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The twice-monthly Lost Knowledge column explores the possible technology of the future in the forgotten ideas of the past (and those just slightly off to the side). Every other Wednesday, we look at retro-tech, “lost” technology, and the make-do, improvised “street tech” of village artisans and tradespeople from around the globe. “Lost Knowledge” was also the theme of MAKE, Volume 17


This week, we take a peek at the not-lost but fast-fading art of wire-wrapping. Wire-wrapping used to be a circuit prototyping and assembly technique found in the repertoire of every electronics geek, but increasingly, generations of wireheads are now coming of age knowing little-to-nothing about it. I, for one, have never operated a wrap tool or populated a wrap card in my life. I got a wire wrap tool in an electronics toolkit at the beginning of my interest in electronics and hadn’t the vaguest idea what it was until, years later, I saw it in a how-to book and thought: “Aha, so THAT’S what that funny-looking tool is for!”

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Wikipedia has a good overview of wire-wrapping:

The electronic parts sometimes plug into sockets. The sockets are attached with cyanoacrylate (or silicone adhesive) to thin plates of glass-fiber-reinforced epoxy.

The sockets have square posts. The usual posts are 0.025 inches (635 micrometres) square, 1 inch (25.4 mm) high, and spaced at 0.1 inch (2.54 mm) intervals. Premium posts are hard-drawn beryllium-copper alloy plated with a 0.000025 inches (25 microinches) (635 nanometres) of gold to prevent corrosion. Less-expensive posts are bronze with tin plating.

30 gauge silver-plated soft copper wire is insulated with a fluorocarbon that does not emit dangerous gases when heated. The most common insulation is “kynar“.

The 30 AWG Kynar is cut into standard lengths, then one inch of insulation is removed on each end.

A “wire wrap tool” has two holes. The wire and one quarter inch (6.35 mm) of insulated wire are placed in a hole near the edge of the tool. The hole in the center of the tool is placed over the post.

The tool is rapidly twisted. The result is that 1.5 to 2 turns of insulated wire are wrapped around the post, and atop that, 7 to 9 turns of bare wire are wrapped around the post. The post has room for three such connections, although usually only one or two are needed. This permits manual wire-wrapping to be used for repairs.

The turn and a half of insulated wire helps prevent wire fatigue where it meets the post.

Above the turn of insulated wire, the bare wire wraps around the post. The corners of the post bite in with pressures of tons per square inch (MPa). This forces all the gases out of the area between the wire’s silver plate and the post’s gold or tin corners. Further, with 28 such connections (seven turns on a four-cornered post), a very reliable connection exists between the wire and the post. Furthermore, the corners of the posts are quite “sharp”.

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The backplane of a Zilog Z80 computer from 1977.

There are three main methods of wire wrapping:

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Manual Wrapping: Here, a small pen-like tool is used to hold and twist the end of the wire onto a square terminal post that’s been inserted into a wire wrap board (or card). This manual method is especially common for small prototyping projects or when doing repairs on large wire-wrapped boards.

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Semi-automatic Wire-Wrapping: For larger wrapping jobs, a manually-powered “squeeze tool” is used. A trigger grip is pumped, which twists the wire onto the terminal post. Used in medium-sized wire-wrapping applications and in field repair.

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Automatic Wire-Wrapping: For really extensive wire-wrapping of large electronics arrays, such as those used on airplanes, telephone switching systems, etc, electronic wrapping guns are used, which greatly speed up the wrapping process.

One of the better intro articles available online is on The Citizen Scientist’s site. In it, author Allan Rydberg runs through the steps of using a manual wrapping tool: 1) stripping the wire, 2) inserting it into the tool, 3) wrapping it onto the terminal post, and 4) inspecting the finished wrap (all seen below).

