As a kid I did lighting for stage shows.
Turns out it was great training for a career in telecom, I learned basic rigging, working at heights, electrical work, patching rats nests of cables and the shared camaraderie that comes from having stayed up all night working on something no one would ever notice, unless you hadn’t done it.
At the time the Strand 520i lighting console was the coolest thing ever, it had support for 4 DMX universes (2048 channels – Who could ever need more than that!?) and cost more than a new car.
One late Friday night browsing online I found one for sale by a University in the state I live in, for $100 or best offer. You better believe I smashed the buy now button so hard my mouse almost broke. I was going to own my very own.
I spent the weekend reading through the old manuals, remembering how to use all the features, then dragged my partner for the road trip the following Monday morning to pick it up.
But before I could do anything fun I had to find a PS/2 keyboard and a VGA screen, which took me a few more days.
Then I needed something to receive DMX – I found everything now uses ArtNet (DMX over IP) and there’s visualisers for simulating an arena / stage lighting setup, but all take ArtNet now, so I ordered a DMX to ArtNet converter.
Inside the unit is pretty much a standard PC (OG Pentium in the Strand 520) with an ISA card for all the lighting control stuff.
The clicking hard drive managed to boot, but I didn’t think it’d last long, having been made more than 20 years ago. So I created a disk image and copied the file system onto a CF card using a CF to IDE adapter. This trick meant it booted faster than ever before.
One thing I’d read about online was the VARTA battery had a tendency to leak battery acid all over the PCB. This one had yet to fully spill its guts, but was looking a bit buldgey and had started to leak a little already.
The battery (I’d read) was only for storing info in a power loss scenario, and if the battery isn’t present it just slows the boot time as everything has to be read from disk, so I took the leap of faith and cut the battery out, and lo, it still all boots.
So now I was OK to get the desk online properly, but was getting semi-regular lock ups where DMX would stop outputting and inputs on the console were not read, but the underlying PC was still working.
I spent a lot time debugging this. BIOS settings, interrupts, I dived into how ISA works, replaced the battery I removed with a brand new one, and at one point I broke out the scope, but nothing worked.
Around the same time I noticed the Ethernet port (BNC!) would work if I just ran plain DOS (could ping from DOS but when the application started the NIC would go dead), which made me think I may be facing a hardware fault with the “CS” – the processor for the console.
Alas being more than 30 years old (this unit was made in 1996) there aren’t a great number of them around to test with, but I found another one on eBay for $50 but it was in the UK, and they weigh a lot.
Shipping this thing was not an option.
But for a bit of of extra cash the seller was willing to crack the case open and strip out the two main boards and post me just those. This had added bonus that the motherboard and CPU of the board sent from the UK was a 520i meaning it has the Pentium II processor – This Strand 520 was now going to be a Strand 520i.
A month later a box appeared at my door containing the boards, but the battery on the CS board from the UK had well and truly spilled its guts, leaving some toxic sludge around all the components nearby. A can of PCB cleaner and a toothbrush (which I will not be using to brush teeth with anymore) and I’d cleaned it up as best I could, but the fan output from the board was well and truly dead, with some of the SMD components just eaten by the acid.
So I put everything back into the case and wired it up. The mounts for the Motherboard were slightly different, and the software that is used for the 520i is different from the 520 (without the i).
The HDD from the UK was unable to boot, but I was able to get it to spin up enough to copy off the ~5Mb of files I needed, then I did a fresh install of MS DOS and copied the installer for the StrandOS.
Finally I had a stable working console. Not just that but the Strand Networker application was now available to me. So I plugged into the 10Mbps connection and set the console to output to Network as well as DMX.
I cranked open Wireshark and there was a mystery signal sent to the broadcast address on UDP…
I patched a single DMX channel and changed the value and when I viewed the data in Wireshark I could see a hex representation of the DMX 0-255 value.
Easy I thought to myself, it’ll just be a grid of channels, each with their value as hex. Ha! I was wrong.
Turns out Strand Shownet used a conditional form of “Run Length Encoding” compression, where if you’ve got channels 1 through 5 at 50% rather than encoding this is 5 bytes each showing 0x80, it uses 2 bytes, to indicate 5 sequential channels (run length) and then the value (0x80). Then there’s another bit to denote how many forward places to move and if the next channel is using RLE or not.
The code got messy; it’s not the best thing I’ve ever written but it works for 2 full universes of DMX (I need to spend more time to understand where the channel encoding overflow happens as I end up a few channels ahead of where I should be on universe 3 and above).
The code is available on Github and I’d love to know if anyone’s using it with these old dinosaurs!