Tensor Light Sculpture

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Finished Project
Tensor
Light Sculpture

Rocking out

People
Creator(s)Kevin "Frostbyte" McCormick
Leader / P.I.
Collaboratorsmany
Status
Date started
Date finished2003
Websitehttp://web.archive.org/web/20090103211840/http://sub-zero.mit.edu/fbyte/ledart/tensor/


Tensor is a light sculpture, a large computer-controlled LED array, made by the late artist Kevin "Frostbyte" McCormick.

Kevin's page about it is here, and you can see some of his other work here. The Tensor 2011 page contains information about current Tensor projects and tasks.

One of the panels was on display at AA when AA was at Joy St, the full piece was prepped for Burning Man 2011 at both the Joy and Tyler Street locations, and major renovations were performed at Tyler St in October 2016 to display the piece at the Maker's Masquerade fundraiser event.

Contents

Overview

The full piece is composed of three panels, each 40 inches wide by 96 inches tall, with a total of 64,800 LEDs, drawing a total of almost 10 kilowatts of power. Each panel has 180 groups of LEDs arranged to form a display 9 groups wide by 20 groups high; all three panels together are 20x27 pixels in an array eight feet tall and ten feet wide. Each pixel group has red, green, and blue LEDs in it. The LED groups use the DMX control system, which was developed to control stage lights in theaters. Originally there were six controllers per panel which received instructions over the Ethernet computer networking system using an early version of Color Kinetics KiNet protocol, and these translated the instructions into DMX for the panels. In October 2016, these were supplemented or replaced by Raspberry Pi embedded Linux computers.

History

After graduating from MIT, Frostbyte went to work for an LED lighting company in the Boston area. One of their early products was a billboard for the Loews theatre near Times Square in Manhattan. Early versions of the LED boards used in the product had to be taken out of service. Using these decommissioned and prototype components, Frostbyte designed Tensor and had his friends assemble it at his loft space home, Warehouse 23.

Frostbyte brought it to Burning Man in 2003 and 2004, in 2006 it was brought out when his remains were dispersed, and it made a return appearance at Burning Man 2011. It was also displayed at the auction of Frostbyte's estate in 2008, at the Hynes Convention Center for First Night 2014, and at the 2016 Artisan's Asylum Maker's Masquerade. Single panels have appeared at a number of other events and in private installations.

The "Shadow" pattern software colorizes and renders parametrized complex functions and two dimensional fractals and was largely written by B. Wenzel.

Moving and Handling

Tensor panels originally had no horizontal crossbracing, which meant that panels had to sit vertically or horizontally; being held face-down or face-up could warp the entire unit. From 2010-2016 crossbraces were added and it is now theoretically possible to suspend the panels.

When moving a dismounted panel (no legs or power supplies), always use at least 3 people; one on each end and one to spot. Avoid holding panels face-down if at all possible, and when face-up ideally sit them on a flat surface rather than supporting them only at the ends. Absolutely never orient a road case with the LED side down; there is nothing in place in the road cases to keep the panel from smashing itself against the LEDs.

For moving an assembled unit more than a couple of feet about five people seems right; a couple to get the main panel, someone to hold the power supplies, someone to spot the front side, and someone to spot the entire process. If it needs to be moved further than a couple of feet, disconnect the laptop and network hub and get them out of the way.

The Ethernet cables can go into any port on the hub except the uplink port, you don't have to bother keeping track of where they were plugged in. The power supplies should be set up so that each of the two output supplies feeds one fanout (power and signal distribution) board.

While designed to be displayed as three panels oriented vertically, it is possible to orient panels horizontally.

Frostbyte enjoyed the fact that the wiring and construction method was viewable from behind the panel, and that the LEDs could be gently touched and the heat of 1000 watts of visible light be felt on the skin.

Troubleshooting

The Tensor panel is a piece of art important to many people which is sometimes on loan to Artisan's Asylum for display. Please do not mess with it if you do not know what you are doing; Andrew is the point person for dealing with it and the best first contact for any problems. A number of other Asylum folks are familiar enough with it to help out if there are problems; circa 2016 these people would be Dewb, Drew, and Jesse.

Troubleshooting Notes:

  • Don't hotplug LED boards; power down the panels before fiddling with wiring. Plugging and unplugging an ethernet cable from a communications board or the hub is ok.
  • If a board of 3 LED groups isn't lighting, it's probably the front-side connector. It's best to have someone familiar with Tensor poke at these.
  • If 1/6 of a panel (a 3 x 10 LED group chunk) isn't lighting, it's likely a comm board problem or a power supply problem. Check the communications board behind the dark section to see if it has lit LEDs on it.
  • Each communications board should have two power supply cables connected, and one ethernet. All six ethernet cables on a panel go to the ethernet hub, as does the control PC. Make sure everything is plugged in: six power supplies (kind of annoying to check as they are stacked on top of each other inside their case), twelve power cables from supplies to comm boards, one control to pc to ethernet hub, six ethernet cables from hub to comm boards, power for the ethernet hub, power for the control pc. Remember, don't move plugs with power on.

Components and construction

Tensor's components were manufactured by Color Kinetics, now part of Philips Corporation.

Loews boards

The LEDs on the panels are arranged in units known as Loews modules. Each Loews module has a number of single-color LEDs, probably the brightest available at the time of manufacture, so colors are produced by mixing the amount of power to the red, green, and blue LEDs on each board. Modules are controlled using the DMX512 protocol. While some CK systems made use of a modified version of the DMX protocol, Tensor's modules are reportedly completely vanilla DMX (with the possible exception of the address assignment system). Not every LED on Tensor can be individually addressed; essentially each Loews module is a single pixel. The DMX protocol was designed to control theatrical lighting systems, so from the standpoint of a theatrical lighting control panel, each Loews module would be three stage lights, one red, one green, and one blue.

