SHARP EL-8116 – calculator with extremely popular chip

Recently, there has already been one calculator coming from Japan, and that was the Canon Canola L100A. Today it’s time for another design from that part of the world, the SHARP EL-8116.

SHARP EL-8 (http://www.calculatormuseum.nl/calculators/sharp_el8.html)

The history of pocket calculators is closely linked to SHARP. After all, it was the Japanese who created the first device in this category. This was the EL-8 model, which today is a white raven. The calculator is best known for its display, made up of several individual VFD tubes with a very fancy character typeface. However, today we will not deal with the first pocket calculator, but its slightly younger brother.

SHARP EL-8116

We are talking about the EL-8116 model. Like its predecessor, today’s hero is a pocket-sized design, launched in 1975. The device is built of plastic in two colors – white and blue. In addition, the area around the display was covered with a layer intended to resemble metal. It is smooth, like the white plastic, only the blue plastic has a slightly rough texture intended to resemble leather. The front of the calculator will be filled primarily with a keyboard, with the display placed slightly above, hidden behind green translucent plastic. Above the display is still the manufacturer’s logo, along with the model designation.  

The calculator can be powered by two AA batteries, or by a dedicated jack adapter. The on/off switch, activating the EL-8116, is located on the left edge. Right next to it there is also a clip that allows you to attach the device to, for example, a lanyard.

A few words about the keyboard, as it surprised me positively. The keys are very “soft”, and their stroke is quite large for such a small design. Given its design, about which more later, it is quite surprising that it still works so well. It is possible that the calculator has spent most of its years in some drawer. The buttons themselves are also made of plastic, with all the markings painted in small recesses, so there’s no possibility of them coming off.

Patent sticker

The back of the calculator contains a nameplate with information about the model, power supply and place of manufacture. Although the device was designed by a Japanese company, it was manufactured in South Korea. Also characteristic of SHARP’s calculators is a sticker with the patent numbers the company owns in the country. Looking at the first of the numbers: 3469085 and 3486015, you can learn that SHARP has a license in the US for a register control system and an arithmetic unit with correction support. 

Calculator when unfolded

Wanting to get to the inside of the EL-8116 we have to unfold the two parts of the case. They are held on plastic latches, also the whole operation should be done carefully so as not to damage them. After opening the calculator, we can see the underside of the motherboard with quite a few tracks, the battery space, the external adapter socket and the back of the display. 

Serial number inside the battery cage

Looking inside the battery basket, we can find another interesting solution. The serial number, which, as you might have noticed, was not on the nameplate, was placed right here, on a paper sticker. The paper itself is also unique, as it has the manufacturer’s mark – SHARP – printed at an angle.

Mysterious aluminum stripes

Looking at the second part of the case, you can see something interesting. Two aluminum strips have been placed under the battery opening. When the calculator is folded, they are located directly above the display. I wondered a bit about their use, but nothing sensible comes to mind, maybe you guys have some ideas, let me know in the comments. 

But let’s go back to the motherboard, there is a hole in the middle of the motherboard, along with a screw that needs to be unscrewed to stand back further. When removing the PCB, be careful, as it is connected to the keyboard PCB by a very short tape.

"modern" keyboard

After removing the two circuit boards and the switch/adapter module connected to them, we can look at the keyboard itself. Its design is quite “modern”, as it resembles very much the buttons used in all kinds of remote controls. Here we have a set of so-called conductive rubber bands that, when pressed, close the electrical circuit. Quite surprising in how good a condition they are, despite the fact that the calculator is almost 50 years old.  

keyboard in its full glory

The perimeter of the keyboard was made very neatly, here we see quite a few squares without soldermask. It is here that the paths short-circuited by most likely graphite or other conductive material covering the silicon rubber bands were placed. 

In the photo you can also see in full glory the display used in the calculator. It is formed by a single nine-character VFD. It is a design of the Japanese company Futaba, which interestingly still exists today. The display itself bears the designation 9-ST-12.  

mainboard

Lifting the keyboard board, you can see the main circuit of the calculator, it contains a single integrated circuit and a handful of associated components. The design is not too complicated a few capacitors, a transistor, diodes, resistors. We can stop for a moment at a small cylinder marked 1291 TDK JAPAN. This is a miniature transformer that allows us to generate the control voltage for the VFD tube. Its manufacturer is TDK, a Japanese company famous for manufacturing electronic components and storage media.

The brain of the EL-8116 calculator is a chip manufactured by NEC with the designation µPD278C. This chip can successfully control the VFD lamp, so there was no need for additional chips. We can describe this design as successful, it supports basic mathematical operations including primes and percentages. Besides, the chip is equipped with a memory. µPD278C was used in a great number of calculators among others: BMC 803PM, BROTHER 202, BROTHER 508ER, COMPEX ST10, DECIMO Strand Memory, DELTEK BUSINESS MACHINES 6002, DETSON 803PM, HANIMEX BCM368, MBO Diplomat II, MBO TR80M (version-2), , PRINZTRONIC MP300, PRINZTRONIC SR99M (version-3), RADIO SHACK EC380 (version-1), RADIO SHACK EC380 (version-2), SANTRON 423R, TESLA OKU202, TOHO TSUSHO F4, UNIMARK 813T. Looking at this list, we can say without hesitation that this was a very popular circuit in its time.

EL or ELSI or ELSIMATE

When describing SHARP’s calculator, one must not forget the question of naming. In fact, today’s hero can be referred to as EL-8116, ELSI-8116 or ELSIMATE-8116, any of which will actually be correct. Such a naming system stems from SHARP’s rather strange practice in naming its devices. Back in the days of the EL-8, any calculator from that company could have the three names EL, ELSI or ELSIMATE, the second part of the name always being a number. All of these designations are, in fact, interchangeable.

Sources:

  • http://www.calcuseum.com/SCRAPBOOK/BONUS/09195/1.htm
  • http://www.calcuseum.com/SCRAPBOOK/BONUS/20408/1.htm
  • https://www.calculator.org/calculators/Sharp_EL-8116.html
  • https://usermanual.wiki/Manual/SharpEL8116.45570951
  • http://mycalcdb.free.fr/main.php?l=0&id=2397
  • http://www.calculatormuseum.nl/calculators/sharp_el8.html

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