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The roles of CAD in electronics

Although computers can now be used as design and drafting tools in many different fields, they’re probably still of greatest value in the industry which spawned them: electronics. Here they are rapidly becoming almost indispensible in the design of a great many products, but particularly things like printed Circuit boards and integrated Circuit chips. This article gives a broad overview of the current State of the art...

by JIM ROWE

In looking at the main areas where CAD has been applied in electronics, I think the best idea is to start with the simplest and easiest to understand, and work our way up to the fanciest.

Probably the simplest application is as a pure drafting aid, for drawing circuit diagrams or “schematics”, and perhaps PC board patterns. Here the CAD package is being used purely as a hi-tech replacement for the traditional drawing board/drafting machinę setup, and/or the adhesive pads and tapes which are still used to produce PCB patterns by the manuał method.

In a sense, this application of a CAD package is rather like using it as a fancy set of electronic drawing stencils. It pro-vides a large “library” of symbols or icons, from which you can cali up any one at will, adjust its size and orienta-tion, and place it accurately where you wish on the diagram or pattern you*re producing. Then you carf join up the various icons using a variety of connec-tion lines. When the whole thing*s fin-ished, you can produce a copy on paper using a dot-matrix printer, laser printer or X-Y plotter.

For producing a Circuit schematic, you use a library of circuit symbol icons; for producing a PCB pattern you use a library of component and IC package mounting pad icons; and so on.

With the simplest • computer-aided drafting packages, these functions are largely all that you can do. Others pro-vide the ability to check for basie er-rors. add notation and component values, and perhaps generate a “bill of materials” to aid in ordering the parts •required. In some cases they might also be capable of producing a net list — or shorthand description of the compo-nents and their connections, for use by other CAD modules or packages.

With the morę elaborate packages, it*s often possible to buy just the drafting module initially, and use it in this way until you’re ready to add the other modules to make things morę automat-ic.

Incidentally a CAD package can be “customised” for doing this kind of sim-ple drafting in almost any discipline, just by providing it with the appropriate

library of icons. You can use it for producing house płans if you wish, by providing it with a library of icons for doors, Windows, washbasins and WCs; or for producing landscape gardening plans, with a library of icons for shrubs, trees and garden beds. For basie electronics drafting, it^łs merely a matter of providing it with the right library of icons for circuit components and PCB pads.

Needless to say, this basie kind of CAD package allows you to produce a square, tidy and fairly professional looking schematic or PCB pattern. And you can do this quickly and efficiently — once you^łve got the hang of driving the package itself.

It’s true that some people find the circuit schematics produced by many of the CAD drafting packages not as at-tractive or as easy to fol Iow as those produced by a good, experienced human draftsperson using stencils and a drafting machinę. That seems to be be-cause the simpler CAD packages often produce only one basie linę thickness, used for virtually everything; there’s no easy way to give various parts of the

A sample of the printout (actual size) from OrCAD/SDT, a schematic Circuit design foo/, madę using a Star SG15 printer. Fuli annotation is provlded. (Courtesy Prometheus Software)

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ELECTRONICS Australia. September 1987