Arts and crafts for test
Brad Thompson, Contributing Technical Editor -- Test & Measurement World, 6/1/2009 2:00:00 AM
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Living in an area that isn't exactly a hotbed of electronics technology, I acquire most components from mail-order sources. Two Radio Shack stores located within 13 miles offer limited (to put it mildly) parts inventories.
Needing a thin, sharply pointed test probe with a long reach, I assembled one from a length of hollow plastic rod, some heat-shrinkable tubing, and a long needle. To obtain the needle, I visited an arts and crafts store. In addition to a plethora of needles in all sizes, I found a variety of materials that might prove useful in the test lab. Note that the engineering characteristics of these materials may vary from source to source.
For example, the craft-supply store offers a range of foamed plastic shapes that can serve as insulation for heat-sensitive circuits, as non-RF-absorbent structural supports for EMI tests, for oddities such as large foam-cored toroidal inductors, and possibly as conical antennas. The consistency of foamed plastic varies, and closed-cell formulations offer more rigidity than open-cell and water-absorbent foams used for supporting live flowers.
Paper-coated foam board comes in handy for assembling structural prototypes and for the layout of a discrete-component printed-circuit board. Glue a 1:1 copy of the component-outline drawing to the board and "stuff" the drawing with through-hole components. Note that foam-core board may prove hazardous to components that are sensitive to electrostatic discharge, so use a sacrificial set of parts.
A local hobby-supply store usually features a selection of metal and plastic structural shapes that includes music wire, tubing, angles and strips, and sheets. You may be familiar with the "gimmick"—two lengths of wire twisted to form a crude capacitor of a few picofarads. As a more formal alternative, you can cut a length of small-gauge brass tubing and slip it over a length of insulated hookup wire. Using AWG #18 PTFE-insulated hookup wire and tubing just large enough to accommodate the wire, I measured approximately 3.2 pF per inch of tubing. Adding a length of heat-shrinkable tubing completes the "capacitor." The same brass tubing can also shield a wire or form the outer conductor of custom-made coaxial cable.
Some call electronic testing an art, but it’s also a craft.
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