TI SR-10 Calculator

 

It's Time To Calculate, 70's Style!

As a frequent visitor to thrift stores, this curios pigeon stumbled across this interesting calculator. It had that "70's" look to it. Interested, I brought it for a dollar.

As with any interesting find, the first thing I did was hit the Internet to gather as much information about my purchase.

The Texas Instruments SR-10 Calculator was originally released in late 1972. There were two follow-up revision that were released, with the final one in 1975. The SR stands for slide-ruler. For those who don't know, a slide ruler was a mechanical computer designed for calculations.

My calculator was actually the second revision that was introduced in December 1973. The original model was powered by 3 rechargeable Ni-CAD AA batteries and could be charged by a adapter. Since I didn't have any rechargeable batteries or the adapter on hand, I figured that I would use the standard alkaline batteries lying around. Sure enough, they worked without issue, and the unit powered on with the glowing red LED display (that is so retro!).

Red LED Display. Very Retro!

Close-up of the LED display

The functions on the SR-10 surprisingly worked given the age of the calculator. Even though it was marketed as a scientific calculator, it's only one in a vaguest since as it predecessor was a scientific slide ruler. It does have slightly more capabilities than a four-function calculator though. Along with the standard functions of addition, subtraction, multiplication, and division; there was also a reciprocal function, square and square root keys, change sign, and a enter exponent key.

One way to tell that my calculator was the second revision was that the SR-10 characters were imprinted on the key plate, whereas on the original model, the SR-10 characters were on the display plate. My wasn't the third revision because that model had a different circuit board layout.

Opening the calculator revealed the nature of 70's solid-state electronics. The main chip on the SR-10 is the TMS0120NC integrated circuit. There are two SN75492 chips, along with two SN75494 chips as well. The purpose of these chips, according to Vintage Calculators, is to interface the low-current capacity of the TMS0120NC main circuit with the high-current requirements of the LED display. These support chips, working alongside with the capacitors, moderated the electrical currents running in the hardware.
Main circuit board.
The main integrated circuit.
Some of the support chips.
Some more support chips working alongside the main circuit.
The board identification.
The bottom of the main board shows a CP-2000033-1 REV D identification, along with the TI logo and the SR-10 branding. One would argue that TI would brand there calculators in the same fashion that ranchers would brand there cattle!

A interesting thrift store find that still worked as well, I was very pleased with the purchase. Granted, I'm not going to use this on a regular basis, but it still makes a nice "addition" (pun intended) to my collection of calculators.

Articles of Interest:

Texas Instruments SR-10 Handheld Electronic Calculator- The National Museum of American History - Smithsonian
http://americanhistory.si.edu/collections/search/object/nmah_334394

Texas Instruments SR-10 - Vintage Calculator Web Museum
https://web.archive.org/web/20170724075627/http://www.vintagecalculators.com/html/texas_instruments_...

Slide rule - Wikipedia
https://en.wikipedia.org/wiki/Slide_rule

Datamath Calculator Museum
Texas Instruments SR-10 Version 1
http://www.datamath.org/Sci/WEDGE/sr-10-v1.htm

Datamath Calculator Museum
Texas Instruments SR-10 Version 2
http://www.datamath.org/Sci/WEDGE/sr-10-v2.htm

Datamath Calculator Museum
Texas Instruments SR-10 Version 3
http://www.datamath.org/Sci/WEDGE/sr-10-v3.htm

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