The Loews modules are mounted in sets of three that share a connector for power and control signals, these are called Loews boards. Loews boards were also made that had one or two modules on them, but Tensor's are the triples.

Each of the three Tensor panels has 3 columns each one board (= 3 modules) wide, and 20 rows of Loews boards, so a single panel is a 9x20 pixel array of 180 Loews modules (on 60 boards), and the complete system is 27 by 20 pixels, 540 Loews modules (on 180 boards) in total.

Each Loews board connects to a communications board to get power and control signals. There are six communications boards per panel, 18 for Tensor in total, and each communications board handles a section of panel one 3-pixel board wide and ten high.

Addressing

A DMX network is generally referred to as a "Universe".

Each Loews module has three DMX addresses somewhere between 1 and 512. These addresses or some sort of sequence number may be written on the backs of the boards in black sharpie. If two of them within the same DMX universe (Tensor has multiple DMX networks) were to have the same address, they would both obey the commands sent to that address. The boards are generally programmed to have sequential addresses. Occasionally this could get messed up by the use of replacement boards or incorrect reassembly, putting boards in the wrong places, or by the firmware EEPROM on a board flaking out and losing its address.

Boards can be assigned an address using a CK device called a Zapi. This sends a certain set of commands over the DMX interface. On most CK hardware, this device can read the addresses, however Loews boards are early enough in the company's history that they do not seem to have this capability and are probably write-only. If a board has an unknown address and no Zapi is handy to set an address, then every DMX address could be tried until the board lights up.

Connectors

Loews boards receive commands over the RS-485 protocol, a high-speed serial protocol that is the default for DMX systems.

Loews boards were originally supplied with a round 4-pin connector made by Switchcraft on the rear of each unit. Boards used in Tensor were modified so that they could be wired from the front with MTA-100 connectors. Thus, an adapter cable is needed to use a Zapi with Tensor's boards. The replacement front connectors are a key maintenance point; they become erratic and need to be cleaned or reseated over time.

Fanout Boards

The fanout boards take power from the power supplies and route it to the Loews boards. They are located on the back side of the panels. Each one has two power supply connectors. Ideally, these should both run to the same 500 watt power supply or to a pair of 250 watt supplies. Each one also has a sub-board hanging off of it. The sub-board contains an ethernet jack and a PIC.

Each fanout board is its own DMX universe. Each fanout board drives a segment of a panel three Loews modules wide and ten high, 30 modules. Each module has 3 DMX addresses, one each for red, green, and blue, so each fanout board is addressing a universe of 90 addresses.

Power Supplies

Each panel uses a mix of Color Kinetics 500 watt power supplies (removed from PDS-500 devices) and 250 watt power supplies. These are housed in a large plastic toolbox. Not all are of the same revision. Six supplies of 500 watts gives a draw of 3 KW per panel, 9 KW for the whole unit. Tensor is generally allocated two or three 20 Amp circuits of standard 120V AC for a full install of all three panels. The power supplies require properly wired ground and neutral.

Each power supply has one or two 4-wire outputs that plug into the fanout boards. The cables on the outputs vary in length, and determine how far from the panel the box of power supplies can be moved.

Many CK power supplies, including PDS-500's, have ethernet jacks on them and provide distribution of the commands. This lets users install systems by simply wiring lights to power supplies, rather than having to worry about running separate power and control wires. Tensor uses only the power supply component of a PDS-500, so the supplies could be replaced with any 500 watt power supply delivering clean 24vdc power.

Software

Two key pieces of software exist for Tensor: the "unattended software" ("Shadow") and Josh' VJ software (which can be found on github).

The panel at Artisan's Asylum is supplied with a laptop which automatically runs the unattended software on bootup, so no intervention is needed but no operator control is possible.

An early version of Josh's VJ software was installed on the laptop at AA, but may not function as desired. In particular, sometimes people moving Tensor panels dismount the communications boards to protect them when moving a panel. They then don't always make sure to mount the boards back on the same segments, essentially scrambling the display. Both the unattended software and the most recent version of Josh's software are designed to be easily reconfigured to deal with this situation.

Replacement Parts and Code

  • There are two ZAPIs in possession of Tensor curators. The code for a ZAPI to program a Loews boards is not standard ZAPI code, but can be uploaded to a ZAPI.
  • A few people have spare Loews boards in the 3-modules-per-board layout Tensor uses. 1 and 2 pixel per board versions also exist, and they could perhaps be substituted, though cabling and fitting might be awkward. The PICs on the Loews boards have had their read-protect fuses activated, and no dumps of the code exist, but Chinese reverse-engineering operations could probably extract the code. It seems unlikely anyone would fund creating new Loews modules due to their high component count and the fact that technology has significantly improved since these were designed.
  • Some comm boards have been damaged and no spares are known to exist. The source code for the comm board PICs is probably lost; at one time one person stated he might have hardcopy, another said that the code or a close version thereof may exist in the Sub-Zero/Warehouse23 CD-ROM and HD archive stack, but they did not materialize. One could theoretically dump and disassemble a pair of existing PICs and compare the code to see where the IP address is stored and if there are any other variables, assuming that those PICs have not has their read-protect fuses activated. Someone has reverse engineered the code that converts UDP to DMX and written equivalent code for a Raspberry Pi. There is a small supply of controllers designed by Frostbyte for a related CK internal project that could be substituted for the damaged controllers.
  • Any 24-volt 500 watt power supply should suffice.

Pictures

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