3 reversing loops.
When the train comes into a reversing loop, the wheels will short the track out.
To stop this, isolate a portion of the track as illustrated.
Connect this circuit to the track.
This circuit can handle 3 reversing loops.
Just duplicate the relay and detection circuitry shown using the following for the different reversing tracks
| track | PIC12C509 | ULN2003 |
| 1 | 2 | 14 |
| 2 | 3 | 13 |
| 3 | 4 | 12 |
With this circuit in place, when a train shorts the tracks coming into or out of the reversing loop, the 3 ohm resistors provide a little current limiting and allow the track voltage inside the loop to drop to zero. This lack of voltage is very quickly detected through the 2 diodes and resistor network.
The PIC Chip then toggles the relay to obtain the correct polarity to remove the short caused by the engine. It does this within 1/20th to 1/50th of a second, depending on what relay you use. The Relay should be a 12VDC, preferably sensitive coil type, but any 12VDC should do the trick!
Josh Bensadon
PS. Copies of the PIC Chip are available, just email me: JoshBensadon@yahoo.com
Josh's files for this can be download here: PCAuto.zip