I tried to reflow the board, with extra flux added, to see if that would help. It didn't, so I decided to try and recover the LEDs from the board... And I learned why they use temperature-controlled hot-plates for this:
Yes, that is melted plastic from one of the LEDs...
I guess that's a failure... Good thing I have excellent ventilation in my kitchen.
So I'm back from the conference, and I finally got to try the solderpaste that arrived before I left. I just quickly went to a local pharmacy to buy the thickest needle they had, I cut that needle with a dremel, and I was ready to go:
First, I applied a small drop of the solderpaste on each of the pads:
Then I carefully placed all the diodes, making sure they are all aligned properly:
Next, I went to the kitchen and switched the stove on:
I waited a bit until the plate got hot, and pushed the board onto it. Then waited until the solderpaste was properly melting, and pushed the board off the plate.
The final effect looks good:
However, it doesn't work. Only one LED ever blinks, and that is only for a short moment.
I think I must have applied too much soldering paste, and there are some internal shorts of the signal pins. Now I'm thinking about some way to recover the LEDs -- I think I will put the board on the hot plate again, and pick the LEDs from it?
The solder paste just arrived! Just as I have to leave to catch the plane to Belgrade. Oh well, next week.
So this is what was born from the #Tiling Pixels experiments. Back then, I assembled a 5×5×5 RGB LED cube by soldering the NeoPixels directly together, and managed to get some very nice lightning effects with that. But the soldering job wasn't very good, the device was brittle, the LEDs would flicker off at a touch, and the walls of the cube became somewhat rounded.
So I decided to do a second approach. This time I'm going to solder the LEDs onto 6 PCBs. I ordered them from DirtyPCBs some time ago, and I was lucky, because the proto-pack contains 12 boards -- enough to make two cubes! Anyways, I only have enough NeoPixels to make one for now, but it's nice to know that I have a spare. The connections on the board follow what I came up back when I worked on #Tiling Pixels:
I already tried to solder one board by hand, and I must say it's hard. There is so little room between the LEDs, and it's so hard to keep them straight... The result is not very pretty:
It would probably look fine if I encased it in a laser-cut box made of matte acrylic, but still, I think I can do better. So I paused with the other boards for now, and ordered a solder paste. I will try to use that together with a hot plate to get better results.
That's it about the outside.
On the inside, I plan to install an ESP8266 module, together with 3D compass and GPS modules. And a small LiPo battery, of course. The hope is that this will let me figure out where in the world the cube is and how it is oriented, and then animate the lights to point to the next way-point. We will see how that works out.