Early Sharp Calculators Internal Photographs

By Alex Knight, May 5, 1998

Sharp EL-8:

The Sharp EL-8 is a first-generation handheld calculator. It utilizes a two-output external AC power supply/charger, Model EL-81, which supplies both 8.7 Volts and 9.6 Volts to the machine, and it uses a Model EL-84 7.2 volt NiCad battery pack, which is connectorized but can be replaced only by opening up the machine. This was one of the largest four-function handheld calculators ever made, and it has fourteen Integrated Circuits inside. It utilizes a reed-switch keyboard, which is very unusual for a handheld machine due to the size and weight of such a keyboard. Another unusual feature of the keyboard is the combined multiply-divide key.

Adding to the machine's size and weight is it's "card-cage" construction - the two Printed Circuit Boards plug into edge-connectors and are held in place by metal card guides. The display uses eight individual Vacuum Fluorescent tubes which are wired to the PCB that contains the display driver ICs. These VF tubes are unusual in that their eight illuminated segments have a curved shape that makes the displayed numbers look almost handwritten, instead of the boxy shape that normal seven-segment displays have. Another small VF tube in the upper right corner is used for error and negative indications. There is an incandescent bulb to indicate that power is turned on.

Image of Sharp EL-8

The above photo is of the EL-8 with its front cover removed, showing the keyboard, eight display tubes, the overflow/negative display tube in the top right corner, and the power-on indicator in the top left corner.

Image of Sharp EL-8

The photo above is of the EL-8 with rear cover removed, showing the reverse side of the main PCB at the bottom and the card-edge connector it is plugged into, with the back side of the power converter partially showing at the top.

Image of Sharp EL-8 display

The above photo shows a closeup of the EL-8 power converter & display tubes.

Image of Sharp EL-8 main PCB

The above photo shows a closeup of the EL-8 main PCB and ICs: This PCB has five Integrated Circuits. The ICs were manufactured by Rockwell and four of them are in their 42-pin ceramic zig-zag package. Clockwise from the top left, the part numbers of these ICs are: NRD2256, AC2261, AU2261, and DC2266, and these are likely the control and arithmetic circuits. The fifth IC is packaged in a round metal can and is Rockwell part number CG1121, and is likely the clock generation circuit. The date codes on these ICs ranged from 7040 to 7043, indicating they were made in the fourth quarter of 1970.

Image of Sharp EL-8 display PCB

The above photo of the EL-8 display and driver PCB shows nine Hitachi 16-pin ceramic Dual Inline Package (DIP) ICs. The three ICs on the right are Hitachi part number HD3121, while the six on the left and center are Hitachi part number HD3120.

Sharp EL-811:

The EL-811 appears to be a second-generation refinement of the EL-8 calculator. It adds memory capability and 16-digit calculation capability, and is packaged in a thinner, sleeker case. It uses the same power supply/charger, the EL-81, and the same 7.2 Volt NiCad battery pack as does the EL-8. Power consumption is listed at 1.3 Watts for the 8.7 Volt supply and 1.9 Watts for the 9.6 Volt supply. Construction is simplified by utilizing a more conventional contact-type keyboard, and by integrating all six of the calculator and display ICs onto one PCB. The EL-811 uses eight of the same type of VF display tubes as does the EL-8.

Image of Sharp EL-811

The above photograph shows the Sharp EL-811 calculator. The overflow/negative VF tube is located to the right of the eight numeric VF tubes. The <-> key, located under the "C" key, displays the least significant digits of a 16-digit result. Underneath it is the MR CM key, which recalls memory on the first press and clears the memory if pressed twice. The calculator has an automatic constant mode, and the red -= key is also used to reset the constant (i.e. to allow chain calculations). A label on the back of the machine explains the operation of these keys.

Image of open Sharp EL-811

The above photo shows the EL-811 with its rear cover removed: the back side of the internal power converter is at the top, with the power connector below that, and the connector to the display across the middle. The main PCB occupies the lower half and plugs into a connector for the keyboard at the bottom of the photo.

Image of Sharp EL-811 PCB

The photo above is acloseup photo of the EL-811 main PCB and ICs: the three display driver ICs, Hitachi part number HD3123P are along the top of the PCB. The two main calculator ICs are Rockwell devices in 42-pin plastic zig-zag packages. The left IC is part number 10572PA and the right IC is part number 10573PA. The date codes for these ICs indicated they were manufactured in the last weeks of 1971. The 16-pin DIP IC in the lower right corner is a Hitachi HD9005.

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Text and images ©Copyright 1998, 1999 by Alex Knight, all rights reserved.