Introduction

Adding LEDs can be a great way to make a printed model that little bit more impressive, and it’s not at all difficult to do. In this tutorial I will go over how I have added LEDs to my newest design: ROACH.

ROACH is a 28mm scale truck model intended for tabletop wargames. It comes prepared with slots for LEDs in the front and rear lights, so it’s ready for lighting straight from the printer. The lights are powered by a coin cell battery on the underside of the model.

For one truck you will need the following materials:

Insulated electronics wire.
Four 1.8mm LEDs, white and red.
Resistors to match your LEDs.
One 3V coin cell battery – either a CR2016 or CR2032. These are basically the same; a CR2032 is thicker however, so it will last longer. You can choose what battery holder to install in the model.

Tips:

I'm using a single colour wire here, but it's better if you have two colours, to more easily tell the difference between positive and negative wires.
Instead of red LEDs, you can just paint white LEDs red, which is what I did here.

You will also need a soldering iron. If you are new to soldering, then I can recommend this video which goes over the process:https://www.youtube.com/watch?v=Qps9woUGkvI.

You might also find you will need some way to hold the LEDs and the wires in place while you solder them. You can use a specialised tool called “helping hands”, but clothes pegs, tweezers or some BluTack can do the job just as well. There are also 3D printable designs available.

Step 1

Each LED has a pair of leads leading to it. The longer one is the positive, called the anode (+) and the shorter one negative, called the cathode (-). The first thing we’ll need to do is trim the (+) leads and solder the resistors to them. Resistors protect the LED from burning out.

To find what resistors you will need for your LEDs, you can use a circuit designer like the one here: https://ledcalculator.net/. You should be able to find the specifications for your LEDs where you bought them. Here is the schematic for the circuit I am building: https://ledcalculator.net/#p=3&v=2.1&c=25&n=4&o=w.

Having said that however, my LEDs were quite happy to be powered straight from the battery, without the resistors. But I thought it better to be safe, as once the model is complete there is no way to replace the LEDs, should they burn out. Another way to simplify the construction is to use just a single resistor on the (+) wire coming out of the battery. While that’s not generally recommended, you might get away with it if all the LEDs are the same.

Tips:

LEDs care about polarity so they won't light up when connected the wrong way around.
If your model is printed in a relatively translucent material, it's worth painting the parts of the LEDs that will not be exposed and around the area where they will be mounted with black paint. This should minimise light shining through parts that it shouldn't be shining through. Metallic paints are also good for this as they tend to be very opaque.

Step 2

The next step is to glue the white LEDs into the front grille part.

Tip:

It's a good idea to test your LEDs regularly by pressing their wires to a battery, to make sure everything is working fine. They are fragile and the handling and heat from the soldering can damage them. It’s best to find out sooner rather than later, when the model is all glued together.

Step 3

Solder the (+) leads together with a length of wire then do the same for the (-).

Step 4

We can now move onto the back of the model. The leads on the LEDs are too short for the rear lights so you will need to solder additional lengths of wire to them.

Step 5

Insert the rear lights into their slots and then join the grille, front and back to the cab. The cab has openings prepared for the wires, so push the wires through those and lead them out of the top of the cab.

Step 6

Prepare the battery holder like so. The (+) wire is shown here on the left and the (-) on the right.

Step 7

Insert the battery holder into the cab. Here you can see the battery installed as well, with the (+) side facing down. The (+) wire is helping hold the battery in place.

Tips:

While there is no switch on the model, it's easy to just use a piece of paper wedged under the (+) wire to break the circuit. I myself am using a piece of brim left over from printing one of the trucks.
Careful not to let the (+) and (-) wires touch as this will short the battery. At the very least it will drain it, but in the worst case it could make it explode or catch fire!

Step 8

We can now solder all the (+) wires together and all the (-) wires together.

Then press them into the cab, making sure the (+) and (-) wires don't touch.

Conclusion

And here is ROACH all assembled. Whether day or night, this model will be ready for action!

I hope you enjoyed this article and that it will inspire you to add LEDs to your own creations. If you would like to learn more, I can recommend this website, which contains a lot of different examples of lighting in miniatures: https://chrisbuxeypaints.com/led-miniatures-tutorials/.

Note: the battery holder is inspired by a design by Victor Antonovich (3cky).