In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Sparks-R-Fun wrote:

[QUOTE="Roy Carlson"] Sparks, 
 
I like your idea but I am clueless as to how to go about doing this on a breadboard.  I could probably figure out how to set up the 555 chip but would I need a 555 clock for each of the 8 Infred LED emmitters or do I drive them all with the same 555 hz signal?
 
If this can be done, then how do I wire up the 8 detectors such that when the infared beam is broken/blocked, I can light a remote LED to indicate the blocked section of track? [/QUOTE]
My thought was to detect the presence of trains using modulated IR light in a manner similar to what is commonly used as a means of obstacle sensing for mobile robots.  Whether or not you can drive all of the emitters from an unbuffered 555 or SX is dependant upon how much current you need to send through them.  It may not need to be much since you will not need the IR beam to shine very far.  Driving all of them with a transistor from the same signal source is certainly doable.

I envision the detection being done by a modulated IR sensor.  It outputs a digital high or low signal depending on whether or not it is detecting an IR modulated signal source.  You could either place an emitter on one side of the track and a detector on the other side of the track to detect a train blocking the beam path or else place them on the same side of the track to detect the beam being reflected by the presence of a train.  You should be able to dim the emitters by reducing the current flowing through them to achieve the sensitivity required without falsely triggering other detectors nearby.  Some light shielding might help to narrow the emitted beans the detector's view as well.

It is just an idea but I know that this detection scheme is used quite often on mobile robots for object detection.

- Sparks

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