RPN scientific calculator firmware for $13 calculator kit

[jklsadf]

I started writing an RPN calculator replacement firmware for the "diyleyuan" calculator here. This is one of the cheapest diy calculator solder kits you can buy (about $13 on ebay) with a full LCD. The original firmware has a fixed point calculator that only operates in chain mode.

My replacement firmware operates in decimal floating point and supports calculating more functions, but doesn't support the original firmware's resistor color code calculator or the hex <=> decimal converter. It does arithmetic with an 18 decimal digit significand, and is reasonably accurate. Eventually, I'd like for it to be able to do all the functions of the original HP 35. The functions supported can be seen in the Qt emulator GUI below:



The diy kit uses an STC microcontroller (which is unfortunate, but likely due to cost). It uses an Intel 8051 compatible architecture instead of a more modern 8-bit architecture like AVR (like in the arduino). But on the bright side, all of these microcontrollers come from the factory with a serial bootloader permanently installed in ROM. All you need to reprogram them is a USB to serial converter dongle thing.