Art-Net #3

Good news is that we’re now successfully receiving & parsing Art-Net packets.  Bad news is the code barfs with more than one universe at full speed (512 channels at 44 Hz) on the wire.

 Next task is to optimize some buffers and convert critical parts of the human-readable code into super-efficient machine language.  Hopefully this will dramatically increase the system throughput.

Estimates at this time is that our single controller will be able to support 5-6 universes of DMX over Art-Net at full speed.  Anyone need a crazy inexpensive Art-Net to DMX bridge?

Good times. More soon.

Art-Net Node: Progress

All the bits and pieces we need to develop the Art-Net receiver arrived a couple days ago.  

Yesterday I cobbled them together and wrote some simple webserver code.

Didn’t figure out how to make it viewable from the outside world, but on the shop’s local network the server was functioning perfectly.

‘Hello World,” served from an $8 microprocessor.

"Hello World," Served from an $8 microcontroller.

Now we know that the ethernet link is good, the next step is to get the Art-Net receiver code up and running.


The Future

A challenge with point source pixels, classic pixels, Tripix and RGB emitters in general is that they require stacks and stacks of data to run properly and smoothly.  Unfortunately, a regular DMX universe contains 512 channels, which is only enough to drive 170 3-color pixels at 8 bits per color.

Last year, my personal rig required the better part of two universes.

This year, folks are running displays based our pixels and sized between 1K and 7K discretely controlled RGB emitters.  On the high end, that’s nearly 20,000 bytes of data for each ‘frame’ of a display scene.  Step that up to video playback speed (30 fps) and the datarate approaches 6 megabits per second, sustained.

Driving a rig that size with regular DMX gear costs a small fortune in cable and connectors alone.  And one of the biggest, baddest $40K lighting consoles in town, the GrandMA, tops out at about 16,000 channels.   

Enter Art-Net.

For the uninitiated, Art-Net is a totally open, freely-published, ethernet-based transport protocol for lighting control data.  It’s based on UDP packets and traverses regular (inexpensive!) ethernet switches and hubs with ease.  It can zip through the air over a wireless internet connection. Even the iPhone / iPod Touch can generate Art-Net packets.  Best of all, the potential bandwidth is massive.  

From the official spec:

A theoretical limit of 255 universes of DMX512 exists in this specification. However a simplistic data rate comparison (DMX runs at 250KBaud, 10BaseT at 10MBaud) suggests a maximum of 40 universes of DMX is the limit. Art-Net uses a simple delta transmission compression technique that will provide about 40 universes. If an installation of more than say 30 universes is contemplated, then it is necessary to use the unicast features of Art-Net II and 100BaseT or better physical layer. If this is done the number of universes limit becomes purely related to the network bandwidth.

Click here for a PDF copy of the Art-Net spec.

But how do you get data out of an ethernet cable and in to your lighting rig?  You need an ‘Art-Net to DMX Bridge.’  They typically contain an ethernet jack and between 1-8 XLR connectors (one per universe).  Lots of companies make them.  Though prices have come down a bit as the technology has matured, current pricing seems to be $200 – $250 per universe of DMX output.

For that reason, we’ve decided to design an Art-Net node that’s directly integrated with the existing Tripix controller.  We’ll bypass the discrete equipment (and cable, and connectors, and cost, and hassle) required for Art-Net–>DMX and DMX–>Tripix and drive the pixels directly.

It’s likely that the node will receive 2 universes (1024 channels) of data.  Thus, it will be trivially easy to drive ~ 340 RGB pixels from a single controller.

Even more attractive is that the network interface will only add about $16 to the parts list of the base controller.

Plus development time.

More soon!

Tripix – Controller Update

Tripix Controller

 Finally!  Some updates.

Above is the board layout for the Tripix controller.  Several copies of the design are being fabricated right now.  Included on the board are

  • High-voltage ‘buck’ type power supply (accepts AC or DC input, up to 15-50 V)
  • DIP switch for setting the system’s start address 
  • Terminals for DMX in & through, isolated DMX receive section
  • RJ45 jacks for driving strings and injecting power
  • USB jack for in-the-field firmware updates and (possible) string control 

Hope to have video clips of 16-20 pixels running various demo patterns later this weekend.