Have you ever wondered why some things in life are written in books and other, equally essential things, just never get printed? You have to learn them from trial, error, and ... more error. What I'm about to convey hasn't been written anywhere (to my knowledge). Yet it plays an essential role in the life of anyone who deals with technology, especially audio and video technology. It has to do with wiring strategy --- not the art of drawing schematic diagrams according to established electrical conventions --- but how to think when planning a complex system.
What follows is my opinion based on having designed and built a half dozen TV studios and countless smaller projects. Other opinions may be just as good, but if you have no opinion at all, feel free to use mine as a place to start.
The need for wiring diagrams -
If you don't think this is important stuff, then maybe you need to spend an afternoon tracing termination troubles in a wild web of wires cloaking the catacombs behind stacks of equipment. Here are some reasons for taking an active role in creating formal wiring diagrams for any substantial system:
1. Sure, you can hook everything together, but a month from now will you know what you did? Will you be able to trace the paths from outputs to inputs when gremlins invade your equipment?
2. If technicians wired your system, will they remember a month from now what they did? Will you be able to figure out what they did if having problems in their absence?
3. Do your technicians use the system so often that they know the wiring diagrams in their heads, and like to keep it that way for "job security?" If so, they may be secure, but you are not. How much do you want to rely on your technicians?
4. Which do you prefer, tracing lines on a paper or hacking your way through a jungle of wire armed with a machete and a few expletives?
5. Is the system used by many clients and maintained by several technicians? Until mental telepathy is mastered, paper is about the only way to transfer wiring information from one person to another.
6. Which do you think will be better: an off-the-cuff speech or a speech that has been thought about, organized and re-organized. Take it from an author, good articles aren't written, they are rewritten. The same is true for wiring. Drawing the diagrams makes you think. It forces you to solve some of your problems in the paper stage where changes are cheap and easy to make.
7. If you built a house without any plans, how do you think it would come out? Plans keep things orderly.
8. If you create the design and expect technicians to carry it out, then of course, the design has to be written in a clear, concise way. Not only do you avoid the errors of miscommunication, but you aid your technicians in planning the construction. The technicians see the whole picture at once and can buy parts and set up space, and can organize the construction process efficiently. It's comparable to going to an on-line edit suite with a well defined edit decision list; the edit process becomes quick and mechanical. You are not spending $400 an hour while professionals and a room full of equipment stand around watching you think. With a wiring diagram, you've done the thinking and except for the inevitable surprises and changes, the installation should progress smoothly.
9. The diagram gives others a chance to review your work and suggest improvements before the plan is put into effect. The more expensive and complex the system, the more you can benefit by the wisdom (and yes, criticism) of others.
10. Patch bays, festooned with inputs and outputs, are notoriously hard to read unless they are logically organized; specific inputs and outputs are difficult to locate. Part of creating a wiring diagram is to organize the content of the patch bays so that similar things are grouped together. Even if patch bays are well organized, when several are involved, it is still easier to glance at a wiring diagram and trace a line to a certain place on a patch bay than it is to read the patch bay, neck kinked at 45° , eyes squinting to read the microprint, searching for a particular item. Anyway you look at it, wiring diagrams and patch bays are synergistic; the good logic that you put into one strengthens the other.
11. Many TV engineers have a tendency to build a system, then add to it willy-nilly making the wiring and patch bays illogical. Since they use the system every day, they get used to this randomness and may not even notice it. For the rest of the world, the system becomes hard to follow and tedious to use. In this regard, creating wiring diagrams creates orderliness and counteracts the entropy of random growth.
Here's an interesting observation: Have you ever noticed how computer programmers dislike writing documentation for their programs? And try getting building contractors to provide "as-builts" showing changes in architectural drawings to reflect adjustments made during the building phase. Police grumble a blue streak about the reports they have to write and many teachers detest report card time as much as their students. Similarly, most of the technicians and engineers that I know despise documenting the web of magic they weave behind the racks. Maybe it seems mundane, uncreative, or too detailed to be any fun. Whatever the reason, documentation seems to drain the adrenaline from technical people.
The role of the computer -
Assuming that you are convinced that you need a diagram, the next question is whether to construct it on a computer or on old-fashion paper. Personally, I use paper, but that's because I can't seem to find the 10 hours or so needed to learn a computer assisted design (CAD) program and don't have access to a plotter to print out the results. If you have already climbed that learning curve and have the plotter, then go for it, use the computer. I still suspect that you'll find yourself sitting with pencil in hand trying to draw the preliminary diagrams the old-fashioned way before stepping up to the keyboard.
