PROTOCOLS - AN HISTORICAL PERSPECTIVE
The following article appeared in ESTA's Protocol, Spring 2000 issue, and is reprinted with permission.
© 2000 Entertainment Services & Technology Association.
By now just about everyone in the entertainment lighting industry has read or heard some retrospective on the amazing technological advancements that took place in the century just past. Think about it - the incandescent lamp was still in its infancy just 100 years ago, and to control its intensity you needed vats of salt water! Now here we are with computerized electronic dimmers, and we control robotic lights over high speed data communications networks. If you check out the March 2000 issue of Entertainment Design you'll see what a number of industry professionals have to say about what was accomplished in the 1900s.
There's a wide range of very thought-provoking opinion on what were the most significant advances, but to me it seemed -- not surprisingly - that most people pointed to inventions that had to do with improved control of show elements. And it was the adoption of standardized ways of accomplishing this control that many saw as critically important. Some advances that became standards, de facto or otherwise, include the ellipsoidal reflector spotlight (arguably more about controlling light than just producing it), the silicon controlled rectifier (SCR) dimmer, and asynchronous serial digital data communications (i.e. DMX512). The developments described here are part one of two related articles examining the evolution of lighting control protocols, how various manufacturers have implemented them, and moves toward standardization. Part two will offer technical information of interest to anyone with legacy dimming equipment that doesn't "speak" a standard language.
In the Old Days
When I started working for Electro Controls in the early 1970s, we were still producing a lot of autotransformer dimming systems, but by then the state of the art had become low voltage analog control of SCR dimmers. When this technique was pioneered in the '60s, it was regarded as a great leap forward since now it was possible to remotely control dimmers with a relatively small console that in some cases was even portable! Our company used a 0-15 volt DC signal to control each dimmer, but I soon discovered that other manufacturers had different ideas about what was the best way to do the job: Kliegl Bros., for example, used 0-28VDC, and Ward Leonard (anyone remember that name?) ran their systems on 24VDC. Strand seemed to be in favor of 0-10 volt control, but products made in Europe required 0 to minus 10 volts (many of these ended up in North America). These were by no means the only control methods around - EDI's 2-7.6VDC springs to mind. At EC most of our dimmers ran on DC control voltage, but there was one product that used 0-24 volts AC.
Let's say you have a dimmer designed to be at full output with 28V control, and you're controlling it with a console whose output is 10V at 100%; clearly there's a compatibility problem. They don't use the same control voltage. And your light won't get past 35 percent Oh well, at least the console doesn't output minus 10V or the light wouldn't be on at all. I could go on, but you get the picture.
Little wonder that by the mid '70s there was a move afoot to try standardizing dimmer control voltages. The push came initially from the New York rental market, where portable control consoles and dimmers from various manufacturers might end up on the same Broadway show. Soon, Colortran, Kliegl, and Strand products were interoperable at 0-10VDC, followed by newcomers like Dilor and LMI. By 1979 you could finally say with some certainty that there was in place a standard way for control systems to communicate with dimming systems. You could (if you'd thought of it at the time) say that there was a standard dimmer control protocol in use in our industry. After all, the basic definition of a communications protocol holds that both the party sending information or commands, and the party receiving them, are in agreement about how the information or commands are sent, received and interpreted.
It was too good to last. Actually, it wasn't good enough in the first place because analog control, as we all know, was unsuitable for the new dimmer-per-circuit systems requiring large (100+) numbers of dimmers. Too many wires! Big, thick control cables! Something had to be done, and, taking advantage of microprocessor technology, two manufacturers had multiplexed control schemes on the market by 1980. Strand introduced a multiplexed analog protocol that later became known as AMX192. Kliegl developed K96, the first truly digital control protocol. Multiplexing allowed individual dimmer control signals that formerly needed one wire each to be placed sequentially on 2 or 3 wires at the console, then de-multiplexed back into individual control signals at the dimmer rack. It was the next great innovation in lighting control, but unfortunately we were back to where we started in terms of cross-compatibility between manufacturers. As if to cement the newly chaotic regime firmly in place, other vendors quickly brought their own proprietary multiplexed dimmer control schemes to market: Avab (A240), Colortran (CMX), Electro Controls (ECmux), NSI (Microplex), and Teatronics (Tmux) to name a few. Strand in Europe came up with an arrangement that was incompatible with their North American version: D54. It should also be noted that most manufacturers, at one time or another, introduced variants to their proprietary control protocols that torpedoed compatibility within their own product lines.
