This weekend’s project turned out to be more of a doozy than expected.
Step 1: Clean the wheels. Spread regular metal polish thinly on the rails, ran a loco in place at full speed for a minute or so before thoroughly cleaning the wheels and track off, spreading a thin layer of no-ox-id on the track, running them in circles for a bit, and cleaning everything thoroughly.
Step 2: Program the decoders for lighting effects.
What I wanted was something more prototypical than the vanilla “Headlights on with F0, front on going forwards, back on reversed” approach. I decided that I wanted front lights to come on with F0, dim with F4, and rear lights (when applicable) to come on with F1. They would stay on regardless of direction, because what engineer says “Back half a car, better turn this light off and -get up- this one on”. Really! Fortunately for me, I really only have 2 kinds of decoders. Digitrax 163 series (FX3), and TCS. This meant that I only had to spend hours wading through manuals instead of days…until the addendum at the end for NCE.
Starting with Digitrax, I decided on F4 for dimming because you can’t remap that.
The digitrax decoder manual is horribly outdated. Don’t even look at it! It talks about CV61, which hasn’t been relevant since the FX3 163s came out a decade ago. Somehow, digitrax hasn’t updated it to include what you need for 163 and 165 decoders!
Now, it took me a while to figure this out….the first thing to tackle is function mapping. CV33, 34, and 35 control the applicable functions. CV33 is F0 on your cab (controller) in the forward direction, CV34 is F0 in reverse, and CV35 is F1 in reverse. Function 1 on the decoder is the white wire to the front headlight and function 2 is the yellow wire to the rear headlight. (I will not be abbreviating these to F1 or F2.) These functions are the same whether there are visible wires or the LED is mounted on the locomotive’s circuit board or decoder. Thanks, NMRA!
In order to control these function wires seperately, you must change CV33-35. By default, CV33=1 (white wire/front headlight on in forward only) CV34=2 (yellow wire/rear headlight on in reverse only) and CV35=4. (green wire in either direction, not applicable in this circumstance.) We want function 1, the front headlight, to come on regardless of direction, so we keep CV33 at 1 and also set CV34 to 1. This means F0 does the same regardless of direction. The rear headlight (yellow/function 2) is function key-less, so we map it to F1 by setting CV35 to 2. If you have more lights, you can map F3 on your cab to be the rear light by changing CV37 to 2 instead of CV35
You can do more calculations including more CVs/functions using this digitrax link
Stopping it auto-dimming on reverse was, as it turned out, impossible. Therefore, if you want a headlight that dims on command with F4 but also dims on reverse, program CV49 to 104. I ended up setting it to 0, since I’d rather have constant headlights all the time than dimmable ones that mess up when you reverse. This means all my future decoders will probably be TCS…
Moving on to TCS (Train Control Systems): TCS decoders generally have more lighting options. They have become my favorite decoders, being only slightly more expensive with more functionality.
In TCS decoders, the front and rear headlights are controlled by 49 and 50. To set the front headlight to manual, set CV49 to 32, and CV50 to 32 for manual reverse. To have the front headlight dim on command from F4, set CV49 to 40. Next, I remapped the reverse light from F0 to F1 by setting CV34 (reverse light function wire) to 4. Easy peasy! I didn’t bother with any rear dimming.
The only complication I had (besides the units with TCS CN decoders refusing to dim) was my RS-10 – It’s set up for long hood forward operation. This means that front is rear and rear is front…the decoder is programmed for the correct direction of travel, but that doesn’t change what is physically wired to what. Since it’s TCS, not a problem. Set CV33 (what would be the front light) to 4, and CV34 (rear light come front) to 1. Next up, this means that F4 dims the rear headlight, so switch the CVs for 49 and 50. (CV49=32, CV50=40). Voila!
I hope this answered a few questions for you. I do have more DCC projects coming up, so keep tuned!
Update: NCE (North Coast Engineering):
It took me a while to figure out NCE decoders. I didn’t have any when I originally wrote this article but recently installed an N12A0 into my Atlas SD7 – A Great Northern unit that runs long hood forward.
Important: NCE does not use CVs 49 and 50 to control anything. They configure functions with CVs 120 to 128 instead.
As with other decoders, CV 33, 34, and 35 map functions (lights) to the function buttons. CV33 is F0 forward, CV34 is F0 reverse, and CV35 is F1 in either direction. By default, as with Digitrax and TCS, these are CV33=1, CV34=2, and CV35=4. To control the front light with F0 in both forward and reverse, set CV33 and CV34 to 1. To control the rear light with F1, set 35 to 2.
What’s that? You came here for directional lighting? Good, me too. This is where I had the CV49/50 problem. CV 120 and 121 act the same way as 49 and 50 on Digitrax decoders. To stop lights from being directional, just set 120 and 121 to 32. If you try to set one to 40, though, it just dims on reverse instead of with a button. Dimming isn’t something I plan to figure out in the near future though.
Special case: As I mentioned, this was a long hood forward locomotive I was programming. This means I had to do a number of things. After setting CV29 to 39 while consulting this calculator (and being very sure to tick the long address box, otherwise the locomotive wouldn’t respond) I tackled the problem of the light outputs not being reversed with the direction. It was easy, though, just had to remap the functions. CV33 and 34 control the short hood, which on a LHF locomotive is the rear end, so I had to set them to be controlled by function 1, setting CV33 and 34 to 2. The long hood light, now the forward, is controlled with F0 by setting CV35 to 1.
Next up may be MRC, as I have that one locomotive….time will tell.