The thing I like about pencil and paper, at least in the preliminary stages, is that there's no "technology" to get in the way of your thinking. When drawing wiring diagrams, there are a lot of details to juggle and the process takes intense concentration. I find it necessary to draw as fast as I can once I get an idea, sketching the interdependent facets before I forget them. Again, if you don't find your computer to be a distraction, then put it to work.
It is not important that you are a fantastic draftsperson or that you adhere to particular schematic "rules." It is important that your drawings are clear and your symbols consistent. Have a ball; develop your own conventions as you go along. Anything that communicates clearly will do fine. Here are some of my thoughts.
The paper -
Have you ever tried to draw a map to your house and ended up with 3/4 of the streets squashed into the upper right-hand 1/16 of the page? The same thing happens with wiring diagrams. I used to draw them on large sheets of paper thinking I would have plenty of room. Invariably the drawing would grow a thick matrix of tendrils occupying 1/16 of the paper leaving the rest of the page blank.
Nowadays, I give in to my poor planning right from the start: I use 8-1/2 x 11 or 11 x 17 pages, and when I reach the end of a page, I attach another page onto it. The pages go wherever the lines go without regard to form or beauty. When the whole works is done, I tack on enough pages to fill in a rectangle of paper and then reshape the drawing to better occupy the space. Remember that step 1 should be thinking, not worrying about elegance.
The patch bays -
Most wiring diagrams involve patch bays. Since everything comes together at the patch bays, they form the heart of the diagram, the center of the web.
Because patch bays all look the same in structure but involve a lot of lines and spaces, I hand-draw one blank patch bay, then photocopy it to make the other patch bays.
Each patch bay gets a letter or number representing the input side and the output side, and each connector gets a number. This will be helpful in specifying the location of things later.
Actual patch bays have outputs on the tops and the inputs on the bottom, thus signals flow downhill. On a diagram, signals flow from left to right or downhill. This results in sources for signals being on the left of the patch bay and the targets being on the right.
Patch bays are either normalled or not normalled. Normalled means that when there is no patch stuck into the socket, the signal automatically travels from the output to the corresponding input side of the bay. It is as if each output had a patch connected to it feeding to the socket directly below it. On paper, it is as if the signal traveled directly from left to right through the patch bay. We indicate this normalling with an "N". On the physical patch bay, I further affix a dot to indicate which outputs are normalled. When a patch bay is not normalled, there is no "N" and the signal doesn't travel anywhere unless it is physically patched.
Where possible, leave room for growth. When going from one group (say camera outputs) to another group (say TBC outputs), leave a couple empty patch bay sockets. This way, if you add another camera, for instance, you can list it on the patch bay next to the other cameras (very logical) without moving all the remaining connections down a slot (vary tedious).
Sources, monitors, and other gadgets -
It seems logical to put all the sources (ie. CD players, videocassette players, etc.) in the same area of the diagram. That way when you look for something on the diagram, you don't have to hunt all over the diagram; you pretty much know where to start. Once you've lined up your sources, you are likely to discover that some items receive signals as well as send them (ie. audio and video recorders). Now you have to decide whether to treat recorders as something different from sources. This is a personal decision, but I tend to put them with sources because most recorders are also used a players and are therefore sources.
The signals fed to the sources have to come from somewhere, preferably from the left of the sources. Invariably you are forced to send signals wrong-way to the left on the page to feed the sources that are on the left.
Once I have the sources figured out, I try to name and number them in a logical sequence. The second audiocassette player might be called CASS-2 or Pioneer CASS to distinguish it from its Sony brother. Each stereo output would be represented by a pair of lines, one marked L and the other marked R.
I like to group TV monitors together, especially if they are in a console. I try to name them the same as their sources (i.e. VCR 1, SAT 2, PRO, PREV, etc.). Sometimes this rule creates a wiring nightmare because some sources are directly monitored (placing the monitors near the sources on the page) and some switchers have their own monitor outputs. They end up in different places in the diagram forcing you to wrap the lines all the way around Robin Hood's barn to keep the monitors together. So, I swallow my compulsive adherence to convention and make two or more blocks of monitors.
