Your Own Sinclair Scientific Calculator

We’ve talked about the Sinclair scientific calculator before many times, and for some of us it was our first scientific calculator. If you can’t find yours or you never had one, now you can build your own using — what else — an Arduino thanks to [Arduino Enigma]. There’s a video, below and the project’s homepage on describes it all perfectly:

The original chip inside the Sinclair Scientific Calculator was reverse engineered by Ken Shirriff, its 320 instruction program extracted and an online emulator written. This project ports that emulator, written in Javascript, to the Arduino Nano and interfaces it to a custom PCB. The result is an object that behaves like the original calculator, with its idiosyncrasies and problems. Calculating PI as arctan(1)*4 yields a value of 3.1440.

Special care was taken in the design of the emulator to match the execution speed of the
original calculator, which varies from acceptable to atrocious for trigonometric functions involving small angles.

Oddly, the calculator started life as a hack on the KIM-1 UNO. However, six board revisions changed the layout quite a bit and made the emulation more and more accurate both software-wise and physically. If you fancy a close look at an original Sinclair we subjected one to a teardown.

The KIM-1 UNO board has had a lot of life poured into it. We used it as a clock and an 1802 emulator. Oscar even built off of the 1802 code to add video output.

19 thoughts on “Your Own Sinclair Scientific Calculator

    1. +1 Hackaday folks: if Nigel is willing to talk, an interview about these amazing days of Sinclair development would be so valuable, informative and help to preserve a unique moment in time… With the recent passing of both Sir Clive and Rick Dickinson (mechanical designer for many things Sinclair and the Jupiter Ace), time is of the essence to get the unique perspectives of those in the thick of it… Thanks in advance

  1. I found one of these calculators recently in a box of stuff from a non-air-conditioned storage room near the ocean. All parts of it were corroded to hell from the salt air; still brought a tear to my eye to drop the thing in the trash can.

  2. ” Calculating PI as arctan(1)*4 yields a value of 3.1440.” …….. UH !?????

    What am I missing here ?
    If that computation yields PI in any form, what does 2+2 give you ? 7 ? 128 ? 14 ?

    On my HP25 (and HP67) that calculation: arctan(1) = 45 x 4 = 180

  3. I have built the Sinclair scientific calculator but cannot program it. Every source of programs for the calculator give errors when I try to compile it on Arduino.
    Can someone please help me overcome this problem and enable me to program the calculator?

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