September 1971 Popular Electronics
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
The extreme level of
complexity and consolidation of circuit functions in today's functional integrated
circuit (IC) blocks makes it so that people with almost no instruction or experience
in circuit and system design can assemble and make work some pretty impressive
creations. The days of vacuum tubes and early discrete semiconductors required a
designer to know how to properly bias and interface various sections of circuits and
systems. Nowadays, with the ready availability of impedance-matched amplifiers,
filters, mixers, couplers, detectors, and other pre-packaged components, even RF and
microwave frequency systems are within the reach of relative amateurs (including but
not necessarily amateur radio operators). Likewise, people interested in digital and
microprocessor circuits and systems have access to many pre-packaged sensors, stepper
motors, displays, programmable logic blocks, imaging, and processor boards.
JK-RS Flip-Flop, Voltage Regulator
It's Not Necessary to Know All the Circuits so Long As You Understand the System
By Walter H. Buchsbaum
Fig. 1 - It might take you quite a few hours to figure out what this
circuit is. The clue is in the pin designation letters. It is a JK-RS IC flip-flop.
Fig. 2 - There are no pin designations to give this circuit a name.
Actually it is an IC power supply regulator. Note that both this and Fig. 1 are quite
complex and are really a waste of time to try to figure out since the complete operation
is shown in the next two figures in a manner far more easy to understand-the system concept.
What makes one man "better" at electronics than another? Is it education? Apparently
not, since we all know some guy just out of high school who can figure out what's wrong
with a complex circuit long before his neighbor who has his BS in EE. Is it work experience?
No, again, because there's always the kid fresh from school who can diagnose a fault
in a piece of electronic gear while the "old timer" is still studying the schematic.
Is it just plain "brightness?" The latter is often used to explain why some people seem
to be so much faster in figuring out how things work. But what is brightness? What seems
to enable one man to "think faster" than another?
Without going into philosophy or psychology, let's consider the words "concept or
systems understanding." This is not a difficult subject because the bright people really
use it all the time - often without even knowing it. Systems, or concept, understanding
permits one man to take a fast look at a faulty piece of gear and come up with a solution
while someone else has to use test instruments and work all day to arrive at the same
conclusion. What bugs most of us is that we often feel we know more about basic electronics
than the other guy, yet he amazes us with his insight into the problem.
What Is the Function? Take a look at the schematic in Fig. 1. Without
reading the caption, what is the circuit and how does it work? If that stumps you, try
the simpler circuit in Fig. 2. If you have. difficulty analyzing these circuits, don't
feel too bad. They happen to be integrated circuits, and while you were wasting your
time trying to figure them out, all the information you really needed was "function"
(what does it do?), "input and output" (what are the signals like?) and "specifications"
(how is it tested?). This information is readily available from the manufacturer's data
sheets. You don't have to figure out a thing; it was all done for you long ago by the
The entire circuit shown in Fig. 1 can be represented by a "black box" such as that
shown in Fig. 3; and this gives you all the information you need to know about that complicated
circuit. The information in Fig. 3 says: When certain voltages (0 or 1) are present on
the J and K inputs and a toggle pulse is applied, the flip-flop may or may not change
states depending on what the J-K or R-S voltages are with respect to each other. Isn't
that a lot simpler than trying to figure out what every transistor in Fig. 1 is doing
at each instant? Consider the time saved.
Now take another look at Fig. 2 and its black box equivalent in Fig. 4. The information
in Fig. 4 says: If the input voltage level is correct, the output voltage must be as
specified or the IC is defective (discounting the discrete components). Of course, in
a system with several black boxes, some other factors enter the picture, but the basic
idea of the black box equivalent remains valid.
Fig. 3 - This is how the flip-flop should be shown. What you see above
gives far more information than shown in Fig. 1.
Fig. 4 - This is complete story on the power supply regulator shown
in Fig. 2. Once again, this gives more information than is contained in complex schematic.
The two examples above show that you do not have to understand the detailed operation
of complex circuits to figure out what is wrong when a problem occurs. All you need to
understand is the concept - what role each black box plays in the overall scheme. This
is what we call concept understanding. It is also called systems science or systems engineering.
Whatever it is called, there is much dispute - even among teachers - as to whether it
is a science, a field of engineering, or a mixture of math, logic, art, and magic.
"Christmas-Tree" Approach. One type of concept understanding was exemplified by the
famous "Christmas Tree" approach. At the top of the tree was a statement of the problem.
The tree's branches then consisted of procedural statements such as "if this happens,
proceed to that" and "if this does not happen, proceed there." In this way, signal flow
Since we do not have a Christmas tree diagram for every electronic device ever built,
however, we must construct one in our mind each time we tackle a system - regardless
of its complexity. This is the aim of concept understanding. Once the basic flow has
been established mentally, a deviation from that flow (which we call improper operation)
can be traced to its origin. Obviously, this means that we must have a good knowledge
of how the system is supposed to operate.
The idea of systems understanding is used in this magazine in nearly all of the articles
involving digital integrated circuits. Logic diagrams are used to show the operation
of the system rather than the extreme complexity of every detail within the IC's.
Posted October 15, 2018