2022 Sci-Fi Contest: Nixie Calculator Is Resplendent In Walnut Enclosure

April 14, 2022 by Lewin Day 8 Comments

The Nixie tube is one of the most popular display technologies amongst the hacker and maker set. Glowing numerals can warm even the coldest heart, particularly when they’re energized with hundreds of volts. [ohad.harel] used these glorious displays to build the TORI Nixie Calculator, with beautiful results.

The build uses seven IN-12 Nixie tubes for numerals, along with an IN-15A which displays mathematical symbols like +, %, and M. It’s equipped with a 32-key keyboard using mechanical key switches. Everything is wrapped up in a beautiful walnut enclosure that fits the tubes and keyboard perfectly, giving the final build a nice mid-century aesthetic.

Impressively, it goes beyond the basic usual calculator functions, also handling conversions between metric and imperial units. It’s a nice feature that would make it a wonderful tool to have on one’s desk beyond the simple aesthetic charm of the Nixie tubes.

Nixie projects never seem to die. Their beauty and warmth captivates builders to this day. Indeed, we’ve even seen some makers go to the trouble of creating new tubes from scratch!

Remoticon 2021 // Rob Weinstein Builds An HP-35 From The Patent Up

April 7, 2022 by Chris Lott 40 Comments

Fifty years ago, Hewlett-Packard introduced the first handheld scientific calculator, the HP-35. It was quite the engineering feat, since equivalent machines of the day were bulky desktop affairs, if not rack-mounted. [Rob Weinstein] has long been a fan of HP calculators, and used an HP-41C for many years until it wore out. Since then he gradually developed a curiosity about these old calculators and what made them tick. The more he read, the more engrossed he became. [Rob] eventually decided to embark on a three year long reverse-engineer journey that culminated a recreation of the original design on a protoboard that operates exactly like the original from 1972 (although not quite pocket-sized). In this presentation he walks us through the history of the calculator design and his efforts in understanding and eventually replicating it using modern FPGAs.

The HP patent ( US Patent 4,001,569 ) contains an extremely detailed explanation of the calculator in nearly every aspect. There are many novel concepts in the design, and [Rob] delves into two of them in his presentation. Early LED devices were a drain on batteries, and HP engineers came up with a clever solution. In a complex orchestra of multiplexed switches, they steered current through inductors and LED segments, storing energy temporarily and eliminating the need for inefficient dropping resistors. But even more complicated is the serial processor architecture of the calculator. The first microprocessors were not available when HP started this design, so the entire processor was done at the gate level. Everything operates on 56-bit registers which are constantly circulating around in circular shift registers. [Rob] has really done his homework here, carefully studying each section of the design in great depth, drawing upon old documents and books when available, and making his own material when not. For example, in the course of figuring everything out, [Rob] prepared 338 pages of timing charts in addition to those in the patent. Continue reading “Remoticon 2021 // Rob Weinstein Builds An HP-35 From The Patent Up” →

Old Casio Calculator Learns New Tricks

April 6, 2022 by Chris Wilkinson 12 Comments

[George Stagg] recently found himself stung by the burden of free time while in lockdown. Needing a project to keep him occupied, he decided to upgrade his 90s Casio CFX-9850G calculator to run custom machine code.

All [George] really wanted was for his vintage calculator to understand Reverse Polish Notation (RPN). The calculator in question can already run its own version of BASIC, however the bespoke Hitachi CPU struggles performance-wise with complex programs, and wouldn’t be a realistic way of using RPN on the calculator. An RPN interpreter written in assembly language would be much faster.

The first step in cracking this calculator wide open was a ROM dump, followed by writing a disassembler. Incredibly, the MAME framework already featured a ‘partial implementation’ of the calculator’s CPU, which was a much needed shot in the arm when it came time to write a full-featured emulator.

With the entire calculator emulated in software, the plan from here involved replacing one of the BASIC commands in ROM with new code that would jump to an address in RAM. With 32KB of RAM there ended up being plenty of room for experimentation, and uploading a program into RAM was simplified by using Casio’s original backup software to dump the RAM onto a PC. Here, the contents of RAM could be easily modified with custom code, then uploaded back into the calculator.

With RAM to burn, new routines were created to write custom characters to the screen, and a new font was created to squeeze more characters onto the display than normal. [George] ended up porting a Forth interpreter, which defaults to RPN style, to finally achieve his humble objective. He also managed to get a version of Conway’s Game Of Life running, check out the video after the break.

We can’t get enough of our calculator hacks here, so make sure to check out the CPU transplant on this vintage Soviet calculator.

Continue reading “Old Casio Calculator Learns New Tricks” →

A vintage pocket calculator with extra exposed circuitry added

I2C Breathes New Life Into Casio Pocket Calculator

February 21, 2022 by Chris Wilkinson 6 Comments

When is a pocket calculator more than just a calculator? [Andrew Menadue] has been pushing the limits of his 1970s Casio FX-502P by adding all sorts of modern functionality via the calculator’s expansion port.

