The following diagram shows the basic laser pointer circuit. It is identical to the infrared circuit except that the infrared LED`s have been replaced by the laser pointer unit.
Due to the long range of these devices this detector method can easily span great distances and could be used to detect trains in a long section of straight track such as in a lader yard or across the throat of a very wide yard.
Laser pointers are not designed for this type of application and careful selection of R1 is required. testing should be carried out to determine the best resistance value for a particular pointer.
It is best to start with a high resistance for R1, 50