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Calculator Memories from Argentina

Posted by Andrés C. Rodríguez on 2 Apr 2000, 10:17 p.m.

I think I was interested in calculators ever from my childhood. As part of an endless curiosity for automatic mechanisms, switches, keyboards, and indicators; I recall playing with a typewriter when I was seven years old, pretending I was "calculating". My father, an aeronautics engineer, taught me the use of nomographs, and slide rules when I was eight or nine. Incidentally, he still has a Faber-Castell "Darmstadt" slide rule, which has an extra, special logarithm scale that allow for easy power and roots calculations.

When I was about eleven, I learned to use a pocket circular slide rule (Concise brand) that the people from Lockheed gave to my father as a souvenir (when C 130 Hercules aircraft entered service with Argentine Air Force). I also had a smaller, circular Concise slide rule, which included a sort of perpetual calendar as a bonus. It was small enough as to be used as a keychain.

At the same time, I was interested in model rocketry, and that brought the need for simple trigonometric notions, in order to calculate the altitude my models had reached. To that end, I resorted to a pocket (but straight) slide rule, Aristo brand, which I still have as a conversation piece near my desk. It was1969, and I was astonished at a drugstore when I saw one of the first cash registers with an electronic display (Nixie tubes). Electronic calculators were big, clumsy machines, only to be available in specialized shops in Buenos Aires (I remember some Sony and Lloyds desktop calculators). All other calculators, the ones you may see at a clerk’s desk, were mechanical or electromechanical at best

About mid 1972, I read an article in Popular Mechanics magazine, featuring several four function pocket calculators. I recall a Canon unit, and the Casio Mini 6, which had a six-digits green display and a "right arrow" key that shifted the contents of the display to show six more digits. LED and Fluorescent displays were usual (no LCD yet), and NiCd batteries were almost mandatory. Some models sported modified seven–segment patterns to make the digits recognizable, even when a segment fails.


Versions of 0 , 6 and 7 used to make the patterns for all 10 digits to differ on more than a single segment. 

Short after that, I had the chance to use the TI Datamath and Bowman calculators. In addition, in 1972, I saw an advertisement of the HP 35. In 1973, I got the HP Journal issue about the HP 80 financial pocket calculator, and near the end of that year found the announcement of the HP 45. It appeared in the "Measurement and Instrumentation News" leaflet from HP, the same issue in which the 9830 with BASIC language was introduced. All pocket calculators were still prohibitively expensive for me. At the same time, I also read a Philips (Netherlands) article, describing a prototype calculator, which used shift registers, pulse-counter logic and a cold cathode display.

I was then sixteen years old, and soon learned about the TI SR series, including the SR 50, which incorporated angular mode selection and some other functions absent in the –35. It seemed to be a good machine (I was not irreversibly converted to RPN yet), but still expensive. (By the way, that TI brochure was my first contact with hexadecimal notation and hyperbolic functions). Near the end of 1974, I bought a TI SR 10, that I later replaced with a SR 11. This last one had a "constant" switch, only valid for multiplication and division. I recall myself using a repetitive "times 10" multiply so to make the calculator work as an event counter. The counter was the two–digit exponent part of the display, and the 10 E 99 overflow did not prevent it to keep counting (multiplying) past 100 events. Lest of scientific notation, 1/x and square root were the only scientific functions of the SR 10 / 11.

I still have my copy of the Popular Electronics January 1975 issue, usually considered as the starting point of the Personal Computer era. It featured the MITS Altair 8800, based on the Intel 8080 microprocessor. It’s cover also showed a scientific calculator kit that sold for U$S 99. That calculator appeared in Argentina as Norman 700, assembled by the car-stereo company of that name, and was popular among college students at that time. The Cifra brand of calculators, made by a local electronics company, was also well known in my country. At that time, a scientific calculator was far more powerful, and usable, than a toggle-switch-based personal computer!

During 1975, I was amazed reading about the HP 65, and even received a sample copy of the PPC newsletter: It only increased my need for a calculator better than the SR 11. One of my best friends bought a HP 45. I remember we talk about what to do with that much memories (nine). I also remember the day when I learned the trick to make the –45 work as a stopwatch, and puzzled my friend with it. The announcement of the HP 25 in the November issue of Popular Electronics made it clear what would be my target, no matter how much to wait for it.

In 1976, I entered the Buenos Aires Institute of Technology (ITBA), to pursue a six-year degree in Electronics Engineering. In the first courses, no calculators were allowed, so we resorted to slide rules and books with logarithms tables. As a vengeance, I wrapped my log-tables book using a HP 65 brochure as a bookcover.

