Automatic reversing

[Texas Zepher]

QUOTE: Originally posted by woodview3
What's a T-detector?

It is a standard MR circuit that is put in series with the track to detect when a train is on that section. Basically two diodes and a transistor. It can be improved with bias resistors and a second transistor. A Single-T can only detect trains in one direction. A Twin-T is two hooked together (sharing the diode set) so it can detect trains in either direction. To be detected the train must be conducting electricity, so without modification only locomotives and lited passenger cars/cabooses are detected.

Here is Bruce Chub's: 

 

[woodview3]

What's a T-detector?

[Texas Zepher]

QUOTE: Originally posted by [e-mail]
from point A to point B, go back to point A. Thank You.

Single track:
1. Break the track into three blocks. One big block in the center, and two tiny (one locomotive long) blocks on either end.
2. A DPDT relay with the contacts used for a direction switch in the track power.
3. Put a single-T detector in the end blocks.
4. The T on the block at the end of the "normal direction" is connected to a SPST relay. The relay both trips the direction relay in (#2 above), and holds itself on.
5. The T on the block at the "reverse direction" end is connected to a SPST relay that when tripped disconnects the power to the other T relay (#4 above).

Double track:
Only requires one Twin-T and one relay.
Two tracks like a passing siding. The turnouts sprung to always switch the train to the opposite track. Once again there are three blocks. The end blocks are past the points of the turnouts.
Basically on the end of the "normal direction" track is a block where a twin-T detector is. This trips a DPDT relay and reverses the locomotive. The locomotive switches to the other track. On this track the train is still detected by the Twin-T and holds the relay on. At the far end the locomotive enters a block that is not detected by the twin-T so the relay untrips and reverses direction. It crosses over to the undetected "normal direction" track.

Double track two trains:
Respond if interested, I developed this circuit for a "light rail" demo for our local city government. It is much more complicated that those above.

One can get electronic relays now instead of the mechanical ones....

[MisterBeasley]

Does the train stop and reverse, or are there loops at each end?

[Anonymous]

[:
)] from point A to point B, go back to point A. Thank You.
[e-mail]