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KISS: Keep it simple, Schweber

I’m a big fan of simple devices that do one well-defined task in the engineering, design, and troubleshooting world. For example, a “breakout box” which lets you access and tap signal lines is very handy for checking both DC and AC signals of the interface.

I recently came across such a box that had been in my collection, but forgotten about: a breakout box for the standard four-wire telephone cable (photo ).



Yes, I know that telco lines seem so “yesterday” now that we have our high-speed cable, wireless links, and other more sophisticated interfaces, but they still play a large role in many systems and applications. For example, most home-security systems use the wired telephone line to signal an alarm. And most homes still have a basic landline phone as their primary means of voice communications, especially when reliability is a primary objective!

The breakout box says “Harris” on it, but I don’t think that Harris Corp made it; I suspect they relabeled it for use as a promotional item or as part of a design or evaluation kit. Regardless of its history, the box meets my criteria for “truly useful”: it does one thing, it’s easy to use, it has nothing to wear out or interfere with the measurement, it neither uses nor requires software, it doesn’t try to analyze the signal. It just helps you do your job, transparently and quietly. And when you dig it out from wherever it has been buried for years, it still works as intended, and needs no instructions or user manual. Similar breakout boxes are common in the RS-232 world, breaking out all 25 pins of the standard DB-25 connector and even letting you “cut” some lines or cross-over lines, using basic jumpers.

I have come across other similarly simple devices and instruments over the years. One that stands out is the model ELS2 AC line splitter from Meterman Test Tools www.metermantesttools.com, which lets you easily clamp an inductive current probe onto the wall-outlet AC line, to measure line current and thus power. (As a convenience, the splitter has x1 and x10 loops) This simple unit doesn’t provide anything you couldn’t build yourself in about an hour and for a few dollars, using an AC plug, an AC receptacle, and some wire—except that you’d have to spend your time rigging it up and also make sure that you properly insulated everything to avoid shock hazard. The beauty of the Meterman unit is in its very single-mindedness and simplicity.

Not all KISS units I have seen are so basic and simple. Many years ago, when I did a lot of work with linear variable differential transformers (LVDT)—a very reliable and sensitive position sensor—we would test our interface circuitry using a real LVDT and a precision mechanical gauge that set and measured displacement of the LVDT core. But this setup was large and somewhat cumbersome to set up, use, and read.

Then one day, an engineer on the team came across a device called a ratio transformer, which was a transformer in a box but with precise taps and front-panel knobs in a decade pattern. With it, you could quickly set a turns ratio in steps, with ten steps per position. Electrically, the transformer looked like the LVDT, but mechanically, it was a nice piece of test gear.

This box, which I believe was made by Gertsch (no longer in business, but I suspect someone else has picked up the product line), made the task of testing the accuracy and linearity of the LVDT signal-conditioning front-end much easier, and more reliable, since the settings were so easy to set and record. It needed no power or software; it just emulated an LVDT but added easy settability. That’s my kind of device!

1 comment on “KISS: Keep it simple, Schweber

  1. ljsdoifjewf
    August 30, 2015

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