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Sharp Compet 22 Electronic Desktop Calculator

Updated 4/27/2024

The Sharp Compet 22 is an expanded capacity version of the earlier groundbreaking Sharp Compet 16. The Compet 16 was the first calculator on the market to utilize MOS (Metal Oxide Semiconductor) Integrated Circuits to implement a significant portion of the calculating logic. Other calculators of the time were based on bipolar small-scale integrated circuits, or still even all-transistor construction.

The calculator exhibited here is a later version of the original Sharp Compet 22, model CS-22A, which debuted in Japan in late 1967. The model shown here is the Model CS-22C, which was released to the market in late 1968. The CS-22C incorporated design changes to reduce the cost of the calculator to help keep it competitive during the insanely cutthroat electronic calculator marketplace of the latter part of the 1960's. From the user perspective, the CS-22C functions the same as the CS-22A.

The Compet 22 looked very similar to the Compet 16, but added two digits of capacity for users who needed the extra capacity for their calculations. Shortly after the Compet 22 (CS-22A) was announced, Sharp introduced the Compet 23, a calculator that was identical to the Compet 22, but omitted the accessory connector on the back panel of the calculator of the Compet 22 to allow it to be connected to an external programmer device called the "Memorizer" (see below).

Comparing the Compet 16S(left) and Compet 22C(right)

The Compet 22 is very similar to the Compet 16 in terms of function and appearance. The size and weight of the machines are the same, and the keyboard layout is identical. The main difference between the Compet 16 and Compet 22 is the addition of two extra digits of capacity, with the Compet 22 offering a full 14 digits of capacity versus the 12-digit computing capacity of the Compet 16. There are also some minor cabinet differences between the two machines, but these are not necessarily model-specific. It appears that somewhere during production, a design change was made to the cabinetry that added an extension to the cabinet providing more of a hood over the display to help eliminate glare from overhead lighting. This change is apparent when comparing the later-production Compet 16S to the older Compet 22C as shown above. The cabinetry components of this series of calculators were generally interchangeable. One of the aspects that could be changed to reduce cost was reducing the complexity of the cabinet and trim components, or making other changes to the cabinet to reduce manufacturing cost. Such cosmetic changes could result in a new version of a calculator that would be reflected in its model number.

A later production Compet 23C
Image Courtesy Ramon On

The Compet 22 exhibited here was actually produced before the Compet 16 exhibited in the museum. The reason for this is that Sharp would frequently make revisions to their calculator models as time went on in order to reduce manufacturing cost. The revisions would allow the calculator model to continue to deliver an acceptable profit margin for Sharp, as well as for the distributors and retailers. In a market where competitors were continually undercutting the retail price of Sharp's machines, it was imperative that Sharp wring as much market lifetime out of a specific model of calculator before it was either priced out of the market, or was technically obsolete (as was most often the case for a model to be discontinued). The nature of the market forced manufacturers to either reduce their margins, or figure out how to make their calculators less-expensive to manufacture in order for a model to remain competitive at the distributor and retail level.

The letter after the model number on the model/serial number tag affixed to the rear panel of Sharp calculators is the revision level of the calculator model, with a given model of a calculator initially introduced by Sharp as the "A" version. Each successive revision of a model would result in the revision letter stepping ahead one letter of the alphabet (in general, but not always). Some letters were always skipped, such as I, L, O, and Q because of the ease at which these letters could be mistaken for each other, or for numbers. For example, the Compet 22 exhibited here was manufactured in February of 1968, while the Compet 16 exhibited in this museum was built almost a year later, in January of 1969. The clue to this disparity is that the Compet 22's model is CS-22C, while the Compet 16's model is CS-16S.

Sometimes revisions were skipped over because as the revision made its way from ideas through engineering, it was decided that perhaps more extensive changes must or could be made, resulting in a "revision to a revision", skipping over the intermediate revision. For example, the calculator shown in this exhibit is a model CS-22C, indicating revision "C", or potentially two revisions later than the original CS-22A. However, after many years of searching for different versions of Sharp's calculator models, not a single example of a Compet 22 model CS-22B (revision B) has been observed. Such research involves pouring through advertising materials, calculators for sale/auction, calculators in the hands of other museums/collections, and manufacturer's literature, as well as many publications at the time that carried coverage of calculator news.

