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Miida MC840 Electronic Calculator

Updated 4/29/2009

The Miida MC840 is a basic four-function home/office calculator from the early 1970's. The MC840 is a clone of a ground-breaking calculator, the Omron 800 which shattered the price barrier for a four-function desktop calculator when it was introduced April of 1971. After a time producing the 800 on its own, Omron made OEM agreements with vendors including Miida and Adler to provide the electronics for their calculators. This allowed other manufacturers to distinguish themselves with their own cabinet designs, using the low-cost insides developed by Omron to keep their prices down. Based on the date codes on the Hitachi-made IC's inside the machine, this machine was likely made in late 1972, after Omron switched their source for the three-chip calculator chipset from Nortec Electronics to Hitachi.

The Miida MC-800
Image Courtesy Will Davis

The MC840 is a follow-on to Miida's calculator based on the original market-buster Omron 800, which set a new bencmark low-price for a basic four-function display-type AC-powered electronic calculator. Miida's version of the Omron 800 was the Miida MC800. The MC840 was functionally identical to the MC800 with the only external differences being the cabinetry and keyboard design, with the MC840 adopting a more "1970's High-Tech Style" look than the MC-800. The only difference in the electronics was the display, with the MC840 using a ten-position vacuum-fluorescent(VF) display panel versus the individual VF display tubes used by MC800. Both calcualtors utilize the same "ALPHA" three-chip calculator chip set originally designed and fabricated by Nortec Electronics under contract to Omron, with Omron manufacturing standardized circuit boards using the chip set that were sold under OEM contract to other manufacturers, including Miida, for use in their calculators. All an OEM customer had to do was provide a cabinet, compatible VF display system, power supply, and keyboard, and utilize the Omron-provided circuit board, and they would have a calculator that they would market, sell, and support under their own brand name, which is exactly what Miida did.

The VF display panel used in the MC840 has eight positions with standard seven-segment digits with a right-hand decimal point. There is a position at the left end of the display panel that contains only a "-" for display of negative numbers. At the right end of the display panel is a special "108" notation that lights to indicate overflow, with the display showing an approximate result if multiplied by 108

Miida 840 With Back Cover Removed

The three-chip calculator chip set used in the MC840 may take different forms, but their function is the same. Omron farmed farmed out the design and manufacture of the chip set to a relatively new player in the large-scale MOS integrated circuit marketplace, Nortec Electronics. Nortec was a spinoff of a pioneer in MOS integrated circuitry called General Micro-electronics (GM-e). During the early days of GM-e, one of its employees had developed a small four-function, eight digit calculator based on GM-e's small-scale bipolar integrated circuit technology. This design was essentially re-implemented using large-scale MOS IC technology to create the chip set developed for Omron by Nortec. The Nortec chips were packaged in ceramic dual-inline packages with metal lids covering the chip, and were identified as ALPHA 1, ALPHA 2, and ALPHA 3. Due to a tactical error made by Nortec, the price charged to Omron for the ALPHA chip set was raised at some point. Omron would have nothing of it, and immediately canceled the contract with Nortec. Since the logic design for the chipset was done by Omron engineers and provided to Nortec to fabricate the chips, the logic design was owned by Omron. Since Omron owned the logi design, they hired Hitachi in Japan to design identically functioning chips using Hitachi's MOS IC technology, and Hitachi began cranking out the chips for Omron at a lower price-per-chip set than they were getting from Nortec. The Hitachi chips were initially packaged in less-expensive plastic pacakged with the Hitachi logo printed on them, but shortly into production, the Hitachi logo was replaced by "OMRON", as is apparent on the chips used in the exhibited example of the MC840, although as far as is known, the chips remained being manufactured by Hitachi during the market lifetime of the MC840. It is not known if any Miida MC840's were made with the Nortec-manufactured ICs, but there were definitely examples of the earlier Miida MC800 that used the Nortec-made chip set. All examples of the MC840 found thus far have the Hitachi-made parts, with part numbers of HD32104, HD32105, and HD32106. It would stand to reason that by the time the MC840 came to market, the switchover to the Hitachi-manufactured IC's would have already occurred, however, it could still be possible that the limited number of early production Miida MC840s may have been made using Nortec-produced chips, which is evidenced by "NE" appearing on the labeling on chips that were manufactured by Nortec Electronics. If you happen to have a Miida MC840 calculator that has chips in it that are not labeled "OMRON", please click the EMail button at the top of the page to send the Old Calculator Museum a message about your calculator.

