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Having Fun with SMD LEDs

One of my favorite aspects of model railroading is lighting. Done discretely, lighting details add an amazing amount of depth to a scene, casting shadows and drawing attention to details that might otherwise be overlooked. I must admit, am no master or lighting or modeling, but I have devoted a year or two adding lights to the PSMRRC club layout and am very happy with the results. Vehicles are an obvious place to add lighting, and usually fairly simple to do – many headlights accept 0804 and 0603 size LEDs without much modification.

When I do vehicles, I prefer to install two phosphor bronze (or copper) wipers to the bottom of the model. I install two similar pads at the location where I want to put the car, and wire them to the layout’s 12v lighting bus.

That way the car can be removed without having to unplug any wires, and repositioned to other places on the layout that have the wipers installed. It also helps protect the hours of work you put into lighting the vehicle from the inevitable grab of a momentarily unsupervised toddler, who really wanted to touch that firetruck with blinking lights. No more torn magnet wires, no more fists of rage and tears of pity.

I use 38 AWG magnet wire scrounged from the armature of an old motor to connect the anode and cathode of the LED to a power source, with a resistor in series. Depending on the color of the LED, and the desired brightness, I’ll choose anywhere between a 700 Ohm and a 2.2K Ohm SMD resistor. The small size of the SMD package allows me to hide it more easily in the car body. I have had good success drilling out the chrome areas of headlights, gluing the wired LED into the hole, and then potting it in place with clear 5 minute epoxy. When it sets, it makes the headlights look like the real thing, and provides a nice strain relief to the wires coming off the diode. The epoxy also diffuses the light. I paint the back of the epoxy blob with silver paint, to simulate a reflector. In situations where I need to avoid all light leakage (where the back of the lamp is in plain sight) I will follow up with a coat of flat black paint.

Sometimes I will even tint the epoxy with a tiny drop of floquil paint to give me the right hue – go outside at night and notice the differences in the warmth of the lights you see. You will see cool blues, neutral whites, yellows, and even orange. In the pictures above, you will see four-five different colored light sources that add to the depth of the scene. If I’m not potting the LED in epoxy, I just paint the diode itself. Doing multiple layers of paint intensifies the saturation of the hue, but also reduces the brightness of the LED. 

Above, you can see one of my first scratch built additions to the club layout. The simple construction light/generator rig was made out of a solid chunk of wood, wire and an axle from a cheap truck that had seen better days. The main feature is the light mast – made up of 4 0603 LEDs soldered directly to 1K SMD resistors. These are then soldered to the copper pole which acts as my cathode. You can see the thin magnet wire looping around the LED array serving as the anode. I really enjoy using parts of the structure as a means of getting power to the LED – this allows me to use less magnet wire (flimsy stuff) and makes it easier to uphold the illusion that this is just a scaled down prototype, without any wires dangling about. I use this technique with most of the street lamps and utility lights.

While industries always have a ton of lights, towns and stations are where lights are often overlooked in many layouts. It’s very easy to figure out where your town might need some LEDs – walk around your local town at night (don’t do it if you are in a bad area) and notice what areas are lit up (and the style of light used). Even little things like phone booths are illuminated.

I hope some of these pictures gave you ideas on how to light up your layout – I’d be glad to hear of techniques others have used, as I am by no means an expert (and if I was, I’d still love to learn new things). My current lighting project is really testing my mettle with a soldering iron, but the final product is a working traffic light that can be hooked up to a microcontroller and programmed to whatever sequence or input I desire.

The LEDs are connected to a 12v lighting bus that runs around the layout. Every town or large industry has a lighting board with two bus bars (positive and negative) mounted underneath it. Using the bus bars I am able to tap into the two lighting bus wires and run multiple 12v connections to the scene above. The lighting bus is powered by two 12v 20 amp power supplies from ebay and is protected by circuit breakers in the event of a short (which happens more often then I would like to admit, especially when installing new lights).

As for powering the LEDs them selves – It depends on the installation. If I don’t have much room, I’ll solder the magnet wires directly to the LED, and then run them inside a building or car where I mount the resister. If I have room, I’ll solder the LED directly to the resistor and then attach my wires to that. Often times I’ll forgo the second wire and just use the structure (if it is conductive) to provide the pathway for the electricity to travel. This lamp post is an example of this. Inside the epoxy blob I have an LED soldered to a resistor, which is soldered to the brass lamp pole. The other side of the LED is connected to some magnet wire that runs inside the pole tube.

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