The calculator is based on low-power 32-bit ARM microcontroller STM32L476 running at 8 MHz, which is more than sufficient for the purpose. The display is the famous Sharp memory LCD module LS027B7DH01 (400x240 pixel monochrome). Keyboard uses light-touch tactile switches Panasonic EVQQ2B01W (50g actuation force). All electronics runs off the 3V lithium battery (CR2032) that should be sufficient to provide power for several years of operation.
The case and keyboard is made of four 3D printed parts (top and bottom parts of the case, keypad and switch spacer). The two parts of the case are held together by simple snap fit joints, no screws are needed. For the moment, while the software is under development, the buttons are labeled with a simple laserjet-printable sticker paper.
Currently, the calculator features:
- Reverse Polish notation with 4-element stack.
- Double-precision arithmetics.
- "Standard" scientific calculator functions (trigonometric, logarithms, exponentiation, square root and power).
- Error function (erf) and its inverse (erfinv).
- Fixed, scientific (SCI) and engineering (ENG) display modes (including SI prefixes in ENG mode), variable 3-10 digits precision.
- Calculations with uncertainties using error-propagation formulas (UNCERT mode). Something that I've never seen in any of the hardware calculators, and very rarely is present in the software ones.
- Low power consumption (~10 uA in standby mode with LCD display on, 2-3 uA with LCD off).