+Home     Museum     Wanted     Specs     Previous     Next  

Friden 1112

Friden 1112 Electronic Desktop Calculator

Updated 7/18/2021

The Friden 1112 is the first example of the Friden Division of Singer using outside expertise to design and manufacture a calculator for sale under the Friden brand name. Before Friden was bought out by Singer sometime in mid-1963, Friden had designed its own electronic calculator... the amazing and historical Friden 130. When Singer purchased Friden, the new management decided that the electronic calculator marketplace was increasingly price-sensitive for Friden's all-American design and manufacturing to be able to compete. Singer management quietly looked off-shore for a company that could design and manufacture electronic calculators to be marketed under the Friden brand name.

Hitachi Model/Serial Tag

Hitachi Model/Serial Number Tag

It took some time, but sometime in 1967, Japanese industrial conglomerate Hitachi turned out to be the connection to low-cost design and manufacturing that Singer management wanted. An arrangement was made for Hitachi, who had introduced a successful electronic calculator in January of 1967, to provide design and manufacturing for a line of machines to be sold under the Friden brand-name in the US and Europe. Hitachi's calculator was selling well in Japan, and seemed to be a good fit for Singer's requirements. This machine was marketed in Japan as the Hitachi TEC-12, or, as listed on the serial number plate, the Model KK Type 12. Friden's 1112 was identical to the TEC-12, with the only difference being a Friden name badge replacing Hitachi's TEC-12 nomenclature. Hitachi also developed a 16-digit version (the TEC-12 had twelve digits of capacity) called the TEC-16, but it was not marketed by Friden. Later, Singer continued this partnership with Hitachi, with an entire line of Friden/Singer 111x-series calculators, including machines ranging from the Friden 1113, through the Friden 1118. The 1112 was the only discrete transistor machine in the 111x series, with rest of the machines in the series utilizing integrated circuit technology ranging from early MOS (Metal-Oxide Semiconductor) small-scale IC's through early LSI (Large Scale Integration) devices.

Friden 1112 Profile

Profile View of Friden 1112

The Friden 1112 is what I class as a second-generation electronic calculator, in the company of a group of calculators that were among the early machines utilizing entirely discrete transistor technology. Earlier, first-generation calculators came out before transistors had become mainstream, using Thyratron (Anita C/VIII) or Parametron circuitry that used significantly more power, consumed more space, made a lot of heat, and did not have the speed and long-term reliability of solid-state electronics.

The Friden 1112 shares many architectural design aspects with other Japanese-designed calculators of the time, including machines like the Sharp Compet 20, and the Canon 161. These machines all share fully-transistorized logic and register storage, along with non-multiplexed display systems. Other machines of this generation used transistorized logic, but utilized other means, such as core memory or acoustic delay lines, for working register storage. Examples of these machines are the Sony ICC-500W and the Olympia-designed Monroe 770.

Friden 1112 Internal View

Friden 1112 With Cabinetry Removed

Internally, the Friden 1112 shares a similar design to those machines which it architecturally resembles. The machine is of a modular design, with a backplane across the back, circuit boards that plug in front-to-back, with Nixie tubes soldered directly to the circuit boards, and power supply situated under the keyboard assembly. The logic of the machine consumes a total of fifteen circuit boards, all of which are made from phenolic material, with circuit interconnections on one side of the board, and components on the other. Each circuit board is unusually shaped, but are roughly 9-inches deep, and 7-inches high. Each circuit board has two sets of edge-connector fingers, which are gold-plated. A total of forty connections are available on each board. Thirteen of the fifteen circuit boards have Nixie tubes soldered to them such that they are arranged to display through a window in the cabinet of the machine. Twelve of the circuit boards have Hitachi CD-70 Nixie tubes attached to them, each of which can display the digits zero through nine, a right-hand decimal point, and a vertical "tick mark" located at the upper-right of the digit for use in indicating separation between the multiplicand and multiplier when performing multiplication operations. The CD-70 Nixie tubes have 5/8-inch tall digits, making for a very easy-to-read display, even at a significant distance from the calculator. The 13th circuit board has a special Nixie tube that displays "+" and "-" for indicating the sign of the number in the display.

