Why IR Optical Sensors / Detectors?

Good question.  This is probably the most untried and untested part of the layout that I'm proposing to build. The conventional wisdom is that block detection (using current) is the preferred method.  Most websites I've gone to prefer it to IR or optical detection.  They may be right.

However, I have a bias toward the IR or Optical Detection.  Let me try and explain so I can better understand it myself. 

With Block Detection, you isolate a section of track and you can then, by using lots of off the shelf detection circuitry, detect things like locomotives, cars with lights, and cars with wheel resistors on them.  The detectors, as I understand them, sense the extra current that flows to power these things, and thus is able to tell when something like that has rolled onto that section of track. 

There are lots of different off the shelf components that do just that.  Both Digitrax and RR-Cirkits makes boards that will sense the current spike that happens.

For optical sensors, or IR detectors, off the shelf components are hard to find.  Most of the stuff I found on the Internet was a "roll your own" type of solution, often involving the soldering of components together to make your own detectors.  And optical sensors have many options - some are simple light sensitive resistors.  Others are IR (infrared).  The regular optical sensors can be fooled by bright sunlight, and don't function in the dark.  IR detectors are a step up from this.  They can operate in the dark, but the complaint online here is that they are often very hard to align. 

In my application, it is very important that I sense exactly when a train reaches a certain point, not just that it has reached a section of track. For instance, in my layout, the commuter train will have a locomotive at one end, and simple rolling stock on the other.  So using block detection, I'd have to make sure that either the last car had a light or similar resistor on it, or I'd have to position the block differently on both ends, and sense when the engine came into the detection block.  (on the West station, the engine will come into the station FIRST, in the East station, the engine will come into the station LAST).  It gets even more complicated with the Acela, because on that train, the "engine" is actually one of the cars, and the "engines" on each end are dummy cars.

IR detection avoids all these issues.  And there is a vendor that makes EXACTLY what I'm looking for.  Boulder Creek Engineering makes a product called the NightScope IR detector that comes as a single unit - both the IR illuminator and the sensor for it.  They are already aligned perfectly for this.  You just drill some holes and mount this under your tracks.  And I'd like to send a shout out to Jim, who quickly answered my questions about how this device would integrate with the Digitrax DS64.  He confirmed that it will work and then sent me a diagram on how to wire it up properly.  While I haven't tested their products yet, I fully intend to, and if they work as advertised, I'll be incorporating them into my layout.

I'm happy to hear from any folks who think I'm crazy for taking this approach.  I'm a noob, so I may be all wet.  Failing feedback, I'll see if I can blaze a trail for IR detection instead of block detection.