Retro-tech HP-25 Calculator

It's an interesting h/w project, especially if you like nixie tubes.

A more mature s/w emulation of many HP classic calulators is at:

https://nonpareil.brouhaha.com/

I routinely use it's HP-41CV on my desktop. To me the Hp-41 represented a breakthrough in programmability.

The RPN user interface of these calulators was also highly superiour entry mode. Sort of the Beta of the Beta VHS shakedown. The superiour solution that lost to a larger marketing budget...

One of the PDF files on the GitHub page has some info about the software implementation:

"* The original C version running on Z80 @ 4MHz was really slow! (maybe 25% of HP-25 speed)

* I started to re-write the emulator in Z80 assembly

* would love to finish this someday, but...

* Then I noticed that CMOS Z80 are available rated up to 20MHz

* I ended up running the Z80 at 16MHz, which results in an emulated speed within about 10% of the original HP-25. Not bad"

The other interesting thing is that this uses the 40-pin DIP version of the Z80, which will be discontinued on June 14, 2024: https://news.ycombinator.com/item?id=40083885

It has a monitor! I take geeky pleasure in looking over other people's monitor code. :)

Wow, so cool to see the photo with an actual HP-25. I bought one in high school (massive outlay at the time) and loved it. Used it all through college.

This is so cool. These magnificent obsessions are always inspiring; at least to me they are. Just super cool, and why not?

only tangentally related you can get a free emulator of their newest calculator the hp prime g2 here https://www.hpcalc.org/details/8939, it's excellent and blazing fast. I'm taking some college classes right now and needed a non-internet-capable calculator. I've barely cracked what it can do, my last physical calculator was a TI-92 before the banned them on everything.