possibly a fool question, but here goes:-
when using DC track wiring, one isolated rail at the end of the track, bridged by a diode ensures that the locomotive can't be driven through the back of the engine shed and can only move out in the 'proper' direction.
can a similar arrangement be made if the layout is DCC powered? if so, how?
If I recall what little I know about electronics a diode operates as a 'one way valve' for DC current.
However, as far as I know DCC works by using an AC current with a signal superimposed on the waveform that the controller used to talk to the chip on the loco to tell it what to do with the DC current that it produces from the AC to be fed to the motor. Therefore the diode wired to the track will not have any effect on the AC current the chip is getting so the loco will sail past the back and out through the back of the shed.
One could use a rail break to stop the loco and a switch to move it back out of the shed, but the problem may be that as soon as the current is switched back on the chip in the loco will carry on doing what it was doing before it locate power - so the loco with still end up driving through the shed wall!
That being said there may be a box of electronics that will do the job (I see such units on sale to control balloon loops and suchlike) but I'll leave that to the experts.
With DCC I think the simple answer is no a diode will not be of use and there is no simple way of doing what you want.
Brian Meldon
There is something sort of similar, but it works in a different way and not all decoders support it.
http://www.dccwiki.com/Automatic_Brake_Control (http://www.dccwiki.com/Automatic_Brake_Control)
I left diodes at stub ends sidings when I first used DCC (in On16.5) if I recall correctly the first loco ran at about half speed but I could not stop it nor change direction but another locomotive went slow but could be controlled. I suspect, though did not follow it up, the different chips were programmed differently. I took the diodes out and I would now only use diodes where there is a good reason relying on buffer stops if the loco overruns or I forget to slow it !
Mac
Thanks for all comments- subject closed