HP-41C, The Forth Edition

October 21, 2022 by Al Williams 38 Comments

If you have an HP-41 — arguably the best calculator ever made, you might not have noticed that there’s a version of Forth for it. The code was written a while back in assembly and will work on anything that actually emulates the device properly, such as a SwissMicros DM41X. [Calculator Clique] shows you how it works in a recent video that you can watch below.

The original code dates back to 1984, but some recent detective work by [Angel Margin] has the code running again. If you know about synthetic programming on the 41C and the oddities of its internal architecture, you can’t help but be impressed.

Of course, Forth is meant to be easy to port over, but if you read about some of the architectural challenges, you start to realize this could be one of the more difficult implementations you’ve ever seen. Don’t forget you have what is, by today’s standards, an extremely limited amount of resources.

That being said, calling the HP41C a calculator is almost a crime. It is really a tiny computer hiding inside a calculator case. Then again, the best calculators always are.

We wonder if the code would run on an emulated 41C? Were you part of the TI calculator gang? No problem.

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Building The DIY HP41C: A Field Report

December 3, 2021 by Al Williams 20 Comments

I have a confession to make. I write about a lot of projects for Hackaday, but there are very few I read about and then go actually build a copy of it. I don’t have a lot of time and I’m usually too busy building my own stuff. But once in a while, something strikes my fancy and I’ll either raid the junk box or buy the kit. The most recent case of that was the PX-41C, a replica of the classic HP-41C.

The HP-41C is a somewhat legendary reverse-polish notation calculator. I still have my original HP-41C from 1979 (a very low serial number). It is still a workhorse but at 43 years old or so, I don’t like to leave it hanging around or near anything that might damage it. It has enough wear from the daily use it received 40 years ago. Sure, I have great emulation on my phone and I use that too, but the PX-41C kit looked fun, and with all through-hole parts it would be a quick build. The black Friday sale on Tindie sealed the deal for me.

Start-Up

The kit arrived on the Saturday after Thanksgiving, I decided to tackle it while waiting for some 3D prints. The components were all nicely bagged and marked. Tearing into the bags was a bit frustrating, but not hard and it did keep everything separate. There was a bill of materials, but — I thought — no instructions. Turns out the last part of the bill of materials is a link to some instructions. They aren’t much and I didn’t realize they were until after completing the board, but it isn’t hard to figure out. All the parts are marked on the silkscreen and you can probably figure it out — with a few caveats.

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Build Your Own HP41C

November 24, 2021 by Al Williams 41 Comments

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.

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