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Sharp Compet 31 (CS-31A) Desktop Calculator

Sharp Compet 31 (CS-31A)
Image Courtesy Takaharu Yoshida

The Compet 31 (Model CS-31A) appears to have been a remake of the earlier Compet 30 Model CS-30B utilizing a small number of integrated circuits to replace discrete transistorized sequencing control logic in the earlier Compet 30. From available information(of which there is not a lot), the Compet 31 is functionally identical to the Compet 30/Model CS-30B. Sharp claims that the Compet 31 (Model CS-31A) is the company's first electronic calculator to utilize small-scale bipolar integrated circuits.

Part of the Sequence Control Circuit Board using Mitsubishi ICs in the Compet 31/CS-31A
Image Courtesy Serge Devidts

The CS-31A uses 28 small-scale integrated circuits made by one of the earliest Japanese integrated circuit manufacturers, Mitsubishi. The devices, which have part number M2340, are in plastic dual-inline packages, and utilize diode-transistor (DTL) construction. Each package contains four two-input NAND gates. Only one of the 13 circuit boards in the Compet 31 uses the integrated circuit devices, with all of the rest of the boards utilizing the same discrete transistor construction as in the Compet 30. The circuit board using the ICs replaces the board in the CS-30B calculator which contains a number of transistorized flip flops that are involved in the sequence control logic of the machine. The logic gates in the ICs are connected in such a way that they create flip flops that take the place of the transistor-based flip flops in the earlier CS-30B, significantly reducing the component count and complexity of this sequencing board.

Stamping in Model CS-30B Calculator Backplane indicating Model CS-31A
Image Courtesy Serge Devidts

It should be noted here that at least one example of a machine with Compet 30 badging and a model/serial number tag indicating it is a model CS-30B is known to exist, but contains the IC-based sequencing circuit board. However, the machine contains a chassis with a stamping (see phone above) indicating that it is a CS-31A backplane.

It is suspected that very early Sharp Compet 31 (Model CS-31A) calculators may have been badged as Compet 30 calculators with Model CS-30B Model/Serial Number tags, but used the IC-based sequencer board and CS-31A backplane, because the production versions of the badging for the Compet 31 were not yet ready. It's assumed that the manufacturing line had already been switched over to manufacturing the Compet 31 sequencer board and backplane, and rather than hold up manufacturing of the Compet 31, the machines were badged Compet 30/CS-30B, since both the Compet 31 and the Compet 30/CS-30B functioned identically, and from a user perspective, were indistinguishable from each other. Once the production Compet 31 badging was ready, the line began using the Compet 31 badge, and placing Compet 31/CS-31A Model/Serial number tags on the machines coming off the line. All that said, this is only supposition at this point, because as of this writing, no known examples of a Compet 31 have been found. If you are reading this, and know of the existence of a Sharp Compet 31 calculator, with the "Compet 31" badge and model number of CS-31A, please EMail the Old Calculator Museum and let us know about it.

The Compet 31 marked the beginning of the proliferation of integrated circuit technology in Sharp's electronic calculators. The next model in the series, the Compet 32, introduced not that long after the Compet 31, marked a new generation of calculators for Sharp, using a completely different architecture than their earlier calcualtors, switching to use of a bit-serial (rather than digit-parallel) mode of operation, and using magnetic core memory for storage of the working registers of the calcualtor versus the individual flip-flops of the earlier generation. This change drastically reduced the complexity of the Compet 32 as compared to the earlier machines, radically shrinking them in size and weight. Despite the architectural change, the same Mitsuibishi M2340 ICs were used in the Compet 32 to further reduce the component count. Successive models of Sharp calculators increased the number of integrated circuits used, at first continuing the use of bipolar ICs, then rapidly switching over Japanese-made Metal-Oxide Semiconductor (MOS) integrated circuits of ever-increasing complexity as Japanese IC manufacturers NEC and Hitachi perfected MOS IC processes, followed shortly by Toshiba. Sharp was the first Japanese electronic calculator company to leverage domestically-made ICs, and it was this move that gave them a distinct competitive advantage over other Japanese calculator manufacturers that relied on more expensive integrated circuits imported from US (Signetics) or European (Philips) IC manufacturers.

If you own or know of a Sharp Compet 31 calculator, please press the EMail button at the top of the page, and send an EMail about the calculator. Even if it isn't available for the Old Calculator Museum to acquire, information you can provide could be very helpful in adding to the story of the Compet 31.

Sharp Compet 31 (CS-31A) Specifications

Manufacturer: Hayakawa Electric Co., Ltd. (Sharp)
Model Number: CS-31A (Compet 31)
Manufactured In: Japan
Date of Introduction: April, 1967
Display Technology: Nixie Tube, 14 Digits
Logic Technology: Small-Scale bipolar(DTL) IC(28) and Diode(1549)-Transistor(553) Logic
Math Functions: Four Function
Digits of Capacity: 14
Decimal Modes: Fixed via keyboard pushbuttons
Settable at 0, 2, 4 or 6 digits behind decimal
Push-on/Push-off Round-Off Mode, [R] key
Memories: One accumulator-style memory register
Constant: Automatic on Multiply & Divide
Size: 17 1/4" wide, 18 3/4" deep, 8 1/2" high
Performance (Manufacturer Claimed): Addition/Subtraction: 15ms
Multiplication: 150ms
Division: 190ms

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