It is suspected that for whatever reason, the CS-22B was skipped over, perhaps because it was decided that as the engineering of the B version of the Compet 22 was well underway, market conditions had changed enough that revision B simply wasn't going to deliver sufficient reduction in manufacturing cost, so it was skipped, and further revisions were made to result in revision "C", which combined the changes from revision B, along with additional modifications to further reduce the cost of manufacturing.

A more extreme example of version stepping is the Sharp Compet 16 exhibited here in the museum. It is a model CS-16S, indicating that it contains substantial modifications made to the original design in order to extend its effective lifetime in the market. It is not known at this time how many different versions of the Compet 16 there actually were. Versions A, B, C, D, and S are the only versions of the Compet 16 that have been encountered over decades of looking for different revisions. Whether there were very small numbers of versions F through R made that have over time been lost(e.g., discarded, accidentally destroyed, or suffering some other situation that took them out of circulation), or are in the hands of people that haven't publicized their existence. There also have been no model revisions found beyond CS-16S, so the exhibited Compet 16 was likely produced near the end of the manufacturing run of Compet 16 calculators.

Note: If you have any Sharp Compet calculator with a two digit model number preceded by "CS", if you would, please consider Emailing the museum and let us know the full model number of your calculator, e.g., for the calculator exhibited here, the full model number is "CS-22C". Please make sure to include the entire model number. If you would also include the serial number of the calculator, which is embossed into the same tag that the model number appears on, that would also be very helpful, as it provides a general time period as to when the calculator was manufactured. Thank you for your consideration.

Due to design changes during the lifetime of this first-generation of Sharp's MOS IC-based calculators, some subtle differences in operation are noted between them. Most notably, the Compet 22 uses an annunciator that lights up "E" when an overflow condition exists but the keyboard is not inhibited and calculations can continue even though an error condition exists. The later-design Compet 16 model CS-16S remedied this problem by eliminating the "E" annunciator, and adding circuitry to automatically clear the calculator, lighting all of the decimal points, and ignoring entries from the keyboard until the [C] key is pressed to reset the machine. The Compet 22, by virtue of it's earlier design, also does not provide an error indication when commanded to perform division by zero. The Compet 22 gives no error condition, and "locks up", apparently looping forever trying to solve an insoluble problem. When locked up by dividing by zero, the machine does not respond to any key-presses except the [C] key. When the Compet 16 CS-16S is commanded to divide by zero, it properly indicates an error condition, refusing to carry out the futile operation. Lastly, a small difference between the Compet 22 and Compet 16 is that the annunciators for memory, error indication, and sign are located at the left end of the display panel on the Compet 22; and the memory and sign annunciators are located at the right end of the display on the Compet 16.

Profile View of Sharp Compet 22

This particular Compet 22 was manufactured in February of 1968 based on information from the serial number of the machine. The Compet 22 (Model CS-22A) was introduced sometime in late 1967. A number of revisions were made (indicated by the alphabetic postfix after the model number) during the life of the model. By the time the exhibited calculator was manufactured, the revision level had reached "C". By February of 1969, the machine retailed for $1175, $180 more than a Compet 16 of the same time period.

The Compet 22 is a 14-digit, fixed decimal, four function electronic calculator with a single accumulating memory register. The calculator provides a constant function for multiplication and division, with a push-on/push-off keyboard key labeled [K] to enable the function. The Compet 22 uses arithmetic logic for addition/subtraction, and algebraic input for multiplication and division.

Like the Compet 16, the Compet 22 uses fixed-decimal point logic. The location of the decimal point is set via a rotary switch on the keyboard panel, Selections for 0, 2, 3, 4, and 6 digits behind the decimal point are provided, with two different settings available for each selection (Denoted by red and black numbers showing through the decimal point selection window). A black setting causes truncation at the selected decimal point location, and the other (red) setting causes results to be rounded off to the selected decimal position. Like the Compet 16, There's an odd blank selection on the decimal point setting switch. Placing the switch in this position results in an immediate input overflow upon trying to operate on any number entered. It isn't clear why this setting exists.

