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Sinclair Cambridge Programmable

Sinclair Cambridge Programmable

Radio Shack EC-4001

Cambridge Programmable.
Radio Shack EC-4001

Sinclair Cambridge Programmable / Radio Shack EC-4001.

Display is 8 digits, red LED (made by National Semiconductor).

Scientific programmable.

Integrated circuits - National Semiconductor MM5799EHY/N and DS7784N, here date coded early 1977.

9v (PP3 battery) - a "pregnant" model, see photograph below.

50 mm x 111 mm x 28 mm.

Made in England.

The Radio Shack EC-4001 model was supplied by Sinclair to the U.S. "Radio Shack" chain of electronics stores.

"Pregnant" bulge

The back of the calculator, showing the "pregnant" bulge of the battery compartment, enlarged to take a 9v PP3 battery rather than the AAA pen-cells that the Cambridge casing had been designed for.

This bulge drastically affects the aesthetics of the pregnant models.


Inside showing the National Semiconductor MM5799EHY/N and DS7784N integrated circuits.

Program libraries

Sinclair Cambridge Programmable dwarfed by the program libraries for it. These were:

  • Vol. 1 - General, finance, statistics.
  • Vol. 2 - Mathematics.
  • Vol. 3 - Physics & engineering.
  • Vol. 4 - Electronics.

Vintage Calculators

© Text & photographs copyright Nigel Tout   2000-2015 except where noted otherwise.