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Sharp EL-804 Desktop Calculator

The Sharp EL-804 seems to be extremely similar to the Sharp EL-803 in the museum. In fact, they use the same single-chip calculator IC, and operate identically. The case styling is similar between the two machines, with the EL-804 being slightly narrower, but slightly deeper than the EL-803. The only real difference that I can see is that the display drive IC's are more integrated in the EL-804 (two chips versus three chips in the EL-803). The EL-804 appears to be a slightly later vintage than the EL-803, which could account for more efficient display driver technology. The EL-804 appears also to have minor design changes which would result in a lower cost to manufacture, which translated to a lower price for the consumer. At the time these machines were made, the price wars that began the shakeout in the calculator business were beginning to occur, and the resulting price pressure was a fact of life, forcing calculator makers to figure out ways to continually reduce manufacturing costs.

Inside View of Sharp EL-804

The EL-804 is a classic four-function calculator. It provides eight digits of capacity, with floating decimal operation. A slide switch selects whether a constant multiplier or divisor can be set for multiplication and division. The display is made up of nine individual vacuum-fluorescent display tubes, using a slightly-modified seven-segment digit rendition. Each tube has a right-hand decimal point. The right-most tube is used only for sign(-) and error(E) indication. The light-blue glow of the vacuum-fluorescent display elements is converted to a bright green by a green filter window positioned between the tubes and the user.. The calculator logic provides leading zero suppression, but does not perform trailing zero suppression. For example performing 12 divided by 3 results in 4.0000000 being displayed.

Close up of EL-804 Circuitry

The EL-804 is based on a Hitachi HD3276 Large Scale calculator chip. A Hitachi HD3253 chip appears to be used for generating the master clock that the LSI chip uses to create its internal timing events. Two display driver chips (HD4350) combine forces to drive the vacuum- fluorescent display tubes. Lastly, a Toshiba-made TD2000TP chip rounds out the group of five integrated circuit devices in the machine. Based on date codes on the integrated circuits, the machine was built in the mid-part of 1973, somewhat later than the EL-803, which further substantiates that this machine was a 'lower-cost' redesign of the earlier EL-803. The circuitry of the machine, except the keyboard assemblies, sits on a single-sided phenolic circuit board. The power supply resides on the main circuit board, and is of a simple zener diode and transistor-regulated linear design.

The EL-804's Display

The keyboard construction and layout of the EL-804 is identical to that of the EL-803. One keyboard module contains the numeric keypad (zero through nine and decimal point), and the other module contains the function keys. This modular design allowed Sharp to use the same keyboard modules in a number of different calculator models, saving on tooling and production costs. The EL-804 function key module contains two 'extra' positions for keycaps, but these extra positions are not wired up to anything. My guess is that these extra positions are populated with memory function keys in higher-end models. The EL-804 forsakes the more modular construction of the EL-803, getting rid of edge-connector wiring for the keyboard modules and the constant slide switch, in favor of directly wired connections. This probably saved both on component and labor costs, at the expense of ease of service. However, by this time in calculator history, the machines were becoming inexpensive enough to simply discard and replace when a failure occurred.

The EL-804 seems a little faster than the EL-803, with 99999999 divided by 1 taking around 1/2 second. 9999.9999 times itself takes about 3/4 second. The display is not blanked while calculations are taking place. This difference in operating speed between the two machines could simply be the result of a slightly faster main clock frequency on the EL-804. Overflow or invalid operations (divide by zero) are indicated by clearing the display to '0', and lighting an "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. It is interesting to note that when first powered up, the EL-804 comes up in "ERROR" mode, with 0.E on the display and the keyboard locked out. Pressing the "C" key clears the machine and readies it for normal operation.

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