Friden 1112 Circuit BoardFriden 1112 Circuit Board

Friden 1112 Circuit Board, Component Side & Print Side

Each of the twelve "digit" circuit boards contain a common set of circuitry related to storing the single four-bit BCD (Binary-Coded Decimal) code for the digit, and the necessary decoding circuitry to translate the BCD digit code to a one-of-ten selector to activate the driver transistor for the appropriate digit in the Nixie tube. Along with the digit-specific logic on each digit board (along with the sign digit board), there is a lot of other logic that is distributed amongst the digit boards to make up the working registers, arithmetic unit, and control logic of the calculator. The remaining two circuit boards contain general logic, including what appears to be keyboard encoding/deb ounce circuitry, clock generation, and other miscellaneous logic. The circuit boards are conservatively laid-out, with relatively wide spacing between components. On most boards, there are jumper wires used on the component side of the board to provide for connectivity that there wasn't room to provide on the printed circuit side of the board. Components are standard resistors and capacitors for passive components, and diodes and transistors as active components. All transistors are made by Hitachi, packaged in metal cans. Four different types of transistors are used, including 2SC284's used for Nixie drivers, 2SA17's used for flip-flops and some logic elements, 2SB77's as buffers, and a small sprinkling of 2SC180's. A total of 507 transistors make up the logic of the calculator, along with a countless array of diodes. The logic is very conventional, with diode-resistor gating, and transistors used for buffering and flip-flops used as counters and shift-registers.

Friden 1112 Backplane

Backplane of the Friden 1112

The circuit boards plug into a hand-wired backplane. The edge-card sockets are retained using an interesting arrangement of brackets that hold the connectors in place. The backplane is a bundled maze of colored wires that provide all of the interconnection between the circuit boards, as well as connections to the power supply and keyboard assemblies.

Friden 1112 Power Supply

Friden 1112 Power Supply

The power supply of the Friden 1112 is very conventional, using a multi-tapped transformer feeding diode rectifiers. The rectified current is sent to zener-diode/transistor-based voltage regulation circuitry, and capacitor filtering. The logic supplies of the calculator are +6 volts, and -12 volts. Along with the logic supplies, a separate set of windings in the transformer generates approximately 220 Volts AC that is rectified and filtered to provide ~200 Volts DC that is used to drive the Nixie tube displays. The power supply assembly is located under the keyboard assembly, with the transformer, a single-sided circuit board containing the rectifiers and regulation circuitry, and a set of terminal strips that supply filter capacitors are wired to. A metal plate provides a mounting point and heatsink for the power transistors that provide the final stage of regulation for the logic supplies.

Friden 1112 Keyboard Detail

Leaf Switch Contact Keyboard Arrangement on Friden 1112

The keyboard of the 1112 is unusual, but not unique. Many early calculators used magnetic-activated reed switches for the keyboard. Magnetic reed-switches have the benefits of clean switching, an indirect connection for the switching (via the magnet on the key stalk), a sealed design (the switch contacts are situated inside a sealed glass envelope) and small size. The Hitachi-designed keyboard forsakes this tried and true design, opting for very simple leaf-switch contacts activated by the plunger on the switch.

Friden 1112 Keyboard Detail

Plastic Keyboard Cover

While inexpensive, this type of keyboard arrangement has its downside, in that the switch contacts are subject to contamination that can cause intermittent connections. Leaf contacts also can require periodic adjustment to maintain proper tension and distance between the contacts. Hitachi's solution was to provide a plastic cover over the switching assembly to keep out contaminants, as well as using two sets of contacts for each switch to provide some redundancy, as well as minimizing the amount of contact bounce. The whole keyboard assembly, along with the power switch, is mounted to a heavy aluminum casting that provides the bezel for the keyboard. The keys and key-stalks are made of plastic, with molded-in key legends.

The workings of the calculator are held together with a large cast-aluminum base plate that provides a firm foundation for the rest of the machine. The card cage is made from stamped sheet-metal, providing both a structural frame, and mounting for various parts of the calculator. Cross-braces across the top of the card cage have rubber block strips that hold the circuit boards apart from each other, and add some shock isolation for the boards. A black sheet-metal plate with slats in it provides a means to hold the Nixie tubes in alignment. The cabinetry is made of high-quality plastic castings. The cabinet is made of two parts, a powder-blue colored unit that covers the card cage, and a white unit that provides the cover for the keyboard. Cooling grilles are molded into the part of the cabinet that covers the card cage. Cooling is by convection only. The machine generates amazingly little heat for a machine of this vintage, and the cooling grilles are perfectly adequate to provide enough air movement to keep the machine's operating temperature in check. The cabinetry is secured to the chassis base by machine screws.

Friden 1112 Keyboard

The Keyboard of the Friden 1112 (Note Hitachi Logo at Upper Left)

From a user perspective, the 1112 is fairly straightforward. Addition and subtraction operate adding machine style, with the [+=] key adding the number currently in the display to the accumulator, and displaying the new content of the accumulator after the addition is completed. The [-=] key does the same, but subtracts. The [X] and [÷] keys have their obvious function, but multiplication on the 1112 is somewhat unusual. Like a few other machines in the museum, such as the Canon 161, and then Brother Calther 412, the 1112 places both the multiplicand and multiplier in the display together, utilizing a special indication between the two numbers. Division operates as expected.

