Hewlett-Packard manufactured arguably the best calculators money could buy forty years ago. Several, including HP itself, attempted to revive the classic spirit more or less successfully. After the fruitful bring the HP 15C back campaign, HP released a Limited Edition of the 15C alongside the 30th anniversary of the HP-12C. They are all gone now, silently sleeping in collectors’ vaults. Of course, SwissMicros is the best HP equivalent calculator manufacturer these days. I wrote about their 41s and cannot wait for the release of the DM32.
But SwissMicros is not the only one on the market, especially if you want something more affordable. In this spirit, I bought two kits from Paxer, the PX 15C and the PX 16C. Today, I decided to build one of them to test my new soldering irons.
Before sharing my feedback on the PX 15C, let me explain this soldering iron business. I have a Hakko FX-100. It is hands down the best soldering iron I have ever owned, and I do not have plans to replace it anytime soon. Nonetheless, sometimes I need to solder a few components, and setting up the Hakko takes too much time. That’s when I used an extra iron. Over the years, I used a no-name $10 model, and I promised myself to buy something better each time. In the meantime, several pen soldering irons were released, and I acquired two of them—the Pro 32 by Sain Smart and the Pine64 Pinecil-BB2. I’ll review the former in a separate post as it has an interesting feature I want to explore. The Pinecil-BB2 is powered by USB-C, making it simple to use anywhere, anytime.
I was surprised by how good and easy it was to use these pen-soldering irons. They are lightweight, pleasant to hold, and fast to heat up (~100C to ~400C). The OLED makes it easy to configure and is packed with functions. I am impressed. I strongly recommend using a very flexible silicon USB-C cable for greater movement freedom. You can put the iron down any time with a limited risk of melting stuff around. Pick it up, and it is ready in a second. As mentioned above, I used the PX 15C kit as a test drive. At the build’s end, I will definitely have it in my everyday tools box!
Back to the PX 15C kit, shall we? It is complete, and each component is well identified. My only concern is the poor-quality double-sided tape needed to secure the LCD to the microcontroller. In exchange, you get an extra key switch. The quality of the Voyage emulator is good, and the assembly is straightforward. The only delicate build step is the alignment of the keys if you plan to buy and use the aluminum plates. I bought them and had to fiddle with the keys and the faceplate. The iron soldering pen was convenient for reflowing a few components to wiggle them. Overall, the PX 15C is a solid kit, easy and fast to build with only through-hole parts.
As a calculator, the PX 15C uses an 8MHz 8-bit ATMEGA328 microcontroller. In terms of improvements over the original HP-15C, the PX has more memory (96 extra registers) and runs 4-5 times faster. The display uses a dot matrix LCD with a resolution of 192 x 64 pixels and has a backlight. A single CR2032 3V battery powers all this. The PX is slightly smaller than the original (10 x 6.7 cm). My biggest concern is about the keyboard. And it is a big one, especially for an HP calculator ersatz. Will I stop using my washed, faithful, and weathered HP-15C? Certainly not. But the PX-15C is a good spin on the beautiful 15C and an excellent kit for beginners.
18 thoughts on “Build yourself an HP-15C”
I love it. I have been a fan of HP calculators ever since the HP35.
Thank you, David. I have a hard question for you – as an HP aficionado. Which model do you fancy the most? If I had to answer this question, I would pick the HP-71B. I am curious.
It was sad day when my HP35 finally gave up the ghost maybe 15 years ago. It was beyond repair even for an electronics engineer.
I currently have an HP33S sitting on my desk, an HP42 emulator on my PC desktop, and an RPN calculator, RealCalc, in my phone. But I can’t really say I have a favourite. If any, the HP35. It had enough functionality without an overwhelming number of options – the HP33S is confounding with a gazillion functions I never use and hard to read print above the keys.
A story: In the early 70’s I did my first microprocessor design. https://patents.google.com/patent/US4205230 (My boss, a useless twit, stole credit on the patent). It used a PACE microprocessor to do some complex statistical estimations. The edit/assemble/debug cycle on my PACE development system and its ASR33 Teletype was horrendously slow. So I developed the algorithms using an HP65 programmable calculator then translated them to the PACE program. In the PACE I wrote my own floating point arithmetic package and a bunch of macros which emulated the RPN architecture of the HP65, so translating the code would be easier!
Sorry to read your 35 is beyond repair. Yeah, the 33S surprised me when it came out. It has an original keyboard for sure and an unusual color scheme. Have you tried the 35S?
Thank you for sharing about your professional design and coding experience – nice patent too. Do you still have your 65?
I never used a teletype per se, but I find them pretty cool. The oldest technology I played with is paper tape. I think I’ll unearth a puncher/reader I have in storage 🙂
The HP65 belonged to my employer. It was very cool, with a small strip of magnetic material for storing programs. That was in the days when the HP brand stood for something other than cheap plastic printers!
Try playing a game like lunar lander on a Teletype connected to a mainframe modem using an acoustic coupler modem. That what we used to do at lunchtime at college back in 1978. I recall that sometimes the game would pause for ten seconds at a time giving you the suspense of not knowing whether you were still on course or had “impacted the ground at 120MPH”.
David. HP has split into so many different companies that I think that all is left for them to separate the ink division from the printers 🙂
Agilent, Keysight, DXC; they all have roots in HP.
That’s hilarious, Duncan.you made my day. Thank you!!
That’s awesome. I have always loved HP calculators best since I discovered them in high school (after the initial confusion of picking one up and wondering where the = key is, and “what’s this ENTER key for?”). One of the best things about the physical construction of the older ones was the indestructible keyboard. Even though I like my 50g that I have here next to me, it makes me sad that they went for the cheaper calculator keys other companies use instead of what I remember from my 41C and 15C (actually I think even my 28S and 48SX had nicer keyboards). Sigh.
And Duncan’s nostalgia is making me want to fire up my Altair to play some Star Trek or Lunar Lander games.
Oh, I forgot about the soldering iron bit. Interesting to see your experience and thoughts on those. I didn’t really think much about the little pencil irons for the longest time but a year or so ago I needed to get a new iron and decided to try the TS80p. I was really pleasantly surprised how well it works, and just use it for everything now.
Hi Steve. I am keeping them among my pens and can plug them into my desk usp c power brick, ready to use at anytime. Really convenient and works well.
Nice review! Are you 3D printing the Bumper?
Thank for for your kind comment, Alex. May I ask what do you mean by Bumper? I tried to find out, but none of the items I can see – maybe I missed it – is 3D printed. But since I 3D print, I may have missed. Please tell me so I can answer you.
The bumper is the sides cover. Check the assembly page:
Hi Alex, thanks for the precision. I don’t remember seeing a bumper in my kit. Is that something you can order when you buy the kit?
The bumper and battery holder are extras. But you can download the stl files and print them yourself.
Nice. Thank you for the precision, Alex.
Can you send me a font memory file
Hi Chen, I am afraid I don’t understand your request. Could you please precise what you mean? Usually, you can find fonts on the web. Some are free of charge, others must be bought. Individuals and companies may spend a lot of time to design a font, and they expect to be compensated for. In which case, those cannot be shared.