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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 moulded 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.


Text and images Copyright ©1997-2011, Rick Bensene.