Radio Shack EC-100 (Version 2)

Date of introduction:  November 1972 Display technology:  LED-modules
New price:  $129.95 Display size:  8
Size:  5.8" x 3.5" x 1.5"
 147 x 88 x 38 mm3
Weight:  6.7 ounces, 191 grams Serial No:  A 16983
Batteries:  4*AA Date of manufacture:  mth 11 year 1972
AC-Adapter:   Origin of manufacture:  USA
Precision:  8 Integrated circuits:  TMS0103, 2*SN75491, 2*SN75492
Memories:   Displays:  DIS40, DIS95
Program steps:   Courtesy of:  Joerg Woerner

This Radio Shack Electronic Calculator EC-100 seems to be a minor variation of the original EC-100 with a small metal piece covering the [K] on the keyboard switch and labeling it correctly with [ON].

Dismantling this Radio Shack EC-100 manufactured in November 1972 reveals a well-known design centered around around a Texas Instruments TMS0103 single-chip calculator circuit and - like most early designs of the wildly successful TMS0100 family - two SN75491 Segment Driver chips and two SN75492 Digit Driver chips, each for the LED display.

The two pre-configured LED-modules (DIS40, DIS95) are based on the TIL360 arrays and soldered directly on the printed circuit board (PCB) of the Electronic Calculator. The remaining components on the PCB are mainly used to generate the necessary supply voltage of the TMS0103 and its clock signal for the internal timing.

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If you have additions to the above article please email:

Joerg Woerner, December 29, 2017. No reprints without written permission.