After the first half of that year, some classmates started showing their brand new HP 25; a TI SR 52 unit (with magnetic cards) also appeared some months later. It was a time when new calculators were announced almost weekly, so we had the chance to look at our friends models, and compare them with ease. In August 1976, I finally received my HP 25, and started wearing it (not merely using it) 24 hours a day.

Two months later, the –25C was introduced, and then the –29C, with more registers and subroutine support; but the –25 was something special for me. Suffice it to say that, in 1978, a distant earthquake made Buenos Aires buildings oscillate for a minute or so (a very uncommon fact). My parents and I left our apartment and went down 12 flights of stairs. I carried only one thing with me: my HP 25.

At the ITBA, there were a good number of HP calculators, and a friendly but competitive fever started. Not only between HP and TI frays, but also about the fastest or shortest program to achieve a function. Battleship, variants of Nim, "Corner the Lady" and Mastermind were popular calculator games. They become programming challenges for us as important as the more formal solutions for matrix algebra, definite integrals, factorials and Fourier transforms. Root finders, linear regression and the Monte Carlo method were concepts that we learned much before the EE curriculum specified, thanks to our programmable handhelds. As for games, as an advertisement put it, the most powerful graphic devices of these years were the brain and the imagination. It may seem strange today, in the multimedia era; but we were much thrilled at the mere sight of a few red digits output of a lunar lander simulation!

A frustrating thing for us, EE students, was the lack of some input/output on our calculators. Being so comfortable programming them, it would only be natural to control external devices from our programs. I read about the –97S, but that kind of machine was absolutely out of reach. Instead, we focus our energy in the rather futile observation of the LED display while running programs (you can decode the angular and display modes from the displayed patterns), and also to the behavior of a "properly shaken" –25 (it may show "rorE" instead of "Error" on its display). Varying the number of digits shown during a PSE instruction was a manner to alter the sound on a nearby radio receiver (RF interference allowed to signal the end of a program, well before BEEP was available on the HP 41). In short, we squeezed every possible drop of juice from the wonderful –25.

I should mention that imported goods were heavily taxed by customs in Argentina during the 1970 and 1980 decades, and in most (but not all) of those years, the average salary was rather low when measured in US dollars. To purchase a sophisticated calculator was not easy, not even to mention a HP-01 watch. Only one thing could ease the "pain" for not owing such a marvel: it was algebraic, not a RPN model!

In 1978 we were taught the first programming course as planned on the EE curriculum. We learned FORTRAN IV and use a special machine to punch cards, rather sumbitted to an IBM 1130 mainframe (the mainframe had 16 K RAM). The same year, a Computer Lab opened at ITBA, and the students helped to build a DEC LSI-11 from a Heathkit set. It ran BASIC and Focal as high level languages. The invariable impression all students shared was that, for "serious" work, it would be preferable to use our calculators rather than a computer; a feeling that remained valid for some five more years.

TI had announced the TI 58 and 59, powerful machines but somehow dull. Although the alphanumeric LED display of the desktop TI 60, showing a "Prompt required" message was a sign of things to come, it was preferable to wait for a new HP than to embark on such adventures. Even the –67, nice indeed, was not far enough from the –25... In the first months of 1979, some friends and I started discussing an imaginary "wish list" of features to appear in "the next HP". Of course, we had no HP contacts, nor any other information to base that list on. When, in 1979, we read about the HP 41C in a Scientific American ad, we were amazed by that calculator; but also because our wish list was quite close to the –41 features!

In 1980, I bought my HP 41C. It was very powerful, friendly and easy to program, particularly when compared against the limited memory and function set available on the -25. Very soon I was solving college and work problems with programs that may be used by others, with labels, prompts, messages and so on. Math I and Circuit Analysis Pacs was useful in my sixth and last year at ITBA (1981). Among other things, I solved Simplex method calculations, run probabilistic simulations, venture into digital filters theory, and integrate RIAA equalization curves easily with my own programs. My HP 41 even let me wrote and run a Cross-Assembler with labels support for the RCA 1802 COSMAC microprocessor which I was experimenting with.

The need for I/O was still there, even more tempting than before. Realizing that HP–IL was not for mere mortals, I solved the "output" part of I/O connecting the beeper leads to the outside (using the gold–balls holes). Using TONE commands, different number of pulses may be sent to a microprocessor or discrete CMOS logic circuitry to communicate the status of the calculator, or to trigger an external event. Synthetic programming helped giving us much more TONEs to choose. To try to give my –41 some means of "input", I’ve tried reducing the batteries voltage (by means of a series diode), and so to flip Flag 49 (Low battery). To communicate via a single flag (almost a Turing Machine proposition) would have been hard, but possible in theory. My "output" experiments were successful, but the "input" idea was not. I tried to peek on the expansion ports with an oscilloscope, specifically on the Flag Input pin. However, I never found a good way to input anything to the HP 41 (short of HP IL, or connecting switches in parallel with the keyboard). Serial buses were not for mere mortals, either.

