Automatic Switch Project 2


Posted on Feb 7, 2014

The eyes of the switch control system allow the microcontroller`s `brain` to know where the trains are located on the layout. This insures that only one train is on the main line at a time and that the switches are set so that the train returns to the proper siding. There are many ways to sense whether or not a train is at a particular spot on a


Automatic Switch Project 2
Click here to download the full size of the above Circuit.

layout. In 2005 I wrote a three part series for LSOL ( Garden Railway Sensors, Part I, Part II and Part III ) that explored a number of ways of sensing a train`s location. I finished up that series with a detailed description of what I feel is the best choice for most of our outdoor train sensing needs. This is device is called a pulsed infrared sensor. I will briefly revisit it here and ask that you refer to the earlier articles for more detailed information. Pulsed infrared sensors are made up of several components. The most visible parts go on either side of a piece of track, the infrared emitter on one side and the infrared detector on the other. When a train passes between them the beam of IR light is broken in much the same way that some automatic doors sense a customer`s presence. What really sets this sensor apart is that the devices operate with infrared light that is pulsed on and off at 38 kHz. This means that the infrared emitter sends out bursts of IR 38, 000 times each second and the detector only reacts if it detects IR pulsing at that frequency. This is important because there are many sources of infrared light in and around our garden railroads. These sources include fluorescent and other lighting devices but most of the extraneous IR comes from the sun. Pulsed IR sensors are not completely immune from the effects of direct sunlight but they perform better than most other technologies. By the way, you use...




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