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| Large as it is, this thing is a third the size of what it replaces. |
At my work, there's an important piece of "middleware" that dates back to 1982. It connects between a late-2010s video switcher and mid-1990s camera control units, and it's the gadget that makes a red "tally" light come on at the front (and elsewhere) of the active camera.
You'd think this would be easy. You'd think this would be standardized. You would be wrong. For example, the switcher is happy using any voltage from 5 to 18 Volts to run the red lights. The camera control units want to see 24 Volts. Well, five of them do. The sixth camera is CCUless, and it didn't come with any sissy red light on the front, either. It did come with a fancy track system and a fancy remote control setup, and so far, it hasn't injured anyone. Barely. It has whacked into the other cameras a few times, occasionally hard enough to do damage, but that's another story. Today's story includes my having to build a red light for it when it was first installed. There was no time to order anything, so the tally light was pieced together from odds and ends -- a plastic parts box, an old pilot-light jewel, a high-brightness red light-emitting diode -- and it is driven directly from the 24-Volt signalling system. That takes more current that merely letting a CCU know you'd like it to turn a light on.
The old system used a card cage holding several huge, hand-wired circuit boards, carrying 1970s digital logic, unobtanium sealed relays, and lots of other parts you either can't get or no one would use for a new design. It was built using a mixture of wire-wrapping and soldered stripboard, the latter a way to make a printed circuit board without any of that tricky designing or messy etching. It's entirely undocumented, and powered by what looks like a 1960s Western Electric DC supply, mounted upside down on a rack panel.* And just to make this more interesting, it is installed in a row of racks in a cul-de-sac off the main rack room, about thirty feet away (and around a corner) from all the things it connects to. (In fairness, it's close to where the camera control units and video switchers used to be -- in 1982.)
I started thinking about a replacement system shortly before the pandemic disrupted everything. When I came back, the particular part I'd chosen (a versatile DIN-rail-mounted solid state relay) had gone obsolete. I found an adequate replacement and started over. It's all DIN-rail stuff: inexpensive, standardized and upgradeable. (Of course, the 1980s original was, too, by the standards of the time.)
Once I had the thing built, I had to trace out everything the system connects to -- it has a few other jobs, too obscure to describe -- and where all the wiring ran, and then work out how to transition to the new version in stages, in the short intervals when the cameras and other equipment wasn't in use. And how to do so in a way that made no irrevocable commitment to the new system: we wanted to put it in and let it run for a week or more before jumping off the cliff. (Okay, for "we" read "I." I have a deep-seated aversion to the high-wire act; if you don't leave yourself a clear line of retreat, you're liable to end up like George Armstrong Custer.)
Yesterday, I finally moved the camera wiring to the new interface. I had three hours. Getting it all moved and tested took two and a half hours, working by myself. The wiring was buried under years of cables and trying to coordinate with a helper would have taken longer than sorting it all out by myself.
So far, it's been working through two long news blocks and a half-hour segment for late night. Here's hoping it will still be okay when I arrive today.
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* The power supply includes an added neon blown-fuse indicator that blows the fuse if you replace it while the supply is on, thanks to a poor choice of socket.
You beat me to the punchline. I was going to comment that, with help, it would have taken you 5 hours. Your next sentence deprived me of the pleasure. Sounds like you and MacGyver went to the same school ; )
ReplyDeleteLooks good! And in a nice enclosure. Forty-some years ago, the engineers here would have made that enclosure from sheet aluminum. We still have the big Pexto shear and a metal brake that must be 100 years old, we don't have time to do that kind of thing anymore.
ReplyDeleteOur prompter monitors have tally lights built into them, and had a similar voltage incompatibility with our switcher. I mounted plastic project boxes in each camera with an optocoupler inside to isolate them. I used a small perfboard and euroblock terminals so it was easy to install at the camera. It felt good to build something for a change.
For other tally lights and streaming relay controls, we've also moved to DIN relays and power supplies.
Cop Car: sometimes, it works out that way. I had spent a couple of days working out the paths the various wires and cables took. We've got a couple of bad choke points, where constricted routes and haphazard practices have created big snarls. Sure enough, the individual tally cables for the cameras passed through all but one of them, on similar but not identical routes that made it impossible to pull out all five as a group. With a helper, there's often a temptation to apply more force when the mess gets stuck, which could have been disastrous. All this work is essentially an in-flight repair: there's a whole TV station running through the same rat's nest and people will notice if I happen to shut it down. (How tangled was it? I use a little loop of brightly-colored Velcro strap to slide along cables I am tracing, which helps find tangles. At three points, the group dived into a mess so thick I had to abandon the Velcro and find where they came out on the other side to continue, trusting that on cutover day, I could work them through, one by one. Between fat camera cables and fatter multiple-pair and multiple-coax tielines, it can be a nightmare.)
ReplyDeleteGrich: that's a standard Bud rackmount "bathtub" chassis. They still make them and Digi-Key sells them for very reasonable prices. The completed project will get a smoked-plex hinged cover, which I hope will look interesting with lights blinking on and off behind it.
You and I are in the same corner when it comes to the high wire act. I learned very early on to leave some way for off shift maintenance to revert to the old system so I could fix it when I came in in the morning instead of at 2 AM.
ReplyDelete