It's an interesting h/w project, especially if you like nixie tubes.<p>A more mature s/w emulation of many HP classic calulators is at:<p><a href="https://nonpareil.brouhaha.com/" rel="nofollow">https://nonpareil.brouhaha.com/</a><p>I routinely use it's HP-41CV on my desktop. To me the Hp-41 represented a breakthrough in programmability.<p>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:<p>"* The original C version running on Z80 @ 4MHz was really slow! (maybe 25% of HP-25 speed)<p>* I started to re-write the emulator in Z80 assembly<p>* would love to finish this someday, but...<p>* Then I noticed that CMOS Z80 are available rated up to 20MHz<p>* I ended up running the Z80 at 16MHz, which results in an emulated speed within about 10% of the original HP-25. Not bad"<p>The other interesting thing is that this uses the 40-pin DIP version of the Z80, which will be discontinued on June 14, 2024: <a href="https://news.ycombinator.com/item?id=40083885">https://news.ycombinator.com/item?id=40083885</a>
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.
only tangentally related you can get a free emulator of their newest calculator the hp prime g2 here <a href="https://www.hpcalc.org/details/8939" rel="nofollow">https://www.hpcalc.org/details/8939</a>, 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.