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My long-latent interest in trains and model trains has recently been rekindled, so I've been exploring the current state of N scale model trains. I frequently ride Amtrak's Vermonter between Burlington, VT and New York, NY, so I've been considering modeling that route. From New York, NY to New Haven, CT, a train of Amfleet I cars are pulled by Amtrak's newish ACS-64 electric locomotive; at New Haven, an erstwhile P42 "Genesis" diesel-electric locomotive takes over. Thus, I've started by purchasing an N scale P42 from Kato, as well as a Digitrax DCC decoder. Like everything else, model trains are digital these days, so digital controllers trackside and digital decoders inside locomotives are used to control trains. In fact, I've been working on a separate project called CalcDCC to control DCC-enabled model trains with a graphing calculator plus an Arduino. But I digress.

Having purchased my P42 and installed the DCC decoder, I discovered that it had LED headlights in the front and back for going forwards and reverse, respectively. However, the red tail lights at each end were colored plastic and did not light up, and the ditch lights at the front of the train only lit up with the front headlights. I figured it might be a fun way to exercise a few rudimentary EE skills and get a little experience with modeling to upgrade my N scale P42 with a few extra LEDs. Before I could do so, I had to install the DCC decoder in my P42. I was happy to discover that the SDN144K0a has a number of extra pads on the board for soldering wires for extra LEDs. The two photos below show the exterior of the P42 with the decoder board next to it (left) and the inside of the locomotive with the decoder installed, with the train's original non-DCC light board next to it (middle). Just for good measure, I had to take a picture of myself and my little P42 next to a real Amtrak P42 in Phase Vb paint. As always, click to enlarge.

Next, I needed to get myself some SMD LEDs. The white LEDs used in Digitrax's decoder are actually a yellowish-white, to emulate the color of incandescent headlights. Therefore, I purchased the following LEDs on Digikey:
  • (Digikey #732-5659-1-ND) Size 1206 white LED, 3000K color temperature (41 cents each)
  • (Digikey #754-1159-1-ND) Size 1206 red LEDs, slightly dimmer (52 cents each)
  • (Digikey #1497-1149-1-ND) Size 1206 red LEDs, slightly brighter (77 cents each)

While I waited for the LEDs to arrive, I started to modify the brackets (hoods?) that Kato designed to hold light pipes at both ends of the P42. The top half of the locomotive is a shell with holes for light pipes, and two gray pieces of plastic that actually hold the light pipes. The bottom half is machined metal, including LEDs, electronics, motors, gears, and trucks. I popped the two gray plastic pieces out of the shell, and started figuring out how to modify them for additional lighting. The back part was easy: I simply drilled out tiny holes behind the shell's opening for the tail lights. The front part was similarly easy: I drilled out similar holes behind the openings for the front tail lights, and the ditch lights already had holes available.

The light pipes are more complicate. At the front of the train, a single clear plastic pipe splits the light from the front white LED to the main headlights, the number board with the locomotive's road number, and the two ditch lights. I cut two pieces out of this trident-shaped piece of clear plastic to turn it into three separate pieces, sanded the ends for better light transmission with incrementally finer grades of sandpaper, then used superglue to re-glue the ditch light pipes into place (first two photos below). I need to bend 0.75mm fiber optic cable to make another pair of light pipes for the front tail lights, and I have spent a great deal of time trying to make that happen. Future posts will add more details. For the back, I'm planning to use two light pipes to connect a single red LED on the right side of the locomotive to both rear tail lights (third photo below). The piece of fiber optic cabling in the photo is a temporary piece I was using to judge how far apart I need to make the bends in the fiber.

My next task was to find a way to fit three SMD LEDs along with associated current-limiting resistors and wires into the front of the locomotive. I originally planned to 3D print a bracket for this, but I discovered that the space was too small for what I had in mind. Therefore, I brainstormed alternatives, and decided to try to solder the SMD LEDs onto 6 pins of 0.1"-spaced male headers. The photos below show the results of that process. I had to use an Xacto knife and diagonal cutters to remove a small piece of the gray plastic hood on both sides to fit the 0.6"-wide section of header, but using tiny 1/8 Watt resistors and the 1206-size SMD LEDs I purchased, the whole light module fits snugly into place.

The work continues; I'll update this topic as it progresses, and I'll probably post news once the project is complete.
Unfortunately, the male header + SMD LED approach turned out to be a very problematic one. For one, the process of soldering resistors and wires to the back of the shortened header pins after soldering on the SMD LEDs tended to damage the LEDs, via mechanical stress and/or heat damage. To make things even worse, after churning through a number of off-white SMD LEDs, I discovered that the male header didn't even fit between the locomotive's metal base and the front hood's light pipes. Therefore, I struck out on another solution: removing the six metal pins from a 6-pin-wide, 0.1" male header, running 30AWG wire through each of the holes left behind, and soldering the LEDs directly to the wires. Then, I superglued each LED in place against the header, bent the wires at a right angle directly behind the header, and brought them up to the DCC decoder PCB, where I added 1/8-Watt resistors inside heat shrink tubing. To secure the header bar of SMD LEDs in place, I added a piece of black electrical tape stuck to the metal base for insulation, then superglued the header on top. The left photo below shows the header being held in place while the glue dried. The right photo shows more of the six wires extending from the LEDs to the decoder.