Switchers and audio mixers compete with patch bays as being the heart of the system. It is hard to decide whether to draw a big mixer and dangle patch bays from it or draw a big patch bay and dangle the mixer and other stuff from it. If the mixer has more inputs and outputs than will fit on one patch bay, then I let the mixer be the center of the system and spread the patch bays around. I generally put a feeding patch bay in front of the mixer (to the left of it) and run the mixer's output to another patch bay to the right of the mixer.
Parallel construction -
Once I have determined the sources, the monitors, the patch bays, and the switcher or mixer inputs and outputs, I list them in a parallel sequence. Thus, if on the left side of my diagram I have VCR 1, VCR 2, VCR 3 in a row, the VCR monitors will run similarly; VCR mon 1, VCR mon 2, and VCR mon 3 etc. The patch bay will keep the same order: VCR 1, VCR 2, VCR 3. If these are inputs to the switcher, they will go VCR 1, VCR 2, VCR 3 so that the buttons on the switcher will also go VCR 1, VCR2, VCR3.
The real world conspires mightily against convention. If you have four cameras, but only two feed directly into the switcher, what do you do --- do you draw your cameras in order 1, 2, 3, 4, then list them in the patch bay in order, but then split the switcher inputs so that the patch bay has input 1, input 2, and for the third and fourth outputs to the patch bay, leave them blank or put something else there? This forces switcher inputs 3 and 4 to be split further away from 1 and 2 on the bay, a lesion in logic. On the other hand, you could have the switcher inputs listed 1, 2, 3, 4 but across from them on the bay's input side, you would camera 1, camera 2, something else, something else, forcing cameras 3 and 4 to be split from 1 and 2. There is no way to make these situations work out perfectly; just decide what will make the most sense to you. I tend to group my cameras and other devices in logical order, allowing switcher and mixer inputs to be split up, but at least I keep them in sequential order, even if there are gaps between.
I try to make the audio patch bays parallel the video patch bays so that once you've made a video patch, you can find the audio patch quickly. An army of Murphy's Laws attack this plan as well. Stereo audio requires twice as many sockets as video, which means that video sources 1 through 11 take up video sockets 1 through 11 while taking up audio sockets 1 through 22. Further, video involves much more processing than audio. I somehow have to work time base correctors, proc amps, monitors, distribution amplifiers, and other paraphernalia into the video patch bay and have very few similar devices to put in the audio patch bay. I still try to build them parallel even though I know I can't. If you have the luxury of extra patch bays so that you can leave some sockets empty, you may be able to construct your audio and video patch bays in a half-parallel fashion. For instance, you might display 11 video sources, leaving 11 sockets empty so that the corresponding audio patch bay can be filled with exactly the same sources. If this method seems too wasteful to you, consider putting some of the video processing equipment (for which there is no audio counterpart) in the remaining 11 sockets on the source patch bay. This at least fills up the patch bay while keeping the video processing equipment grouped together.
Drawing the lines-
Once you have organized your sources, patch bays, monitors, and switchers (or mixers), it is time to draw the lines between them. I used to draw one line to connect every single item on the page. This has ended up with lines of angel hair spaghetti, many of them parallel, non of them easy to follow. A draftsman convinced me that it was alright to group lines together if they were all going to approximately the same place. Thus, ten sources would have their lines joined together, perhaps travel to a patch bay, then split out again for the patch bay. After the patch bay, some lines would regroup to a single line and travel to a switcher where they split again.
In order to trace which line goes where, each one needs a name. Every line, before it joins a group, gets little flag telling where it is going. If VCR2 feeds patch bay input R14, then its line gets flag listing R14 as its destination. At the patch bay end, no flag is necessary because the patch bay already lists VCR2 as the source. Similarly, switcher input #1 which might be camera #1, gets a flag on its line showing that the line comes from patch bay K, position #1. Thus, all the wires, even if grouped together, can be traced from their source to their destination.
When connecting the actual wires, each gets a label on the end telling where it's going. In most cases, the label reads the same as the flag on the diagram.
Some wires connect to other rooms, which in turn have their own wiring diagrams. To avoid cramming too much onto one diagram, simply flag these lines with an arrow indicating their destination on the next diagram.
Surprises uncovered -
What happens when you feed the Y/C output from a VCR to a compatible Y/C TBC, to another VCR or a switcher? If the signals are travelling as Y/C, they require a special connector. How do you put that in the patch bay? One solution is to purchase or make a breakout connector which separates the Y/C wires into separate coax wires. These each get their own terminal on the patch bay. Now you will be able to patch Y/C signals between various sources and processing devices. Just make sure your patch cables are the same length or else the C might not arrive at the same time as the Y.
