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Singer/Friden EC1115 Calculator
The Singer/Friden 1115 is a stablemate of the Singer/Friden 1114, with a goal of reducing the sticker shock associated with electronic calculator technology of the late 1960's and early 1970's. The two machines share very similar mechanical aspects, and use the same technology to do their jobs. The 1115 is a 12-digit four-function calculator, in contrast to the 14-digit capacity of the 1114. The 1115 does not provide the memory functionality of the 1114. The 1115 has IC's with date codes ranging from early to mid-1970, making it likely to have been built sometime in mid to late 1970.
Like all of the machines in the Singer/Friden 111x series of calculators, this machine was designed and manufactured in Japan by Hitachi, in partnership with the Friden division of Singer. When Singer bought out Friden Calculating Machine Company, most of the team that designed Friden's early electronic calculators (such as the Friden 130) was disbanded, in favor of lower-cost offshore design and manufacturing. The Japanese had become expert in electronic calculator technology, and Hitachi was ahead of many other manufactrers in applying their well-developed PMOS integrated circuit technology to the design of electronic calculators that were less expensive than could be made in the U.S. with its higher labor costs.
EC1115 Internals
The 1115 is built from four circuit boards
(in contrast to the five boards in the 1114). The top-most board provides
power-supply functions, and is hard wired into the machine rather than
plugging into the backplane as the power-supply board in the EC1114 does.
The power supplies of the two machines appear to use the same basic design,
in fact, many components are identical between the 1114 and 1115 power
supply subsystem. The three boards that make up the calculator logic of the
1115 are of very similar design to the boards in the 1114, and plug into
a hand-wired backplane.
Singer/Friden 1115 Circuit Boards The top plug-in board contains the display subsystem, including
12 Hitachi CD 79 Nixie tubes and the discrete transistor driving circuitry.
The remaining two boards make up the calculating logic of the machine,
and are populated with numerous small-scale integration IC's, with a fairly
high part count of discrete components mixed in. All of the 45 Hitachi-made IC's that make up the logic of the
machine are in Hitachi's HD31xx-series of PMOS small and medium-scale
integrated circuits. The EC1115 uses the same compliment of chips
as does the 1114, just fewer of them. I'm assuming that
the difference in chip count (45 for the 1115, 59 for the 1114) is
accounted for by the reduction in capabilities of the 1115.
A Detailed Look at some of the IC's in the 1115 The 1115 operates with floating decimal input, and fixed decimal
output. This means that on input, the decimal point can be positioned
anywhere, but the results in the display always have the decimal point at
a fixed location. The decimal point location is set by a three-position
slide switch on the keyboard panel, providing settings of 0, 2 or 5 digits
behind the decimal point. The machine provides a "K" constant
key which is a push-on/push-off key that enables the constant function
when depressed. The constant function works for multiplication and
division only. The "R" key swaps the content of the hidden 'operand'
register and the display. The "CE" key clears the display of erroneous
entries, and the "C" key clears the entire machine except for the memory
register. A push-on/push-off keyboard button labelled "R/O" sets the
rounding mode of the machine. Back View of 1115 A neon indicator labelled "OVF" (in contrast to the "UDF"
designation on the 1114) on the left end of the display indicates
overflow. A similar neon indicator on the right end of the display shows
when a negative number is in the display. The 1115 doesn't provide an
error indication when division by zero is attempted. When a divide by
zero is attempted, the machine enters a curious state. The right-most digit
in the display appears to be counting at a furious rate...making it appear
as if all digits in the Nixie tube are on at once, and the divisor
is 'superimposed' over zeros on the remaining digits of the display.
Pressing and holding down the "CE" key while this is happening results in
the right-most digit displaying both "0" and "1" digits on at the same time.
When the "CE" key is released, the counting in the right-most digit resumes,
and the rest of the display contains zeroes. Pressing any other keys
during this attempt of the machine to do the impossible results in no
response. Pressing the "C" key stops the churn, and returns the machine
to a sane state. The keyboard assembly of the 1115 is very similar to the 1114,
made up of magnetically actuated microswitches mounted in a heavy
metal frame. The keyboard connects into the backplane of the machine via
a rather military-style looking multi-pin connector located at the back
upper right corner of the machine.
