'Wall of Enlightenment' v2 - the next instalment
Saturday, October 17, 2015 at 9:19AM
Steve Upton in Makespace, woe
It's taken a while (the original post was Feb!) but it's time to tell the story of the full size screen, which I've named 'The Wall of Enlightenment'. As a reminder the aim was to build a 2 metre wide, 1 metre high screen which could be hung on the side of the Pitt building in Cambridge as part of Science week.

Having created the initial small prototype my intention was to use the same materials, and scale it up. The prototype went down well at the Guildhall exhibition and I was given the green light to build the full size screen. Ordering 75m of LED strips from China was an interesting experience but once I'd got through the complexities of sending the money they arrived within a week. Construction could then be started on the floor of my home office.
70m of LEDs was a great box to open


The Wall is based around a Raspberry Pi which then uses Fadecandy cards to control the addressable LED strips. The maximum length of these before any lag is visible is estimated to be 64, from details on the Fadecandy site. With 32 LED per metre strips that gave me the 2 metre width I was looking for, so I started by cutting the strips and constructing the frame around them from 25mm black plastic conduit.
Initial construction

Using the same aspect ration on the vertical meant that I needed 32 rows and with 8 strips per Fadecandy that was 4 cards. As these were small my intention was to hide them inside the trunking but to get things running initially I wired them up outside. I also added a length of nylon line to the end of each strip and sealed the end with hit glue and heat shrink tubing. This would make it waterproof and the line could be used to tension the strips so that they didn't sag once the screen was hanging in position.
Once I had the first 8 lines connected I tested to ensure things were working as expected. I used the fadecandy server on the pi and streamed a video from my laptop. At a friends suggestion I used the ipod video advert as it was great for motion and colours. The result was great and can be seen here
Once I knew that worked I was confident that I could complete the rest the same way and after many long nights of soldering, sticking and threading wiring the construction was complete.
Construction complete

So, time to fire up this gigantic beast and enjoy the fruits of my labours, again the same video with the result here. However, something wasn't right. There was way more 'noise' on the display and the colours were not consistent. Something was wrong and this wouldn't be good enough for the display. I started to look at the wiring, the connections, the power levels to determine where the issue was. I also posted on the fadecandy google group and got some great feedback. Unfortunately the more I did the worse it got, with complete strips starting to die and more and more noise.
Here's the last test with some scrolling text: https://www.youtube.com/watch?v=wWNaVCvFfiM
At this point time wise it was the first day that the screen was due to be on display but there was no way it was up to that, it was dead on the office floor.
Dead on the office floor

This wasn't going to beat me. I needed a rethink and some new ideas, while continuing with the design I had may have worked there were some issues that had arisen that really needed to be addressed:

So I sat down with some friends at Makespace later that week and we designed version 3.

 

Article originally appeared on ste5eu.com (http://www.ste5eu.com/).
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