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One might think there’s little-to-no reason to use this technology anymore, that it’s been completely superseded by solderless breadboarding in prototyping and soldered electronics in more permanent applications. But there are still situations where wire-wrapping makes sense. It is a purely mechanical connection that’s extremely reliable (especially in situations where a solder joint might be prone to failure over time). Also, in field applications, it can be easier for a tech to use a wrapping tool instead of a soldering iron to do repair work. With the onward march of miniaturization, and surface-mounted components, wire-wrapping has greatly diminished, but it’s still an option in some situations, especially for high-reliability systems, such as in aviation, military tech, and telcos (tho I’m not sure how many new systems are being built these days with wire-wrap technology). Maybe some wire-wrap aficionados will chime in in comments and tell us where this tech is still in active use.

There’s amazingly little information online about wire-wrapping. Here are a few resources:

Wire Wrapping on Citizen Scientist
How to Wire Wrap
Wire-Wrapping Techniques
Wire-wrap pics from Steve Chamberlin’s home-built CPU

 

More:

Gareth Branwyn

Gareth Branwyn is a freelancer writer and the former Editorial Director of Maker Media. He is the author or editor of a dozen books on technology, DIY, and geek culture, including the first book about the web (Mosaic Quick Tour) and the Absolute Beginner’s Guide to Building Robots. He is currently working on a best-of collection of his writing, called Borg Like Me.


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Comments

  1. Gizmo says:

    Now I feel old.

    When “Lost Knowledge:” is “Carving Mammoth Tusks” I don’t feel so bad. But when “Lost Knowledge:” is something I’ve done for years, then I feel a bit like a mammoth.

    I probably still have some wire-wrapped things on a shelf.

  2. joem says:

    I respectfully say “good riddance” to wire wrapping. Its time has come and gone. Learned it once, but couldn’t see any advantage (for me) over my beloved solderless breadboard.

  3. screaminscott says:

    I remember reading the book “The Soul Of A New Machine” by Tracy Kidder. In it, he describes the creation of a new mini computer at Data General Corporation. I still remember his descriptions of the wirewrapped circuit boards, and the frustrating troublshooting of one elusive problem. Eventually one of the team-leads picked up the board (to the gasps of the engineers) as a diagnostic tool was running, and shook it.

    The board failed right there, with the same error message they had been getting all along. The team set about re-wrapping all the connections, and the board worked fine afterwards.

    That lesson has always taught me to look outside my expertise as a computer programmer when I encounter bugs in my systems.

    http://en.wikipedia.org/wiki/The_Soul_of_a_New_Machine

  4. Paul @ FiscalGeek says:

    I have to agree with Gizmo, this is making me feel old. I’ve done this thousands of times terminating T-1 lines back in my ISP running days. I used the exact automatic unit you have shown in the article. Ah those were the days.

  5. mightyohm says:

    This is a skill I wish I had, if just for the geek cred!

  6. jeff-o says:

    Where I work, we use bed-of-nails test fixtures for in circuit testing. The test fixtures are wired up almost entirely using wire wrapping. It would be a nightmare to get a hot soldering iron in there to fix or change connections, but a manual wire wrap tool works great.

  7. Tai O says:

    I built a Z80 based computer using wire wrap. It is definitely the way to go for any prototype involving many connections. My Z80 computer project can be seen here: http://www.derivedlogic.com/Z80%20Microcomputer/z80micro.html . If starting a project like this, make sure you order enough wire! I went through about 400ft!

    1. Gizmo says:

      I made a similar Z80-based board. I had video out to an RGB display (same display circuit as the commodore 128d) and all of my code was stored in battery-backed ram. Ah, memories.

    2. Dave Kennedy says:

      I love the Z80 based computer! Thanks for sharing. Although mine is not nearly as impressive, I thought I should follow your lead and share my own project. Here is my page for my Intel 8088 based computer. This was a project for a microprocessors class at Utah State Uni, Fall 2007. This was part of my Computer Science BS. (yep, science, not engineering). http://davidwkennedy.com/photos_8088.htm

      1. Gareth Branwyn says:

        Wow. Nice wrap job, David! Thanks for posting that.

