Resistor for wheel sets
Wattage doesn't matter, since 10k Ohms at 16 volts is trivial current:
16/10000 = 0.0016 A, or 1.6 mA
Wattage = I-square R: or 0.0016 x 0.0016 / 10000 = 0.0256 or 1/40 Watt
or E-square R: 16 x 16 / 10000 = 0.0256 W
I would be concerned more about adding the friction to all the cars.
What about the several light detection integration circuit methods: There is at least one I.C. that incorporates a tiny photocell and transister circuitry and can detect when light is blocked out. Not useful for night running maybe, unless you can install invisible infrared LED arrays overhead and use infrared-detecting versions of the I.C.s.
You can use Mega-Arduino boards to detect and process many such digital (or even analog) inputs and process those to control switches and lights.
If you want to get clever, you can also program the Arduino board to calculate the speed between two close-by points when light between cars is detected. Have to be careful not to have the logic confused by different length cars, so have to measure time between two points for the same inter-car space.
(I suggest the Mega board, since it has up to I think 55 digital inputs, plus can have up to 4 serial channel ports. I think (have to check) the mega board can have many of its inputs "programmed" to act as either an input or an output.
You can daisy-chain Arduino boards to handle multiple sensors. Or you can just use one Arduino board per section. I have a fairly complex switch yard with a ladder track switching to 5 parallel classification tracks (also connected at the other end through turnouts), 3 through tracks (one double through track on the south side and a single through track on the north side. Lots of turnouts, which I hope to add insulators judiciously so that each turnout can enable or disable a short section of track on its two "outputs" (if one thinks of the outputs as the end that attaches to two tracks). In other words, when an engine approaches a turnout turned the wrong way, it will run into a short dead section of track and hopefully stop. (That won't stop an engine from backing cars into a turnout that is turned the wrong way. That part just requires some smart operations, but having red-green LEDs beside each output leg of a turnout would go a long way to helping manual operations. Don't think you even need an Arduino board for that if the "dead track section" method is used, but having the LEDs lit beside each turnout would not look realistic. But wouldn't it be cool. Of course, an Arduino board could be used to light red/green LEDs on an operations board, by sensing which way each turnout is set. That should not be hard if the Arduino board is used to control the turnouts.
Also, if you use an Arduino board to control the turnouts, you don't have to purchase expensive tortoises. You can get 5 volt rotary "servo motors" from eBay for $2 each if you purchase in bulk. Those have a 180 degree arc of movement, that can be controlled precisely in small angular increments by the programming in the Arduino board. These servo motors have short plastic arms with holes in them that I simply attach mildly stiff and slightly springy sections of "memory wire" from Walmart's crafts section (used for making jewelry I think). Thin but strong enough to operation N-scale and HO gauge Peco turnouts. I attach the sections of wire by bending through the holes in the plastic armatures with fine needle nose pliers. Once the appropriate thin hole is drilled and cut through the layout's board, and shaped so that the wire can work back and forth, and the solenoid/servo attached (Flex Glue?) to the bottom of the layout board, as the wire is inserted through the hole in the Peco turnout, the wire can be cut to shorten the length as needed. With layout using plywood, this is easy, but with thick foam board one might want to dig a hole into the foam so that the servo motor is closer to the bottom of the turnout so that the length of the memory wire is not so long. (Longer the length, the less strength to move stiff turnouts -- Archimedes lever principle)
Google "Arduino Servo Motors" to see pics and videos.
I think the Arduino mega boards are somewhere around $18 ea. (Google "Arduino Mega". You'll see pics and links to pinout diagrams.)
-- Henry Stinson