A New Standard
It was apparent by the mid-'80s that when it came to control protocols, there were two self-interested factions in the lighting control industry. Some manufacturers tended to view their installed equipment base as a sort of strategic asset, since customers would almost certainly have to purchase their next control system from the same company that supplied the dimming system. Tight control over proprietary technology, i.e. the dimmer control protocol, would ensure this. In fact it wasn't until the early '90s that most vendors were willing to release the details of their protocols.
Equipment owners and users, on the other hand, were again in the position of clamoring for an open standard of interoperability to realize the widest range of choice and highest value in their purchases. Inevitably the greater good triumphed and the rest, as they say, is history. No one can argue that USITT DMX512 has brought order, interoperability and major economic benefits to all sectors of the entertainment lighting industry. New industries were created; the "interface" sector, for example - you need a protocol converter or your new board won't talk to your old rack.
As the kids like to harp, "Are we there yet?" Well, not exactly. As clearly written as the present DMX512 standard is, many equipment designers and users couldn't resist the urge to take liberties with it, for what I'm sure they felt were good technical or commercial reasons. As a result, the so-called "DMX512/2000" redefinition process (currently underway as BSR E1.11 within the ESTA Technical Standards Program) is forced to contend with present-day realities including connector styles other than the 5-pin XLR, the presence of potentially damaging voltages on signal pins, grounding issues, and whether a DMX device should be allowed to send and receive data on the same wire pair. The danger, of course, is that vendor-specific issues might once again conspire to, at best, water down the standard, or at worst, render apparently compatible equipment non-interoperable. Alternatively, strict adherence to the standard raises the prospect of orphaning significant amounts of DMX equipment sold during the past decade.
The Next Generation
Against this backdrop, it would appear from my standpoint that history is, for the third time, repeating itself. The 1990s saw new advances like the moving light fixture take firm hold, not to mention more powerful PC-based control systems and ever-greater demands on lighting rigs not only from users but indeed by audiences. In no time at all, DMX512 was being stretched beyond its capabilities. It was forced to give way to more advanced means of moving data around facilities, and -guess what? We're back to proprietary protocols once again. Ethernet-based products are now available from Amazing Controls!, Artistic Licence, Avab, Colortran, Compulite, EDI, ETC, Rosco/ET, and Strand Lighting (did I forget anyone?). How many of these will inter-operate? You'd be right if you guessed none. Luckily, some will be able to migrate towards compatibility with the new ACN (Advanced Control Network) standard now under development by the ESTA/TSP-sponsored Control Protocols Working Group.
The new standard, when made public, will offer vendors and users unparalleled opportunities for the design and utilization of new features, products and systems (see Steve Carlson's article "ACN Explained" in the Winter 2000 issue of Protocol). But until then, there exists the very real possibility of entrenchment of certain proprietary technologies and techniques. It may simply be too difficult or too expensive for certain types of vendors or users to migrate to the new standard. After all, very large sums of money have already been invested in R&D for existing Ethernet-based products. Will vendors be able to recover these costs before having to re-engineer their technology to work in an ACN world? Or will there be pressure to water-down the ACN effort to make it more inclusive of established ways of doing things (e.g. the DMX512 situation)?
As history has shown, however, standardized control protocols are in the best long-term interest of our industry. Certainly the very people who spend money on equipment have always demanded standardization, and will continue to do so. And besides, good old standards never seem to die; they just go on and on producing value for people who depend on them every day. That relic from the "old days," 0-10 volt analog control, is still in widespread use. It will even get a permanent lease on life when ESTA releases E1.3 - 0 to 10V Analog Control Specification. Similarly, DMX512 will not fade away (pun intended) in the face of ACN. Paradoxically, it may receive a boost from the sheer utility that ACN will bring to the industry. For a long time to come DMX will remain the most reliable, cost-effective way to control most of the devices it controls today. That's good news for manufacturers and users alike.
David Higgins has had a varied 27-year career in the entertainment lighting industry. His previous experience includes production, field service, systems design and sales for a number of different manufacturers including Electro Controls, Dilor and Strand. Dave is a member ESTA's Control Protocols Working Group of Protocol's Editorial Board. He is also the founder and President of Pathway Connectivity, where daily homage is paid to the DMX512 standard.