The On-Line Magazine of Rideable Model Railroading
  NUMBER 106


© April 06, 2008   

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Signal Track Circuit For Live Steam


A simple track Circuit for operating signals on your railroad

Written by Robbie Diehl

The main problem with Signals in our hobby is snow and rain on the track. Snow and rain conduct electricity and will show the false presents of a train in a block. I have tested this in both snow and rain and it works well. The circuit works with the track completely submerged in water !!! The type of ballast that you use and moisture content of your soil also effect the operation of the circuit. I have used it with 1/4 minus crushed river rock ballast and volcanic cinders with good results.  This is not a fail safe system. What I mean by this is that it does not protect you from component failure or power loss. Full size railroad signaling that costs thousands of dollars protects against a false clear (Green) indication with many system back up circuits and is fail safe. I will not be responsible for damages caused by this circuit. You use it at your own risk.
With that said all you need is two components for the circuit. Radio Shack Reed Relay Catalog #: 275-233 200 OHM 2 Watt Resistor (I use the NTE Brand Just make sure it is 2 Watt) DO NOT SUBSTITUTE PARTS. PLEASE NOTE THAT THIS IS A 2 WATT RESISTOR You can build these on PC Boards using the Radio Shack PC Board  Kit Catalog #: 276-1576 and make 4 circuits at once. (see diagram on right). The reason you should do this is because a typical siding has at least 4 blocks.
  • 1 Block for the siding
  • 1 Block for the Mainline
  • 1 Block for the East Approach
  • 1 Block for the West Approach

Print the circuit board template out and tape it to the PC Board. Full size when printed should be 3 inches by 3 ˝ inches. Drill the holes then connect the holes like the lines on the template using the ink pen in the Kit. I use a smaller drill bit then the one in the Kit. Use a drill bit that will fit the biggest wire you solder to the PC board snugly. Follow the instructions in the PC board kit to etch the board then solder the components in (right).

click to enlarge

click to enlarge

I use the Oaktree Systems Model RR interface system to control my signals and the Railroad & Company Software Oaktree will be coming out with their own software this year that is less expensive then the Railroad & Company Software. The output of the track circuit board (Yellow and Blue Wires) connects to one of the inputs of the Oaktree I/O 48 board. 
I also use the Maxstream 9excite 900 MHZ radios to send a 232 signal from my computer to the Oaktree 485 converter and then to the I/O 48 board. I buy the 900MHz 4mw Radio Modem Development Kit 38400 Baud from B&B Electronics Part number XC09-038-DK.

click to enlarge

This kit gives you two radios that is enough to signal your first siding. Be sure to pick a radio set that works for your conditions i/e distance from the Base Station to Remote Station. You can connect the output of this circuit to any circuit that you would like to control your signals. The Reed Relay is always closed until a train enters the block then the Reed Relay will open.


Written by Robbie Diehl


Editors Note:  There are dozens (if not more) ways to configure train detection and signaling circuits. We are interested in how it's done at your railroad.  Please send us an article explaining how you do it.  E-mail me today.

Information contained in this article is for reference only. 
We at and our authors are not responsible for any loss that might occur from the practical application of ideas presented here. Regardless of what is contained here, always protect your projects with sound engineering techniques. Use current limiting devices and ground fault protection on all circuits. To not rely on signals to provide proof positive that track is clear of traffic.


Would you like to discuss the ideas in this article? 
Post a comment or question here.

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