Texas Instruments SR-10 Version 1 (Clear-Case Prototype)

Date of introduction:  (November 1973) Display technology:  LED modules + lens
New price:  ($149.95) Display size:  8 + 2
Size:  6.3" x 3.1" x 1.5"
 158 x 78 x 38 mm3
Weight:  9.2 ounces, 262 grams Serial No:  (381099)
Batteries:  3*AA NiCd Date of manufacture:  wk 48 year 1973
AC-Adapter:  AC9200, AC9130 Origin of manufacture:  USA
Precision:  8 Integrated circuits:  TMS0120, 2*SN75493, 2*SN27423
Logic:  Chain Displays:  DIS115F (12*DISXXX)
Program steps:   Courtesy of:  Joerg Woerner
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The SR-10 was introduced only few month after TI's first calculator, the famous Datamath or TI-2500. Today we wouldn't call it a Scientific calculator, but it used the scientific notation on the display. Texas Instruments targeted the slide rules, guess what the abbreviation "SR" in the designation stands for.

SR-10-V1_DISP.jpg (18223 Byte)The first series of the SR-10 lacked of the poor readability of the TIL-360 display known from the Datamath calculator. 

SR-10_Proto_DISP.jpg (27302 Byte)Texas Instruments experimented with different solutions and created some prototypes with lenses attached to the 6-digit LED-modules.

This SR-10 Clear-Case Prototype manufactured in November 1973 used different LED-modules with an additional magnification lens to enhance readability of the display. We assume that engineers at Texas Instruments decided to use transparent plastic material with the original mold of the first generation SR-10 to verify clearances of the new display with the housing. Compare this prototype with the later SR-10 Version 2.


The SR-10 makes use of the TMS0120 single-chip calculator circuit derived from the TMS1802, better known as first
"calculator-on-a-chip". The remaining components found inside an early SR-10 are known from the Datamath, too. The two plus two display-drivers SN75493 and SN27423 (SN75494) located in the featured SR-10 are improvements of the original SN75491/SN75492 chips introduced with the TMS1802 but allow for operation at lower voltages. The lower half of the printed circuit board (PCB) contains mainly a discrete power converter to generate the three different supplies voltages used with the calculator and the generation of the clock signal for the TMS0120 chip.

Klixon™ type keyboard looks very similar to the Datamath calculator with some additional keys placed in the upper line. Later calculators like the SR-11 changed the style of keys but the extreme wedge-style of the housing consists nearly 2 years. Last model in the wedge design was the SR-16. Don't miss to explore the huge wedge calculators SR-20 and SR-22.

horizontal rule

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© Joerg Woerner, November 18, 2018. No reprints without written permission.