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