Tab Electronics Guide to Understanding Electricity ... - Sciences Club

Linear Electronic Circuits
259
CAD Methods of PC Board
Development
Before leaving this discussion on PC board fabrication, I would like to
briefly describe the newer generation of CAD (i.e., computer-automated
design) programs available for PC board development. In bygone days, an
electrical engineer was forced to sit down with a schematic diagram, a
tablet of graph paper, and a sordid collection of templates, rulers, and
other drawing instruments, in the attempt to design a PC board layout
for a new circuit design. This was usually an aggravating and time-consuming
project, requiring the engineer to draw out trial-and-error track
runs, reposition component placement, and redefine board dimensions,
and all the while the designer had to think in an upside-down perspective
as to how the track runs on the bottom of the board would connect
to the component leads on top. As PC board complexities increased,
this process became proportionally more difficult—in the case of modern
multilayer PC boards, it became virtually impossible.
During the 1970s and 1980s, industry began developing various CAD
programs to facilitate the difficult task of PC board layout design. Later,
these CAD programs were “humanized” to make them more “user
friendly,” and marketed to electronic hobbyists for the purpose of
designing “home-brew” PC boards. Currently, these PC board layout programs
are available at modest pricing, and they are so easy to use that
almost anyone can design PC boards at home. If you anticipate that you
will be involved with electronics as an ongoing hobby or profession, I
highly recommend that you purchase a good PC board layout program.
It will be well worth the investment.
If you are new to CAD PC board layout programs, you may be wondering
how you would use such a tool in a practical way. Allow me to
provide a hypothetical example. Suppose you wanted to construct a
small, portable guitar amplifier with tone control. You could combine
the preamplifier circuit of Fig. 8-6 with the tone control circuit of Fig.
8-7 and the 12-watt power amplifier of Fig. 8-8. Obviously, you could construct
all of these circuits using perfboard or a universal breadboard,
but the process is time-consuming and the finished product doesn’t
look very professional. In contrast, it would probably take you about an
hour and a half to combine all three of these circuits into a single circuit
design, download to a layout program, and come up with a single,
finished, professional-quality PC board design. You would then use your