magnets fitted to the bases of the vehicles. Unipolar and bipolar Hall switches can also achieve the same objective. However, a permanent magnet must always be present on the train to act as a trigger element.Although normal light barriers cannot be used for direction-dependent control, with a bit of additional effort and expense they can be built such that trains selectively trigger switching operations in the desired direction. To prevent the gaps between carriages or wagons from generating undesired pulses, an adjustable dead time is added after the sensor.