<del>Mechanical</del> Electronic calculators: TI-58

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Of course, this is not a mechanical calculator, but it is an important member of my collection, for reasons I'll mention ahead.

This machine was manufactured by Texas Instruments in the USA, in the late 1970s. The TI-58 was launched, along with the TI-57 and the TI-59 in 1977, all three programmable electronic calculators. The TI-57 was simpler, but the TI-58 and the TI-59 were richer in programming features. Neither are capable of retaining the program in memory when turned off, but the TI-59 sported a magnetic card reader, so programs could be stored and retrieved to memory. This limitation was overcome later, with the launch of the TI-58C (for Constant Memory). TI-58 and 59 had a door in their underside in which a ROM module is kept. Machines came with a set of 20 useful programs in a Master Library Module, and soon TI launched many other modules, with programs for statistics, real estate, surveying, navigation, aviation, and many more (see a list here).

TIs from that time descended from an earlier line of TI calculators prefixed “SR”, as in SR-52 (the 58/59's immediate predecessor) and others. SR comes from “Slide Rule” (!!), which tells us much about the intentions of the manufacturer with these machines. Mechanical calculators (and early electronic ones) were usually limited to the arithmetic operations and maybe square roots, and slide rules were the most popular resource to get access to functions such as logarithms, trigonometric and others. Their competition was with Hewlett-Packard, who produced and sold a more sophisticated and more expensive line of calculators.

Nevertheless, TIs were not exactly cheap: TI-58 sold for $95 at launch, and TI-59 at $240. Adjusting these values for inflation between 1977 and 2013, we find approximately $500 and $1230. Quite an investment! Notice that in 1977 the so-called “trinity” of personal computers was at its peak: Apple II, Tandy/Radio Shack TRS-80, and Commodore 64. An Apple II in 1977 cost something around $1300, so even at those prices programmable calculators still had a large market share.

Mine was purchased in early 1980, right after I passed the “vestibular” admission exam to attend UFMG (Universidade Federal de Minas Gerais, one of the most important in Brazil). At the time, getting accepted to the Civil Engineering course meant facing 9.8 candidates for each enrollment spot. My parents got me the calculator (I remember desiring a car, or at least permission to use one, but I was 16, and the minimum age for driving over here is 18), and even before classes started I was getting a crack at programming in the TI-58. This was, therefore, my first programmable device. As a result, I aced not only Computer Programming (in ALGOL, using punch cards) but also Numerical Analysis and Surveying classes, and got a taste that led me towards BASIC in a PC, then FORTRAN, Pascal, C and much more.

Later on, being an “engineer who knew how to program” was decisive in my early career, and defined my later shift towards Computer Science, through Master's and PhD also at UFMG.

Well, the TI-58 was stored somewhere, after a number of mishaps involving its battery, the AC adapter, and the battery contacts in the calculator's PC board. Metal contacts got corroded, so the battery was inadvertently disconnected. However, in these TIs the battery is part of the power supply circuit, acting as a sort of voltage regulator. AC in with no battery means damage. The AC adapter's cable was also faulty. There was no point in finding a repair shop, so I got a simpler calculator for some courses I took in the 1990s, and the TI-58 stayed in a drawer ever since.

Further on, maybe in the late 1990s, I tried to bring it back to life, by soldering the battery to the PC board directly. It turned on, but the battery was useless, it wasn't easy to get a new one, and I gave up.

In January 2023 I retrieved it from the drawer, went online for reference material, and tried again. The old, 43-year-old battery pack was replaced by an old-fashioned pack of 3 AAA NiMH batteries ($10), 3.6V, used in baby monitors, cordless phones, toys and the like. I revised the soldering of wires in the place the metal contacts used to be, and connected in the NiMH pack. It worked.

I then found online (https://www.thingiverse.com/thing:4368165) and printed a cover for the battery pack, got some self-adhesive silicone feet, and replaced the AC adapter's plug with a similar connector, saved from a 40mm fan.

Have a mechanical calculator stored somewhere, and want to get rid of it? Send it to me!

1980 TI-58 s/n 060338

Ad with price annotations, from 1977


After repair


3D-printed back cover


ROM Module

 Memory Module

Display – the LED digits are quite small, and the machine has a row of lenses to increase their size


More about this machine

Datamath Calculator Museum

Dejan Ristanovic's dedicated Web site

Texas Instruments Reference Manuals: operations, programming, technical, schematics and much more, including the programming sheets that came with the machines

The full range of Texas programmable calculators

A list of videos on Texas calculators

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ti-58.txt · Last modified: 2023/01/14 17:13 by clodoveu
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