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Sunday, 17 May 2015

Fitting custom interior lighting into N-scale coaches

I've been trying to put interior lighting into my N-scale passenger cars for some time now. Of course I could have used kits prepared by the well known companies but I did not like that idea that much due to the reasons described here. That's how my chase after a perfect and universal lighting kit started.

The N-scale is difficult when it comes to putting anything inside the cars. The available space is extremely small, so I had to be very picky about the components I would use. The LED strips are very cheap and around 9mm in width so they seemed like a perfect choice for a start. But I knew of course, that I would need to fit more in there.

My very first attempt was also a very simple one. I used a piece of a LED strip 3 segments long (~15cm and length) and connected a resistor in series. Installation was very easy thanks to the adhesive back of the strip. This is what it looked like:

Just the LED strip and a 4.7kOhm resistor
And it worked of course as can be seen in this video from over a year ago:

But of course the solution was too simple to be good. It had two major flaws:
  • the light in the car was active in one direction of travel only due to the LEDs requiring a correct polarity
  • the light was flickering when the track was not 100% clean
So I've made another attempt and created a circuit that was supposed to work better. Two rectifiers were added (two not one - to minimize internal wiring) along with some capacitors. The components were SMD type and they were sufficiently small. Here is what it looked like:

2x100uF capacitors
Please notice the rectifiers at both ends of the LED strip. They're soldered at 90 degrees so that they fit into the car's shape. This is N-scale after all and any space is hardly available. Attaching them exactly at the required angle was pretty difficult.

The result was better than in the first attempt. The light was active no matter what the polarity was. And that was important to me since I was doing DCC operation at that point already. And the LEDs were blinking much less thanks to the capacitors. If only the soldering was easier...

That was also the moment when I started experimenting more seriously with different versions of electrical circuits. I discovered that my current solution was not an optimal one due to wrong placements of the capacitors. They should have had an additional resistor before the LEDs to increase the discharge time. Just as described here.

That circuit would have been extremely difficult to solder on a LED strip. And that's why I decided to try using a PCB board as a base instead of the strip. I knew nothing about PCBs so I just bought a universal one and started building the electrical circuit. The result probably violated dr. Frankestein's intellectual property rights.

One 100uF capacitor in this circuit gives a better result than two in the previous one
It was extremely difficult to solder. It took me an entire day just to make that one piece. But did it work well? Oh yes, it worked exactly as I wanted my lighting solution to work. Flawless operation in both directions and hardly any noticeable blinking.

But that soldering effort was unacceptable. I had to come up with something better. And at that moment one of my colleagues suggested that I should design my own PCB.

This was again a topic I knew very little about. But it turned out not to be that difficult at all. In less than two evenings I had my design ready and was looking up for ways to build it.

The PCB is designed in a way that allows cutting it to any needed length
To my surprise, PCB making is actually cheap. I've found an engineer who would do it for less than 2 Euro per piece. The boards arrived two weeks later.

They did not look that great but they did not have any real flaws, either. So as soon as I had the time, I've decided to build one lighting solution.

To my surprise (again!) soldering elements to this kind of board was extremely easy. I've built the complete circuit in around one hour. And what's also easy to notice, it looked quite nice even despite my rather poor soldering skills.

A flexible wire is needed for wheel pickups connection. Here I'm using a wire extracted from some old headphones.
And of course it worked great, as expected... I'm going to equip all my coaches with this kind of lighting.


It took me over a year of thinking, gathering knowledge and experimenting before I actually came up with something that I'm happy with. And I can now create a lighting kit in less than one hour with a total cost of around 3 Euro. Pretty good, I think, for somebody who started from scratch.

Here's a video showing comparison of two cars of the same type - one equipped with my initial kit, and one equipped with the latest one. Or in other words: blinking vs no blinking:

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