As I was closely–attached to my HP 41, it was only natural to look for HP Journals and to subscribe to HP Key Notes. When this newsletter opened a contest for a language name for the –41, I submitted EUREKA, as an acronym for the calculator main features:

(By the way, I never knew the result for that contest).

I have some 50 magnetic cards with HP 41 programs of my own creation. Sadly, the card reader capstan weared out some time ago, so I am unable to replay them. The calculator itself is still in more or less working order; but some loose contacts between the boards appeared after the first years of use, and the flex circuit backplane become corroded by battery leakage. Not being able to repair it, I bought a HP–42S in 1990, which I still have. In my opinion, the –28 and –48 models are very unfriendly, even for a RPN fanatic (I could not believe an argument is needed to roll–down or drop the stack!). Certainly, I would like HP to offer again a –42 like machine.

Some of my –41 mag cards contain what I think was my best tribute to the HP 41 power: a Flight Simulator. It was based in simplified but quite real equations, taking speed, altitude, attitude, angle of attack, potential and kinetic energy, gravitational, lift and drag forces into account, adding even a random factor. It actually let the user control the glide and landing of a space-shuttle-like vehicle in the final approach phase. The controls available are the elevators, an aerodynamic brake, and a "turn around" function that makes the shuttle to slowly invert the horizontal direction of its flight. The LCD showed the altitude, attitude indicator, speed and distance to the runway on a single display line updated every six seconds. The ubiquitous "colon" separated the fields, and a leading-zero routine kept the same display alignment in all phases of the "flight". The flag zero indicator meant that a 180° turn was in course. The attitude indicator was "graphical", using combination of dashes as follows:


The main loop of the program was executed in six seconds, and that was the "delta t" value used for the equations, so the simulation ran in "real time". The mission was to land the shuttle in a runway 4000 meters long, at some 200 km/h . The starting point was 20 km far from the runway and at some 700 m altitude. After a successful landing (with good vertical speed, attitude and horizontal position parameters), the shuttle will coast to a stop at the end of the runway. Then a "Over" message was displayed, with a BEEP. A "Crash" legend appears otherwise. The program fits and runs on a standard –41C, without extra memory. I think I exploited every possible trick on this program, but I am now unable to load it from the magnetic cards, and have no complete listings on paper.

To tie these memories up, the "calculator" I most use these days is an HP LX100, which I received as a gift in 1994. Although the newer LXs with Windows CE are very nice machines (I would however prefer a Compaq C-series over the HPs), and as smart as a PalmPilot may be, none offers a calculator function good enough to relegate the LX 100, or the –42S for that matter. My –41C may still be turned on, but not much more. With regard to my –25, I lend it to a friend and it was stolen from him. I miss it a lot. However, the excellent Java simulation available through the Museum of HP Calculators let it live in every PC I use.

Andrés C. Rodríguez

Buenos Aires, Argentina


About the author:

Andrés C. Rodríguez was born in Buenos Aires, Argentina in 1958. He graduated as an Electronics Engineer from ITBA in 1981, and has worked for 20 years in the computer and information technology industry. He is an IEEE member since 1978, a Microsoft MSCE and a Compaq ASE; and has been appointed in Who is Who listings. He is married (’83) with Claudia V. Tróccoli, and has two daughters: María Julieta (’84) and Ana Inés (‘89). He owned a HP 25, a HP 41C, a HP 42S, a HP 32S and a HP LX 100.

 This article was written in December 1998, only from ideas, experiences, and actual memories of the author. No manuals, books or other reference material was used to prepare it. All photographs are from the author’s archive, from 1979-1982.

Trying to peek (with poor results) into my HP25. Note the Tektronix 465 oscilloscope with a DM 44 multimeter optional feature in top.

A homebrew RCA 1802 microprocessor (COSMAC) prototype system, used to "read" TONE commands from my HP 41C.

Using the HP 41C to calibrate an analog-to-digital converter, that monitors a compressor in a computer-controlled CO2 production plant.

A prototype of a microprocessor based controller for a chemical plant. The HP 41 was used to develop algorithms used in this device.

My HP 41C helped in the design of a custom interface prototype (white breadboard). A Data General Dasher terminal, a plotter, and a Tektronix graphics terminal (with storage CRT) are also shown (left to right).

Close up view of my HP 41C board, showing the connection of the TONE interface. A series resistor, used as a limited short-circuit and ESD protection, was inside the heat-shrunk tube.


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