Lego Minifig LED Party Jumpers

These minifigs are ready to rock the party season with their LED colour-changing jumpers!

They glow adorably thanks to an LED embedded in clear hot glue, inside a cut-out body - I've used colour-changing rainbow LEDs and a coin cell battery holder, but any LED would work and they can be powered either from a battery or a microcontroller like a Raspberry Pi or Arduino. The arms and legs are still fully functional so they can also add some glow and character to larger Lego builds.

They make great gifts or seasonal decorations and are really quick to build, I made the five shown in this tutorial in under an hour, so you still have time!

If you can't see the embedded video it's at https://youtu.be/8yRPDt7nv5g - the full how-to video should be published in the next few days. Let's get to the build.

Donor Sweater

First thing we need to do is select a donor sweater. This can be any torso piece from a minifigure.

Next we need to cut out the middle part, leaving the sides and top intact. Remove the arms (these are a bit tight sometimes, don't worry they'll clip back on later). It's easiest to keep the head on at this point.

Now take a junior hacksaw and cut down through the body in line with the sides, cutting about 1mm in from the edge and as far as the underside of the neck. You can clamp the head in a vice if that makes it easier, I found that cutting on a piece of wood with a hole to hold the head-stud steady is just as easy. It should only take a few seconds to cut through so don't get too carried away!

Once your vertical cuts are done, take a pair of small pliers and pry away the centre part of the body. this is a bit fiddly, don't worry if the edges are a bit uneven.

With most of the body removed take a small file (I used a square one but an emery board would work just as well) and neaten up the edges.

Leg Trim

We're going to be fitting an LED inside the body, and the leg connectors are pretty long, so we need to trim those down a bit. I normally chop about 2mm off the connectors, so that the glue still has part of it to stick to. If you use a small enough LED or aren't fussed about it being in the middle of the chest you may not need to do this bit.

LED & Battery

It's easiest to prepare the LED first, so you can be sure it works!

Bend the LED wires 90 degrees at the bulb end so you can insert it vertically - the minifig chest isn't all that deep so putting it in this way makes sure all of it will be within the hot glue sweater.

It's also best to do any soldering at this point, for example if you're connecting the LED to longer wires or a battery holder. Once installed any heat to the LED pins will tend to melt the hot glue, which can spoil the effect. It's worth covering at least one of the LED legs with insulation or heat shrink so there are no exposed wires and you have a nice neat final result.

You could solder the LED directly to a 3v coin cell battery holder as I've done, or to jumper cables if you're planning to connect it to a Raspberry Pi or Arduino.

I've used colour-changing "rainbow" LEDs here, but you could use whatever you like - a flashing red one makes a nice heartbeat effect (for the one you love) or an ultraviolet version is cool if you used a "Spooky Goth" minifig, to show up those tiny black-light posters.

Hot Glue Jumper

I've tried a couple of different ways to make the perfect jumper, starting with a minifig ice/chocolate mould. This went OK but glue seeped out the front, leaving a big belly. It did make a really smooth finish though, so I continued to use it by resting the figure on the flat part of the silicon mould, a flat silicon baking sheet would be even easier. Aluminium foil also works well but can rip when peeling it off so use thick stuff and peel carefully!

Take your legs and hollowed out body and place them face-down on the silicon/foil sheet, making sure they're fitted together snugly. You may need to hold them together or use some blu-tac on the outside while you're filling the glue. Pop the arms back in as well - the glue will stick them in one position but you'll be able to move them again once it's fully dry.

Be prepared for the next part, you'll need to work pretty fast if your workshop is as cold as mine! First squirt in a thin layer of hot glue, making sure you get into all the corners. Before this sets insert your LED and hold it until it sticks in place. Now fill the rest of the sweater with hot glue, so that it covers the LED and is flush with the back. Stand holding it like a lemon until you're sure it's cooled.

Peel, Dress and Party!

When you're certain the glue is dry you can peel those party people off the silicon/foil sheet, and you should have a nice neat LED sweater! Add a head and hat/hair of your choice and wiggle those arms to break the glue seal and let them move again.

If you've used a coin cell battery case, a nice touch is to glue a 1x2 plate on top of it so it acts as a display platform.

You don't have to use a battery though, you could power the LED from a Raspberry Pi or Arduino and have more control of it, making it flash like a heartbeat or coming on as a notification or night light. You could even use a single pixel RGB LED to have full control over the colour displayed.

You can make one of these from scratch in about 15-20 minutes if you have the tools & parts handy - what are you waiting for?

Thanks for reading! My other projects are all at https://www.hackster.io/martin-mander/projects

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