Experimental setup. The IR detector drives an Uhlenbrock 63350 feedback decoder. This is a Loconet device. My DCC controller is an Uhlenbrock Intellibox.

The IR LED and the IS471 chip mounted side by side on a small piece of prototyping board. I had to put a shrink wrap tube around the LED to prevent leakage of the light. Actually, I ultimately had to remove this tube and put a much longer one.

Another view of the detector.

Small test track on cork roadbed on a piece of scrap 1/2" plywood. The idea was to see whether the detector would work
in a realistic track configuration.

The hole I drilled for the detector. It turned out to be a bit larger than needed. What I need is a slot corresponding to the space between two ties.

I used Scotch double sided mounting squares to hold the detector in place.

The installed detector. The shrink wrap tube is barely visible. The missing tie is most certainly visible :-)

It turned out that ordinary freight cars do not reflect enough IR light for the detector to trigger so I had to put a tiny rectangle of shiny sheet aluminum on the bogie pivot to get it to trigger. I will have to do the same with locomotives as well.

Second approach to installing sensor: use separate, adjacent, holes for LED and sensor.