MICRO explores the small universe that is our body and mind. It consists of an 8ft x 12 ft x 8ft structure that has 200 translucent balls hanging from the top of the structure, each ball containing a speaker. When a ball is bumped into it generates a unique sound, and lights up with one of 5 different colors. As people play with the balls they are engulfed by a symphony of lights and sounds surrounding them on all sides.

Overview

Each ball is independent from all the other balls, and contains a custom made circuit board inside. Since the installation needed to run for days (and later on for months), and we didn’t want to be changing batteries all the time, external power is run into each ball. MICRO also needed to stand up to the elements as it was to be shown outdoors originally. All of this proved to be quite the engineering problem. Here’s how we did it…

Inside a sphere

The circuit board contains a microcontroller, an audio amplifier, a flash storage chip for the audio file, a tilt switch, and a voltage regulator, as well as various transistors, capacitors and resistors. A high power LED plugs into the circuit board and floats above the board. The speaker attaches to the bottom of the circuit via velcro.

The first task was to figure out how the interaction would work. When someone touches a ball the goal, of course, was that the ball should light up and make sound. We originally considered using an accelerometer, but those are expensive and a little overkill for our intended use. I ended up finding a $.70 tilt switch which worked beautifully:

We didn’t want wind triggering the balls, but the tilt switch had its own solution to this. Inside the tilt switch there is a ball bearing that rests in a little cone. If the ball moves in a smooth arc, much like how it would move when the wind blows, due to centrifugal force the ball bearing stays at the bottom of the cone and the ball is not triggered:

For the microcontroller we went with a Trinket from Adafruit. It was cheap, and had the added feature that it could PWM an audio file. Adafruit has a wonderful tutorial about how to play audio with the Trinket here. In a nut shell, the trinket emits the audio as a square wave, then a low pass filter is used to smooth out the PWM into a listenable audio source.

Most of the circuit operates on 3.3V, but we found we needed 5V to really get the most out of the LED. 5V is fed to the circuit and the LED, then the voltage regulator brings the 5V down to 3.3V for everything else. One of the problems we discovered early on is that high power LED’s need constant current. This means that if the current starts getting too high it is brought down, if it gets too low it is brought up. Here’s a great instructable on building a constant current circuit with a few resistors and transistors. You can see the constant current circuit I designed in the lower right of the MICRO schematic. Its those two FET’s, one transistor, and two resistors. It worked great, no more blown LED’s:

Originally we showed MICRO at Burning Man and we needed to be sure it would withstand the elements. It can get quite hot on the playa, Eric Rosenthal (my mentor through many parts of this project) was encouraging me to throw the circuit in my oven. Hesitantly I did so, testing the circuit’s temperature with an infrared thermometer and hoping it would still work:

Moving outward

We used clear light fixtures for the balls, in three diameters: 6″, 9″ and 12″. We dipped them in rubber dip multiple times to get the texture and translucency we were looking for. We laser cut the bottoms for the spheres out of acrylic, and did the same rubber dip treatment to them.

We used a truss structure to suspend the spheres. This was great because it was easy to assemble, relatively light, and very strong. To keep the truss from blowing away in the high winds that often happen at Burning Man, we guy wired the top edges down to the ground. We lined LED strips on the guy wires so unsuspecting people on bikes and in art cars would not have an unpleasant (and possibly quite dangerous) surprise finding a guy wire where they didn’t expect one.

Power for 200 spheres was a problem. We needed to switch 120V AC down to 5V DC for 200 separate circuits, and make sure we had enough amperage for the LED’s and audio. We ended up using 11 of these switching power supplies that could deliver 30 amps each. These also have a watertight rating when hung in their included case vertically. They’ve proven quite reliable:

Without whom it would not of happened

One of the most wonderful parts of this project was meeting so many generous and amazing people who helped out along the way, I would be remiss to overlook all of you. You all have special places in our hearts and in the hearts of all those who have experienced MICRO. This doesn’t do you credit, but here you are:

Made possible with generous support from:
Burning Man Arts, Federation Square/Pause Fest, Cameron Arts Museum

A Purring Tiger collaboration:

Concept/Design/Creative Direction
Kiori Kawai

Concept/Music/Electrical Design
Aaron Sherwood

Crew
Andy Sigler, Lisa Park, Rosalie Yu, Laura Chen,
Wyna Liu, Scott Horton, Mark Hebert, Elise Knudson, Chris Hallvik, Angela Orofino,
Momo Nakayama, Logan Scharadin, Julia Montepagani, Chelsea Southard, Ni Cai

Performers
Betta Lambertini, Logan Scharadin, Julia Montepagani,
Matthew Hardy, Joshua batson, Kris Seto, Elise Knudson, Kiori Kawai

Cinematography
Roy Rochlin, Talya Stein, Momo Nakayama

Guardian Angel
Eric Rosenthal

Special thanks
The Generator Inc., Big Bang The, Camp Contact, River School Farm

Photography
Momo Nakayama, Kiori Kawai

Thank you all!

www.purringt.com/micro