If you have been an engineer (or similar) since the 80s or 90s, it is almost certain you owned a scientific programmable calculator. Funny as it is, I am not among them. However, I remember a friend who had an HP-41CV, and one day he showed me a game running it. It was a lunar lander game where you could only see a few numbers on the screen showing the speed, fuel and distance to the surface – no spaceship, no animation, just numbers. The 15 years-old me was fascinated and intrigued by how a calculator could run that.

Another characteristic that was very interesting to me was the fact that the HPs used RPN or Reverse Polish Notation. As you might know, this notation writes mathematic expressions with the operands followed by the operators from left to right. For example, instead of writing 3 + 2, you write the expression 3 2 +. Another characteristic of this method is the lack of parenthesis to indicate what order the expression is resolved, so something like 3 + (2 * 3) would be written as HP-41CV. I apologize to all the Mathematicians out there for such a simplistic explanation, but I think it gives the necessary information here!

At one point while in college, I borrowed that calculator shortly after it was stolen. Since that model wasn’t available anymore, I bought an HP-42S as a replacement and gave it back to my friend.

So as you can see, my story with HP RPN Calculators isn’t the same as many of you that owned one and used it for school and work at length. Despite that, the way these calculators work and their design fascinate me to this day.

HP-16C

When I got into retro computers almost ten years ago, I started learning a bit of assembler for the MOS 6502, so I could help Commodore is Awesome to release some intros and help with the music in my game Mission:Moon.

While doing it, I needed to perform some logic operations (OR, AND, etc) and was doing it using paper or some online calculator. As a collector, I started looking at programmer’s calculators and found the HP-16C, the only calculator released by HP targeting programmers only. Compared to other models, the HP-16C is limited, but it performs very well what was created for. I decided I had to have one!

The HP-16C is one of the HP’s Voyager series calculators, including the HP10C, 11, 12, 15, and 16C. They are nearly identical, with a few differences since each one of them targets a different objective.

• HP-10C – basic scientific calculator (1982–1984).
• HP-11C – mid-range scientific calculator (1981–1989).
• HP-12C – business/financial calculator (1981–present).
• HP-15C – advanced scientific calculator (1982–1989, 2011).
• HP-16C – computer programmer’s calculator (1982–1989).

The 12C is still in production today apparently because, according to HP, the 12C is still one of only two standard calculators permitted for use during financial professional certification exams. The 15C was discontinued in 1989, but HP released a limited edition in 2011.

The HP-16C, according to HP’s owner’s manual, is the calculator for Computer Scientists, professionals, and students who work with computers and microprocessors. It offers integer arithmetic in four number bases (Hexadecimal, decimal, octal and binary), operating in 1’s and 2’s complement or Unsigned mode. You can also change the word size to a maximum of 64 bits and perform the usual logical and bit manipulations. This is pretty much all that one programming in assembler has to do all the time!

As I said at the beginning of this post, what fascinates me the most is the programming capabilities of these calculators. The smaller models, including the 16C, don’t have the same capabilities as the bigger models (41CV, etc), but they can still let you create small programs to help you cut time performing repetitive tasks. Programming the HP-16C is an easy matter, based simply on recording the keystroke sequence used when calculating manually, which it is also called “keystroke programming” (Owner’s guide)

This programming calculator offers a whooping 203 bytes of user memory, which can be translated into up to 203 program lines. Despite the “keystroke programming” term seeming like a fancy name for macros, the programmer could enter data to be used by the program and create programs that could perform interactions through conditional and unconditional branching.

The HP-16C is a sought collectible; it is impossible to find one on eBay for less than US$ 300. One in the original box with all components can go for way more than that. As I write this, even one is sealed in the box for US$1,999!

Since I don’t have one to help me write this post, I borrowed one from Claudio Rodrigues, a fellow retro computer collector here in town. The first time I held one in my hands, I was impressed with its beautiful look. Although the first voyager-series model was released in 1981, the design is very much a late 70s one with mostly brown case and silver metal around the LCD. It reminds me a little of the Atari 8-bit computer design and some sound systems of the time!

I still want to have one in my collection, but with the current prices, it might take me a while to get one, but something else surprised me while I was doing my research.

SwissMicros

While researching the HP-16C, I came across SwissMicros, a small company based in Switzerland that produces clones of the all voyager series calculator, plus clones of the HP-41CX and HP-42S. I was intrigued because I’d seen some kit on eBay called PX-16C, which does the same as the original but doesn’t look as great. The calculators sold by SwissMicros looked, let’s say, too professional and industrialized to be true! Also, they claim they have the most precise RPN calculators in the World! Michael Steinmann, responsible for hardware and CAD development, founded the company. All the software development is done by his partner David Brunner.

I emailed them, and Michael Steinmann was kind enough to reserve a time to talk to me about his company and his products. While talking to Michael, it is clear how passionate and proud he is about his products. In its early days circa 2011, Swissmicros, albeit a serious endeavour, was still a side hustle that Michael had started because of his interest in this type of calculator and his history with the HP RPN calculators (He started his journey with HP as a teenager using a HP-15C) after realizing that, other than the HP-12, there were no good options for RPN calculators in the market anymore.

