Ralph
With 3 rail the insulated rail method is the cheapest and most reliable. I would not use IR detectors for collision avoidance due to poor reliability. However having said that if they were made reliable I think the link circuit could be made to work,even with less relays assuming the detector circuit had sufficient hysteresis and would hold in as the train left. (and not go on and off between cars as it passes the detector)
If it is just a stop circuit and not collision avoidance the consequence of a malfunction is less of a problem.
A reed switch and magnet integrated with a latching circuit either mechanical or electrical might be a better choice. I would have to think about it and sketch it out. That could be installed without tearing up track.
Blocks can be cut with a dremel maybe without picking up track.
There are a lot of ways to do things but since we put up with the 3rd rail we may as well use it as it is a natural block detection advantage over 2 rail.
The basic circuit linked before would cost about $35 to build. Maybe $70 with a time delay and crude soft starting. Cost depends on the amount of realism we want. Real trains do not jack rabbit out in a split second of each other. In conventional this can be overcome with additional circuitry.
Dale H
