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1/87 Scale Traffic Lights

In a previous post, I mentioned using SMD LEDs to make my own traffic lights – I remembered taking step by step photos of the process, but I forgot where I put them and wrote it off as a lost cause. A few days ago I found the files in an unlabeled folder – looks like this post will happen after all!

Like most of my projects, this one started off as a personal challenge – how hard could it be to make working traffic lights that didn’t look stupidly out of proportion in a small town? I started out by cutting some PC board leftovers from hand laying HO scale turnouts – turns out they are the perfect size for traffic lights. A dremel with a diamond cut off wheel made quick work of the job.

I made a few cuts while the traffic light “body” was still attached to the section of PC board – the top section is the common ground for the LEDs, the three isolated sections are for the individual LED (+) terminals. Making these cuts after cutting the body from the board would have been nearly impossible, due to its small size.

After finishing the cuts on the front side of the traffic light, I turned my attention to the back. I decided that one single resistor could be used for all 3 LEDs, as long as I only lit one of them at a time. The LEDs would be wired in parallel with each other, and the single resistor would be put in series next to them. The LEDs would all be white, so I didn’t have to worry about matching the resistor to even out the brightness. 1K would do the job, allowing me to run the lights on either 12v or 5v. 

Tinning the pads and soldering the resistor was made easier using a clamp to hold the traffic light body in place.

The front side was a bit harder to do, as the LEDs are smaller and spaced closer together. 

I make it a habit to test my LEDs before I go on with the project. I haven’t had too many times where this has paid off, but the extra check lets me sleep at night. 

After soldering all three LEDs, I needed to complete the circuitry in the lights. This was fairly easy – I use recycled enamel wire from old motor windings.

I use the enamel wire to connect the common ground strip on the front of the traffic light with one of the pads on the back side, connecting the parallel LED circuit in series with the resistor on the back.

Then I solder individual leads to the LEDs. I make sure to mark them to keep track which wires are connected to what.

With all of the soldering out of the way, it was time to work on the appearance of the unit. I took a shortcut earlier by using only white LEDs, instead of messing around with red, amber and green. Now I needed to paint over the diodes to change the color of the light they emit. The proper colors were easily achieved by using Floquil Caboose Red, Reefer Yellow, and Dark Green. I used a micro brush to carefully apply the paint. It took a few layers to make the resulting light color vibrant. Sure, I lost a bit of the LED brightness, but they were still plenty bright for a traffic light.

While the paint was drying, I started working on the rest of the cosmetics. I cut a rectangle from a sheet of styrene and drilled holes for the LEDs to protrude through. Then I glued it to the traffic light body using medium CA.

After finishing up the front shield (not sure what the proper terminology is here) I made the light shades. I cut some 3/32″ K&S brass tubing into 1/8″ long pieces and then shaped them with a dremel sanding disk and a hand file.

Then, I epoxied the hoods in place over the LEDs, creating a bit of an epoxy lens in the process. This potted the LEDs and secured the hoods. I like to use epoxy to protect small and delicate electronics from any abuse they may see (during installation and throughout their life). The downside of this is that it makes it nearly impossible to fix the unit in the even that an LED burns out – and even if I could, it would probably be faster just to make another traffic light to replace it.

At this point, all I had to do was paint it to look like a traffic light! Some Reefer Yellow and Weathered Black did the job nicely.

That’s it for now folks! Hope you enjoyed the write up. Unfortunately, I left the lights at the PSMRRC club (as I don’t have an HO scale layout at home) so I can’t show any pictures of them installed, or video of them running. Making one traffic light took me about 3 hours, so I could easily make a a street’s worth in a week. It would be fairly easy to animate them using an arduino (there was even a thread on here about that, which I found quite helpful). Overall, it was a fun proof of concept project that has the capability to add some nice animation to town streets. As always, I’ll do my best to answer any questions that pop up.

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