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Sharp EL-160 Electronic Calculator
The Sharp EL-160 is a stylish, somewhat more capable follow-on to the ground-breaking Sharp QT-8D, the first electronic calculator to use large-scale MOS integrated circuit technology. The technology used in the EL-160 is the same as the earlier QT-8D, with some design changes to two of the four chips in the chipset to provide some additional functions, including double precision multiplication and a memory register. Burroughs was an OEM customer of Sharp, and offered a machine using the EL-160's guts as the Burroughs C3260. The Burroughs machine is identical in electronics and function, but uses a boxy cabinet design and a different keyboard layout. The EL-160 is the desktop version of Sharp's "handheld" EL-8M portable calculator.
Profile View of the Sharp EL-160
The EL-160 is a basic four-function, 8 digit floating decimal calculator with memory (or double precision, depending on a mode switch on the keyboard). As with the other related machines, it uses individual Itron vacuum fluorescent display tubes for the display. Itron tubes use a unique segmented pattern to create digits that look more 'handwritten' than the traditional 7-segment digit rendition.
The EL-160 display assembly
The Itron tubes in the EL-160 are a bit larger than those used in the portable Itron-display calculators in museum, with a digit height of 5/8-inch versus the 1/2-inch digits on the portable machines. These larger digits make the display very clear and easy to read. The digits glow a fluorescent blue, but are situated behind a green filter which provides a pleasant green color to the digits.
The back side of the display board showing the Iseden & NEC Itron Tubes
The digit tubes in the EL-160 are made by NEC, under license from Iseden, the original developer of the tubes. The display resides on a plug-in circuit board that contains the display tubes, a frame for supporting the tubes, the driver hybrids, and a few other discrete components. The digit tubes are part number DG12B, and the sign tube (made by Iseden rather than NEC) has part number SP12A. The digit tubes contain the standard Itron-format 9-segment digit rendition with right-hand decimal point, and a "tick" to the upper left of each digit. The "tick" isn't used in this application. It's interesting to note that one of the tubes (the fifth tube from the left) doesn't have the tick mark, though it shares the same part number as the rest of the tubes. An interesting mystery. The right-most tube is a special tube used for indicating the sign of the number on the display. If a negative number is displayed, a "-" lights up to provide the indication. The sign tube also contains an "I" symbol, usually used on Sharp calculators for indicating non-zero content in a memory register, but on the EL-160 this indicator is not used even though the calculator has a memory register.
The EL-160 with Cabinet Opened Up
As with the other of Sharp's ELSI-based (ELSI stands for Extra Large Scale Integration) machines, the EL-160 uses a four-chip chipset to make up its brains. The IC's in this machine are manufactured by Rockwell, but were designed by Sharp. The chips have part numbers 2256, 2271, 1152, and 1156. The first two chips are shared with the earlier Sharp EL-8, but the 1152 and 1156 chips are newer designs that were first used on the Sharp EL-8M, a revision of the EL-8 that adds the functionality of the memory register and double precision mode.
The EL-160's "CPU" board
Two other IC devices provide support for the calculator chipset; a can-packaged clock generator for the chipset (part number CG1121), and a DIP-packaged small-scale Hitachi HD3113. All of the IC's mount on a printed circuit board that plugs into an edge connector that connects the calculating circuitry to the rest of the machine. The display assembly resides on a separate board that plugs into another backplane connector. The display is multiplexed, using three hybrid circuit modules as the high-voltage drivers for the vacuum-fluorescent Itron tubes.
Close up of calculator chipset
A printed-circuit backplane board provides sockets for the main logic and display boards, as well as providing a connection point for the keyboard cable. The power supply extends along the back section of the calculator, which is a traditional transistor-regulated linear design.
Sharp EL-160 Keyboard Detail
Like Sharp's QT-8D, QT-8B, EL-8, and EL-8M, an unusual keyboard arrangement is used to minimize the number of keys on the keyboard, by combining the multiply and divide functions onto one key. To multiply, the first number is entered, followed by the [X÷] key (note the red ÷ symbol), then the second number is typed in, followed by the [+=] key to calculate the product. The same sequence is used for division, but rather than pressing the [+=] key to complete the operation, the red [-=] key is pressed to generate the result. The EL-160 provides three keys for controlling the memory register, along with the [M/D] key, which is a push-on/push-off switch which controls the mode of the memory function keys. When the [M/D] key is in the up position ("M"), the memory function keys operate as expected, with [M+] adding the content of the display to the memory register, the [MR] key recalling the content of the memory register to the display, and the [CM] key clearing the memory register. When the [M/D] key is in the depressed position, double precision mode is engaged, and the memory register is redefined to serve as storage for the least significant eight digits of a double precision result, allowing results of multiplication operations to return answers up to 16 significant digits in length. In this mode, when a result is greater than 8 significant digits, the display shows the upper eight significant digits of the result upon completion of the calculation. The [MR] key can then be pressed to display the lower eight digits of the result. When the lowest digits are being displayed, a single press of the [C] key will return the upper-most digits of the answer to the display. In double precision mode, the [M+] key is disabled. Double precision mode is good only for use on single calculations...chain calculations in this mode result in the low part of the answer being lost. When in double precision mode, the [CM] key simply clears the storage register that contains the lowest eight digits of results.
Sharp EL-160 overflow indication
The EL-160 is quite fast, with all calculations providing results in around a tenth of a second, even when operating in double- precision mode. The machine indicates overflow or division by zero error by clearing the display to all zeroes, and lighting all the decimal points. The error condition is cleared by pressing the [C] key, which clears the machine.