The other day
my neighbor said to me, “Every time I ask
you guys a technical question you start
drawing boxes and squares!” By “you guys” he
was referring to three or four engineers of
his acquaintance.
His provocative
observation started me thinking about how
the symbolism of engineering has evolved as
engineering design has gotten more complex
and abstract. To help recall some of the
earlier ways that circuits and systems were
graphically depicted, I visited a nearby
university library. I first scanned several
issues of the Electrical Review from
1884 (the year AIEE was founded). Subtitled
“A weekly journal of electric light,
telephone, telegraph, and scientific
progress,” it had illustrations that were
almost entirely
electromechanical—telephones, telegraph
keys, phone jacks, motors, and dynamos. All
were pictured literally in circuit diagrams,
the only element shown symbolically being
the battery.
I then went on
to the works of Nikola Tesla. When he was
active in the late 19th century, his work, too, was
illustrated quite literally. In a paper
delivered to the IEE in London in 1892, he
used many drawings of the actual electrical
components. The following year, in a lecture
at the Franklin Institute in Philadelphia,
he used circuit drawings that were hybrids—a
mix of literal sketches of generators and
switches along with symbols for coils,
transformers, and capacitors.
The Wiring
Diagram. This approach to illustrating
electrical connections, useful to
electricians, technicians, and craftsmen,
came into its own in the first part of the
20th century. These were very pictorial, and
were designed to avoid ambiguities in
connecting components or assembling and
installing equipment.
Schematics. The
arrival of electronics, driven by the advent
of the vacuum tube, spurred engineers to
develop and standardize component symbols.
These symbols became the essence of circuit
schematic diagrams. The symbol for the
vacuum tube underwent a few variations, with
its grids alternating between squiggles and
dashed lines, the latter eventually
prevailing.
I found a paper
by Edwin Armstrong published in the
Proceedings of the IRE in 1915. In it
were schematics that depicted the audion
(vacuum triode) minus the envelope, with the
grid and plate in a vertical position. In
another Armstrong Proceedings
publication, this one in 1924 on the
super-heterodyne receiver, the tube elements
were shown in the now generally accepted
horizontal position, and were encased in an
oval that represented the physical envelope.
The Box
Arrives. The various functions of a radio
receiver were called stages (e.g., r.f.
amplifier stage, detector stage, etc.) and
soon were represented simply as rectangles
in a “block diagram.” The blocks in a block
diagram quickly caught on as a shorthand way
to represent larger and larger sections of
more complex systems, and, when convenient,
entire subsystems that were readily
available “off the shelf.”
I came across a
1936 Armstrong paper on frequency modulation
in which he used many block diagrams. He
referred to them, taken together, as
“diagrammatic arrangements” or “general
arrangements” of a circuit. Individual
blocks were, typically, amplifiers,
frequency multipliers, filters, detectors,
conversion systems, etc.
Systems
Analysis and Design. The increasing
complexity of systems inspired serious
attempts to organize systems planning,
design, development, and manufacture into
logical steps. This challenge helped spawn
the disciplines of systems engineering and
systems management and their concomitant
graphical tools. Who among us has not used
flowcharts, pert charts and matrices to good
advantage? And, of course, block diagrams to
designate the physical partitioning,
operational functions, and required physical
interfaces of large systems. Today’s
textbooks on systems engineering are
peppered with block diagrams representing
not simply system partitioning but complex
interactions at all phases of engineering
from conception to deployment. On the other
hand, many of the mathematically-based
graphic aids aimed at comprehending large
systems remain stalled at the academic
level. Even the well-known Venn diagram has
its limitations. Two- or three-set Venn
diagrams are readily interpreted visually,
suggesting common characteristics of
individual sets in their areas of overlap.
But higher-order Venn diagrams, while
visually interesting, are increasingly
difficult to interpret.
The
tricotyledon theory of system design is
based on mathematical set theory. One way to
illustrate its state transitions and outputs
is through the use of circles with arrows
looping between and among them. Yet
examining a moderately complex system using
this notation can boggle the mind.
The Entrenched
Box. The IEC (International Electrotechnical
Commission) has long since abandoned the
traditional logic gate symbols (AND, NOR,
OR, etc.) for a standard square. And while
it may be resisted by many oldtimers, the
“new” resistor symbol is a long rectangle.
My neighbor was
right. My quick trip through history
confirmed the importance of the box. It has
become an abstraction for more interesting
stuff inside it that we either take for
granted or have forgotten completely. We
cannot design without the box. I suppose
there are certain specialists (antenna
designers, perhaps) who might even go for
several months without drawing a box.
Computer engineers, on the other hand, would
be hard pressed to resist the beckoning call of
the box for more than an hour or so.
Except for the
physicists, the days of representing
transistors and ICs in cross section have
virtually vanished. ICs themselves are
represented as rectangles and because of
their high pin-count we leave it to the
computer to interconnect them. This opens
the Pandora’s box (no pun intended) of
design automation and its subset, schematic
capture. But I’ll leave that for another
time.
Meanwhile, call
it what we may—block, square,
rectangle—the box is here to stay. Long live
the box!
References
Tesla, N.,
“Experiments with Alternating Currents of
High Potential and High Frequency,” Lecture,
Institute of Electrical Engineers, Feb.
1892.
Tesla, N., “On
Light and Other High Frequency Phenomena,”
Lecture, Franklin Institute, Feb. 1893.
Armstrong, E.H.,
“Some Recent Developments in the Audion
Receiver,” Proceedings of the IRE,
Sept. 1915.
Armstrong, E.H.,
“The Super-Heterodyne,” Proceedings of
the IRE, Oct. 1924.
Armstrong, E.H.,
“A Method of Reducing Disturbance in Radio
Signaling by a System of Frequency
Modulation,” Proceedings of the IRE,
May 1936.
Wymore, A.W.,
Systems Engineering Methodology for
Interdisciplinary Teams, John Wiley,
1976.
Edwards, A.W.F.,
Cogwheels of the Mind: The Story of Venn
Diagrams, Johns Hopkins University
Press, 2004.
IEC Graphical
Symbols
http://tc3.iec.ch
Symbols to
Standardize Computer Concepts
http://umw.electronicstalk.com/news/inw103.html
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