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Remington EDC-1201GT Lektronic

Updated 12/16/2018

The Sperry Rand/Remington Lektronic is a product of the time when integrated circut technology was undergoing its first revoltion from the time that ICs were first being used in calculators. Early IC-based calculators used a few small-scale ICs that might have had four logic gates, or a flip flop inside each IC package, but still used a lot of transistors and diodes for the majority of the logic. As small-scale IC technology advanced, machines would use more ICs and fewer discrete components. At one point, machines would consist of mostly small-scale ICs and very few active discrete components, with most of the discrete devices being resistors and capaitors. Then, IC technology changed. More and more transistors could be placed on a single chip, and suddenly a new class of IC appeared on the scene -- the Medium-Scale Integration (MSI) device. One of the first calculator functions to be packed into a single MSI chip was the complex serial adder. Prior to MSI, the adder logic would use ten to fifteen small scale ICs. Now, it could fit on one slightly larger IC. MSI IC technology was developed in the US, but the Japanese had learned to make thier own ICs, and quickly adapted to the processes required to make medium-scale devices. The Lektronic benefitted from this technology to pack more calculating power into a small (but unusual horizontal form-factor) package.

The Lektronic's Cousin, the Casio 121-B
Image Courtesy Andy Anderson

Sperry-Remington was a US-based company that had made a run at the calculator market with a line of calculators that utilized small-scale IC logic and a magnetostrictive delay line. These machines were designed and built by Sperry-Remington, and included the EDC-I, EDC-ID, EDC-III, and the EDC-IIIA. All of these calculators were somewhat behind the times from a technology and feature standpoint, and were also rather expensive, especially compared to Japanese-made electronic calculators, which were beginning to take the world by storm due to their significantly lower cost. Sperry-Remington's calculators, while built to very high quality standards, were simply a bit weak on features as well as being overpriced for the market. Sperry-Remington management realized that its calculator business wasn't going to be a profitable venture unless something changed. The change involved forging a formal relationship with the well-established and respected Japanese electronic calculator manufacturer, Casio Computer Co., Ltd. in the fall of 1967. Prior to this formal agreement, Sperry-Remington had been, through Australian distributors, branding Casio calculators with the Remington brand, beginning with the Casio 101 (Casio's first export-ready electronic calculator), and selling the calculators into the Australian market. Through some distribution channels, some of the Australian Remington-badged Casio calculators were modified to meet US electrical standards, and were sold in limited numbers in America. While allowed by Casio, this practice was rather gray market, and the formal agreement allowed for direct import of Casio-made calculators into the US for sale under the Sperry-Remington brand name. When the agreement with Casio was forged, Sperry-Remington abandoned any further development of its own calculators (though the EDC-III/EDC-IIIA designs were completed and sales EDC I/ID/III/IIIA machines continued for a time), and instead began selling Sperry-Remington-badged versions of Casio's calculators in the North American market.

Advertisement for Remington "Casio" AS-A (aka Casio 121-A), September, 1970

The calculator exhibited here is the Sperry-Remington EDC-1201GT Lektronic, which is functionally and electronically identical to the Casio 121-B/AS-B calculator, with the only difference being cabinet and keyboard color schemes, with the Sperry-Remington version adopting a much more colorful cabinet and keyboard color scheme compared to Casio's rather subdued colors.

Inside the "Lektronic"

The calculator's logic circuitry is contained on two tightly stacked circuit boards interconnected by hand-wired jumpers. The top circuit board (visible above) is home mostly to display multiplexing/driving functions, keyboard encoding, and master clock generation.

Detail of Nixie Display Tubes

The display is made up of 12 individual and unusually small Nixie tubes put together in a package which assures that the tubes are lined up accurately and also provides mechanical stability for the rather delicate Nixie tubes. The Nixie tubes benefit from integrated circuit drivers, being one of the few Nixie-display calculators that I've run across that have the Nixie tube displays driven directly by integrated circuits rather than discrete transistors.

The Main Calculating Board

The main logic board, sandwiched below the display board, makes up the calculating engine of the machine, consisting of a number of Small- and Medium-Scale Integration IC's. The small-scale devices contain simple gates and flip-flops used for logic and sequencing functions. The medium-scale devices consist of shift registers (used for register storage), and the main adder circuit. The adder IC, a Hitachi HD3112, puts all of the circuitry that performs serial BCD (Binary-Coded Decimal) addition on one chip. In earlier Casio calculators such as the Commodore AL-1000 (made by Casio for Commodore), the functions contained on this single IC required an entire 12x7-inch circuit board full of discrete components.

The Lektronic is a very simple-minded calculator, performing only the four basic math functions. It has no capability to deal with input of decimal points (notice that there is no decimal point key on the keyboard). The Nixie displays have decimal points in them, but they are only used for displaying the decimal point in quotients, and then, sometimes a non-intuitive method is required to determine the result. For example, in operations which result in only a fractional result, the decimal point will position itself such that the user starts at the decimal point, working to the right, and when the right end of the display is hit, the user must 'wrap around' to the left end of the display to get the answer. For example, 1 divided by 10 results in a display of '100000000000.' In another example, 1 divided by 1000 results in '1000000000.00', which really means .001. The machine also represents negative numbers as their 10's compliment; for example, -1 is displayed as 999999999999. Pressing the [-=] key will compliment the number on the display. Overall, the machine can require a bit of thought when in use because of its limitations. The machine has no error or overflow indication. Dividing by zero results in the machine trying forever to position the divisor such that subtraction from the dividend can begin -- an endless venture which results in all of the decimal points flickering wildly, and the machine being non-responsive to anything but the [C] key. Addition and subtraction operations which cause overdraft simply toss the overflow, wrapping back around; e.g., 999999999999 + 1 = 000000000000. Multiplies which overflow give useless results. All operations operate as expected for a machine of this vintage, with the [+=] and [-=] key adding to/subtracting from the number in the display, and multiply and divide generating a result by pressing the [+=] key. The machine calculates at a reasonable pace (considering its relatively slow master clock frequency of 45KHz), with the benchmark division of 999999999999 ÷ 1 taking less than 1 second to perform. A small slider positioned in front of the display window allows the user to manually position the commas (groups of 3 digits) to make it easier to read numbers on the display. The machine does sport a memory register that automatically accumulates the sum of products during multiply operations. The [R] key on the keyboard recalls this register to the display, clearing the register after the recall.

The keyboard of the Lektronic uses high-quality keycaps with moulded in nomenclature. As is common on machines from this era, the keyboard uses magnetically-activated reed switches. The keyboard connects to the calculating engine board via an edge connector. The machine uses a simple transistor-regulated linear power supply which resides on a circuit board located in the bottom of the case, along with a small transformer.

Text and images Copyright ©1997-2019, Rick Bensene.