The Compet 22 allows entry of any number of digits behind the decimal point, but flags an error when the number of digits exceeds the decimal point selection. The error indication does not lock out entry of any further digits.

Compet 22 Sign, Memory, and Overflow Status Indicators at Left end of Display

The machine uses the dominant display technology of the time, Nixie tubes. There are fourteen individual Hitachi-made CD-81 tubes with 1/2-inch tall digits providing the display to the user. Decimal points are positioned within the Nixie tube to the right and slightly below the digit electrodes. Three neon indicators are located to the left of the bank of Nixie tubes, one that that shows the sign of the number (lighting up a "-" when the number in the display is negative); another that lights "M" when the memory accumulator has non-zero content, and the last, which lights an "E" when an error condition is detected. The Nixie tubes are multiplexed and use discrete transistor driver circuitry.

The Compet 22's Keyboard Layout

The keyboard of the Compet 22 is identical to that of the Compet 16. The left-most group of keys contains the constant [K] key; the [CE] (Clear Entry), and [C] (Clear) keys. The [CE] key clears the content of the entry register, allowing entry errors to be corrected. The [C] key clears the working registers of the calculator except the memory register, and extinguishes the "E" (error) indicator if it is lit. The next grouping of keys is the traditional numeric keypad, with a double-width zero key. The numeric entry keys feature a mechanical interlock that prevents the depression of more than one key at a time.

Lighted Multiply and Divide Keys

The math function keys make up the next group, with lighted [X] and [÷] keys. These keys have a molded-in red-colored jeweled nomenclature, with incandescent lamps mounted beneath the key that light when a multiply or divide operation is pending. The white [=] key serves as the addition function key, and also triggers the machine to calculate the result of multiplication and division operations. The red [=] key is used for subtraction. The [RC] key swaps the content of the entry and operand registers. The right-most group of keys controls the operation of the memory register. The [CM] key clears the memory register, extinguishing the memory annunciator on the display panel. The [MR] key pulls the content of the memory register into the display. The [M-] and [M+] keys subtract or add the current content of the display to the memory accumulator register. If the memory add or subtract operation results in an overflow, the "E" (error) indicator is lit, but it appears that the machine goes ahead and carries out the operation, resulting in a roll-over of the memory register. For example, performing 99999999999999, [M+], 11, [M+] will result in the "E" indication coming on. Then pressing the [MR] key at this point will recall a result of -99999999999990.

Model/Serial Number Tag

The Compet 22 does not have an automatic power-on-clear function. The power-on clear function that clears the entry/result register at power-on (yet doesn't clear the memory accumulator) appears to have been added as part of the later revisions of the Compet 16 design, and wasn't yet designed into the earlier Compet 22C. When the Compet 22 is first turned on, the display is filled with gibberish consisting of random digits, some with multiple numerals lit inside the same tube. Pressing the [C] key after power-up will initialize the calculator, except the memory register still contains garbage. Therefore, it is necessary to press both the [C] and [CM] keys after the Compet 22 is powered up to assure that all registers are clear and ready for normal operation.

Inside the Sharp Compet 22

It's clear from looking inside the Compet 22 that it's design is somewhat older than that of the Compet 16 "S" (Model CS-16S) version. The Compet 22C uses a lot more discrete components, especially diodes, where the later Compet 16S seems to have substituted more IC's for the discrete components. Both machines have their circuitry populated on two circuit boards. It is interesting to note that the user manual for the Compet 22 boldly states on its front cover that it is a "Sharp ALL IC Compet". The author would debate that claim due to the large count of discrete components that contribute to the logic of the calculator.

