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Hardware PC Board Designs

The PC boards were layed out directly from the schematics developed in previous sections. No auto-routing was used during the layout process, mostly because it was not entirely trusted. This is especially true in cases where audio signals and noisy digital signals share board space. Another point in favor of manual layout was that many of the parts had to be in specific positions on the PC board because of panel-mounting, etc. With many specific parts positions, some auto-routers become confused and produce routing of poor quality. Many parts were chosen that were not in the default PowerPCB library. This required creating a custom library of parts. Once a stock of parts was on hand, a caliper and fine-scale ruler were used to take measurements of pins and case sizes. These measurements were used to construct a component layout for the custom parts library. To be sure the appropriate modeling was done, a real-size version of the part was printed and fitted with the actual part. Any variations or discrepancies were then fixed. PADS Software's PowerPCB software was used for all board layouts. Once boards had been designed, proofed, and test-fitted, Gerber output was generated. Separate Gerber files are produced for top and bottom routing, solder masking, drilling, and silkscreening. All Gerber output was checked with GCPREVUE, a freeware Gerber viewer. Once convinced of the quality of the output, the Gerber files were sent to the PCB house via the Internet. EP Circuits, a fabrication house located in Canada, offered the best price/performance ratio for board prototyping. It was decided that all boards in the mixer unit would be treated with solder mask, mainly because of the use of surface-mount components that were to be hand-soldered. All boards produced for the control board did not have solder masking applied. This was done in an attempt to save precious development funds.

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Steve Richardson 2000-07-06
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