01/19/2018 - Figured out some details about the real calculator.

A project log for Sinclair Scientific Calculator Emulator

A register level TMS0805 CPU emulator on an Arduino Nano runs the original 320 instruction calculator program. A custom PCB houses it all.

Arduino EnigmaArduino Enigma 04/13/2018 at 06:390 Comments

So far, I had been using Ken Shirriff's simulator ( and things were matching. Trawling through instagram, I find a person that owns a Sinclair Scientific. I ask him to post a video of a calculation being performed and he graciously does it.

I realize three things: 

1) The display goes blank when computing a result. (at the time I did not notice in the video that the decimal point stays on and did not implement that)

2) The emulator was running faster than the real calculator.

3) If I am serious about this project, I must get my hands into an original Sinclair Scientific. Asking people on the internet to post videos is not going to cut it. The search on ebay has been started already. 

Items 1 and 2 are partially corrected and a video is taken:

Time for a quick instagram post: