Smallest 4x4x4 LED Cube Yet

0805 White SMD LEDs, 70 of. What could I possibly make with these?

I tried many ways of holding these ridiculous little devices. In the end I discovered a sticky surface is by far the best. Preferably a large sticky surface because they are legendary for pinging out of tweezers and skittering across a desk to become dust-bunny breakfast.

One bounce on this stuff and they stop dead, if they ever launch. So far I've handled 64 of the little bleeders numerous times and not lost one.

Step One, Sticky Tape. More on this later.

This is hard work, one row and I'm already sweating.

The others fall off when you touch the wire anywhere, so they have to be held together on two points while soldering one. Luckily, this is a diode array and is already a grid, I can use that.

Holding four of them proved to be a bit of a problem, so I attempted to rewire the cube with the layers flat instead.

I spent ages lining these up, bit of a waste of time as it turned out.

Step 2, Repetition. Thats the key to working with small devices.

Every one takes concentration, so minimising that is key.

They only have to be laid out roughly, and the tip of the soldering iron rolls the wire into place, lining them all up neatly horizontally. A little prod with the tip of a scalpel and they sit nice against the wire if you tin them first.

128 pads isnt so bad stuck to sticky tape after all, even if they are less than a mm across.

So small they are getting hard to photograph reliably to scale.

I deliberately left the bearers as tails so I could use them to mount the completed layers. They are the column wires, I'll need something to connect to eventually as well.

126 pieces in a 13x10x10mm cube, soldered freehand using a fine-tipped 15w iron. Despite testing each LED, row and grid so far to make sure there were no shorts I had grave doubts it would work 100%.

So far so good, all the LEDs light up when addressed by a layer and a column as they should.

Now to wire it to a processor.. I hadnt thought about this much, (Oh, magnet wire...) until it came to strip and tin 20 bits of it and solder them to the tails. I did one. I did another. I touched the second one putting the third one on and it fell off, so I cussed and gave up. Some things are just too hard.

More than one way of skinning a cat

Putting 16 balls of solder on top of zipwire without burning the insulation was challenging enough without the device tails in the way. I gave up trying to get row three on when I inevitably spilled one next to the one I was trying to bury the bearer in.

Step 3, Conduction soldering.

In the end I cut them off, and replaced them with long thick wires threaded through the board. Soldering them into place at the board also heats the far end, connecting them to the LED at the same time. I tinned the ends first with a small blob of solder, mounted the cube on two corners and threaded them through first to hold it, and the rest were conduction soldered to the LEDs.

Remember not to hold the other end with bare fingers, the heat will travel as a wave up it and reach the far end, burning you on the way. Man I love copper... ;-)

After adding a resistor network underneath for the four Anode connections at the layers, I hooked it up to a MCU and bingo!

The world's smallest deadbugged LED Cube, 13x10x10mm excluding mounts and electronics.

See the logs for details on how to make that even smaller and neater.

* New Feature * Outtakes

Sunday Morning Soldering Like A Bat

Project Logs

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Clumsy Me
Morning.Star • 09/26/2018 at 22:58 • 4 comments

Oops, I broke it in half again.
@salec commented that I was single-tentacly creating a new Moore's Law for LED Cubes.
Hehe, he has a point. Luckily though, with the next generation of 0201s thats as far as it goes. Its highly doubtful discretes will ever get any smaller and still be available to hackers...
First up, I managed to avoid the problems I was having with insulation by changing the wiring sequence. This was only possible by gluing the LEDs, although I think I can make a jig for that too, and go back to metal tape.
These LEDs are the same size as the legs of regular components. Very easy to make a castellated bar to wrap the wires on, all identical.
I ran out of red LEDs to complete a cube with, these really do not like to be messed with and die with little provocation. They are one-shot. So I switched to the blue, and printed out a motivational template.
The electronics measure 4.5mm, but its sat on a 5mm chip of plastic as a bearer.
26 pieces, 5x5.
I'm going to be doing these in my sleep soon.
Still 5mm, still cant believe I managed it..
I scratched my head trying to think of an easy way to cable these, and then remembered a piece of PATA EIDE cable. It has 80 cores in the space of 40, and they are solid copper. Perfect...
Gluing , stacking, stitching the layers together.
Testing... All still 100% perfect, I've been doing this every step to avoid finding a short when its too late.
Typically, the very last solder joint bridged. Maybe I was getting excited. Maybe its just a pain in the ass. I dunno, but this always happens. It wouldnt shift, and eventually the LED fell out. So I pulled the wires out straight, held the LED in tweezers and bravely soldered the anode to the crosswire and pushed it back, then folded the cathode wire back and beaded them.
One is now slightly conky, in the bottom back left corner. I know its there... OK so its 98.4375% perfect, dammit. ;-p
I found some series resistors and fitted a pin header for the Mega.
But unfortunately it wont program and I dont know why... I'll get to the bottom of it.
It still nearly works correctly. There's already a propeller sketch inside the Mega for the previous cube, but the wiring's different.

I got a bit of video, I'll crack it tomorrow.
Kind of working. The software isnt yet, but thats still a record. :-D
NanoBugging
Morning.Star • 09/23/2018 at 07:38 • 0 comments

Well.

The 0402 LEDs duly turned up in time for a weekend of burning the tip of my nose, Welder's Flu and another attempt at the world record for Extreme Cussing. ;-)

First off, I decided to dispense with my usual have-a-go attitude and built a decent workstation. After the 0805 LEDs gave me neck ache hunched over a desk I put a box on my knees and rested a board on it so it was inches from my face. Much more comfortable...