A smaller circuit board contains the display electronics, along with the bank of Nixie tubes. The display circuit board handles the multiplexing and driving of the display. The other circuit board, which takes up the base of the machine, contains the majority of the calculating logic of the machine. As with all Sharp electronic calculators beginning with the Compet 20, the machine uses a microprogrammed architecture for sequence control, utilizing a diode ROM array to store the micro-sequence bit patterns.

The Main Circuit Board
Diode/resistor array at right makes up microcode ROM

The integrated circuits in the Compet 22 are manufactured by Hitachi. The devices are all members of Hitachi's first-generation MOS HD-70x-series integrated circuits in TO-100(10-pin) or TO-101(12-pin) can-type packages. A total of 83 IC devices, combined with a large component count of discrete transistors and diodes make up the active devices in the calculator.

The circuit boards in the Compet 22 are of the same design as those in the Compet 16. The boards are made of phenolic, with etched copper traces on both sides of the boards and plated- through feed-throughs connecting traces on each side. The boards are flow- soldered. The main circuit board edge connector fingers are gold-plated for durability and superior electrical connectivity. The main circuit board plugs into two edge connectors that connect to the power supply, keyboard, and display board by a point-to-point wiring harness.

The greenish-colored "Memorizer" Connector

The Compet 22 sports a special connector at the back of the machine that is connected into the keyboard circuitry. This connector can be accessed by removing the model/serial number tag screws. This connector was provided for connecting an external device called a "Memorizer" that allowed sequences of 30 or 60 (depending on the model of the Memorizer) keystrokes to be "learned" and played back to allow automated operation of the calculator for linear (e.g., non-branching) programs.

The Model CSA-12 "Memorizer 60" Programming Accessory

The Memorizer device is similar in size to the Compet 22, with a few keys for controlling the operation of the device as well as a two digit Nixie tube display for showing the step number, and a panel of indicators that display the operation stored at the indicated step. The CSA-12 shown above has two program storage areas of 30 steps each combining for a total of 60 program steps. The program is selected by a slide switch on the front panel of the machine.

Rear panel with Display? Connector and the plug that goes into the it

A feature unique to the Compet 22 that does not appear on the Compet 16 is the addition of a connector on the back panel of the machine next to the model/serial number tag. This connector has a special plug plugged into it. If this plug is not in place when the calculator is powered up, the display comes up blank. The connector into which this plug is placed has a small (three or four wires) wiring harness that plugs into an edge-card connector on the display board. It appears that perhaps this connector allows an external printer to be connected to the Compet 22. The plug also provides for an external power supply (such as a battery pack) to connect to the calculator to provide mobile calculating capability.

The Compet 22 uses exactly the same zener diode/transistor-regulated linear power supply assembly as the Compet 16.

The Compet 22 has the same operational quirks as the Compet 16. Both machines share the blank setting on the decimal point selection rotary switch that causes an input overflow when an operation is attempted with the switch in this position. Another quirk shared with the Compet 16 is that the Compet 22 can't handle division problems where the dividend contains more than 13 digits. For example, dividing 88888888888888 by 1, with the decimal point selection set at zero results in an error indication, and a nonsense result in the display. The reason for this is that the uppermost digit in the working register is used as a counter during the division process.

The Compet 22 is only slightly slower than the Compet 16, likely due to the additional time it takes to process the extra two digits. As with most calculators, the Compet 16 and 22 (and their little brother, the Compet 17) use a bit-serial logic architecture. This means that each additional digit of capacity requires additional time as the digits circulate through the arithmetic logic. Addition and subtraction complete so quickly that no real difference can be observed in the speed of the Compet 22 versus the Compet 16. Multiplication and division, being more complex operations, take just a bit longer on the Compet 22. Multiplication of 9999999 by itself takes about 1/2 second to perform. Thirteen 9's divided by 1 (with decimal point set to 0) takes about 3/4-second to perform. Performing identical operations on the Compet 16 and Compet 22 deliver results in in just slightly more time on the Compet 22, but in general, the difference is not really noticeable. The clock frequency of both machines is the same at approximately 50KHz. Like the Compet 16, the Nixie tubes are not blanked during calculation and flicker wonderfully as calculations are performed.

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

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