Date codes on all of the chips in the exhibited MC840 are 2E, indicating May, 1972. Given that the chips were made some time before the circuit board was made, and the circuit board was made some time before the calculator was assembled, it stands to reason that the exhibited calcaltor would likely have been manufactured sometime toward the end of 1972. The MC840 uses Toshiba-made VF display driver ICs, part number TM4352. The MC840 uses a good-quality sealed magnetic reed switch keyboard, and a basic transistor-regulated power supply, with an internal voltage selection switch to select between 100V (Japan) or 115V(US) line voltage. The main board connects to the VF display panel through two 14-pin IC-sockets on wire pigtails from the main board that plug onto two groups of mating pins on the back of the display module.

Miida 840 Circuit Board

The MC840 provides automatic floating decimal point placement, positioning the decimal point to provide the maximum accuracy possible. It has the unusual distinction of having left to right digit entry. Many calculators of that timeframe used right to left digit entry. As each digit is entered, the existing number is shifted to the right, and the new digit entered in the left-most digit position of the display. The calculator operatres adding-machine style for addition and subtraction, with the [+=] key adding the entered number to the number previously in the display, and the [-=] key subtracting it, immediately displaying the result. Multiplication and division operate algebraicly, with the user entering the first number, pressing the [X] or [÷] key, entering the second number, then pressing the {+=] key to calculate the product or quotient. The [CE] key is used to clear an existing entry in case of an entry error, resetting the display to "0." The [C] key clears the entire calculator, including any pending math operation. At power-on, the calculator is automatically cleared and is ready for immediate operation. The power switch is located at the top upper right corner of the cabinet, a push-on/push-off type switch with a black top with a recessed brushed aluminum surround. The bottom of the cabinet has a label attached that is silver colored with black printing that provides basic operating procedures for the calculator. Also attached is Model/Serial number tag, which is an aluminum piece with black lettering and a stamped in serial number that screws to the back of the cabinet. The cabinet is of nice quality, giving the calculator a solid and substantial feel. Four screws secure the upper and lower halves of the cabinet together.

The MC840 has a rather different contstant function implementation. The [K] key is a push-on/push-off key, which is the norm for calculators of the time. However, when the [K] key is depressed and locks down, the [+=] and [-=] keys are ignored if they are pressed. Only the multiply and divide keys perform any function when the constant function is active. The constant is entered on the keyboard, then the [K] key is depressed, then any number that is desired to be multiplied or divided by the constant is entered, and lastly the [X] or [÷] key pressed to calculate the result. Any other numbers that are desired to be multiplied or divided by the constant can then be entered, followed by [X] or [÷] to calculate the result, for as long as the constant is needed. If the constant is no longer needed, or a different constant is required, [K] key must be pressed to release it and the [C] key pressed to clear the constant. If a new constant is desired, it is entered and the [K] key depressed again. If no further constant is required, normal operation of the calculator will resume after the [C] key is pressed. This is a very unusual method for providing a constant function, and in some ways, rather confusing.

Profile View of Miida 840

The Miida MC840 indicates overflow by lighting the "108" indicator, and ignoring any keyboard input except the [C] key. Pressing the [C] key clears the overflow condition (and the machine). Division by zero, oddly, results in a zero answer (or -0 if the dividend was negative). While the [C] key is depressed, the display remains blanked, which can be disconcerting. Sometimes when the machine is powered up, the display is completely blank, requiring a press of the [C] key to bring the machine to life. The machine performs the "all nines" divided by 1 in about 1/3 second.


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