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.

Happy 4th!