Calculate Like It’s 1989 With This HP15C Emulator

An HP15-C emulator PCB

Back in the day, your choice of calculator said a lot about your chops, and nothing made a stronger statement than the legendary Hewlett-Packard Voyager series of programmable calculators. From the landscape layout to the cryptic keycaps to the Reverse Polish Notation, everything about these calculators spoke to a seriousness of purpose.

Sadly, these calculators are hard to come by at any price these days. So if you covet their unique look and feel, your best bet might be to do like [alxgarza] and build your own Voyager-series emulator. This particular build emulates the HP15C and runs on an ATMega328. Purists may object to the 192×64 LCD matrix display rather than the ten-digit seven-segment display of the original, but we don’t mind the update at all. The PCB that the emulator is built on is just about the right size, and the keyboard is built up from discrete switches that are as satisfyingly clicky as the originals. We also appreciate the use of nothing but through-hole components — it seems suitably retro. The video below shows that the calculator is perfectly usable without a case; a 3D-printed case is available, though, as is an overlay that replicates the keypad of the original.

We’ve seen emulators for other classic calculators of yore, including Sinclair, Texas Instruments, and even other HP lines. But this one has a really nice design that gets us going.

41 thoughts on “Calculate Like It’s 1989 With This HP15C Emulator

  1. Very cool! I have a 15C that’s my daily driver since 1982. I recently replaced the batteries for only the third time since I got it. The keyboard is still perfect, unlike my POS HP49G+ that failed in about a year. If my HP15c ever gives out I may build one of these.

    1. I have a 32s from 1987, just started its 3rd set of batteries about a year ago. Only have that b/c somehow my 11c grew legs and ran away in the 15 or 20 minutes that I accidentally left it in the lab.

      1. I once bought a HP-41C at a thrift store for $2.50. It was new in box, still had the Oregon State University Bookstore $250.00 price tag on it. The calculator was pristine. Never even had the batteries installed. Not a scratch on the contacts. It had all the paperwork and even the three Energizer N cells in their box, two of them still tested full voltage while the 3rd was dead.

        I put it up for auction on eBay and got $450.00! Who knows how high it would’ve gone had it been a 41CX?

      1. Slots aren’t needed – you load ROM files into its flash memory. People have been using software HP41 emulators for decades now, so huge numbers of ROM files are freely available for download.

    1. Typical “I want to auction it but don’t want to get low balled” tactic.

      The worst thing is that, depending on I don’t know what, an accepted offer of $50 may still show as sold for the 20K. (Argue all you want, but I have a number of buys that have done that. ex: I made an offer of $60 on a Fluke-45 listed for $250. Shows in sold items as 250, not best offer. Not crossed out with best offer accepted.)

      1. Interesting.
        It seems dishonest, but, if someone can get away with it…
        If you really have bought a $250 listed item for $50, I’m going to be a bit more aggressive on (Make an Offer).

        1. Be aggressive. Worst that happens is a ‘no’.

          I figured out that there is weirdness the first time a flea market seller pulled up a listing and said “this just sold on ebay for…” and it was an item I bought. I had to pull up my purchase to convince him. I do believe he was peeved.

          (IIRC, it was about 2010, and the item was a parts-unit dial test indicator, mechanical type. I think I paid about $US5 plus shipping, and the original listing was about $500, or twice retail for a NEW unit. You see the same thing today- like the U2741A listed for $US2200, used. New is $US1300, direct from Keysight via a rep. I’m tempted to offer $US200, but really can’t justify it right now)

    1. 16C from swissmicros, or obtain the voyager code and use this platform, as it can run any voyager series.

      I still have and use my 16C, though I don’t use it every day. (My daily drivers are 11C’s, a DL15C, and a 32S. The original 35 stays on the shelf, mostly)

    2. Why can this not be any of the Voyagers? The 15 was the big honker when it came to ROM and RAM, so all the others should be able to fit on the platform.
      I will admit that I don’t really understand the fascination with the 16C, though that possibly only speaks to the limits of my imagination. It was pre IEEE 754, and can’t we do bit ops in our head? But to each their own.
      If the firmware is open source then you can have your 16C (or whatever) with ease. Many use Eric Smith’s (no, not the murderer) “Nonpareil”. [I have disassembled some 3rd party products and found the source to derive from Eric’s even though the vendor claimed it not to be — naughty, naughty.] You’re free to use that non-commercially and I had ported it to a PIC microcontroller in 2010 so I can attest that it’s totally doable.
      If the author of this project shares his source then you’ll be able to slip in a different ROM image with ease. If (s)he really re-wrote an simulation of the 15C, then you’ll have a bit more work, but I can attest it’s just a few weekends’ effort.
      Personally, my fave is the 11C. It had everything I needed. The matrix stuff was just weird on the 15C, and I didn’t especially need the solver. What I would like to have had was connectivity, but this was the early 1980’s, and if you wanted a ’41 you knew where to find them. And I did; I gave away my 11C when I upgraded to a 41 and then later the same to a 28, and I always had the fondest memories of my 11C. Just perfect.

  2. Neat. Nice job there!

    Still use the 15C that I bought at college back in the 80s. I first had an 11C which I then let my sister have for college. Also bought the 16C too. Somehow that first 16C disappeared on a job I was doing in another state. Had to find another one which I did finally. We use the 12C for our general purpose calculator at home. These calculators are the perfect size to just slip in a shirt pocket too. Wouldn’t be without my RPN calculators.

  3. I love those old HP calculators and still own three of them. The first I bought, the 15C, came in a well crafted, cloth-lined leather sleeve with innr seams and a premium feel to it. The next, the 16C, came in a much cheaper-feeling faux (I believe) leather sleeve, again with inner seams. The last I bought, the 32S, is clearly for the “masses” and not a premium product. It has a vertical layout as opposed to the other two’s horizontal layout, a drab colour scheme and comes with a plastic sleeve with an outer seam from two halves melted together.

    They are all in good working order and I still use them occasionally, mostly the HP16C when I am doing software development.

  4. I lent my 15c to is friend to work in Asia, he crash landed in a chopper the case cracked and so did the screen but it still worked, sent to HP for repair, came back, no charge best story ever, new case serial number engraved. Still works 30 years later. Now that legendary HP quality.

  5. The google playstore is raft with free and paid emulators that look and work pretty much like many fine HP calculators, and are constantly at hand on your phone… My physcial calculator is rarely at hand when I need it so the emulators are great.

    1. When I need a calculator, my phone is ‘rarely’ at hand. But the HPs are within reach. Plus it is nice to have something physical in your hand. Like a book, instead of a pdf… Anyway, the phone is usually upstairs or somewhere. In fact, once I retire (phone required for work), I can’t wait to just ‘loose’ that phone completely. :)

  6. I still use my HP-25C. I replaced the batteries with NiMH AA batteries and it’s running very well. I taught my son (14) how RPN works and I showed him how to program it and it is the calculator he uses for his High School. Lovely. Strong after ~43+ years…

  7. RPN calcs are still available. This year I purchased two new HP RPN calcs, the 35s (I was lucky to get the Philippines-made one), and an HP Prime. The 35s is great for daily use but it doesn’t do matrices well and doesn’t like negative complex number trig (which the Prime does fine). My old fave 32S has the failing elastomer contact issue and so far I’m not brave enough to try to fix that. Anyway to the project at hand: very cool. I am on the Tindie notice list for stock kits. And adding my question to the other reader who wants to know if the source code is available? How was it verified? If I were to use this kit at work there would be consequences, hence the interest. Thanks!

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