The job: Build a two-part light-box wall 3 feet high by 15 feet long and 3 ft by 21 ft. The box’s panels must be interchangeable to accommodate different designs. The backlighting for the wall must be pixel-controllable for animated wipes and patterns.
This light box was to be installed in a television studio to cover up an existing ugly concrete wall. Designs were done in SketchUp during the planning process.
The varied list of required materials meant I had to go to several suppliers. I would be doing everything: design of the LEDs and the lightbox, assembly, installation, testing, and programming. The only thing I wasn’t in charge of was the artwork for the panels, although I did have to order the acrylic panels and make Photoshop templates.
The list of materials:
- Addressable (WS2812) pixel tape
- 80/20 profiles and hardware
- Advatek PixLite 16 controllers
- Power supplies (2x 450 watt, 1x 600 watt @ 5 volts)
- Madrix software
- Acrylic panels
- 1×3 lumber
- 22 and 12 awg wire
- Mogami 2368 mic cable
For the lightbox’s frame, I decided to go with a company called 80/20. They make extruded aluminum pieces that fit together like erector sets. The profile I used has a channel that fits 1/4″ plexi perfectly. I spent a lot of time talking to a sales rep from Numatic Engineering who helped me visualize some of the pieces I’d need. I wish they could have just brought a truck load of parts for me to pull out what I needed and just sent the rest back. Instead, I had to account for every bolt, butt fastener, clearance hole milling, and angle bracket before-hand. The downloadable 3D CAD files on their website really helped in this regard.
The frame is technically self-supporting as built, but I decided to bolt it to the wall, lest someone pull it off the wall by accident. 1/4″ drop-in concrete anchors did the job, along with a hammer drill and appropriate bit.
Pixel Tape and Power Supplies
The backlighting was to be provided by addressable LEDs. This was a challenge for a few reasons. The sheer number of LEDs meant one heck of a controller, and a lot of power. The amount of work required to install all of those LEDs was also quite a bit. In all I ended up spending about $1,000 in just LEDs before the frame was even built. I got the pixels from China from Shenzhen Optosun. Despite it being an overseas order, I received them in less than a week. The pixels use the WS2812 IC, which is a quite popular serial LED driver. The IC is embedded in the LED package itself, so the only other component on the board is a capacitor. The LEDs I got are 5 volts, 60 LEDs/meter, cuttable every 1 LED. There are some 12 volt pixel strips, but since the logic voltage of the controller IC is usually 5 volts, the majority of pixel LED tape runs at 5 volts. My plan for mounting was to paint a sheet of plywood white and tape the cut strips to that, then hang it inside the box. That way if there’s a problem, the panel can be switched out easily. This also means I can assemble it on a table instead of inside the lightbox.
The pixel count per row is 89, rows per panel is 9. The current draw of one panel at full blast (white) comes out to 192 W, or 38.5 A. Multiply that by 7, and you get 1,334 watts! The controller for all of these pixels is made by Advatek Lights in Australia. Luke Taylor helped me out with a lot of technical questions before I even bought anything. I ended up going with two PixLite 16 controllers. The PixLite 4 wasn’t out when I started this project, so I went with 2 of the 16 output controllers.
The PixLite 16 controller has 16 outputs, which can drive 340 pixels each. 89 times 3 is 267, so the strips are linked in groups of 3. This means that each panel has 3 “groups” of pixels, so 3 data lines are required per panel. The data input to the pixels is directional, and has to be daisy-chained to the next strip, so the second strip is run the opposite direction of the first and third in a zig-zag pattern.
Getting the data from the controller to the strips required a shielded cable, since the interference over that distance would cause undesired effects. I opted for a Mogami thin mic cable. At only $0.22 per foot, it was a good deal for a very flexible and easy to work with cable.
Here is what happens when you don’t use a shielded cable:
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Power is provided on two terminal strips on the backside of the panels. Since voltage drop across the strip is a concern, each strip had power at the left edge, no daisy-chaining power here. The power coming to the board is over 12 awg cable to minimize drop.
Control for the pixels comes from Madrix software that talks to the controllers over E1.31, also known as sACN. This is fairly simple to set up. The Advatek controller has a Windows based utility to assign the address of the first pixel of each output. I patched everything in Madrix first, then used that data to fill in the info for the controllers. Since the pixels are self-addressing, you only need to set the first address and tell the controller how many pixels are in a row, and the pixels take care of the rest. Once the Madrix patch was built, I could start designing patterns and bringing in media. The resolution of the whole installation comes out to a very weird 630 x 9. A template in After Effects makes it easy to do custom animations and wipes.
It looks really good. Currently we have generic white acrylic which gives us the most flexibility. It is a pretty simple job to swap out the panels if the decision is ever made to brand the wall somehow.
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