An Electronic Slide Rule
the multiplier. R7 controls the gain and
the amount of modulated sine wave in
the output. R3 controls the amount of
un-modulated voice in the output. The
offset null potentiometers, R8, R9, and
R10 are used to zero the outputs of
the op-amps when the inputs are zero.
■ FIGURE 12. AD633JN
Ring Modulator Circuit.
Decline of the Slide Rule
While logarithmic amplifiers may
be alive and well, the death toll for the
mechanical slide rule began when
Hewlett-Packard engineers started to
develop a scientific calculator so small
that it could fit in a shirt pocket. Four
years later — in July of 1972 — the HP-
35 scientific calculator, was born ... and
slide-rule usage began to decline. With
the HP- 35, you no longer had to try to
keep track of the decimal point location and it was accurate to 10 digits.
The HP- 35’s original price was
$395. The market of pocket calculators exploded during 1972 through
1974. Dozens of manufacturers and
hundreds of models appeared around
the world during that period. Now
that computing capability can be
found at the “everything for a dollar”
store. In 1975, Keuffel & Esser — one
of the major manufacturers of slide
rules — manufactured its last slide rule.
The slide-rule continued its decline
We’ve taken a trip down memory
lane with the slide rule and have
looked at the electronic equivalent.
We have explored a couple of applications of logarithmic amplifiers,
namely the frequency doubler and
the ring modulator. Today’s techno-
logical buzzwords include
multifunction,” “energy efficient,”
and “always-on.” The
sliderule reminds us that
old technology can
sometimes meet today’s
buzzword criteria. NV
■ FIGURE 13. The HP- 35 Slide Rule Killer.
Photo courtesy of The Museum of
November 2006 47