Version 5

    This post is the first in a series describing the design and construction of The Grid, an installation displayed at Electromagnetic Field (EMF) 2014, a camping festival for hackers, artists, geeks, crafters, scientists, and engineers held just outside Bletchley at the end of August.  We'll start by outlining our vision for The Grid and how the idea came about.


    The other posts in the series cover:

    1. Structural: Making it stand up.
    2. Electricals: A lot of power, and an awful lot of cable.
    3. Electronics: Basically just switches.
    4. Software: Computer Vision can't be that hard...
    5. Retrospective: Lessons learned the hard way.


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    Back in June, we (Adam and David, housemates in Cambridge) were making initial plans for our “village” at EMF.  These are groups of people camping together, usually united by some common cause. The specific details of our village weren't important, but there was no question that it needed a lot of LEDs.  You've gotta outdo the neighbouring villages! While shopping around on Alibaba, prices seemed rather cheap for a full carton, 250m, of individually-addressable RGB LED strip.  This is rather more than can be justifiably applied to a couple of tents, which raised the question of what to do with so much LED strip.  Ideas included a giant LED teepee or circle around our village marquee, but we decided instead to go the route of creating an installation, rather than just village decorations.

     

    We quite quickly converged on the idea of a grid of illuminated poles.  At this point we were still planning to use individually addressable full colour LED strip (using the WS2812b addressable LEDs with integrated controllers), which would have created a massive volumetric display.  There were some issues, though. Pushing the control data for so many LEDs into the grid would be a challenge, necessitating a high speed data bus. For 300 LEDs per pole and 50 poles, with three bytes of colour data per LED, each frame requires 45kB, so over 10Mbit/s for 30fps. These addressable LEDs have quite precise timing requirements, so to keep them all in sync would require serious control hardware - probably an FPGA. Each pole in the grid would almost 3A at 5V, which leads to a lot of voltage drop over long runs of cable. Amongst these technical difficulties with this design, our cost estimates for the LEDs turned out to be rather optimistic – by more than a factor of five!

     

    At the expense of flexibility, we were able to bring the project back on budget by replacing the full colour addressable LED strip with plain white non-addressable strip.  While perhaps not as cool as 7,500 individually addressable LEDs, we decided this could still be a very exciting installation (without upsetting our banks quite so much). We would be able to put more thought into the display patterns and it would simplify the rest of the software, which is never a bad thing.

     

    Having settled on white, non-addressable LEDs in a grid formation, the design quickly condensed.  A rough model in Blender, after several hours of trying to achieve believable lighting in the rendering, looked like this:

     

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    To further enhance the impact of the large, bright, poles switching on and off, we decided each pole should make an audible click when switching.  This idea was borrowed from the Listening Post installation, which makes incredible use of sound effects to enhance what at first appears to be an entirely visual installation, notably including clicks as its many displays turn on and off. The best we could think of to create click noises was an electric relay being toggled, so we were somewhat relieved to find that the Listening Post had used the same idea.


    Of course such a large installation would require interactivity. We hoped people would want to walk around inside The Grid, so it would be great to have it somehow react to their presence. Figuring out what the best way to do this would be took some time - watch out for the post on it to see what we ended up with.

     

    The idea was settled – we would create a 7-by-7 grid of poles, each standing 2.5m tall.  Each would be illuminated by bright white LEDs which make a noticeable click when switched on and off.  They would display a number of pre-programmed patterns in addition to interactive modes which depend on the movement of people inside The Grid. All that was left was to work out how to make the poles strong enough, what materials to choose, creating the control electronics, calculate voltage drops over the long wire runs, write a whole bunch of software, and install the whole thing into a field...


    Check out the next article, about how the structures all came together, here.