Texas Instruments SR-20

Date of introduction:  Sept.11, 1973 Display technology:  Panaplex II
New price:  $179.95 Display size:  10+2
Size:  9.1" x 6.5" x 2.6"
 232 x 165 x 67 mm3
Weight:  31.0 ounces, 881 grams Serial No:  200047163
Batteries:   Date of manufacture:  wk 44 year 1973
AC-Adapter:  120 V Origin of manufacture:  USA
Precision:   Integrated circuits:  TMS0202, TMS0304
Program steps:   Courtesy of:  Joerg Woerner

The SR-20 is one of the few scientific desktop calculators manufactured by Texas Instruments. In a housing with the size of a TI-3500 but the extreme wedge shape of the SR-10 you find some useful scientific functions but no memory.

sr-20_pcb.jpg (163432 Byte)The displays used in the SR-20 are Panaplex II devices. Produced by Burroughs they are long-life, cold-cathode, glow-discharge display panels. Keep your fingers away, normal voltage is about 150V. With their orange glow they give a perfect readability even in bright ambient situations.
A similar calculator performing conversions between octal, decimal and hexadecimal number bases was the SR-22

sr-20_IC.jpg (34753 Byte)The TI-450 used the same two-chip calculator brain but lacked the scientific functions. The first usage of the chip set was the TI-4000 and the Canon 121F.

It took about 10 years before the next scientific desktop calculator manufactured by TI appeared. Do you know it? View it here.

Some parts of the calculator housing and the display could be found in an industrial product, view the 5TI PLC programmer.    

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If you have additions to the above article please email:

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