DATAMATH

DATAMATH CALCULATOR MUSEUM

Texas Instruments SR-40 Prototype

Date of introduction:	Never	Display technology:	LED-stick
New price:		Display size:	10 + 2
Size:	5.8" x 3.2" x 1.3"
Weight:	9 ounces	Serial No:	001P
Batteries:	BP1A	Date of manufacture:	wk 22 year 1975
AC-Adapter:	AC9130	Origin of manufacture:	USA
Precision:	10	Integrated circuits:	TMS1111
Memories:	1
Program steps:		Courtesy of:	Bob Patton

At first glance this rare SR-40 matches perfectly with the successful scientific calculators SR-50A and SR-51A introduced in March resp. June, 1975.

But this SR-40 was never released to the market, the pictured calculator is a rare prototype with the impressive serial number 001P. Nevertheless do we all know the final SR-40 - a sibbling of the best selling TI-30 calculator introduced June 13, 1976.

The proud owner of this prototype, Bob Patton, provided the Datamath Museum some pictures of his calculator to reveal the story behind it.

Dismantling the SR-40 001P explains immediately the idea behind this project:

• The housing is identical to the SR-50A and uses still the BP1A battery pack.
The later SR-16 II uses another arrangement of the battery contacts with standard batteries.
The TI-2550 II got the BP2 battery pack.
• Instead the powerful TMC0501 architecture of the SR-50A and SR-51A this SR-40 P-001 is
build up around the TMS1111. This chip doubles the memory capacity of the original TMS1000
single-chip calculator found in the SR-16.
The additional memory space was used for the trigonometrical functions, unfortunately the
algorithm are worse compared to the TMC0501.
• The display is the standard LED-stick of the SR-50A.

Fellow collector Miroslav Krob discovered in November 2009 the real sensation of the SR-40 Prototype: Please look carefully at the keyboard, there are two keys with parentheses! The first ones on a calculator from Texas Instruments! Thanks, Miroslav!

The datecode on the TMS1111 and the internal construction allows a precise placement of the SR-40 P001 in the history of Texas Instruments:

Timeline	Calculator	Comment	Link
January 1974	SR-50	First scientific calculator including trigonometric functions based on the TMC0501 building blocks.
October 1974	SR-16	First use of the TMS1000 single-chip calculator in the old SR-11 housing.
March 1975	SR-50A	Cost reduction of the original SR-50. Main differences are the housing and arrangement of the printed circuit boards.
June 1975	SR-40	Sandwiched between the SR-50A and SR-16 II. Expensive battery pack and colourful keyboard from the big brother combined with the poor algorithm of the smaller brother. Not the best choice !
August 1975	SR-16 II	Cost reduction of the original SR-16, makes use of the SR-50A housing, standard batteries and cheap black keys.
October 1975	TI-2550 II	Introduction of the BP2, a rechargable battery pack with only 2 AA-cells instead the 3 AA-cells of the BP1A.

Interested in failed calculators ? Don't miss the first TI-88 scheduled for release in 1982.

Running Mike Sebastian's "Calculator forensics" gives an unacceptable bad result of 10.271817 instead the expected value close to 9.0000. This places the SR-40 in the league of calculators like the Canon F-6 (12.199423) and Rockwell 61R (10.4328).

All other Texas Instruments calculators fit between the TI-35 PLUS (8.99999798135) and TI-45 (9.177087103).

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