Hello all, 

Getting close to getting some trains running at my mill. I am using Tortoise switch machines and have a few questions and ideas to bounce across the group before taking the next step. 

I have a DCC layout with a reversing section working fine.
NCE power cab and Digitrax AR1.
If I want to hook my system to a DC power pack will it hurt the AR1 or back feed and hurt the Power cab?
If I have a test track that can be either DC or DCC and that creates a momentary short while connected to the DC power will that harm either the AR1 or the Power Cab / PCP?

If so, is there a tested circuit design to automatically isolate those components when DC power is applyed?

Thank you for any information.

In my blog, on page 19, I describe a lighting project I'm working on.

As can be seen from code and description, 14 LEDs will be used, with two on each of seven pins. Assuming 18-20 mA each with a 470 ohm resistor per pair, this would exceed the 200 mA total for board. As I am anything but an electronic whiz, what would be the minimum resistor I would need to drop total amperage below that total?

I have received the tower lights for both of the yards on my layout. They came with separate resistors that need to be soldered to each light. Does it matter which of the two wires  (assuming one is a positive lead and one a negative) the resistor is soldered to? Once done, I plan on sliding shrink tubing over the resistor to prevent damage.