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Sharp Compet 229

Updated 5/28/2024

The Sharp Compet 229 is about as generic an office calculator as an early 1974 machine can be. Calculators like these dutifully churned through calculations prior to the development of desktop computers for places like the North Carolina Department of Motor Vehicles, which is where the exhibited machine served out its useful life. Fortunately, rather than being tossed in the trash, as was the fate of so many calculators that outlived their usefulness, this one ended up at a surplus auction and was spared the indignity of ending up in a landfill.

Internal view of Sharp Compet 229

The Compet 229 is of a clean, straigtforward design, that was designed to fit in well in any office environment. The keyboard panel is an off-white color, all plastic, with mostly dark-colored keys with contrasting white nomenclature to make them easy to read. The subtraction key[-=] is red, to better differentiate it from the addition [+=] key. The memory function keys are a medium-blue in color to visually separate them from the rest of the calculator keys. The wedge-shaped cabinet is made from two pieces, upper and lower parts. The upper part of the cabinet contains the keyboard assembly and the display nacelle and smoked-plastic window that the display shines through. The lower part contains the main logic board with the display, and the power supply. The two halves screw together with six screws that are recessed in holes in the bottom of the cabinet, three across the front edge of the machine, and one toward the middle, and two across the back edge. The display nacelle is colored a dark gray that provides contrast to the off-white of the keyboard panel, as well as providing a nice visual contrast for the display, which shows through a smoked lens mounted into the display nacalle. The plastic of the cabinet is of high-quality, with thick-wall castings for durability, and a very nice fit and finish. Overall, the Compet 229 is very nice for everyday use, with smooth and positive keyboard action, and a very clear, easy-to-read display.

The exhibited Compet 229 is one of countless many in the line of Compet (CS-series) electronic calculators that Sharp began making in 1964 and still produces various versions of to this day. The exhibited calculator was built in the early 1974 time frame, based on date codes from late '73 through the 1st week of 1974 on the IC's within the machine.

The 229 uses a two-chip HD32128 and HD32129 MOS/LSI calculator chip-set made by Hitachi for its calculating logic. For the display a Hitachi-made (H1831B) Burroughs Panaplex-style (likely manufactured under license from Burroughs) planar gas-discharge display module does the job, with discrete transistor-based driver circuitry. Five Hitachi HD3233 small-scale integration chips provide glue functions, both on the main calculator board, and also on a small circuit board attached to the keyboard assembly.

The planar gas-discharge display of the Compet 229

The Compet 229 provides the four basic math functions with a full-function accumulator-style memory register. The machine calculates to twelve digits of capacity, with an apparent 13th guard digit (for round-off functionality). It provides fixed (but flexible) decimal point logic, with switch-selectable settings of 0, 1, 2, 3, 4, or 6 digits behind the decimal point. The flexible aspect of the decimal point logic is that the machine will automatically back off on the number of digits displayed behind the decimal point if the whole part of the number is too large to be displayed with the selected number of digits behind the decimal point. This is a nice feature, as traditional fixed decimal mode calculators would give an overflow condition for such a calculation. At the far right end of the display module, an extra digit position is used for indicating negative number (-) and memory register(') in use status. A switch on the keyboard panel selects round-off or truncate mode for the hidden guard digit behind the least-significant digit in calculated results. The rounding switch provides three settings. One setting will round the lease-significant displayed digit up if the guard digit is >=5, and leave the least significant displayed digit alone if the guard digit is <5. Another setting ignores the guard digit, always leaving the least significant the least-significant digit of the result alone. The third setting always rounds the least-significant displayed digit up regardless of the value of the guard digit. The Compet 229 provides a constant function for multiply and divide when the push-on/push-off [K] key is in the depressed and locked position. The constant is retained in a hidden register for the multiplier or the dividend, depending on the function key (X or ÷) pressed before the constant is entered. The constant is cleared by use of the [C] key. The [RC] key swaps the order of operands in multiply and divide operations. The calculator supports full chain and mixed calculations.

Overflow or error (divide by zero) Indication

Overflow or error conditions are indicated by the display cleared with only decimal points lit. Division by zero is trapped as an error condition, as are all possible overflow situations. The keyboard is logically locked out (other than the [C] key) when an error/overflow condition is present. The [C] key must be pressed to reset any overflow/error condition, which clears the machine except for the memory register. If the memory register overflows, the same indication is given, however, in this case, the [C] key must be pressed, followed by the [CM] key to clear the overflow condition. The [CE] key provides a Clear Entry function to allow correction of incorrectly entered numbers, but will not clear an overflow/error condition. Pressing the [CE] key clears the number entry register, but does not clear any pending math operations. The CS-229 provides leading zero suppression, A manually positionable slider under the display window is used to visually, via three small pointers, group the display digits in groups of three to allow for easier reading and transcription of the results of calculations.

Detail of the Sharp Compet 229 Keyboard Assembly

The Compet 229 uses a magnetic reed-switch style keyboard for long-term reliability and clean switching when keys are pressed. The keyboard has hand-wired connections to an edge-connector that plugs into the main board of the calculator. The key caps on the keyboard have molded-in legends to provide long-life visibility of the nomenclature on the keys that will not wear off as printed-on legends can. The key caps are also made of a high-quality plastic that resists staining and wear. The keys on the exhibited calculator look nearly like new with vertually no detectible wear, although the calculator likely saw extensive use during its lifetime.

The main circuit board is a single-sided printed circuit board with jumper wires on the component side of the circuit board used to provide connections between the traces on the back side of the board. The circuit board appears to be made of a phenolic-like material, but is lighter in color than typical reddish-brown phenolic.

The power supply of the CS-229 is a transformer-based linear supply with an unusually large transformer for an electronic calculator of this vintage. The transformer's secondary voltages are rectified by diodes into DC, and then are regulated by zener diode/pass-transistors to provide the final voltages. The power supply utilizes a grounded three-pin power plug that is Sharp proprietary (e.g., non-IEC).

The 229 calculates a shade on the slow side. The typical 999,999,999,999 divided by one benchmark takes just about 3/4 of a second to complete, making it one of the slower electronic calculators in the museum. During calculations, the display is completely blanked, hiding any of the "dancing digits" that would display as the calculator performs the math if it weren't blanked. The slow calculation is likely due to a conservative clocking frequency for the still relatively-early MOS two device chip-set, but this calculation time is for a worst-case condition and overall, the calculator delivers results plenty quickly.

Text and images Copyright ©1997-2024, Rick Bensene.

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