02/08/2018 - Original Sinclair calculators arrive!

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 18:050 Comments

And a couple of orders from eBay arrive.

The one on the left was an impulse purchase.... It is a much better calculator, more accurate, faster, uses only 2 AAA batteries. No online simulators or other information on the chip though...

These things are tiny! Its hard to explain the feeling of holding one in your hands. A picture with a quarter, like Sparkfun used to do, is taken for scale.

In retrospect, this purchase was a good decision. To make a good simulator, it helps to have access to the original item. 

Playing with the calculator, I start to notice all sort of normal little display glitches. The biggest find yet is that when the calculator is computing a result, the display goes blank AND the decimal point stays on. The emulator is immediately modified to account for this.

Now I can see how long different operations take and adjust the refresh display delay to try to match the emulator speed. Problem is if I adjust the delay to match the arccos, the arctan speed is off. I begin to suspect this has something to do with the speed at which the emulated CPU instructions execute. Simpler instructions take less time to run. I start thinking of a way to make all CPU instructions take the same time to execute...

Time for a couple of quick tweets: