Hackaday Prize Entry: The 70s Called. They Want This Calculator

For those of us who grew up during TI’s calculator revolution, the concept of reverse polish notation (RPN) might be foreign. For other more worldly calculator users, however, the HP calculator was ubiquitous. Hewlett-Packard peaked (at least as far as calculators are concerned) decades ago and the market has remained dominated by TI since. Lucky for those few holdouts there is now a new microcode emulator of these classic calculators.

Called the NP25 (for Nonpariel Physical), the calculator fully emulates the HP-21, HP-25C and HP-33C. It’s a standalone microcode emulator, which means that these calculators work exactly as well as the original HP calculators of the 70s did. The new calculators, however, are powered by a low power MSP430G2553 processor and presumably uses many, many fewer batteries than the original did. It has an LED display to cut power costs as well, and was built with the goal of being buildable by the average electronics hobbyist.

Even if you didn’t grow up in the 70s with one of these in your desk drawer, it’d still be a great project and would help even the most avid TI user appreciate the fact that you don’t have to use RPN to input data into calculators anymore. Not that there’s anything wrong with that. This isn’t the only calculator we’ve featured here, either, so be sure to check out another free and open calculator for other calculator-based ideas.

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32 thoughts on “Hackaday Prize Entry: The 70s Called. They Want This Calculator

          1. I wish I took a slide rule to finals in college. Both my calculators circuits fried, presumably from heat exposure that day, and I failed the course.

        1. Give a kid a slide rule and he’ll spend the rest of the day trying to figure out where the batteries go.
          Give a kid a slide rule and he’ll poke his eye out with the slide.

          1. When I was a kid (in the nineties) I found my mother’s old slide rule and worked out for myself how to use it. My parents could no longer tell me how to use it.

  1. Nice post, can imagine ease returning to my hobbyist days as I’m approaching retirement shortly before I reach 3 digits ;-) With the dearth of so called verge collection (junked) laptops & the like it should be feasible to collect all sorts of disparate parts to construct working units of any number of calculators even later additions like the 71B etc…Thanks for posting, takes me back :-]

    In my earliest uni days (1980) at Western Australia Institute of Technology (now Curtin University at Bentley), I relied on it for lab work & ran a business selling many of the HP-41C, CV & CX versions with various memory modules, bar code wand, HP-IL comms interface,maths pacs etc.

    My last device failed to reset/start some 14 yrs ago but, happily found a really good emulator on the net (Eg by Warren Furlow, Virtual HP-41C version 7B) which has a really nice graphic rendition aestehtically & closely matching the practical operation of the calculator & use it quite often, runs great on XP & later windows versions here:-
    some HP related & surprisingly recent updates here:-

    RPN has been, for IT/embedded enthused engineers, a very nice intuitive stack like operation much like Forth with good keystroke efficiency & ease of sequence program replication

    It would be an interesting exercise to see how well & fast these would run on a modern computing platform. Alternatively use the HP-41C keyboard/LCD but, replace the CPU/serial eeprom with a modern micro emulating original hp microcode at a GHz or so – yikes !

    Have often thought some similar windows simple script setup could enable a PC to far more useful for neophytes if it could adopt some of the simple 41C programming methodology.

        1. “draw less power than LED display.”
          Very unlikely. A VFD draws several tens of mA for the filament, plus needs a high voltage boost supply, typically also drawing tens of mA, for well over 100 mA draw, continuously. LEDs draw about 2 mA per segment. Unless you are in the habit of displaying 8888888.88 on the display, and LED will win over a VFD any day for power consumption..

      1. My father worked for Rockwell and on this calculator. We had one. Not only did it have the big green numbers and little rubber feet, it also had a button that flipped up a cover over the display. I was a kid and really loved this specimen, as well as the jingle which I remembered all these years as well.

  2. It took a good six years, but I’ve finally forgotten enough about how to use my old TI that it’s no longer faster than pulling up Alpha or whatever when I need to do something Mathy.

    Still makes me all nostalgic, though. I used to be able to touch-type on that thing. I tried to write some code a while back for old time’s sake, and it blows my mind I was ever able to put up with that goofy-ass language. Yet it’s where I learned to program…in orchestra class. <3

  3. One of the best things about a genuine HP calculator is its keyfeel. My HP-41C from 1981 *still* has a better tactile feedback than any modern spongy-nub key calculator (never mind a bloody touch screen). My slightly newer HP-32sII is even better. Sadly, they blew it on the “re-imagined” release of the HP-15C Limited Edition — keyfeel is inconsistent from key to key, misses some keystrokes, doubles others. Reminds me of an old TI.

    1. I used to use Nonpareil, but then I discovered V41. I wrote to Eric and asked him if he was planning to add support for the relocatable plug in Modules and never got a response. V41 supports them…

  4. I hope the keypad is debounced better than old TI-30/TI-55 LED calculators… those old calcs were awful. I used to do 69 factorial (69!) as the slowest computation in high school cuz I was bored. How long on an MSP430 or a lookup table used?

  5. No calculator for me in the 70s. I was barely born! But… I still learned on RPN and prefer it today. I had an HP48 graphing calculator when I was in High School. My parents bought it for me b/c the sales guy explained (truthfully) how it was more powerful than the TI calculators everyone else used. My teachers didn’t care so long as I took it upon myself to learn to do whatever they were teaching the TI kids to do. It was rough but my parents had given it to me for Christmas, customized it with a name plate and optional zipper pouch and everything. I didn’t have the heart to replace it!

    There was one other kid with an HP48. He helped me sometimes. I was in a graduating class of only 40 so that’s 1 in 20 for HP & RPN.

    My old HP48’s screen cracked years ago and I threw it away. Happily I kept the big fat manual. Today I still get annoyed when I have to use a ‘regular’ caluclator. About a year ago I discovered that there are emulators! :-) HP actually released the ROM images on their website so I’m not even stealing when I use it! My HP48 is dead but long live my HP48, I have it on my phone and all the computers that I regularly use, both Windows and Linux. I don’t think you can get it for iOS though since Apple forbids emulators. Just another reason to NEVER EVER buy Apple. Friends don’t let friends buy Apple! At least not without some ribbing!

    1. The hard part of using it btw wasn’t because it was RPN. It was all the advanced graphing features that the teachers walked the TI kids through step by step that I had to figure out completely differently. Real fun was when the calculators estimated things differently.

  6. I have both the HP12C and HP16C which I bought when they were introduced.

    I’ve been using these calculators extensively throughout the decades. The original batteries are still going strong, although once in awhile I must take an ink eraser to the outer casing of the three batteries in each calculator to clean some sort of film that builds up periodically which prevents conductivity. I am not sure what it is, but am certain it is not corrosion. I cannot even get a reading on my voltmeter until after the removal of the film.

    The stainless/chrome metal spring (+) positive battery contact of the calculator never requires cleaning, yet the (-) negative brass(?) battery contact sometimes requires something a tad more abrasive than the ink eraser to get things operational again.

    The HP12C has recently begun to exhibit keybounce issues, sometimes irritatingly causing numbers to repeat when a button is pressed. I think this might be due to flexing the calculator, even ever so slightly.

    I am surprised at the endurance of these little fellas. The lifespan of the batteries is mind boggling!

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