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I have used HP RPN calculators all my life. I wonder why there aren’t any RPN calculators anymore. They have been phased out in favor of the standard infix calculators.
Anyway, I’ve always wanted an HP15c calculator and never got the chance to buy one.

So this is my take on building one.

It is designed with only through hole parts. For easy soldering.

The brains of the calculator is the ATMEGA328. It takes care of everything (display, keypad scanning, sound, clock, etc.).

I decided to use the ATMEGA328 since it is pretty common in the Arduino community and it is one of the few microcontrollers still produced as a through hole part. No other semiconductor is used.

Even though the ATMEGA328 is an 8 bit microcontroller and running at 8Mhz, it is still pretty fast. In the end, the emulation is about 4 to 5 times faster than the original.

I’ve added a speaker for audible Keyboard feedback. And a 32.768khz crystal for the real time clock.

The emulator can run any of the Voyager series calculator as well as the HP41C (my personal favorite!).”

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