Train detection

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Ted Lewis

New Member
Can someone please advise me on an alternative detection method.
I am using reed switches mounted between the rails to change turnout position and reverse center section polarity on a point-to-point track. Reverse loops at each end.
The reed switches are passing 5vdc.
I must use engines that are equipped with a magnet. Also if the engine stalls near the reed, the Atlas switch machines get a constant current and melt down.
So, another design would work with any piece of equipment passing a certain point. And would result in only a momentary contact. Thanks in advance for any help.

Iron Horseman

Well-Known Member
Can someone please advise me on an alternative detection method.
Lots of options. My first thought would be switching to an optical sensor. When the train blocks the light it triggers the sensor. Then put in a relay such that that once tripped, it turns off the load and also holds itself tripped. This would be so that the turnout motor only gets a single shot of electricity. Finally a timer to release the relay after a while to reset itself once the train is gone.

Another way would be similar to above but instead of the relay also have an electrical switch on the turnout such that if the turnout is already thrown the direction that is desired it does not apply power.

Since you said it is a loop to loop layout, how are you changing polarity of the track? Seems like that same polarity reversal could also change the exiting turnout.

Ted Lewis

New Member
The loops at each end are fed voltage at a fixed polarity, one loop the outside rail is (+), the other loop outside rail is (-). A DPDT latching relay is activated at the same time that turnouts are thrown. Power for the center section is fed into the common terminals of the relay. The feed to the track comes off both the internally fed terminals, one pair of feeders being crossed over. I will look into using a light-based replacement for the reed switches. And surely another latching relay could protect the turnouts from melting down. is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to - An online railroad bookstore featuring a curated selection of new and used railroad books. Railroad pictorials, railroad history, steam locomotives, passenger trains, modern railroading. Hundreds of titles available, most at discount prices! We also have a video and children's book section. - An online model railroad bookstore featuring a curated selection of new and used books. Layout design, track plans, scenery and structure building, wiring, DCC, Tinplate, Toy Trains, Price Guides and more.