Shadow Engine

designed and built by Kevin McCormick and Carl Gruesz

Shadow Engine is an interactive light sculpture. A curved Lexan wall, seven feet tall by six feel wide, is covered with an array of 1120 red, yellow, green and blue LEDs. Facing this wall, eight feet away, is a curved aluminum fence, about 15 feet long. This fence supports 1120 light sensors (phototransistors), pointed at the LEDs.

The computer controlling the Shadow Engine can set the LED display to some image, then read the intensities from the light sensors. It can then calculate a new image to display, based on what the light sensors reported. So the system feeds back on itself, changing what pattern it shows based on how it sees itself through the sensors. People can walk in between the two walls and cast their shadows on the sensors, changing the way the system behaves.

The Shadow Engine was first shown at Burning Man 2001. Due to time constraints and persistent electrical problems only the LED wall was set up, displaying patterns that did not rely on feedback. Despite not having the phototransistors, the Shadow Engine was still a big hit. It was located in the central theme art area at Burning Man, a very high-traffic location, and it was visible from over a thousand feet away. Bayard Wenzel wrote the software that ran all the patterns at Burning Man.

Setting up the LED wall, Monday afternoon. (photo: Sawyer Fuller)

Attaching the polycarbonate. (photo: Sawyer Fuller)

Complete.

(photo: Sawyer Fuller)

(photo: Sawyer Fuller)

Here are some short video clips of the Shadow Engine at Burning Man, taken by Sawyer Fuller. (You may have to use QuickTime Player to view these.)

On Display

The Shadow Engine has been shown at a few events since it returned from Burning Man.

superCollision at MIT, October 6, 2001

Radiate, Washington DC Armory, November 24, 2001 (setup, night before)

Radiate - in the drum and bass room

Construction

The Shadow Engine has two basically independent parts: the LED wall and the phototransistor fence.

The LED wall has 1120 LEDs, driven by 64 PIC microcontrollers on a common, custom high-speed serial bus. This serial bus is driven by a parallel port interface attached to a Linux PC. Each LED is individually addressable and each can be set to 256 different brightness levels. The whole set of LEDs can be updated 40 times per second.

One assembled LED board, which controls 20 LEDs.

Carl assembles the LED wall frame at Warehouse 23

Farhad and Sawyer glue LEDs into holes in the Lexan sheet while Jeff (left) watches

Farhad glues some more

The LED wall itself is four sheets of Lexan (actually, Hyzod brand) polycarbonate. These sheets are supported by a grooved plywood base and top piece, held together with iron pipe.

The wall of light sensors is fence-like, with 35 vertical aluminum rails joined together at the top and bottom. Each rail has 32 light sensors along its length. The entire wall of sensors captures a set of intensities in about 2 milliseconds, then the results are sent back to the control computer. The wall can be sampled about 30 times a second.

29 of the 35 rails assembled, at Warehouse 23

One of the 35 phototransistor sampler boards

More to come.

Many thanks to: Jason Rolfe, Dan Good, Jeremy Braun, Pete Gamache, Jon Barchi, Dustin Ledbetter, Gene Shuman, Matt Beck, Jan Nelson, Michael Cyrulnik, Farhad Ebrahimi, Eric Traub, Sarah Low, Sherri Davidoff, Justin Kent, Bayard Wenzel, Ben Stabler, Andrew Sudbury, Sawyer Fuller, Ariel Salomon, Mario Corsetti and Nate Janos. Assembling the Shadow Engine took a massive amount of labor, and could not have been done in time without their help.