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A schematic drawn on paper can be manually converted to a net list and part list to start a PCB layout, but from now on we’ll turn our attention to circuit board design using computers. Most technical activities these days take advantage of the increased speed and accuracy of computer-aided design (CAD), so we’ll leave the old methods for the historians to study. Software packages have been developed for electronics, and schematic concepts can be captured using a graphical user interface to do the following:
- Select symbols from a CAD library;
- Place symbols on the screen; and
- Connect the symbols together.
You may not even need to assign reference designators or pin numbers to the symbols, unless you want to force specific arrangements (like connector pin assignments or logic gate assignments, for example) because the software can make these assignments automatically during the packaging process. The computer will or should make sure that each symbol is given a unique reference designator, assign pin numbers based on the selected component type, and report any conflicts or discrepancies. After the packaging process has been completed successfully, the schematic should be “back-annotated” with the pin number and reference designator assignments. Modern technology can provide assistance in other ways, too. For example, circuits can be moved, rotated or copied into many similar circuits with just a few mouse clicks.Read the full column here.Editor's Note: This column originally appeared in the April 2013 issue of The PCB Design Magazine.