East of the Blue Ridge

Chronicles of an On30 quarry railroad

Trigger Rails

The track being laid in the Cove area of the layout completes a reverse loop.

The bright green turnout in the plan controls the entrance to the reverse loop.

The normal operation of the layout will not see trains going completely around the loop. The railroad will make a linear progression from Cove, past the Dust Mill, then past Meridian Quarry, and come to an end in the small transfer yard at Winwood. The track that closes the loop by running between the Transfer Warehouse and Winwood Mill will have the place where it passes through the wall hidden as much as possible.

While the loop feature will not be used most of the time, it will be very handy when I just want to watch the trains run. The other end of the mainline will also form a large reverse loop, so trains will be able to run continuously from loop to loop. But running electric trains in and out of reverse loops requires some power and track management. I am trying to automate these management tasks using electronic components from DCC Specialties.

The polarity of the track power in a reverse loop needs to be isolated and reversible in order for a locomotive to be able to pass through the loop without causing a short circuit. I am using a PSX-AR unit to manage the reverse loop track power. It can detect when a locomotive is entering the reverse loop power district, and correct the polarity of the track power so quickly that a locomotive doesn't even hesitate entering or leaving the loop.

The green turnout in the track diagram will determine which way a train will go when it enters the reverse loop. Eventually, the train will approach the green turnout from the other direction, which will require throwing the turnout in order for the train to continue out of the loop. I am using the "trigger rail" feature of DCC Specialties Hare stationary decoders to automatically line up the route for a train approaching the turnout at the entrance to the reverse loop.

Two short isolated sections of rail in the reverse loop have feeder wires soldered to them. The feeders send an occupancy signal back to the Hare when a train runs over the "trigger rail", letting the Hare know that a train is approaching the turnout, and from which direction.

The Hare will then automatically throw the turnout to line up the route for the train to exit the reverse loop.

I routed the feeders for the trigger rails through this "Frankensteinian" knife switch. The switch allows the trigger rails to be disconnected from the Hare decoder, and instead be powered directly by the power buss. This effectively turns off the automatic function of the reverse loop turnout, preventing the possibility of it being thrown inadvertently during "real" operation of the railroad.