Here, I tested the new LEDs. The left and right ditch light pipes are in place, but the center headlight light pipe is misaligned, and the front tail light light pipes are entirely missing. The first photo shows the train in reverse, with the front tail light LED and rear headlight LED both illuminated.

Unfortunately, in trying to adjust the front headlight light pipe, I managed to snap it off. Turns out that cyanoacrylate (superglue) makes plastic brittle rather than flexible. To repair this, I first painstakingly used an Xacto knife to remove the excess superglue around the two cylindrical sections of light pipe leading through the gray plastic hood, then used a sewing needle to poke out the remaining pieces. I may or may not have accidentally stabbed myself through the thumb with the sewing needle the first time. To replace the missing light pipe, I shaped two pieces of 0.75mm optical fiber with the heat from a soldering iron, then superglued them in place. The first screenshot shows the missing light pipe, the second the two small pieces of optical fiber, and the last the new light pipe in place.

Next I needed to complete the rear tail light light pipes. I managed to thread a new piece of optical fiber in an S shape and superglue it into place (to help with twitchy alignment with the holes in the locomotive's shell), add a second piece of optical fiber going straight to the other tail light, and then bond the two together so that they could be positioned in front of an LED. The photos below show two views of this setup.

I tested the SMD LED that I added for the purpose after soldering it to a wire and a resistor and thence to the DCC decoder, found it functional, then tested it with the light pipe. The last screenshot below shows that there's light leakage out of the right rear door, which I subsequently fixed with heat shrink tubing around the LED and black Sharpie on the inner piece of clear plastic leading to that door.

Finally, the interior of the locomotive is complete, with all four new SMD LEDs in place and wired in. At the last minute, I had to remove the 330uF, 25V capacitor that maintains sound functions over small discontinuities in the rail, because there was no longer any space for it. I'll be replacing it with a physically and electrically smaller capacitor.

Next time, look for the final light pipe in the front hood for the front tail lights, and a short video.

Edit: Updates from work done on November 8th, 2015:

My one remaining hurdle with the physical modifications to my P42 was the light pipe pair for the front tail lights. Before I created the rear tail light lights pipes and front headlight light pipes, I had attempted to make the light pipes for the front tail lights, but my lack of experience made that a very unsuccessful endeavor indeed. To make things even trickier, the holes drilled in the gray plastic hood piece did not exactly match the holes in the outer shell, so the light pipe had to be created at just the right angle. With lots of trial and error (and superglue), I finally got the front tail light light pipe working correctly, as shown below. The first two photos show the light pipe in place, and the latter two show the front and rear tail lights. Note the low light leakage (and it's even better in person) as well as the eliminated light leakage at the right rear door.

Finally, two views showing the completed interior wiring and light pipes. New in these photos are some additional black electrical tape to cut down light leakage even futher. I also programmed the DCC decoder to properly blink the ditch lights, but I'll save that for a video.

This project is complete, but I want to finish it off with a few final "action" photos and a video of the locomotive running, playing sounds, and using all of its new lights.

Edit: Updates from work up to December 7th, 2015:

It turned out that I wasn't quite as finished with this project as I thought. Specifically, I had removed the capacitor used to smooth power over rough or tarnished rails, and in testing, that did not yield realistic operation at all. Therefore, I had to put the capacitor back in, but I also had to find a place to fit it. The space between the top of the body and the inside of the shell was very small indeed, so the only place I could find was in front of the decoder, on top of the worm gear that transfers power to the front wheels. In order to fit the capacitor there, I had to make two changes: (1) bend the leads of the front headlight LED to make a space, and (2) mill the plastic over the worm gear away so that the capacitor could sit partially inside the body of the locomotive. I ended up having to cut, bend, and re-solder the LED leads in order to add extra length to them, as shown in the photos below. Once I had milled away the plastic and added a layer of electrical tape around the capacitor to insulate it, the cover fit nicely onto the engine:

With those changes made, the locomotive was truly completed, so I was able to take the photos and video below showing the locomotive in action, including its lights and sounds.

Looks nice! I was looking into doing some model train stuff a while back, but life and money got in the way, so I never did.
Looks nice! Now you have to put that ESP8266 I gave you in there and make it internet controlled, all the cool kids are doing it Razz
pimath: I hope that you get to explore it again some time. I currently don't have the space to build any permanent layout, but I hope that one day I will.

Ivoah: Thanks! But wouldn't it make more sense to make the controller (a la my CalcDCC project) the WiFi-enabled part?

Edit: Just as a note to myself, the following links are relevant:
KermMartian wrote:
Ivoah: Thanks! But wouldn't it make more sense to make the controller (a la my CalcDCC project) the WiFi-enabled part?

Yeah, that'd probably be better.
I edited the second post in this topic with my work from yesterday. I finished off the last of the modifications to the locomotive, including getting the light pipe for the front tail lights fabricated and the decoder programmed to use the ditch lights correctly. I'll have "action" photos and a video soon-ish so I can put a bow on this project.
I once again edited the second post in this topic with the final work on this P42 project, including the video below. I think I can call this project complete; I'll be posting front-page news on it soon.

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