Controlled Lighting

Last year I made a post about some of the options for inexpensive DMX control. For those not familiar, DMX is a serial control protocol used in most modern professional lighting systems for theaters, concert halls, rock tours, etc. I continue to receive feedback on my original posting, some of which I still plan to respond to. In the meantime I would like to pose a few more ideas for you to think about and resources to investigate.

One of the interesting aspects of professional sound and lighting work is that, over time, it has become more and more integrated with computers and more recently, computer networks. Modern sound consoles can use “digital snake” technology and digital control technology which allows for much more flexible installations. In the lighting arena it is incresingly popular to run DMX over (relatively inexpensive) ethernet networks instead of dedicated serial cabling.

As with much of the technology found in production environments DMX over ethernet has been way overpriced. Be it the small demand for the technology compared with “consumer” technology or just the long track record of paying a premium for production technology DMX over ethernet has been out of a reasonable price range for most schools and non-profit theaters.

While poking around on the internet one day updating myself on current production technology I stumbled across the work of Simon Newton. Simon has created an open source driver for ArtNet (one of the popular and standardized protocols for DMX over ethernet). His project, called libartnet is specific to POSIX based systems, including both Linux and Mac OS X.

But what can you do with it, you might ask. Right now if you wanted to control some lights with a PC (using Martin’s LightJockey for instance) you would run a program which would output DMX on some kind of hardware interface (either proprietary or open source) which you would run into an ArtNet converter box and convert to ethernet. That seems kind of silly to me. After all, most PCs already have an ethernet port so why buy two more pieces of hardware? (Remember what I said about production technology being too expensive…) Anyway, with libartnet (assuming your control software recognized it) you could output DMX straight from your ethernet interface. But what software has libartnet support? Well, DMX4Linux does for sure and that means almost any lighting control software that runs on Linux will. Specifically, the GUI based Q Light Controller will. See how useful having a driver abstraction layer such as DMX4Linux is, but I digress. Another benefit of coming directly out of an ethernet port is the support for wireless.

Wireless ethernet is increasingly prevalent and compared with exisiting wireless DMX products it is downright cheap. Now we have solved the problem of wanting wireless control, after all with technology like this you could focus lights using your PDA with it’s built in 802.11x capability. But what about the other applications for wireless DMX? Simply routing the DMX signal between trusses or pipes in a large theater can present a problem. As I mentioned traditional wireless DMX is incredibly expensive and not all that great a technology. It turns out I have a solution for this as well. A few weeks ago I suggested to a hardware engineer I work with that he look into the possibility of using a pre-certified 802.11x transmitter (such as those from Digi International) to create an inexpensive wireless DMX product. After looking around on the internet a couple of weeks later I discovered that wireless ArtNet tranceivers already exist, but as can be expected with production technology, are wildly overpriced.

One of the most interesting solutions I found came from the same Simon Newton who developed libartnet. Simon was able to replace the OS on a Netgear router with a version of Linux and libartnet. Then, using the USB port on the router he was able to connect up some USB-DMX adapters and create an extremely inexpensive wireless ArtNet node. See this page for more information and specifics. The solution isn’t esxpecially elegant but it does show how inexpensively this could be done and gives some hope for future inexpensive ethernet to DMX adapters based on embedded system technology.

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