Texas Instruments TI-1200 (Version 1)

Introduced in March 1975, the TI-1200 started together with the TI-1250 a great career with millions and millions units manufactured over the course of about 2 years. As a successor to both the stylish TI-1500 and the Exactra line, the TI-1200 demonstrated already the impressive design and technical engineering behind the TI-30. 

A lot of variants of this calculator followed in the year 1976. Most differed from the TI-1200 and TI-1250 only with the design of the faceplate. Don't miss e.g. the fancy LADY 1200 or the Spirit of '76. A very interesting model in this line was the TI-1265, this one used a blue-green vacuum fluorescent display. Don't miss the rare CONCEPT I. Marketing guys at Texas Instruments added later the TI-1400 and TI-1450, both carried under there brown housing the technology of the TI-1200 and TI-1250.

The only known models in the TI-1200 family with rechargeable batteries instead the 9V battery are the rare TI-1205, TI-1255 and the limited function calculator ABLE developed for educational purposes.

Read more about power consumption of electronic calculators here.

The TI-1200 was the base of some experimental calculators, too. Don't miss the TI-MEC.

Unfortunately this cheap calculator killed the TI-150.

Dismantling the featured TI-1200 with Date code 3275 LTA and manufactured in August 1975 in Lubbock, Texas reveals a very efficient and cost-optimized design with a single-sided printed circuit board (PCB) centered around a TMS0952 single-chip calculator circuit based on the TMS1000, the World's first Microcomputer. Compared to earlier designs like the TMS0100 or TMS0800, the TMS0952 integrated both the segment and digit drivers for a 9-digit LED display and clock circuitry, resulting in just 6 discrete components (4 resistors, 1 capacitor and [ON-OFF] switch) on the PCB.

Early calculators of the TI-1200 and TI-1400 family use a keyboard with a 6*4 matrix having only 5 key-dome rows populated for a total of 20 keys. The unused key is hidden with the metal faceplate and removing it would add the missing [CS] or [+/-] key. Later the keyboard was cost-optimized to a 5*4 matrix. Find two of them in the Speak & Spell introduced in the year 1978.

This original design of the TI-1200/TI-1250 was only manufactured for a few months, Texas Instruments changed the PCB slightly to accommodate four additional 330Ω resistors to pull down the four keymatrix input lines of the TMS0952 Chip to V_DD. The appearance and functionality of the revised TI-1200 did not change.

The TMS0952 was soon replaced with the TMS0972, a pin-compatible design dropping the additional resistors and capacitor and further reducing the manufacturing costs of the TI-1200 series. While dropping a few discrete components from the PCB doesn't sound too impressive, did the little improvements here and there add up quickly. With the Calculator War starting in 1975, manufacturing costs of basic 4-function electronic calculators were under extreme pressure and the calculator chip was one of the main cost drivers. The manufacturing costs of an Integrated Circuit (IC) are calculated with:

With the die cost roughly proportional to the die area, testing and packaging costs roughly proportional to the pin count, and the final test yield mostly inverse proportional to the die area, goals are well defined: Keep the die size as small as possible for a set of requirements agreed on. While the original design of the TMS0952 resulted in a die size of approximately 200 mils * 210 mils / 5.1 mm * 5.3 mm, was Texas Instrument's engineering team able to shrink the die of the TMS0972 - while keeping its functionality - to 190 mils * 160 mils / 4.8 mm * 4.0 mm or a reduction of almost 30%.

Another contribution of cost cutting had a side effect for the customer, Texas Instruments decided to use with the TMS0972 an 8-digit LED display instead of the previous 9-digit display. While the 9^th (leftmost) digit was originally used only for the negative sign and didn't impact most calculations, should you try this example: 

Please notice that the TI-1265 wasn't effected by these changes, this calculator is based on the TMS1043 single-chip calculator circuit shared with the TI-1650.

The final step of cost reduction of the TI-1200/TI-1250 family was introduced just a few months before its discontinuation and included a smaller encapsulation of the TMS0972 Chip. While the original design was using a 0.6” wide 28-pin DIP (Plastic Dual In-line Package with a 0.1” / 2.54 mm lead pitch) encapsulation, switched the final design to a 0.4” wide 28-pin SPDIP (Shrink Plastic Dual In-line Package with a 0.07” / 1.778 mm lead pitch) encapsulation.

Summarizing the internal design of the TI-1200/TI-1250 calculator family, we differentiate between four different printed circuit boards and five different versions:

Please notice that the above table lists only TI-1200/TI-1250 calculators manufactured in the Lubbock, Texas facility, both calculators were actually manufactured in Brazil, Hong Kong, Italy and Spain, too but design changes were typically introduced in the US facilities first.

Texas Instruments did not only change the internal pieces of the TI-1200/TI-1250 over time, even the Product Labels on the rear of the calculators evolved over the years and we differentiate for the US version between three different styles and number ranges (Examples for TI-1200) plus a special label used for repairs:

Some members of the TI-1200/TI-1250 family - like the colorful TI-1205 - sport different labels, we identified so far 3½ additional designs:

Here at the Datamath Calculator Museum we classify the featured TI-1200 as Hardware Version 1, PCB Type 1 and Product Label Style 1, 6-Digit.

Please find the label of a TI-1200 manufactured in Hong Kong here. 

Calculators based on the TI-1200 with different nameplates were sold both from Western Auto and True Value Hardware with the models Electronic Wizard M4986 resp. T-1220. 

In the TI-1250 section you'll find a lot of calculators using the TMS0972 calculator chip like the NS835A, Bohsei 3000, Conic EL-601 and Privileg 842M. But only one lacked the 4-key Memory, don't miss the wonderful Barbie calculator.

Don't miss the Sharp EL-204 calculator, changing the 6x4 layout of the keyboard into a 5x5 matrix with an additional sqr(X) function.

The TI-1200 is featured in the Texas Instruments Deutschland GmbH leaflets ER-1975 and ER-1976 dated 1975 resp. 1976.

If you have additions to the above article please email: joerg@datamath.org.

© Joerg Woerner, January 4, 2002. No reprints without written permission.