DIGITAL COMMAND CONTROL (DCC) AUTO-STOP

ON THE TETON SHORT LINE

Wayne Roderick, 3rd Division, PNR, NMRA (life)

08/26/06 rev 01/15/07

The term auto-stop in our case means to stop the train automatically without operator intervention. I'm sure you can imagine a number of reasons to do this, for example it would be wise to stop the train before it dropped to the floor at a lift-out or open bridge. A pretty simple task, just cut the track power near the unsafe opening with some kind of a switch.

Our challenge was a bit messier-- The staging tracks for TSl traffic are located in another room away from the main activity. When a train is made up by the yard crew it is set out on a "departure track" awaiting the road crew to take it over. Further, the departure track extends blindly out of the view of the yard crew, so we don't know when the train has reached the far end. Well, that shouldn't be hard to fix with an occupancy detector and indicator light(s) or maybe a even video camera.

There is more to it of course (I told you it was messy). While the train is stopped on the departure track, we have to switch control from the yard to the road crew. For DCC, this means a change in cab assignments must be made. OK, no big deal.

With the new cab assignment made, somebody has to restore track power- Whose job is that? Whoever takes this responsibility must insure that the cab reassignment is made else we might jackrabbit start into CTC territory with disastrous results when the power is restored.

Sidebar-- If you are running Rail-Lynx instead of DCC, the loco decoder forgets its speed setting and will not move when power comes back on It just sits there awaiting a new command from its new crew. Handy- all you need to do is cut the power for a few seconds and then let it come back on. There are other gimmicks for DCC that require unique decoders and/or decoder programming but we're not going there.

We decided to automate the whole process and make sure it would work with any decoder. The picture describes the state logic that we implemented. After the blind auto-stop the yard hostler reassigns his cab for his next job. The dispatcher has the ultimate say as to when power is restored and he does it simply by giving a clear or approach light to go after the new crew has assured him that they are on board and ready to go.

Computer software recognizes the signal indication and pulls in the relay to power up the track.

autostop.jpg

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