The 1112 has a capacity of twelve digits, plus sign. Decimal point position is determined automatically. As somewhat unexpected aspect of the automatic decimal point positioning system is that it can only provide a maximum of nine digits behind the decimal for division operations. For example, performing 2 ÷ 3 results in +000.666666666 being displayed. The calculator is capable of representing numbers with more than 9 digits behind the decimal point, and properly handles them in addition, subtraction, and multiplication. For example, performing 1.23456789012 + 3 properly results in +4.23456789012. Dividing this result by 1 will result in +004.234567890. This limitation appears to be related to the way that division was implemented in the circuitry of the machine.

The 1112 provides a few additional features, including the ability to accumulate sum of products. The [Σ] key, a push-on/push-off switch, enables product accumulation when activated. A neon indicator under an orange jewel next to the key lights to indicate when sum of products mode is activated. When enabled, and successive multiplications are performed, the sum of the individual products is automatically accumulated in the display.

Friden 1112 Power-On Display

The "Jumbled" Display at Power-On

The calculator retains the first operand in multiplication, and the second operand in division problems, and allows this operand to be recalled to the display using the [R] (for Repeat) key. This provides a rudimentary, manually-activated constant function. The [←] key allows for digit at a time correction of numbers entered from the keyboard. Unlike some calculators from the era that also have this functionality, the 1112 keeps track of the decimal point position when this key is used, allowing correction of numbers before and after the decimal point. The large [C] key clears the calculator. The 1112 does not have power-on clear circuitry, resulting in a jumble of digits on the display when the calculator is first powered up. Pressing the [C] key clears the machine, and readies it for operation.

The 1112 is not without a few quirks. First off, the machine has no overflow detection. Adding 999999999999. and 1. results in "+000000000000" in the display. Performing multiplications that exceed the capacity of the machine can result varying symptoms, ranging from simply incorrect results, to results that have multiple digits within a single Nixie tube lit at the same time, to a wild dance of futility where the calculator gets very confused, requiring a press of the [C] key to stop the madness. Unlike some other calculators of this era, the 1112 does provide fully accurate answers to multiplication problems that are within its capacity. For example, performing 999999 X 999999 properly results in "+999998000001." Multiplication does have one quirk during entry of problems. If the multiplicand (the first number in a multiplication problem) has a factional portion (digits behind the decimal point), the decimal point in the number disappears (but is properly kept track of internally) when the [X] key is pressed. It's a bit disconcerting, but the machine does give the correct answer. For example, performing 1.25 X 3.55 would be entered and displayed as below (with the "|" indicating the special multiplication separation indicator):

Friden 1112 Multiplication Display

Multiplication Display (Note Vertical Bar Separating Multiplicand [1.25] from Multiplier [3.55])

Keyboard Entry     Display
    C           +000000000000.
    1           +000000000001.
    .           +000000000001.
    2           +00000000001.2
    5           +0000000001.25
    X           +000000000125|.   Note Disappearance of Decimal in "1.25"
    3           +00000000125|3.
    .           +00000000125|3.
    5           +0000000125|3.5
    5           +000000125|3.55
   +=           +00000004.4375

Friden 1112 Multiplication

Close up of Multiplication "Bar" on Friden 1112

The 1112 does not perform detection of division by zero. If a division by zero occurs, the machine goes into an infinite loop, trying to solve a problem that has no solution. The decimal point and multiplication indicators quickly strobe across the display during this process, and the only way to terminate the futility is to press the "C" key. Division also has a quirk in that the dividend can not exceed ten significant digits, or the division process gets very confused, sometimes resulting in strange answers, or even causing the calculator to lock up, requiring a press of the [C] key to return it to operation.

Calculating speed on the 1112 is about the norm for machines of this era. Clocking speeds of the transistor circuitry were typically limited to 100KHz at the very high-end, with typical clocking speeds in the 20 to 50 KHz range. These low (as compared to today) clocking rates helped to keep power consumption down, and allowed the use of lower-cost transistors with slower switching speeds. For a desktop calculator application, such speeds were a major improvement over desktop electromechanical calculators, which were lucky to operate at rates of 30 cycles per second. Addition and subtraction complete in scant milliseconds, with operations requiring decimal point positioning prior to the addition taking the longest, perhaps 50 milliseconds at most. Multiplication clips right along also, with the 999999 X 999999 (most complex multiplication operation) problem taking a little under 1/2-second. Division is the slowest operation, with the most difficult division calculation (999999999 ÷ 1) taking just under one second to complete.

Sincere thanks to Serge Devidts, curator of the vast calculator collection exhibited on his (Calcuseum web site. Serge was instrumental in brokering the acquisition of this calculator and arranging its shipping from Belgium to the Old Calculator Museum in Oregon, USA.

Text and images Copyright ©1997-2023, Rick Bensene.

All content on this site is not to be gathered, scraped, replicated, or accesed in any way for any use in populating machine learning or intelligence (Artificial Intelligence, a.k.a. AI) databases, language models, graphs, or other AI-related data structures. Such use is a violation of copyright law. Any such access will be reported to the Oregon Attorney General and prosecuted to the fullest extent the law allows.