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Obelisk

Updated: Aug 10, 2021

A local restaurant owner and community friend of ours was putting on a Sacramento music and arts festival called TBD Fest in a dusty field along the shores of the American River. He invited our team come and create whatever we wanted.


It was immediately settled that we wanted to build something interactive. We tossed around ideas for a life size operation game, a giant version of Pong with each pixel made of an LED illuminated ping pong ball, and the like.

But, from past experiences, we thought it would be nice to have something we could leave out without needing to manage it's operation (or the scores of drunk people who would interact with it at a music festival). We wanted something that both active and passive users could enjoy.


We landed on glowing spinning obelisks. Each would have a detachable concrete (Home Depot bucket) base that we buried in the ground so the columns looked as if they were growing out of the ground of the dusty field.


Electronics

We built four towers, each made up of five illuminated cubes. Inside each cube we placed 4 mechanical switches allowing us to keep track of when and how each cube was being rotated so we could change it's color as its spun. We extended each switch with heatshrink so it would flex and actuate the switch as the cube turned (janky but surprisingly effective).


All the wiring was attached to the center post and routed to the controls in the pyramid on top of each tower. This meant all the wiring and LEDs got to remain static while the individual cubes spun around them.

We cleaned up this ratsnest (a little) and hid it at the top of each tower (out of reach)

We picked a Beaglebone to drive each tower because it had lots of pins available but mostly since none of us gotten a chance to play with one before. But, since we still ended up with more information going in and out than we had pins, we added a PWM driver and a GPIO expander.


The GPIO expander allowed us to receive input from all the switches (20 per tower) while the PWM (pulse-width modulation) driver would pulse the LEDs hundreds of times a second to control the color in each cube. Both of these were connected to the Beaglebone through just two pins over I2C.

We designed a quick little circuit board for each cube. This board would take in PWM signals from the top of the tower and switch on and off 12V to power each color in the LED strips (red, green and blue) using three N-channel mosfets.

Construction


Since we weren't contacted until 2 weeks before the music festival, we planned and executed as fast as we could. After sketching everything out and ordering parts, the entirety of the build (coding, wiring, home depot runs and construction) all happened in less than 4 (very long) days. Since we were all working full time jobs this meant lots of trading off, scrapping of unnecessary features and on-the-fly decision making.


Lighting up Hacker Lab

While the rest of us were working, Meritt wandered around with a camera and put together this super slick making of video which captures the process better than I probably can with words.


Functionality

The towers we set up to be networked together (locally since we figured any sort of Wifi would be unreliable at a music festival). Andy Axton then built a 3D modeled simulation tool allowing us to try out custom animations digitally. With the towers you could play a simplistic rubix cube game to line up all of the cubes to match the color of the pyramids at the top, after which the tower would excitedly flash celebrating your victory.



But we could also switch the towers to display preprogrammed animations and even act as an equalizer. As music played from nearby stages at the festival, each tower would dance along, displaying the pulsing beat of a specific frequency band.


Materials

I don't know too much about the finances of music festivals but I thought it wouldn't hurt to approach the design with the assumption we might never get paid. I have always enjoyed the challenge of trying to waste as little as possible. This turned out to have been a wise choice since... whoops!

For light diffusion I chose sheets of low density polyethylene (tupperware plastic). Polyethylene is my spirit plastic. It's unpretentious and inexpensive (about 1/5th of the cost of acrylic). It can go through almost anything and come out unscathed. It can be dropped, kicked, knocked around and instead of cracking or shattering, it's molecules just lazily unfold to absorb the problem. Nothing really sticks to it, glues, spray paint, everything but spaghetti sauce just rolls off and leaves it unchanged. Even if you toss it in with scary, intimidating acids, including things that can eat through a building or dissolve a body (Hydrofluoric Acid, Mountain Dew), it just shrugs them off unimpressed. It's also a thermoplastic rather than a thermoset so even if you heat it up and melt it down, it's not gone. It's ready to be recycled made anew.

Wasted PE was 512sqin of 23040 -> 2.2%

Since both LDPE and Plywood (top and bottom of each cube) come in 4x8 sheets, we let the material drive the dimensions. Each cube would be just shy of 16" so we could run the sheets through a table saw very quickly and with very little waste.

Styrene extrusions

For the black plastic trim, I used styrene extrusion from Outwater Plastics in Arizona. They were very nice over the phone and have a dinosaur for their logo. I like dinosaurs.





Installation


We buried each pillars base in the ground, dug trenches for wiring and fabricated a reflective box to house our electronics, beer cooler and serve as a bench while we watched the crowds enjoy our project.

After the festival was over we fabricated bases for each tower and shared our project to an art show, a couple Maker Faires and what turned out to be a truly bizarre '70s themed Halloween party at the home of a bigwig in the Sacramento art scene.


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