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My next project is to be a hackable, wearable LED toy. I’m designing it to be self-contained, with a lithium cell, charging circuit, and boost regulator all on the same board. To that end, I figured the easiest pathway to follow to make it easily hackable would be to use an ATMega32U4 MCU, and have it present over USB in the same way the Arduino Leonardo does.

Since I’d already measured the average power usage of the prototype at around 100mA, I figured I’d start with the power system.

Panacea denied

This kills the cell.

This kills the cell.

I began my search looking for an all-in-one solution which could charge the battery, provide boost regulation to 5V for the LEDs, and provide an undervoltage lockout during discharge. While the lithium cell I’ve chosen in the interim has a protection PCB built-in (as will any future cell), said protection circuits are designed solely to save the battery from catastrophic failure modes — swelling, leaking, bursting into flames — but not from any mistreatment which will “only” shorten its cycle life by a large factor. And unless there’s something I’ve grossly misunderstood about protection circuits, I figure having a second UVLO can only add to the safety margin.

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Burning Man is an event which by its nature asks a lot of its participants. If you don’t go with the attitude of “I’ll damn well thrive, come hell bugs or high water winds“, you won’t last long. Art projects don’t just show up — they take determination from the moment of “I’m going to bring this crazy thing to the desert” right up until you dismantle, gift, or burn your project (and if you burn it, you’ve then got ash to deal with… nope).

The Tripper Trapper made a good blocker for the front of our camp, serving to lead people into our bar while simultaneously walling off our shower, greywater evaporation pond and generators (i.e. all the stuff people don’t want near their tents) from the outside world.

The funny thing about things that are shaped like other things is, a lot of the time, they act like the things they are shaped like. This means when your project consists of what amounts to a giant sail, it’s going to catch the wind.
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How the rib was run

The communication line makes a stop at the rib’s intersection with the spine. Here is where the occupancy sensors are positioned. The Cat5e cable continues to the end of the rib, where the LED strip begins.

Making your biggest project to date is a tall order, and is bound to come with all sorts of unforeseen problems. This one was a matter of communication.

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Joke's on them, I was listening to VNV Nation!

Joke’s on them, I was listening to VNV Nation!

The past week for me had the singular focus of assembling the housing for the Tripper Trapper’s power system. It encloses a set of deep-cycle batteries, a busbar each for the battery bank and load distribution, a circuit breaker panel, and a solar charge controller.

Since material in the US is generally only available in English sizes (for some reason, the U.S. saw fit to overthrow their oppressors, but not to abandon England’s ancient system of units), I’ve had to adapt to using inches and feet. It’s odd, but manageable. The box is 21.5″ x 20.5″ x 17″, and its structure is made entirely of scrap material donated by other burners in the community.

Pictured: battery-O-fail, storage busbar, breaker rail.

Pictured: battery-O-fail, storage busbar, breaker rail.

I took some pictures, since watching glue dry is 99.444439% (±0.555561%) as much fun as watching paint dry, and I figured I ought to share that fun.

Wiring the battery array was much more fun. I read what I could find online about using batteries in a parallel configuration, and what I found was that for ideal performance, each battery should see equal series resistance. People have a funny way of making that look hard on the Internet; maybe they just haven’t heard of busbars.

Diagram of how I wired the busbar

Left: 2P configuration with equal series resistance. Centre: 4P configuration with equal series resistance, based on what I’d seen online. Right: 8P configuration used in the Powerhaus.

It looks a little haphazard, but I wanted to keep the layout somewhat symmetrical, so I put the charge and load terminals in the middle. If you trace the current path from the charge controller, through any battery, and back to the charge controller, you’ll see that whichever path you take, you go through the same resistance: the leads to the busbar, four ring terminals, 6 terminal-spacings worth of busbar, two spade terminals, and a constant amount of battery cable (since I kept them the same length). Same goes for the load, which means that this array is kept balanced by design. Since the batteries are AGM lead-acids, there is no need to apply an equaliastion charge, or to balance the cells electrically like in lithium-ion batteries.

This part of the project gave me a lot to research, and I now know a lot more about power systems as a result. The Tripper Trapper has turned out to be the most rewarding thing I’ve built to date.

Sometimes it's all a bit much.

Sometimes it’s all a bit much.

Grandiose projects can give a sense of wondrous fulfillment when completed, but they can be a hard slog, and the time between inception and gratification can be disheartening. I’ve come to realise that having a small task in my backlog can help at times like these, so that I have some way to get a quick hit of satisfaction.

These can be short tasks like changing out a blue power LED for some other colour (which is good for your health if you sleep near it), or longer-burning (but periodically rewarding) challenges such as learning the best way to digitally encode video using command-line tools.

Not a day has gone by in the last fortnight when I have not worked on the Tripper Trapper, and it was beginning to wear me down. So after cutting, re-soldering and re-sealing six short LED strip segments, I took some “me time” and improved my bench light.

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Dare to fail

Dare to fail

In the early stages of designing the Tripper Trapper, I decided to use 5V addressable LED strip for two reasons: firstly, the mad resolution of 1-LED pixels which would look nice up-close, and secondly because the newer, faster, flicker-free four-wire APA-102C LEDs that I wanted to use didn’t (and still don’t) have a 12V variant.

So I set about finding some point-of-load (POL) DC-DC converters to convert the lead-acid battery voltage (between 10.5V and 14.4V 13.8V) to the 5V needed for the LEDs. I found some quality converters which were rated for a maximum of 14V at 10A continuous output, but would require the fabrication of a PCB with either sockets for these or solder pads for these. Being lazy[1], I kept looking and found some prepackaged BEC modules which HobbyKing were selling for $14.

Bargain, right?

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It's a tarp! Well, okay, it's a bunch of PVC pipe too.

It’s a tarp!
Well, okay, it’s a bunch of PVC pipe too.

This year’s Burning Man festival looked to be an easy one at first: since most of the new toys I had intended to bring to the playa last year didn’t make it there, I’d be able to take it easy and just show them off this year. I didn’t feel any pressure to build anything grand. That was, until our camp mayor got an email from the coordinator of our village stating that we’d be the centrepiece now that another camp had left, and that for us to get favourable placement we’d need something interactive out front, day and night.

Since we already had a daytime activity for this year (an aerialist rig), plus a till-relatively-late activity (the bar), all we needed was something that would be interactive all night. Thus came about…

The Tripper Trapper.

Designs

The basic concept was explained as such:

Sounds like a perfect time to make the Trippy Trap Tunnel. It sits there all nice and glowy with some dull rainbow chases….until the victim gets to the center. All of a sudden, strobes and a klaxon…..How the hell do you get out? Here, have a drink.

The jury’s still out on this thing making noise, but the rest of the idea stuck immediately. We would build the Trapper as a monkeyhut, and attach LED strip to the inside of the ribs. Since this would best be seen up close (people are meant to wander through it, after all), it would use 1-LED pixels (5V strip). Needless to say, it wasn’t long before I was hard at work, calculating how big and bright we could make it with a materials budget of around $1000…

T – 4 weeks

I stayed in Brisbane for a few weeks either side of Easter. I had no projects in mind for this period, apart from maybe whipping up something quick to light my campsite at a doof I was going to. Before I’d even left — long before I’d had the chance to show off my Kaiju suit to my local hackerspace to show it off — a friend informed me of a charming man who had recently joined, who had a plan to build an art car in the coming weeks, just in time for the very festival I would be attending. He put me in touch, and by the time I’d made it to HSBNE, I’d already signed on.

T – 3 weeks

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Here we are, marching in the Intergalactic Krewe of Chewbacchus 2015.
Photo credit: Enigma Arts Photography

So, New Orleans has this crazy vibe during Carnival season. On a scale between “a literal city” and “Burning Man”, it ranks somewhere around “the square root of WTF”, with parades running first on weekends, then increasing to every day as Mardi Gras approaches. So naturally, I figured the best way to experience this would be to dive right in. When I heard that the Kaiju Flambeaux Corps was looking for people to march in radio-synchronised LED suits, I jumped at the chance.

A good portion of any lit costume like this is finding a garment to use. Our parameters were something relatively-translucent and white. I found a dinner jacket on Amazon, then ordered it from the manufacturer’s website for about $10 less.

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Okay, so I have some bad news and some good news.

"This case is empty". "What do you mean, empty?" "Empty! The opposite of full!"

At least he got the case.

The bad news is that somewhere between LAX and SFO, the box containing the Blinkenlights prototype and the Glowbek mysteriously disappeared. Despite having my address clearly labelled on the package, it was not found or returned.

The good news is that this gives me all the more reason to step up my game. Glowbek 2.0 won’t be an Arduino and a prototyping board; it will be its own PCB. Blinkenlights 3.0 will be USB-programmable/chargeable and have its own battery. And in the meantime, I had to whip up something for another party, because being a darkwad just doesn’t appeal to me :)

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