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Singer/Friden EC1115 Calculator

Updated 12/19/2010

The Singer/Friden 1115 is a stable-mate 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. Hitachi marketed this machine in their home market (Asia) as the Hitachi ELCA-32. After Singer bought out Friden Calculating Machine Company in late 1963, there was a slow drain of much of the electronic calculator design expertise within Friden caused by folks who left or had been reassigned to other projects. Singer management felt that more money could be made by importing electronic calculators made in Japan due to lower design and manufacturing costs. The Japanese had become expert in electronic calculator technology, and Hitachi was ahead of many other manufacturers 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 upon 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 backplane rather than plugging into the backplane as does the power-supply board in the EC1114. The power supplies of the two calculators 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 are of very similar general 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 twelve Hitachi CD 79 Nixie tubes and their discrete transistor driving circuitry. The middle board contains the master clock oscillator, the shift registers that make up the working registers of the calculator, and the arithmetic unit. The bottom-most circuit board contains the control and sequencing logic.

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 type of chips as does the 1114, just fewer of them. The difference in chip count between the 1114 and 1115 (45 for the 1115, 59 for the 1114) is accounted for by the reduction in capabilities of the 1115.

Some of the Hitachi IC's used in the Friden 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 calculator provides a constant key, [K], a push-on/push-off key that enables the constant function when depressed. The constant function works for multiplication and division only.

A look at the Friden 1115 Keyboard

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 calculator's registers and any pending operations. A push-on/push-off key labeled [R/O] sets the rounding mode of the machine, with the up position truncating results and when depressed, results are rounded to the number of decimal places set by the decimal point setting switch.

Back View of 1115

A neon indicator labeled "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, and if performed the calculator 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 reed switches. The keyboard is mounted in a heavy metal frame and connects into the backplane of the calculator via a rather military-style multi-pin connector located at the back upper right corner of the machine.

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