RPN-duino

[Chasfield]

I have been busy with a home brew RPN calculator project based on the Arduino Nano mini board. The impulse to get going with it came from finding an Arduino starter kit that had been sitting unused since last Christmas, linked to the discovery that Rockwell once turned out four banger calculators with an easily detachable modular keyboard. I cannibalised a 20 key unit from a model 18R. These keyboards have a nice, almost HP48-like action and are perfect for adding custom key labels to. These old calcs are cheap on auction sites.

As the pictures show, I finished up with a fairly chunky device in a custom case. It features varnished pine trim, which I believe is a first for calculators!

The back-lit display is the ubiquitous and ridiculously cheap 2x16 character 1602 unit. And power comes from a PP3 battery, which should be good for about 20 hours use at 30 mA current draw. That isn't bad, given that the calculator has a real on/off switch. A reflective type LCD would double the battery life but I quite like the blue and white glow of the one used - easy on middle aged eyes as it is.

Calculating accuracy surpasses the Sinclair Scientific by a couple of decimal places but floating point maths is not a strong feature of regular low cost Arduino boards. At the moment, standard form number handling isn't programmed - big/small numbers with exponents display as 0. Digging the bits of them out of Arduino "float" type variables and doing something useful with them is a project in progress.