And this week in “Jez makes things”…
Rebate guides on planers are awesome. I’m going to rebate everything now, for ever more.
Also, Fusion 360 makes it really easy to turn models into drawings. Admittedly, three of the five components here were just rectangles so the drawings were pretty simple, but it’s all practice, right?
Bonus free internet points to anyone who can spot what I edited out.
I’m taking a break from spinning LED things and doing something else.
My Kiwiburn art project is not:
While lying on damp, cold, and hard ground at Kiwiburn one night, we decided that festivals are more fun when dry, warm, soft, and fluffy. So we made a festival blanket that we named the Flying Carpet – fluff on the top, waterproof underneath, padding in the middle, and LED animations around the edge (Teensy, FastLED, Li-ions, as per usual).
Heteronormatively, Wendy did the fabric; I did the electronics. Here’s her tutorial on how to make one yourself.
In short: the Mitochondrion looks as stunning as I hoped for about five years ago.
My journey into the obsession of making LED staffs
About five years ago, I stopped fire spinning and started building LED staffs. I wanted to have images hanging in space around me while I am spinning staff. Technology (and my skills) have finally got to that point where I’m pretty happy with the Mitochondrion, Mark 5.3.
The path has been:
Mark 1 – I learnt so much by designing the first one that there was no point building it. Straight on to…
Mark 2 – Ran without a microcontroller and had some fundamental flaws, like not turning on. I learnt enough to build the next one…
Mark 3 – The first of those pictured above. 44 LEDs controlled by a Picaxe. Twenty-eight bytes of memory, home-etched circuit boards, sketchy wooden parts, and bubble-wrap.
Mark 4 – First to use LED strips, 88 LPD8806 controlled by an Arduino Nano, twenty NiMH cells, and 3D printed parts. Eventually became bomb-proof enough that various I was happy to let randoms play with it at festivals.
Mark 5.2 – Teensy 3.1, 800 NeoPixels as four parallel strips of 200, and lithium cells. It looked good at Burning Man until the overloaded Voltage converters tried to catch fire.
Mark 5.3 – The brief details are: twelve 14500 Lithium rechargable cells powering 800 APA102/DotStar LEDs in four strips, controlled by a Teensy 3.2 microcontroller, with a motion sensor to turn it on and off, running the wonderful FastLED library and my own multitasking code to display a hundred images. You may have seen version this at Kiwiburn this year.
The not-so-brief details are explored below, with an emphasis on the inevitable trade-offs that you face when trying to push to the boundary of what’s possible.
What are the limits?
First limit is size, because here we’re trading off between ease of holding, stiffness, and internal diameter. The outside diameter of the tube can only be so big before it gets hard to hold. 32 mm is already fatter than I’d like for a staff. The only possible material for the tube is polycarbonate and that’s pretty flexible stuff. That diameter tubing comes in two choices of wall thickness and 1.6 mm is like a noodle. So 3.2 mm wall it is, giving a 25.4 mm inner diameter. That fact alone drives the rest of the design.
Second limit is energy storage. I want this to be kicking out the lumens all night long, or at least as long I last at a festival. (So that’s till about half-way through the night when everyone is kicking off and I say “I’m just going back to camp to get more water” and then I sneak off and crash out. But I digress.) I also want to fit four LED strips along with the necessary wiring and internal structure. Turns out 14500 cells (AAA size) fit, with about a quarter of millimetre spare. Twelve of them give me 33 Watt-hours, which is sufficient. Splitting them into two groups puts the heavy cells at the tube ends for good weight distribution when spinning. Keeping those two groups as one pack, i.e. all the cells in parallel, makes charging so much easier. Charging from USB is handled by Peskie Products tiny 800 mA board.
The cross-section looks like:
Third limit is power. I’m keen on ridiculous peak powers. And 800 LEDs could peak at 150 Watts. Sadly, that would pull 4 Amps per cell, a rate of 6C. There are high discharge rate 14500 cells, but I’ve yet to find any that are also protected and 50 mm long. The Trustfire Flame cells I’m using have a detectable Voltage sag at anything above 0.1 Amps, so I chose to cap the power at 10 Watts. More is certainly possible, but the green and blue LEDs fade out leading to a noticeable colour change. And 10 Watts is still the brightest LED flow tool that I’ve seen in NZ. (At some point, I’ll try higher discharge cells…)
Fourth limit is features. Here the trade-off is between time writing code (and getting it to work) and just building the bloody thing. I’m at the point where it does images. It doesn’t visualise music, yet, but that’s the plan for Mark 5.4.
Fifth is durability. Making a long, thin electrical device and then repeatedly throwing it on the ground is just hard. So everything is solidly mounted, there’s 3D printed ninja-flex bumpers at the ends, all structural parts are aluminium, thick 3D printed nylon, or FR4. All wires are as short as they can be, with locking connectors. All solder connections between parts that could move are sewn. All cell holders are screwed in place as well as soldered.
Key design features for the Mark 5.3
Power architecture – the great thing about APA102 LED strips is that they will happily run off 3.7 Volts, meaning no need to step Voltages up to 5 Volts as with NeoPixels. (They also just work, unlike NeoPixel’s tricky timing requirements.) This simplifies the power architecture greatly and avoids using UBECs. The downside is that they pull 1 milliAmp per LED even when the LEDs are set to off. I don’t have room for a physical power switch, so to keep the stand-by life at more than a day, there’s MOSFETs between cells and strips which cut or enable power to the strips. This also allows for control of the strips on start up – the Mark 5.2 didn’t have this. On power-up, the NeoPixels could light before the microcontroller had booted up, getting stuck in a high-current draw mode, preventing the Teensy from starting and damaging other components from overheating. The Mark 5.3 holds power off to the strips until explicitly commanded by the microcontroller.
Here’s a block diagram, clickable for enlargement:
Overall Arrangement and Physical Alignment – Accuracy is hard. Or rather, accuracy is expensive and time consuming. Squeezing everything in gets to be a pain in the arse, when you have quarter-millimetre tolerances. Making everything stiff enough and strong enough is bonus arse pain. So rather than try to make structural components myself, I used the PCBs as structure, alignment, and circuitry. Board shops will happily drill holes for no cost with micron accuracy. Then everything just screws together and fits together. The four sides are in two pairs with L-brackets holding each pair. There’s hinges between each pair so you can remove the internals and open the whole thing up for access.
Physical power switches – I said this doesn’t have room for one. It doesn’t, at the ends. One end holds the charging port, the other the microphone. I probably could squeeze one in, but there’s lots of current so the switch isn’t going to be small and the ends are the parts that get most knocked-about, so it’s not going to be durable. Still, power switches are necessary for debugging and resets, so there’s two tiny, board-mounted six Amp switches, one for each battery pack.
Multi-tasking code and timing
The code is all built on Alan Bleaklow’s Very Simple Arduino Task Manager. Every feature is an object that gets called every X milliseconds. The pattern generator and display refresh run every 2 milliseconds; the motion sensor every 250 milliseconds when spinning and every 500 milliseconds when stationary. Communication between objects is by message passing, with a SwitchModes object running a finite state machine to hand smooth transitions between spinning, ambient, and timed-out modes. Transitions between images happen every few seconds, or on reversal of the spin direction. The transitions are sharp, but could be gradual.
This code is probably a bit over the top for just displaying images, but is a solid platform for more complex behaviour.
The interface is entirely motion-based. Spinning wakes it, not spinning drops it into mellow ambient modes, rolling it turns it black.
With a Teensy at 72 MHz and data to strips at 10 MHz, updating 200 LEDs takes 1.5 ms. The display aims to update every 2 milliseconds, leaving 0.5 milliseconds to get new the next column of image data or generate the next frame of a pattern, or do other stuff. This is plenty.
Images
I wanted a strong visual identity to take to Burning Man – something very New Zealand. I also wanted bright colours and not too much complexity, coz the Teensy is pretty tight on memory. Luckily, NZ was having a competition to replace our flag, which provided a source of bold designs that look great in a palette of only 16 colours. (Unluckily, the proposed replacement flag is crap so we might be sticking with the original.)
Some are 256 colours, most are 16 colour for two pixels per byte. Images are 32, 48, or 72 pixels high.
So I rounded up a heap from the flag competition, along with lots of traditional tuktuku and kowhaiwhai patterns, and some mandala drawn by Spiralishis, and some mathematical designs sourced from Wikipedia. Some of these were tweaked in Gimp with conversion to polar co-ordinates, shifted, and faded brightness in the rectangular originals to give round and even brightness in when displayed by the rotating Mitochondrion.
Like this, original on left, what it looks like on right:
The images are processed from GIFs by a hacked version of Philip Burgess’ LED poi converter. It takes a directory full of images and writes out a header file full of image data and palettes, which then gets picked up by the compile.
And of course, we had to include Laser Kiwi. It’s the People’s Choice!
I’ll admit to being quite pleased with this version.
Photo credits
All spinning pics by Gordon Lehany of Platnam Images, who mostly does landscape and event photography, and platinum printing, but is game.
We’ve had a bee swarm come past once before, but this one settled.
So we rang Tricia and Martin from the Wellington Beekeepers Assocation and set about collecting the swarm.
Andrea in a borrowed suit:
Terrorist? Or Burning Man? Or makeshift bee photographer?
Of course, the swarm was up a tree on the steepest and densest part of our place.
The bees were pretty relaxed, given that we’d just cut down the branch they’d chosen.
Tricia said this was the biggest swarm she’d seen – twenty-five to thirty thousand bees.
Success. They are off to frolic in the kanuka above Karori.
Nominal.
My new countersinking technique is unstoppable.
Hmm… twenty one boards into a twenty five mm tube, with quarter mm clearances? I think I might mock that up with paper and cardboard, just to check nothing clashes.
So old school.
And then I’ll get all the circuit boards made and bits 3D printed and it’ll all just fit together, right? RIGHT?
[EDIT, eight hours later – Yeah, I’m really glad I did this before ordering the boards… ]
I finally got together with Grist for some pictures of the Mitochondrion Mark 5.2, my 800 LED glowstaff. After mending it after Burning Man, that is.
Images from the NZ flag competition. And of course, had to do Laser Kiwi – it’s the people’s choice!
I was helping someone to unload the dishwasher at work…
Her: “Thanks for helping.”
Me: “No problem, I like easily achieved tasks with clear outcomes.”
Her: “So why do you work in policy then?”
Me: “umm… I’ll get my coat.”
Which is a long-winded way of saying, for those who don’t know yet, I’ve left MPI and I’m now working for MBIE, managing their investments in materials and manufacturing research.
Andrea’s sister & niece, Johanna’s book on foraging, and the flowers in our garden were featured in this week’s episode of Topp Country, streamable from the TVNZ site (ours is the middle section, not the lavender or the roses).
For those of you outside of NZ, the Topp twins are country singers, activists, and comedians. They’re NZ icons.
And I’m going to try nasturtiums and fuschias in an omelette, once summer comes around again.
I wanted to give my Burning Man camp-mates LED strips for their bikes/clothes, running unique patterns, so I could find them in the dark. I wanted these to be bomb-proof and to last all night.
They were bomb-proof. You could kick these across the room and you’re more likely to hurt your foot than the drivers. There were not, however, sufficiently dust-proof. The two that were used in people’s pockets or bags worked fine; the three that were on bikes all died due to dust in the switch.
(Of course there will be a next version.)
I wouldn’t use this design again. Or rather, I’ve learnt enough from building these that I can see all the better ways to do it. But the info here may provide some inspiration and guideance.
Diptrace schematic and board
Order this board from OSH Park, if you must. It’s all through-hole, for easy assembly.
Bill of Materials
The case and switch came from Jaycar; the 16340 PCB-mount cell holders from Mr Positive; the UBEC from Hobby King; the rest was E14.
Drilling the case
Deep playa, one morning before it got too hot and dusty:
Burn night, just inside the circle of art cars:
Sunrise the morning after, from the top of a Robot Heart art car in a heap of blankets and warm people:
Ambling home, complete with bonus Temple. They burned that one too though:
In short, coz back in Vegas:
Burning Man – I was aiming to survive and I succeeded. I’m told this year was particularly hard. There was lots of this:
Highlights being camp mates, surprise tackle-hugging Kiwi, the Temple of Mazu burn, the deep playa, and all the pretties. Low points being the brutal dust storms, the heat, and the wind.
As for my LED projects:
When I get home, I’ll do detailed write-ups of the Hat and LED strip drivers. For now, we have to wash and then fly a fair chunk around the world.
…or something like that.
I got bad culture shock in SF (and still have more to write about that).
Then we went to Vegas. Oh Jesus.
So now we’re going to Burning Man…
Best part of Vegas was chilling with an old friend who works here. In her pool, in the ‘burbs.
Totally chilled.
Oh, and if you need to contact me, it’ll have to wait.
…after a Vegas birthday that took in two circus shows, one training session, and one visit to Walmart – it is connection that I value, not spectacle.
Also warmth.
Hence I am delighted by this present from Andrea, helped by Shyamtara, from a photo of me spinning the Mitochondrion Mark 4 at Kiwiburn in 2013 by Kellective.
I shall be wrapping myself in this at Burning Man.
We caught up with a wonderful surfer/aerial friend at some cafe down by Ocean Beach. They had toast, apparently causing everyone to blame the techies. In their defense, it was very good toast.
It was like this:
As Andrea says, “you never see that the other way around – surfers carrying their skateboards”.
Saw sand dollars and a syringe on the beach.
Caught up with another lovely friend and went to the cafe at the de Young art gallery. It is entirely clad in bronze, because someone had too much money.
On the wall of the de Young was a huge copper slab ten foot tall listing their major donors. I could try to claim this as a piece of art that asks questions about the place of Art in America, but I have enough culture shock already.
✔ Drive in the USA
✔ Get cut up by a BMW
✔ Get cut up by a Lexus
✔ Get cut up by a white van
✔ Get cut up by a pickup with a bed full of rusty engine parts
✔ Catch a bus in the USA
✔ Catch a bus going in the right direction in the USA
✔ Be mistaken for a Canadian
