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Sharp ELSI 817S Desktop Calculator

This calculator is an example of why Sharp became so successful in the calculator marketplace, and is one of the 'survivors' today. This little machine was cranked out by the 10's of thousands (if not more), and was a simple, low-cost, home/office calculator. This particular machine was built on 7/8/74, based on the date on the manufacturing tag still in good shape on the bottom of the machine. The IC's inside have date codes of late '73 to early '74, which further substantiate the date of manufacture.

Inside View of ELSI 817S

The 817S provides the basic necessities for a home/office calculator -- it of course provides the four basic math functions. It is a full-floating decimal machine, with eight digit capacity. It has a single memory register, with a M+ (add to memory), MR (memory recall), and MC(memory clear) key. It has a constant function, which is enabled by the "K" key, which toggles constant mode on/off which each depression. A "K" legend lights up in the display when the constant is enabled. The constant function works for all four math functions. It is clear that the same basic machine was offered with a "M-" key to make it easier to subtract from memory. In the picture above, note the 'empty' key location above the "M+" key. The keyboard on this machine is 'modular', with a standard set of keys for zero through nine and decimal point making up one 'module', and the other containing the 'functions'. A different 'function key' module, with an M- key in the 'empty' location, along with a top cabinet panel with an extra hole for the "M-" key and different model number tag would make a 'higher power machine', and fetch a slightly higher sales price, even though the electronics and manufacturing cost is essentially identical.

Close up of 817S Circuitry

The Sharp ELSI (ELSI was an acronym for "Extra Large Scale Integration") 817S is based on a single-chip LSI IC, part number 15331, made by Sharp. A trio of Toshiba-made display driver chips make up the rest of the IC's in the machine (2 TM4358, and 1 TM4352). The components are placed on a single-sided phenolic circuit board, which uses jumpers on the component side to make interconnections between traces on the etch side of the board.

The Futaba-made Display Module

The display is a Futaba-made integrated Vacuum Fluorescent display module, which plugs into the main board via an edge-connector. The display module as 8 7-segment digit positions, and a ninth position at the right end which has indicators for memory having non-zero content (I), negative number (-), and constant mode active (K). A green filter in the top part of the case turns blue glow of the VF display into green digits as presented to the user. The calculator uses a linear power supply with zener-diode based voltage regulation. The keyboard modules use 'spring'-type contacts.

The 817S is fast, but since it's so simple, it is really no surprise. 99999999 divided by 1 takes just a blink of an eye. Overflow or invalid operations (divide by zero) lock the machine with all digit positions showing '0' and all decimal points turned on. A single press of the "C" key clears the error, leaving 0 on the display. In non-error conditions, one press of the "C" key clears the display, with a second press clearing the whole machine (except for the memory register).

Text and images Copyright ©1997-2023, Rick Bensene.

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