Wiring and switching a programming track to use a SPROG

[37201xoIM]

Developing my layout, I have a siding in mind that lends itself to being a dual-purpose, integral programming track.  

 

My layout being small, I've decided to keep my basic Roco Multimaus (with 10764 amplifier / booster) just to run the trains (trains only, accessories are analogue).  But for programming, I've treated myself to a SPROG II which I will hook up to my laptop to read and write to locos.   

 

So I'd like to be able to switch the power going to the siding between the track output of the Roco system (to make life simpler the 10764 doesn't even have a separate programming output anyway!) and the SPROG's output (again, helpfully, that only has one output too!).   

 

Ignoring, just for now, the question of whether I need to have an intermediate isolating track (see below - I suspect I may not!), am I right in thinking that I could use a DPDT switch (centre off), with one end activating the output from the Roco unit and the other end activating the SPROG's output?  

 

Apologies that the above is probably a somewhat stupid question, but I haven't got a great head for electrics, to say the least!

 

Separately, the track layout approaching the siding in question is a bit unusual: a train will leave the mainline and travel to the end of a short branch / siding.... then it will, if going to the programming siding, go onto a segment turntable, and then reverse out onto the actual siding which doubles as a programming track.  Because I have this segment turntable separating the programming track from the rest of the layout, I'm thinking that I really don't need an extra isolating section... so what I propose above with a "simple" (ahem!) DPDT switch might be adequate and 'safe'?

 

Any thoughts or advice would be greatly appreciated - as I say, I'm a bit of a numpty in these things in all honesty.  

 

Thanks a lot!

Edited March 6, 2021 by 37201xoIM

[Nigelcliffe]

Up to you on electrical risks of cross-connecting the two systems, which is bad news for one of the systems.   
I don't think your turntable necessarily solves the bridging problem :   which system is the turntable wired into ?   The siding with the "Sprog/Roco" switch, or the "Roco only" layout ?   In either case, there is a turntable orientation where a loco entering the turntable will bridge both systems.    Only if the turntable deck gets its power from the aligned fixed rails (ie. it changes its power source as it rotates) is the isolation complete.  

 

Far simpler is to just have two wires into the layout (a single two-pin socket) and fit each system with a plug for that socket.  Only one system (plug) can connect to the socket, its really safe.   After the socket, fit a isolating switch ( DPDT ), which can isolate the whole layout other than your siding.     Then, you choose which system to use (Roco or Sprog).   And, should you wish to in future, you can use the Sprog as "Sprog Command Station" to setup things with Programming on the Main, by changing the preferences in the Sprog and throwing the switch.  

 

 

[37201xoIM]

Thanks!   Yes, that sounds a potentially straightforward solution.  

 

Of course I've just belatedly realised that my segment turntable itself lends itself to being the isolating section...!   Should have been obvious to me, but there you go.......

 

Cheers