Wednesday, 25 January 2017

Light up Lego droids

Having a Lego R2-D2 and not making it light up - after getting Luke and Darth Vader to hold their own light-up lightsabres - seemed like a crime. So I ordered some tiny 0805 LEDs in red and blue. At first it was tempting to just make R2's eye lens light up. But that's not how he works. There's a little light just below the eye lens, that - in the movies - flashes red and blue.

So I figured I'd do that.

(the little black dot immediately under the eye lens was originally a red dot painted onto the head, which I drilled out with a 0.8mm PCB drill bit)

(the back of the head showing where the tiny hole was drilled - you can just about see if on the right hand side of the inside of the head)

But soldering two 0805 LEDs without bridging the terminals proved to be really really tricky. So I got some twin LEDs in a single 0805 package. If truth be told, these are probably more like 0806 or 0807 sized packages - they're ever-so-slightly wider than a regular 0805 component. But not by much. Not much at all!

This turned out to be an exercise in hand-soldering really little components. And not even doing it the easy way, with a pcb and a hotplate and solder paste (where you can just heat the whole lot up and let the surface tension of the solder simply pull everything into place).

This was spot-soldering onto pads half the usual width of an 0805 LED. In short, it was tricky. But, after a few goes (and uncrossing my eyes a couple of times) I managed to do it!

the whole assembly is really tiny - smaller than it appears in the photo because I had to place the LED closer to the camera lens than my fingers, in order to get it to focus

So with a single LED with three trailing wires, I can make either the red or the blue side light up (or both for a reddy-purpley colour). Which means that next time I'll be looking to put the smallest PIC I have available into R2D2's tummy to toggle between the two colours.

For now though, I need to do something that doesn't involve keeping my nose just an inch or so away from the end of my soldering iron!

(the components will be held in place with translucent hot glue, acting as a light tunnel, so both the red and blue sides of the LED will be allowed to shine out through the drilled hole)

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