Texas Instruments SR-40

Date of introduction:  June 13, 1976 Display technology:  LED-stick
New price:  $49.95, £26.95 Display size:  8 (5 + 2)
Size:  5.8" x 3.1" x 1.4"
 148 x 78 x 36 mm3
Weight:  4.0 ounces, 114 grams Serial No:  2200153
Batteries:  BP5, BP8 Date of manufacture:  wk 50 year 1976
AC-Adapter:  AC9131, AC9132 Origin of manufacture:  USA
Precision:  10 Integrated circuits:  TMC0981
Memories:  1    
Program steps:   Courtesy of:  Joerg Woerner
Download leaflet:   (US: 2.4M Bytes) Download manual:   (US: 5.3M Bytes)

The SR-40 was introduced mid of 1976 together with the entry calculator TI-30 and the financial calculator Business Analyst. These three calculators defined a new manufacturing approach within Texas Instruments. Everything is snapped together, not a single screw is used within the whole calculator. Compared with the earlier SR-50A or SR-16-II and even the failed SR-40 Prototype calculators, the electronics was squeezed dramatically. The preceding calculators used a main printed circuit board (PCB) and a small daughter board carrying the display.

SR-40_PCB.jpg (76427 Byte)The SR-40 and all other (except the SR-51-II and TI-45) calculators in the Majestic-line used a LED-stick carrying the whole electronics! If you dismantle such a calculator you'll find the LED-stick, one resistor and one integrated circuit in a 28 pin housing. The electronics of the SR-40 is centered around a TMC0981 circuit, a member of the TMC0980 single-chip calculator family, while the TI-45 uses a chip from the TMC1980 family. Both designs are based on the TMS1000 Microcomputer series with an increased memory capacity of 18,432 Bits Read-Only Memory (ROM, 2k*9 Bits) and 576 Bits Random-Access Memory (RAM, 9 Registers * 16 digits). Main differences between the TMC0980 and TMC1980 are the display drivers - while the former supports LED displays, adds the latter high-voltage drivers for Vacuum Fluorescent Displays (VFD). In addition includes the TMC1980 both an integrated charge pump driver to generate the high voltage (around -22V) for the Anodes and Grids of the VF-Display and integrated drivers for the Filament (heater) allowing for reasonable manufacturing costs.

If you are interested in the calculating accuracy of scientific calculators don't miss the Calculator forensics.

If we discover the sources of the components used in this SR-40 we locate:

• The LED chips were furnished by the SC Group in Dallas.
• The lens by an Ohio supplier. 
• The circuit board and the IC are from TI Singapore. 
• The board assembly was by TI Taiwan. 
• The keyboard was made at TI Lubbock 
• and assembled to the board in the Lubbock or Abilene plant.

Within the Majestic-line you'll find two base architectures with only small differences:

The entry line uses a 9-digit LED-stick giving either 8 digits display in normal mode or 5+2 digits in scientific mode. The calculators uses ON/OFF keys.

Simply by comparing the designation of the integrated circuits of the entry line "Majestic" calculators, you'll get the all members of this family:

• TMC0980    Goulds Pumpulator uses a custom design ROM (CD9801)
• TMC0981    TI-30 and SR-40
• TMC0982    Business Analyst and TI-41
• TMC0983    Programmer
• TMC0984    TI-33

Digging deeper into the TMC098x calculator chips you'll locate an OEM-chip used on a TI-30 "clone" manufactured in Hong Kong:

• TMC0985    Amelia Scientific 2001

The upper line uses a 12-digit LED-stick giving either 8 or 10 digits in normal mode and 8+2 digits in scientific mode. The calculators use an ON/OFF slider.

The usage of these modern calculators was easy, Texas Instruments invented with the SR-52 the AOS entry that allowed up to three pending operations within the parantheses.

Later in production the metallized TI logo was replaced with an unmetallized. View here the SR-40 w/o chrome.

AOS™ is a trademark of Texas Instruments.

The SR-40 is featured in the Texas Instruments Incorporated bulletin CL-217A dated 1977.

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© Joerg Woerner, December 5, 2001. No reprints without written permission.