RPN scientific calculator firmware for $13 calculator kit

[jklsadf]

The newer STC microcontrollers have a direct USB interface, instead of serial. The entire industry is moving towards that direction (e.g. arduinos used to have a separate FTDI USB-to-serial converter chip, but the new ones just use a microcontroller with USB built in). The STC microcontrollers aren't bad, and are much faster per clock than the original 8051 (like most modern implementations). I'd consider their main advantage though (other than 8051 compatibility) to be their extremely low cost. The surface-mount version of the chip used in this calculator is less than a dollar in one-off quantities: https://lcsc.com/product-detail/STC_IAP1...08538.html

I would personally probably use an Atmel/Microchip ATxmega for new projects that needed an external memory bus (but still the simplicity of an 8-bit microcontroller), just for the better compiler support for programming in "high-level" languages like C. For anything more powerful, probably an ARM microcontroller. I personally don't mind surface-mount components as long as the pin pitch isn't too fine. Also, there are a lot of really small ARM development boards like the teensy which can be through-hole mounted.

If you're already used to 8051 programming it might not be too bad though. It was my first time though, as I mentioned in the writeup under "Implementation on an STC 8051 Microcontroller". I had originally written the firmware kind of similar to the BigNumber library where functions take pointers to the bignums, but that quickly filled up all available code space, and I had to rewrite large parts of it to just use globals.