Several older Casio calculators included an expansion port for connecting cassette tape storage and printing functionality. Data on the FX-502P could be saved on cassette tape using the well-known Kansas City standard, however this signal was produced by Casio’s FA-1 calculator cradle, not the FX-502P itself. To interact with the calculator itself would require an understanding of whatever protocol Casio designed for this particular model.

It turns out that the protocol is a little quirky compared to its contemporaries, with variable length data packets and inverted data logic, (zero volts is ‘1’ and three volts is ‘0’). Once the protocol was untangled, it was ‘simply’ a matter of connecting the calculator to the GPIO interface on the STM32, and using some software wizardry to start shooting data packets back and forth.

This hack can be used to send and receive data from an SD card (via a RAM buffer), however it’s the other expansion capabilities that really make us wonder. [Andrew] has demonstrated how easy it is to add a real-time clock or thermal printer. Using the I²C capabilities of the STM32, it’s likely that all sorts of gadgets and sensors could be coupled with this vintage calculator, and many others like it.

You can find even more details about this hack over here, including some follow up videos to the original hack. No stranger to vintage calculators, we last featured [Andrew] after he retrofitted a modern LCD display to an old Casio. It’s charming to see how these calculators are far from obsolete.

Continue reading “I2C Breathes New Life Into Casio Pocket Calculator” →

Building The DIY HP41C: A Field Report

December 3, 2021 by Al Williams 20 Comments

I have a confession to make. I write about a lot of projects for Hackaday, but there are very few I read about and then go actually build a copy of it. I don’t have a lot of time and I’m usually too busy building my own stuff. But once in a while, something strikes my fancy and I’ll either raid the junk box or buy the kit. The most recent case of that was the PX-41C, a replica of the classic HP-41C.

The HP-41C is a somewhat legendary reverse-polish notation calculator. I still have my original HP-41C from 1979 (a very low serial number). It is still a workhorse but at 43 years old or so, I don’t like to leave it hanging around or near anything that might damage it. It has enough wear from the daily use it received 40 years ago. Sure, I have great emulation on my phone and I use that too, but the PX-41C kit looked fun, and with all through-hole parts it would be a quick build. The black Friday sale on Tindie sealed the deal for me.

Start-Up

The kit arrived on the Saturday after Thanksgiving, I decided to tackle it while waiting for some 3D prints. The components were all nicely bagged and marked. Tearing into the bags was a bit frustrating, but not hard and it did keep everything separate. There was a bill of materials, but — I thought — no instructions. Turns out the last part of the bill of materials is a link to some instructions. They aren’t much and I didn’t realize they were until after completing the board, but it isn’t hard to figure out. All the parts are marked on the silkscreen and you can probably figure it out — with a few caveats.

Continue reading “Building The DIY HP41C: A Field Report” →

Build Your Own HP41C

November 24, 2021 by Al Williams 41 Comments

There was a time when engineers carried slide rules. Then there was a time when we all carried calculators. Sure, calculators are still around, but you are more likely to use your phone. If you really need serious number crunching, you’ll turn to a full computer. But there was that awkward time when calculators were very important and computers were very expensive that calculators tried to be what we needed from full-blown computers. The HP41C was probably the pinnacle of that trend. If you’ve ever had one, you know that is a marvel of the day’s technology with alphanumeric capabilities and four plug in ports for more memory or ROMs. It really was a little hand-held computer. Didn’t have one? Don’t worry, you can now build your own. In fact, the HP emulator will also act like an HP15C or 16C, if you prefer.

You can see the device in action in the video below. As you might expect, this version uses a through-hole ATMEGA328 and even at 8 MHz, the emulation is faster than the original calculator. The machine also has over double the memory the original calculator had along with a real-time clock built-in. The display is also backlit, something we all wanted in the original.

Continue reading “Build Your Own HP41C” →

Hacking An Obsolete Yet Modern Calculator

November 1, 2021 by Bryan Cockfield 7 Comments

The gold standard for graphing calculators, at least in the US, are the Texas Instruments TI-84 series. Some black sheep may have other types, but largely due to standardized testing these calculators dominate the market. Also because of standardized testing, these calculators have remained essentially unchanged for decades. While this isn’t great for getting value for money, it does mean that generations of students have been able to hack on these calculators to do all kinds of interesting things as [George Hilliard] outlines.

Even before the creation of these graphing calculators, the z80 processor behind them was first produced over four decades ago and was ubiquitous in the computer scene at the time, which also lends to its hackability. There’s plenty to catch up on here, too, from custom TI games that trick the two-tone display into grayscale to Game Boy emulators that can play Zelda since the TI and Game Boy share the same processors. There are also several methods of running native code or otherwise “jailbreaking” these devices to run arbitrary code.

It looks like the world of TI hacking is alive and well now, and with several decades of projects to browse there’s always something new to find. As it stands, there may be more decades of these types of projects to come, since neither TI nor the various testing standardization companies and government agencies show any signs of changing any time soon.

Thanks to [Adrian] for the tip!