My own interior lighting for coaches - electrical aspect

I remember very well that the moment I bought my first N-scale coach, I immediately thought: I have to have some light inside it. I've been trying to get that since then, applying several different solutions. Surprisingly I got to a satisfactory result just recently.

My first attempt was of course to buy and use a ready-to-install lighting kits from my coaches' manufacturers. I tried that for two coaches and was not really impressed with the outcome:

• the kits did not provide a nice lighting effect - they were just a light bulb with a light diffuser so the brightness was not constant throughout the entire car's length
• the cars from different manufacturers could not be used together, since the colour of the light and its brightness were completely different in each of the kits
• the kits were flickering a lot, unless the track was completely clean
• the price...

And then I started working on my own solution. There were several goals I wanted to achieve. My own lighting kit had to:

• be DC and DCC compatible
• be safe for the cars (no heat)
• be safe for the power supply (low power usage)
• work regardless of the tracks polarity
• be flicker-free
• use as little electrical components as possible (so that it could fit into the N-scale coaches)

The scary thing is that I'm an electronic engineer by profession and it still took me several tries to create a kit I was happy with. The very first attempts were promising as can be seen in this video:

but it was still a long way before I was happy with the outcome. Let's skip however all the failed attempts here and just show the final (for now) electrical circuit:

My lighting solution works on LEDs. This way:

• it produces no heat
• it uses very little power
• I have the freedom to space the LEDs the way I want and have the brightness I need (both in terms of intensity and distribution)
• I have the freedom to choose the colour of the light, since LEDs are available as both "warm" and "cold"

Other than the LEDs, there are just four electrical components:

• Bridge - ensures correct polarity on the LEDs and makes the solution compatible with any DC or DCC layout
• C1 - keeps a little bit of electrical charge to allow flicker-free operation. The bigger the better. I'm getting good results starting at 100uF.
• R1 - lowers the electrical current during start-up when the capacitor is completely discharged. I had no problem running my coaches without R1 but better safe than sorry. Especially considering my growing collection of cars.
• R2 - lowers the current flowing through the LEDs and ensures a proper level of brightness. I'm using 4.7kOhm currently but it's slightly too bright for the N-scale. I might be using a higher rated resistor in the future.

All those components are available in very small packages so it all fits into an N-scale coach. The capacitor was the biggest challenge and the solution was using a tantalum SMD one. But how exactly I fit that into my cars is a topic for another story...