RPN scientific calculator firmware for $13 calculator kit

[jklsadf]

The button labels are a huge plus. I think the transparent button keycap cover for relabeling might be an innovation of the Chinese clones. The original Omron B3F series doesn't have these transparent keycap covers. Not many of the major manufacturers have tactile switches with re-labelable keycaps, or if they do they're either very large or expensive (or both).

Reprogramming is fairly straightforward. There is a prebuilt main.hex file in the binaries folder. You do have to solder at least 3 additional wires (Rx, Tx, and ground), or 4 wires including +5V if you're powering with the USB-to-(logic-level)-serial adapter. You need to purchase (or already have) such an adapter, preferably one that supports 5V operation like this one: https://www.amazon.com/HiLetgo-FT232RL-C...00IJXZQ7C/

I do talk a lot more about other hardware stuff in the writeup (e.g. you need to crossover Rx/Tx), but in the end it's just a matter of soldering and connecting 4 extra wires. Once soldered, run the freely-available programmer program to actually program the chip (see the "Programming with stcgal" section).