I don't see a lot of technical messages in any of the forums that I participate in, so I usually don't post. I like to build / make things for my own modules. I don't have a lot of storage or running space so I make a few modules, sell them and make more. Currently I am trying to get my N-Trak centric club to accept T-Trak modellers. It's an uphill battle.
I am going to attempt to post a photo of two devices - the bigger of the two is an IR reflective sensor. I use these a lot in Sumo Robotics, and was using them a bit in N-Gauge modules, but they are big (compare to some N-Gauge Kato track in the photo). In the photo also is an STMicrosystems TOF sensor. The TOF, when triggered measures the amount of time that a signal sent from the emitter takes to return to the sensor. There is a processor on board of this device that turns that into a distance. This device is very fast, you can trigger it often enough to use it as a speed detector. (I am working up the code to do this, so that I can create a model railroad mini-radar gun.) This device is also tiny, small enough to put between the ties of N-Guage track (or hidden looking like a tie). I will be using these as optical sensors for trains passing a position.
If this type of thing interests people here, I can post code and files.