  8. eric says:

    I have been wire wrapping since the late 80′s. many of the old patch bays at work still use this technology. I can not tell you the number of hours I have spent cramped behind a patch bay shooting wires. Good times.

  9. Mac says:

    During the summer of 1979, my senior year at Kansas State University, I worked as an intern at NCR in Wichita, Kansas. My task was to wire wrap a prototype controller for one of the first 5 1/4-inch Winchester hard drives (It was huge, compared to 5 1/4-inch hard drives of the 1990′s!). I was fortunate to be able to use a motorized wire-wrap gun, rather than a manual tool. After many hundreds of connections wrapped and tested for continuity, only one connection was found to be incorrect during testing with the Winchester drive! On my last day at NCR, before returning to college, it was very satisfying to see the controller successfully commanding the hard drive to seek sectors and read and write data.

    Nowadays, I still use 30-gauge Kynar and my manual wire-wrap tool for some electronics projects and “blue wire” repairs. I now use Kynar wire and the tool to wrap around solder-tail socket pins and then solder the connections. This is more like Vector wiring, I think. I still have a number of wire-wrap sockets, though. Just a couple of weeks ago, I repaired a memory stick after the USB connector was sheared off. Yes, Kynar is still useful, even if it is used in ways other than it was originally intended. I hope they don’t stop making it.

    Ah, the memories!

    1. clayton says:

      The power industry has never stopped using wire wrapping. The latest Siemens T3000 distributed control system still uses thousands of these to connect the devices from the field to the input modules.

      Tip
      A wire wrap gun with a bit of electrical tap at the end is the best thing to use to prevent a short circuit when wrapping.

  10. Mac says:

    I am currently wiring a large pipe organ. I use wire-wrap for many of the main cable splices/junctions. I use the squeeze tool, and standard cat-3 24 gauge twisted pair (6, 12, 25 and 32 pair)

    Like many of you, I learned it in the Telecom industry. It’s used daily.

  11. Rob Cruickshank says:

    Funny, I was just teaching an intro to electronic fabrication workshop, and right at the end, after teaching everyone to solder, I found some wirewrap tools, and showed the students what it was all about. It’s a great techique if you have a lot of chips to wire, and might want to change your mind about things. It has the flixibilty of breadboarding combined with the permanence of soldering, which is handy. I haven’t built anything big with it for a while, but I kinda miss doing it.
    Another forgotten skill that is very handy is cable lacing:
    http://en.wikipedia.org/wiki/Cable_lacing

    1. Gareth Branwyn says:

      I’m planning on doing Cable Lacing as the subject of next week’s Lost Knowledge column.

  12. cheap computers says:

    It is a purely mechanical connection that’s extremely reliable.

  13. drivedisc says:

    I restore old mainframes and minicomputers for the Living Computer Museum in Seattle. We more than occasionally have to build an interface for some old piece of equipment, and wirewrap is the the obvious choice. If we need to build more than one of something, we will generate a printed circuit board after we work out the kinks with wirewrap.

    Keith Perez
    Senior Software Engineer
    Vulcan, Inc.

  14. None says:

    Not exactly “lost knowledge” – wrapping is used all of the time for prototype construction.

  15. In the Flesh says:

    This technology really isn’t lost. It is still used in the telephone industry, just not real often. I’m contracted to AT&T, installing their telephony equipment. Occasionally some of the equipment we install requires wire wrapping and cable lacing.

    1. Znapel says:

      Indeed. Back when I had a stint working with DSL a few years ago I had to wire wrap cross-connects on pairs that were to be tied into our DSLAM. All of the CO’s I visit still have all of the pairs wired up like this. I had no idea it was used outside of telecom. When I passed on the gig to the next person they were just as amazed as I initially was at how strong of a mechanical connection it creates. Luckily I had to do the odd pair here and there, never hundreds of new pairs for a big expansion or turn up.

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  17. Stephen L. says:

    Still use it today to prototype ICs that don’t have a DIP option for the breadboard. Works great and is much cheaper and quicker than soldering an IC onto an adpater.

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