On the audio side, consider how many of your devices use balanced lines (3-prong XLR connectors), versus unbalanced lines (RCA, mini, or phono connectors). Balanced and unbalanced equipment do not like to be connected directly together. In order to take advantage of balanced line's better signal characteristics, a balancing transformer is needed. This should show up in the diagram somewhere.
It would be wise to convert all inputs and outputs to balanced or unbalanced lines so that users wouldn't accidentally patch from one to the other. The same is true for high and low level signals. Distortion can occur if an unsuspecting user were to patch a high level source into a low level input.
On the video side, it is good to keep RF (radio frequency) and video signals separate. Antenna, TV cable, and modulated video signals should not be patched directly to video equipment. Keeping the RF inputs and outputs on a separate patch bay or a separate section of the patch bay, and perhaps color coding the patch bay labels will help keep these signals kosher.
Labeling wires and buttons -
Unlabeled buttons, sockets, and wires are close to useless. Every wire should have a flag attached to each end. Every button should tell what it does, and every socket should tell where it feeds. The wiring diagram is helpful here too. Once you have selected formal names for your sources, patch bay legends, and labeled the lines as they emerged from groups in the drawing, you have everything you need to make logical labels on the wires and equipment itself. The wires could either list what item they are feeding to or from, or could list the patch bay number that they connect to, or could simply have an accession number (a serially selected number that doesn't mean anything except to designate an identity for the wire). If such serial numbers are used, they should be listed on the wiring diagram also so that the cables can be easily traced.
Naming the switches and sockets the same as they are named on the wiring diagram simplifies the process of referring back and forth between the diagram and the real world.
Separation of labor -
Making wiring diagrams is tedious and takes a lot of thought, but it is something the average, intelligent audio or video person can do. Engineering firms charge thousands of dollars to create these diagrams, and if your time is very expensive, maybe this is a good deal. Even if your time is expensive, the thinking that goes into the first version of these diagrams is productive work; you need to do a lot of soul searching about how you want your system to operate, what is its default state (what happens when there are no patches, and everything simply gets turned on) should be. As you develop your diagrams, you learn more about the flexibility of your system and may discover interconnections you hadn't thought of before. You may also discover problems about sychronization, timing, cable length, and signal distribution. You will quickly learn how many distribution amplifiers you will need to buy if you are sending signals to several places. Many a policy in this world has changed when the boss had to sit down and actually write it. That's when he finally discovered how foolish it appeared, once in print. Wiring diagrams are very instructive.
After creating your rough diagram, you can:
1. Redraw it neatly on a large piece of paper.
2. Get someone else to redraw it neatly on a large piece of paper.
3. Enter it into a computer and have the CPU redraw the diagram.
Professional draftspeople can do a neat job of reorganizing your schematic spaghetti into a neat package. Since the thinking has already been done, these people do not have to be experts in your field, making their services somewhat affordable (as opposed to having an engineering firm do the drawings). Similarly, when the time comes to label the wires, buttons, and sockets, a moderately paid person with neat handwriting could be employed. The diagram tells all; the labeling becomes a mechanical job.
If you have access to large photocopiers or blueprint making equipment, you could create your wiring diagram on a large single sheet. If you do not have access to this equipment, you might consider creating your diagram on a matrix of 8-1/2 x 11 sheets. The sheets would be easy to photocopy and could then be taped or mounted together into a larger display. If one part of the facility changed, you would only need to update one page of the master, photocopy it, and stick the photocopy where the old page used to be.
I like to mount my diagrams onto foamcore, perhaps putting the video wiring on one side and the audio wiring on the other. The foamcore could then be slipped behind the console or hung on the wall for easy reference.
I am a neat freak. I am compulsive about having drawers, switches, and sockets neatly labeled. Some people can quickly find things in a messy pile, but I cannot (I often cannot even find things when they are neatly filed). I desperately need wiring diagrams when troubletracing. Further, I am too impatient to read all the lettering on a patch bay to find the socket that I want; I love zipping over to the wiring diagram to track my way down to the appropriate socket, and then look for it on the patch bay. If you are like Felix Unger and I, there are wiring diagrams in your future. If not, never ask the likes of me to help you fix anything; spaghetti is for eating, not for untangling and tracing.
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