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Sharp Compet 229

The Sharp Compet 229 is about as generic an office calculator as an early 1974 machine can get. Calculators like these dutifully churned through numbers for places like the North Carolina Department of Motor Vehicles, which is where this 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 shot of Sharp Compet 229

This Compet 229, one of many in the line of Compet electronic calculators that Sharp produced for years on end, was built in the early 1974 timeframe, based on date codes from late '73 through the 1st week of 1974 on the IC's within the machine. It uses a two-chip (HD32128 and HD32129) calculator chipset made by Hitachi for the calculating brains of the machine. For displaying the results, a Hitachi-made (H1831B) Panaplex-style 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 Panaplex-style display of the Compet 229

The Compet 229 provides the function of a four-function office calculator with a full-function memory. The machine calculates results to 12-digits, with an apparent 13th guard digit (for round-off funcionality), and uses fixed (but flexible) decimal point logic, with switch-selectable settings of 0, 1, 2, 3, 4, or 6 digits behind the decimal point. I say flexible, because 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. At the far right end of the display module, a special digit position contains indicators for negative number and memory register in use. A switch on the keyboard panel selects round-off or truncate mode for the least-significant digit in results. The calculator provides a constant function (when the "K" key is in the 'locked down' position) for multiplication and division only. The "RC" key swaps the order of operands in multiply and divide operations.

Overflow or error (divide by zero) Indication

Overflow or error conditions are indicated by the display cleared with only decimal points lit. The "C" key must be used to reset any overflow/error condition. The "CE" key provides a "Clear Entry" function to allow correction of incorrectly entered numbers. The machine provides leading zero suppression, which, combined with a small slider under the display window (that is used to group the display digits in groups of three) makes for easy reading and transcription of the results of calculations.

Detail of the Sharp Compet 229 Keyboard Assembly

The Compet 229 uses a reliable magnetic reed-switch style keyboard, with hand-wired connections to an edge-connector which plugs into the main board of the calculator. The main board is a single-sided printed circuit board. The power supply of the machine is a transformer-based linear supply, with transistor-regulated voltages.

The 229 calculates a little on the slow side. 'All nines' divided by one takes just about 3/4 of a second to complete, making it one of the slower electronic calculators in the museum. The display is blanked during calculation.


Text and images Copyright ©1997-2011, Rick Bensene.