In 2011, he found David’s prototype of an HP-15C clone based on a PIC processor and a Nokia LCD. They started to collaborate to produce a full-size HP-15 clone, but later on, they learned that HP was about to re-release the HP-15 as a special edition and, based on that, decided to create a credit card size model, shown below:

The DM15 got a lot of interest and made Michael take the plunge and prepare the first batch. This first batch was finally shipped in February 2012, and in July of the same year, the second batch was also shipped. Another two years went by, and SwissMicros was born officially in 2014.

Since the recently relaunched HP-15C Limited Edition would stay forever in the market, Michael went back with his original plan to release a full-size version of the DM15. That means Michael had to learn everything about designing and producing a very complex consumer product, including the risk of a larger investment. The DM15L went on sale on August 2015, featuring a customizing case, actual buttons, and a larger LCD screen. Following the DM15, SwissMicros released the DM16L and DM41L in December of the same year. The DM16L is a clone of the HP-16, and the DM41L is a landscape version of the HP-41CX. All three models shared the same housing but had a slightly different button configuration to match the HP models that inspired them.

Michael was kind enough to send me a DM16L, and as soon as I got it, I was mesmerized by its built quality! No offence to SwissMicros, but I honestly was expecting a more amateur product since, in my mind, building an electronic device like that is no easy task. After seeing it and feeling it in my hands, I confess how wrong I was. This is a product you could be buying at any BestBuy (or whatever electronic retail store you have in your area!) and anyone would think it is created and produced by a small company in Switzerland!

I also borrowed (for too long!) an original HP-16C so I could compare both side-by-side. They are slightly different, as you can see below, but the DM16L doesn’t feel “inferior” at all. Due to its architecture, the DM16L has some advantages, like the USB connector that allows you to update the firmware when needed.

After the Voyager series’ success, SwissMicros kept innovating and released two new calculators, the DM41X and DM42. These two models are larger and more powerful, featuring a new portrait-oriented housing and a bigger display.

The best-seller DM42 is an HP-42S clone. The software is based on the free42 open-source project, created by Thomas Okken, but it was modified and improved to meet Michael and David’s requirements for the product. The DM42 simulates the HP-42S software, which means the software was rewritten based on the original. The advantage of simulating instead of emulating is that the DM42 can deliver more, still being compatible with the original. The main benefit is the precision and the amount of memory available.

SwissMicros has to stay up to speed with the free42 project, so they keep updating their version two or three times a year. Initially, they used the Free42 project as is, adding their secret sauce to preserve battery life and other features needed for an electronic device. Thomas Okken contacted them at some point and told Michael that since they are using the Free42 code, they would need to open-source the whole project. SwissMicros put a lot of investment in developing of the code to handle hardware, so to make sure they preserved the investment, they split the code in a way that they can still use the Free42 codebase while keeping their proprietary code protected without breaking the license (GPL).

SwissMicros is working on a new model, the DM32 – a clone of the HP32S2. This model is planned to be released in the first semester of 2023 and is already in the final stages of development. To ensure they are all clear regarding software licenses, this time David developed the HP32S simulator from scratch, which will be used by the DM32, and could be the base of new modules in the future.

As a small company, SwissMicros still faces challenges with the chip shortage. He mentioned that he placed an order for the CPU he currently uses, and the delivery date is estimated for 2027! (we are in 2023, btw). Due to this problem, he and David have been working on using a new generation of this CPU, which will require hardware changes, but at least they can get them in thirty days instead of 5 years! They still have the DM42 and DM41X in stock using the old CPU.

SwissMicros is successful in what it aims to create and sell, but not without bumps on the road! When Michael released the credit card size DM15, HP lawyers contacted him, first asking how many he had sold. Michael didn’t answer that question, but he believes they assumed he had made and sold thousands and thousands of the DM15, and they gave him three options. The first option was that Michael had to pay 25% royalties. The second option was that they would buy the project from Michael, and the third option was that they would go to court. After some back and forth, the lawyers told him they would think about the options and return to him. That was the last time Michael heard from them.

A few years later, Michael got an order from an HP employee, and they got in contact. Michael didn’t miss the opportunity to say, “Thanks for your order, but I wonder if I am in trouble with HP!” That employee actually went to check what happened, and as far as he could see, nothing had happened, and SwissMicros was in the clear. He told Michael that the people he had talked to actually said that what SwissMicros is doing is cool! Nice compliment! (Note: HP doesn’t produce calculators anymore – the ones in the market are produced by another manufacturer using HP’s brand).

SwissMicros is a good example of how passion can become a successful business. Although there is a lot of nostalgia behind the RPN calculators used in the 70s and 80s, SwissMicros offers a modern and serious product for people who still want to use this powerful tool without relying on 30+ years old hardware.  Michael can now work full-time in his company and has a lot of plans to keep the RPN calculators used and relevant to this day!

You can learn more about SwissMicros and its line of calculators by following the link below. If you end up ordering one, mention that you learned about them via Vintage is The New Old! If you are interested in the subject, I recommend joining the HP Calculator Fan Club | Facebook.

Link: SwissMicros