Build Your Own HP41C

There was a time when engineers carried slide rules. Then there was a time when we all carried calculators. Sure, calculators are still around, but you are more likely to use your phone. If you really need serious number crunching, you’ll turn to a full computer. But there was that awkward time when calculators were very important and computers were very expensive that calculators tried to be what we needed from full-blown computers. The HP41C was probably the pinnacle of that trend. If you’ve ever had one, you know that is a marvel of the day’s technology with alphanumeric capabilities and four plug in ports for more memory or ROMs. It really was a little hand-held computer. Didn’t have one? Don’t worry, you can now build your own. In fact, the HP emulator will also act like an HP15C or 16C, if you prefer.

You can see the device in action in the video below. As you might expect, this version uses a through-hole ATMEGA328 and even at 8 MHz, the emulation is faster than the original calculator. The machine also has over double the memory the original calculator had along with a real-time clock built-in. The display is also backlit, something we all wanted in the original.

What we really liked, though, was the 3D printed cases you can download for the calculators. You can see that in the video, too. We were a little sad that the kit is in an HP15-C like landscape orientation unlike the HP41’s portrait format. Then again, the schematics are there so maybe someone will lay out a nice HP41-specific board.

Of course, HP calculators used RPN, but if you grew up with a slide rule that’s fine. For everyone else, it is usually a bit of a learning curve. Also, as great as the HP41C was, it didn’t have binary or hex or even octal math unless you used “synthetic programming” and though we imagine the emulators used can handle synthetic programming (sort of assembly language for the HP41C) it was never fun to work on non-decimal problems with this machine. Still, what a great calculator and it is fun to see it reborn in modern form.

We’ve seen another fake HP41C that we think is using the same emulation software but required SMD soldering. We wonder if the KIM Uno or 1802UNO could be made to run on the same hardware? Seems like it would.