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Sharp EL-803 Desktop Calculator
The Sharp EL-803 is a very typical
example of an single-chip LSI desktop calculator for use in home
or office. During the year 1972, electronic calculators went through
a great deal of change in a short period of time. In late 1971, most
calculators were built with small and medium-scale IC's, or multi-chip LSI
calculator chipsets. There were some calculators available as early
as mid-1971 that used single-chip LSI's for their brains (an example
being the Casio AS-8A), but the mainstream
proliferation of single-chip designs came about during 1972. Each successive
chip design could leverage the rapidly increasing integration level of IC's,
and by mid-year 1972, it was relatively commonplace to put the entire
calculating guts of a four-function calculator on a single chip. The only
other circuitry necessary with these early calculator-on-a-chip
implementations was the driver circuitry to run the displays, and occasionally
a simple support chip for clock generation.
Inside View of Sharp EL-803 The EL-803 is a basic four-function
calculator, with floating decimal and switch-selectable constant
function. The constant function operates only on multiply and divide
functions. The display consistes of nine individual vacuum-fluorescent
display tubes, using traditional seven-segment digit rendition. Each tube
also has a right-hand decimal point. The right-most tube is used only for
sign(-) and error(E) indication. The tubes are contained in a metal
frame that provides alignment and shock protection. The normal light-blue
glow of the vacuum-fluorescent display elements is converted to a bright
green by a green filter window. The calculator logic provides leading zero
suppression.
Close up of EL-803 Circuitry
The EL-803 is based on a Hitachi-made HD3276 Large Scale IC. A
Hitachi HD3253 chip appears to be involved in clock generation for
the calculator LSI. Three Toshiba display driver IC's (TM4352) complete
the complement of IC's in the machine. The entire circuitry of the machine,
including power supply, resides on a single-sided phenolic circuit board.
The power supply of the machine is a simple zener diode and
transistor-regulated linear design.
A Profile view, showing the unusual styling of the EL-803 The keyboard of the EL-803 is made
in a modular fashion, with two modules. One module contains the
numeric keypad (zero through nine and decimal point), and the other
module contains the function keys. This modular design allows the
manufacturer to use identical numeric keypads for different calculator
models that provide varying functions. The keypad modules themselves
use 'dome' style switches, with plastic keycaps that have molded in
keycap nomenclature. The keyboard modules, along with the
constant switch, connect to the main circuit board via an edge connector.
Close up View of Display The EL-803 is not a fast machine.
99999999 divided by 1 takes around 3/4 second to complete. 9999.9999
times itself takes almost a full second. The display churns quite a bit
while calculations are taking place. Overflow or invalid operations
(divide by zero) are indicated by clearing the display to '0', and lighting
and "E" in the right-most display tube. A single press of the "C" key clears
the error. The "CE" key allows correction of incorrect numeric entry
by clearing only the entry made thus far.