Computer Running Lighting

[Chris Pflieger]

I'd be surprised if you can get DMX-512 spec compliant timing from an FTDI chip.

A lot of dongles may use an FTDI chip as a USB front end - that saves them from writing their own USB drivers and comm stack. That chip then talks to a low end microcontroller (e.g. Cortex M0, Atmel, PIC18) which does the actual DMX transmission through a common RS-485 transceiver.

 

[dbaxter]

In the least expensive DMX dongles, the DMX waveform timing comes from the host computer software drivers. An example is the Enttec Open. In contrast, the Enttec Pro, MK2, DMX King models, etc. use an internal clock independent of the host computer. To calculate the brightness value of 100 lights every 40 msec and still keep a stable waveform seems to cause many computers issues - in my experience.

I'm curious (and this will probably create a snowstorm of comments) why the comment appears frequently about the risk of a "computer crash" ? Why is a standalone computer program any more subject to a problem than the computer program running in a lighting console? We run a standalone program at Blackfriars, the computers are on 24/7/365, rebooted and updated weekly, disk drives changed after 50000 hours, and we've never had a 'show stopping' crash in hundreds of performances. I don't deny the 'sleep at night' value of a backup computer, and we have one in the props room. But do houses with consoles keep a backup console? Who's more at risk here? It scares me every time I power on the dimmer racks that they won't come to life more than my control computer does.
I don't have a theater degree or the wide background that many have here, so please help me understand and educate me.

 

[FMEng]

A standalone computer is fine, provided it is setup and used properly. The danger is that, most of the time, computers aren't setup for the task. I would do the following:

1. Use a desktop model, and install it so it isn't moved around. It is less likely than a laptop to get dropped, suffer from a broken connector, or get stolen. Desktops are just generally better hardware.
2. Install a solid state drive
3. Use a machine with ample horsepower and RAM.
4. Keep it disconnected from the internet.
5. Keep games and other non-essential software off of it.
6. If it is connected to the internet, it must be kept updated and have high quality antivirus and malware protection.
7. Turn off all auto updates and do it manually at appropriate maintenance times.
8. If it is on the internet, discourage the use of a browser.
9. Set power management to for always on, high performance.
10. Power the machine from an online UPS. Run the self test on it periodically.

Several of these items are to prevent human induced problems. Lighting consoles run industrial operating systems and can't browse the internet, therefore users can't get them infected or do other things to them that cause stability problems. An industrial OS is stripped down so it is far more stable, has very few security vulnerabilities. A simplified user interface that prevents problems from someone messing under the hood.

 

[StradivariusBone]

To calculate the brightness value of 100 lights every 40 msec and still keep a stable waveform seems to cause many computers issues - in my experience

I'm wondering then if perhaps the output of the Express going through the dongle I was using was causing problems as an input device to the computer for that exact reason. Maybe the timing on the Express was arguing with the clock in the dongle. The dongle that appeared to work better does not have a discrete clock so far as I can tell. The issues I'm getting are random flashes of light that I'm assuming is errant data being interpreted. It does act like some sort of buffering issue. Console output has been tested fine and the questionable dongle works fine as an output device.

Why is a standalone computer program any more subject to a problem than the computer program running in a lighting console?

A standalone computer is fine, provided it is setup and used properly.

Lighting consoles run industrial operating systems and can't browse the internet, therefore users can't get them infected or do other things to them that cause stability problems

I think that's the gist. Windows is a very stable OS until you start screwing with it. Updates, patches, hotfixes, random cat fact apps or whatever else my kids try and download to the computer will create a non-standard operating environment that no developer can predict. Random combinations of hardware with different drivers are so numerous that there is no way to test for all conceivable configurations. When a company like ETC sets down to make a console, I imagine they start with prototyping some sort of hardware to run the OS and interface with the DMX (or now ArtNet, sACN, whatever) hardware and they use either off-the-shelf parts or custom chipsets that they pay a premium for to ensure compatibility with every facet of the computer inside. There's no risk of some kid throwing in a 1080 ti and trying to overclock an Express, so they are able to test that specific hardware and software config with absolute certainty that nothing will go wrong- at least from a hardware/software compatibility perspective.

As an interesting aside, I'm seeing in the lighting industry now what has been the norm in the video game industry for a couple of decades now. Consoles vs. PC. With the consoles you've got a plug and play setup, everything works as it should and it's reliable as gravity. But, you might sacrifice some flexibility in how you implement it. With the PC the sky is pretty much the limit on what you want to use, but you sacrifice the potential reliability in that your software devs won't always cover you with every piece of hardware you want to use.

That said, with prep like what FMEng mentioned you are prepared for the inevitable problems that crop up with using a PC in this fashion. For our setup we have the license key for our software (LightFactory) on a USB key and our show file is backed up regularly on a remote server. If the PC running it fails, I would grab my laptop and plug in the USB hub that has all the dongles and the USB key, download the show file and be back up in around 10 minutes. The show file also updates everytime I turn on the laptop so even if I lose connectivity, chances are I have something close to current to get us back on our feet.

Granted, that does require that my lighting PC be connected to the internet, but I do monitor what my techs do on it and they are all trained that it is not to be used to browse the internet. It's running 7 so there's no worries about the 10 update nonsense at the moment. I am upgrading it soon to a thin client style computer (but with an SSD) and multiple DP outputs since this one is getting a little long in the tooth.