Can I use ethernet instead of DMX for DIY led lighting?

Question

I've read that while most pro-lighting is uses dmx, some intelligent lighting rigs use ethernet. I'm interested in building some MCU controlled L.E.D. footlights for my stage show, and currently know nothing about dmx and damn little about lighting period. Would love to hear pros and cons of just using ethernet protocols instead. From my perspective as a pro-coder/hobby-EE, the path of least resistance would seem to be OSC over ethernet between my controlling machine (likely a Pi or something) and the lighting brains, (likely something like a Teensy). I am definitely on Mount Stupid in this area, input appreciated. I have built controllable l.e.d rigs on costumes already but nothing powerful enough for stage lighting.

Edit for clarification based on comment: In our case, interoperability with standard controllers is not a concern at all, but reliability definitely is. We are jugglers, and we are almost never a priority with the lights and sound guys, so we are trying to build a system where we roll in our stuff, drive off our controllers that we start, and tell the regular light/sound guys to do nothing until we're done. In a corporate gig situation we don't trust them to hit our cues EVER. lol

thanks!

Answer 1

This depends if you want interoperability with the equipment and wiring likely to be installed. Most theatres already have miles of suitable DMX cabling, plenty of ports and the distribution infrastructure to get the signals around. Many will also have a DMX capable lighting desk, even if it's very basic.

DMX is so popular because it's basic and relies on very simple technology.. but it works very well. The noise immunity offered by RS485 (essentially, see here) works great in an environment where there's lots of other electrical noise. Whilst ethernet now seems like a simple solution with inexpensive parts it certainly wasn't 25 years ago.

If you can run your own wiring then ethernet has enough noise immunity for a theatre environment. It's probably overkill, but if you have a microcontroller or modules that support ethernet and a higher layer protocol it should work fine.

Note that many modern lighting desks will also support ethernet but are likely to run their own proprietary protocols on top. Unless you can figure out those details it's unlikely you can interface with them.

Answer 2

You can do what you like; you could use the old Rank Strand analogue multiplex if you like (it's a joy to watch on an oscilloscope, for a start). The issue is whether you want your light units, whatever they are, to also be able to interface to DMX. If not, knock yourself out.

DMX may be more robust than ethernet in an electrically noisy environment, though it is a bit long in the tooth (it started coming in about 30 years ago, if the length of my teeth is a reliable guide). It's also designed to be transmitted over robust connectors rather than weedy RJ45s.

It probably depends on how pro you are, or want to be, or to look. Using a non-standard system is fine at first but if you invest a lot in it, then need to standardise, you're throwing a lot away.

NB I used to be a theatre lighting engineer but haven't been for a long while. Back in my day, real men used multicores with +10 or -10 control voltages.

edit Bear in mind that interoperability is not just about interfacing to other rigs. You may want to purchase a unit yourself to add to your own rig, which would obviously need a standard interface.

Answer 3

Traditional DMX (not RDM) uses one master multiple slaves bus topology and is single direction. The Ethernet versions, 10base-2 and 10base-5, that use bus topology are obsolete. So Ethernet needs switches.

DMX is simple. Practically any microcontroller with an UART interface can easily be made into a DMX receiver. With Ethernet, you probably want to use the IP stack. The stack is widely available for any popular platform, but it does add complexity. Alternatively you can choose to "farm-out" the network interface by using some pre-packaged solution like Ethernet to UART bridge.

DMX has slow data rate and is good for controlling objects with simple numerical values only. There is no bidirectional communication.

DMX equipments may or may not be isolated and non-isolated DMX implementation can potentially be a source of ground loop issues. Ethernet from 10Base-T on up are isolated.

While DMX still dominates in professional lighting applications, IoT and smart devices based on general networking are getting popular and will be more and more so.