Its tempting to clear a space in front of you at a table with decent daylight for this.

You will be mistaken. ;-) Firstly, you wont be able to see a thing without magnification, and a table magnifier seems like a good idea. That actually makes it harder, because you are working at arms length and while you can see the movements you are making they are hard to control. Fine work like this requires both hands rested on the work-surface, and that so much easier in front of your face.

Light is also an issue. Decent daylight throws shadows, and at this scale things vanish in them way too easily, plus these contacts are 0.25mm wide. Nearly invisible without contrast...

So I modified my jewellers loupe with a set of LEDs that dont throw massive shadows where I can see them. The do throw them, but they are always behind what I'm looking at, out of the way.

The next task, try and line up these fresh little pips.

Oh, thats handy. They are the same width as the wires cut from these 3mm LEDs. Thats a spherical 3x3x3 cube, its the head for my Angry Snowman. More on him later, I was fiddling while waiting for the 0402s.

I can use them to line up the LEDs while I roll the anode wire onto them with the soldering iron. While its hot, the wire slides on the glue, and as soon as it touches the tinned LEDs its on there.

Arrrgh, 4mm wide. This is going to break my own goal of 5x5x5mm...

But I'm not happy with that at all.

They wont keep still no matter what I do. The guides do keep them in place, but there is enough play that they rattle, sit up on their ends and generally take the piss.

Pity, because this works really well for handling the little devils dry.

0805 for scale. I dont have any bananas handy.

Thus inspired, I decided to have at it micro style, and built first a jig to hold them steady, and then a full micro-vise which clamped them all together and held the ends down to stop them rocking.

Awww, commented @Stuart Longland , You've put the little baby LEDs to bed.

Hehehe, yeah I thought so too. I added a guide to hold the wire in the right place, and thought I had this sewn up like a Singer factory.

Muahahahah! Tidy and beautiful, just 4mm across and all works. This is going to be too easy I told myself.

Until I tried to solder them together.

I could not bring myself to photograph the resulting mess. You plain cannot touch those wires with the iron or all the LEDs fall off it. There was no way I could build a grid with these.

Time for a rethink then.

I decided to go back to the original idea of sticking them down in grids and hopping the wires like before. I printed a grid out so I could space them properly, and decided to give myself a bit of wiggle room.

5x5x5mm is plenty small enough for these things, besides, it was going to be 5mm tall anyway because of the wiring. These tolerances are getting a bit much in any case.

I tried a different glue. This is a Hi-Tack double sided tape. Its a layer of rubber, very thin and very sticky. It doesnt melt either, like the others. Must be based on Latex...

I bought better tools too, and modified them to handle components smaller than they were made for. A pair of nylon-tipped tweezers clipped with nail clippers and sanded with a fine emery board to pickup sub-mm devices without too much trouble.

Stll not small enough lol.

Neither was the soldering iron. I tried several different wires on this in an attempt to do two things. One, I dont have a TCO, thats a plain 15W Antex with a needle bit. Way too hot and too big, the tip is...
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MicroBugging
Morning.Star • 09/10/2018 at 09:05 • 0 comments

I'm using a large area of sticky tape, which holds these little devils so well you can also deconstruct and repair structures that would just fall apart. Careful modular construction prevents most of the problems anyway.

I spent quite a lot of time trying out various sticky surfaces. Double-sided tape is great as a working surface. It isnt too sticky, but it melts under the iron and tacks onto the LEDs making them sticky once soldered. The solder also tins it, which may or may not be useful.

I also tried Kapton, which was a dream compared to soldering on double-sided tape because it doesnt melt, and neither does the glue on it. However, the solder has a slight tendency to bead on the glue and leave edges on the wires but it doesnt actually tin it.

Last of all I tried metal tape. This is absolutely perfect, doesnt wrinkle or shrink even under abusive desoldering and the glue repels the solder in beads. I just layout a surface with double-sided tape and put a patch of ali tape inside it, glue upwards.

I took the cube apart so I could make it smaller after it occurred to me that the wire could also be used to line them up laterally.

So I made a guide, which worked really well. I just taped down the far ends and let the tape's glue hold it in place properly. Finally I added a patch of ali tape glue-down to rest my fingertips on while soldering under magnification. It doesnt stick that much, but it is enough to be annoying after a hundred times or more. ;-)

And finally, to form the wires properly I added a tiny jig the sits on the LEDs, lines them up correctly and provides a neat grid to run them over.

Jiggery Pokery

Simply bead and solder the top end, then press it into the grooves and remove the jig to solder the dips to the cathodes leaving clear loops over the anodes, which are all connected to the horizontals.

The above grid measures 9x8mm and is 2mm tall, making the completed device 9x8x8mm.

I am however running out of LEDs, they do not like being repeatedly heated and I have now got some dead ones, and one the contact stripped off. Any more problems from here on in, and I'll have dead pixels in the finished cube. However, I am witing on an order 0f 0402s to replicate this cube using double-sided LED banks so it is visible 360 degrees. Currently it is not visible from the back, as these LEDs are solid based.

The resulting room gained by using a device half the size will be lost by using two of them, and allowing a little more wiggle room for the wiring underneath, so the new version will be bicolour as well as 9x8x8mm.

The current cube is just Plexed, the LEDs go from anode to cathode in a grid. The new one will be Charlie-Plexed, which adds a new dimension to the code too. By switching the LEDs between red and blue using PWM, I can generate purple...