Milestones in the History of Calculators

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In the 1980s, circuit manufacturers introduced quite a few chips based on an existing type from another manufacturer. In general, they do not have exactly the same structure and there are differences in their operation, but their common feature is that they can be used to easily produce the so-called clones that are more or less identical to the original models in their operation, keyboard arrangement and display layout. Taking advantage of the similarities, several manufacturers made copies by reproducing the appearance of the originals, as well as fakes by labeling the original company and model designations on these machines. In the first part of our series, we present one of the best-known clone families.

Their history can be read in detail in the article on the Sharp EL-506 series. In short, Sharp released the EL-506H scientific pocket calculator in 1981, which has become a very popular model among students and technicians. Due to the great success, not only the series was continued with newer and newer versions, but the original model — with minor modifications — was continuously produced in China until 1989. From 1984, the more advanced EL-506P was in production in Japan, which was also produced in very large quantities. In 1990, the predecessors were replaced by a newer model, the EL-506A..

1. Functional clones of EL-506P

The great success has prompted some companies to copy the EL-506H/P. After Samsung built its KS6041 chip, which was functionally equivalent to Toshiba's SC6992 IC used in the original EL-506P, all it had to do was put it in the right box to dominate the market for years - from electronics stores to Chinese markets. The best-known clones were built in a housing copied from the EL-506H, creating a never-before-existent “hybrid” copy: a new machine in an old housing. Over the years, several manufacturers have made it in several versions. Unfortunately, they were usually of very poor quality, often assembled with miniature screws used commonly in the watch industry, which prevented the machines from surviving not only accidental dropping but also battery replacement. The unknown manufacturer printed anything on the machines what the customer wanted, so these clones were marketed under several brands. Many times they were not deterred from using the original “SHARP” branding either. Most often, however, the type designation “EL-506P” was used. Their printed circuit board reads the model number Yk587, the chip used is Samsung’s KS6041 or KS6042, or their licensed and modified versions. The other version is more similar in shape to the original Sharp EL-506P, but with a different color scheme. It is also made with rubber or plastic buttons, and its display has a traditional zebra striped conductive rubber or connected with a thin foil cable. Its manufacturer was the newly founded Truly company, their original type designations were Truly 101 and 107. The versions built with a display with a “zebra stripe” connection are surprisingly good quality and are generally functional to this day. They are identified by the right-aligned 10-DIGIT SCIENTIFIC CALCULATOR labeling above the display.

Of course, with this chip, countless scientific calculators were made in a different housing, which is not even similar to the above types of Sharp. Even today, we can find such types in the product range of most Chinese factories, which can be recognized by the fact that they have 56 functions.

2. Calculators with Sharp LI3301A chip

It has an interesting history of the programmable “EL-506H” machines. Sharp produced quite a few chips that were also marketed so anyone could build a calculator with them. One of the most interesting of these is the LI3301A circuit, which made it possible to build a simple programmable scientific calculator. Hard to investigate who built the first calculator with that chip, but the most known manufacturers (Sanyo, Citizen, Radio Shack etc.) introduced after the noname versions flooded the market. The programming model of the machines is the same as the EL-512 (and several others), but its program memory size and number of K-registers are different. The “2F” displaying that appears when you press the 2ndF key to access secondary functions is also interesting.

Several manufacturers built a calculator with this chip, some of which were housed in the copied housing of the EL-506H, creating “Sharp” copies built with a Sharp chip. Interestingly, original Sharp calculator was never made with this chip.

Some of the best-known representatives of the type in Hungary are Citizen SRP-45, Sanyo CZ 1206 and MBO Alpha 610 PR, all of these are also available in at least two versions.

Shangji SJ-560 is very interesting machine — which was also available in Hungary —, because its housing was similar to the original, but the manufacturer rearranged the keyboard.

3. Copies of Casio fx-82LB

Casio fx-82LB-looking clones and fakes appeared in the early 2000s are very interesting: they were built with Samsung’s KS6042 chip, so they are identical to the Sharp EL-506P. This becomes clear as we look at their keyboard. They were made in at least two designs: the previous version was built with a single printed circuit board in better quality. The later version represents the lowest quality ever produced in calculators: the front of the keyboard is made of paper, and the back, which tries to keep the Bible-paper-thin printed circuit board level, is made of cardboard. The plastic housing has an undemanding design in both versions, it cracks and breaks easily. Its rubber keyboard is of uncritical quality, strong pressure is required for the electrical connection, and the conductive layer wears off very quickly. Because of these, although it was available for years, it soon wore out of use.

4. Other EL-506P-like machines

Two more interesting things to mention: first, the EL-506P-looking machine, which was actually made with one of Toshiba's commercially available chips, which is interesting in that it performs calculations with the same microprogram as the Sharp EL-506H, so the two machines gives identical results for calculations. The machine is simpler than the EL-506H and EL-506P, so instead of redesigning the front panel, the manufacturer included some keys twice: [DRG] next to [2ndF] and under [CE], and [C] is doubled as [ON] in the upper right corner. The machine's memory is cleared when the power is turned off, so “MEMORY SAFE GUARD”, which refers to non-volatile memory, is replaced with “MEMORY INCLUDED”. The labels of the conversion between number systems have been replaced by the symbols of the four basic operations. The button labels on the plastic keys were made in very poor quality, so they were worn out very quickly. Apart from this, the machines are of good quality and are generally still operational today. In German-speaking areas, they have been marketed mainly under the type designation "ASTOR 2".

5. Fake copy of Sharp EL-506A

Finally, we must introduce a rare fake copy of the Sharp EL-506P: the EL-506A version of the “Sharp” made in 2001 is actually one of a kind of clones of the EL-506P that has been produced for decades. The solution to the problem of fewer keys was found to be that, like the machine mentioned in point 4, the [ON/C] key was duplicated as [C]. In terms of quality, it belongs to the middle category.

6. Sharp’s new EL-501 series

A particularly interesting ending to this topic could be described as the fact that in 2001, Sharp created a clone of its own machine. After Sharp introduced the Advanced DAL system (which calculates the whole entered expression once), all of the scientific models built with that, so there is no model in production that have the classical algebraic logic feature. These types of competitors continued to be successful, so Sharp took the EL-506P back into production in 2001. The new EL-501V model was built with a rearranged keyboard similar to other scientifics, but has identical functionality to the previous EL-506P, and to the clones discussed above. This model is still in production today, its latest version (EL-501T) was released in September 2019.