Friday, 6 January 2017

Light up Lego

This Xmas, I was surrounded by friends and family and, inevitably, small children. Which meant Lego. Lots of Lego.

As a child in the late 70s and early 80s, I had barrels and barrels of Lego. But it was all plain blocks. There was the odd wheel. About the most exciting pieces were little windows. There was no such a thing as MiniFigs. And only the rich, posh kids at school had those specialist pieces (my friend up the road had not only the pieces to make an amazing double-decker bus, but the printed instructions too!)

This Christmas, Star Wars Lego seemed to be the toy of 2016 (ok, it's only last year that any toy could be the toy of 2016!) But loads of the kids had loads of Lego. And I was feeling a little bit left out.

So I thought I'd get some Lego.
And make it really cool.
Then give it away.

The first thing that sprung to mind was making a laser-cut Death Star (the genuine Lego version costs about £250 and - as much as I love my nieces and nephews - there's no way I'm paying that much for a toy for any of them). The playset could be made from interlocking pieces of mdf, with lego "plates" embedded in it (so their Star Wars Minifigs could stand up in it).

But after getting my hands on a Minifig Darth Vader (who, with a removable helmet, is already pretty cool) I thought "wouldn't it be cool if his light sabre, you know, lit up?"

Same for Obi Wan and Luke Skywalker.
Wouldn't it be cool if, as you plugged them onto the Lego board, their lightsabres would light up?

In theory, it could be relatively simple (although in practice, a little bit fiddly).
Simply put some contacts in the legs of the minifigs and some pins on the top of the Lego pieces. Connect all the pins on a diagonal to either power and ground.

If we put our minifig on the top-left corner of the board (above) we'd have power going up the left leg and ground on the right. But if it's plugged into the bottom-left corner, then ground would be on the left leg, and power on the right.

Luckily there's enough room (with a bit of hacking) inside the minifig body to put a small sot-23 sized full-wave rectifier

Now, if we connect the contacts in the legs to pins 2 and 3, it shouldn't matter which is power and which is ground - we should always get Vcc on pin 4 and ground on pin 1. Perfect for lighting up LEDs!

So now it's just a matter of choosing the right components.
At this stage, we're still not sure whether we'll be running the whole thing  off a power supply (at 5V) or a lipo battery (at 3.7V) or a couple of AA batteries (making up to 3V). Whichever supply voltage we end up using, we want to provide some inline protection for our (surface mount) LEDs, so we're looking at putting an SMT LED and an SMT resistor inside a Lego lightsabre.

A 1206 is ever-so-slightly too large to fit inside the end of a Lego lightsabre. True, we might be able to make some grooves with a knife or otherwise modify the plastic. But it's just possible....

.... that we can fit both an 0805 LED and an 0805 resistor (220ohm) stacked on top of each other, into the end of a lightsabre handle. And better still....

.... the blade part still fits!
Which means we need to get the magnifying glass out and do some super-fiddly soldering!
We set the two components at 90 degrees to each other. This allows us to solder two ends together easily, while keeping the other ends separate with little risk of accidentally bridging them with solder, when connecting the wires.

A 1mm hole up the length of the handle and a smaller, shallower 1mm hole at ninety degrees about half-way down provided a channel to thread some super-thin magnet wire.

All that was left was to wire the thing up, plug in and see how it looked. Here's the result of putting an 0806 blue LED in the end of a blue lightsabre.

Wow. Running straight off a lipo battery, the result was pretty impressive! So that's one light sabre down, another two to go (a green one for Luke Jedi and, of course, the red one for Darth Vader). Maybe there's even room to try making C3P0's eyes light up.....

I still need to drill Obi Wan's arm (for it is, indeed, his blue light sabre that's been wired up) and fit this into his hand and try to make a complete light-up minifig. But so far, the overall effect is pretty convincing.