LED Tester Also Calculates Resistor For Target Voltage

December 2, 2023 by 12 Comments

[mircemk] built a slick-looking LED tester with a couple handy functions built in. Not only can one select a target current to put through an LED, but by providing a target voltage, the system will automatically calculate the necessary series resistor. If for example the LED is destined for 14 V, this device will not only show how the LED looks at the chosen current, but will calculate the required resistor to get the same results on a 14 V system.

The buttons on the left control the target current and the voltage of the destination system. Once an LED is connected it will light up and the display indicates the LED’s forward voltage, the LED current, and the calculated series resistor value to obtain the same result at the selected target voltage. It’s a handy way to empirically dial in LED brightness values without needing to actually set up any particular test environment.

On the inside there’s little more than a handful of passive components, an Arduino, an LCD display, and a few buttons. This kind of tool reminds us of the highly clever component testers that hit the hobbyist scene years ago, showing what kind of advanced tricks a modern microcontroller is capable of with the right programming. (Here’s a look at how those work, if you’re interested in some deeper details.)

[mircemk] demonstrates his tool in the video, embedded below. We particularly like the attention he paid to the enclosure, giving it a very functional layout. It goes to show that when designing something, it’s never too early to consider enclosure and UI layout.

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Nixie Tube RPN Calculator Project

November 7, 2023 by 12 Comments

If you like Nixie tubes and/or DIY calculators, checkout this interesting talk from the HP Handheld Conference in Orlando last month by [Eric Smith] from Brouhaha and [John Doran] from Time Fracture. For 20-some years, [Eric] and the late [Richard Ottosen] have been incrementally developing various DIY calculators — this paper from the 2005 HHC conference is an excellent overview of the early project. [John] got one of those early DIY calculators and set about modifying it to use Nixie tubes. However, he got distracted by other things and set it aside — until reviving it earlier this year and enlisting [Eric]’s aid.

This presentation goes over the hardware aspects of the design. Unlike the earlier PIC-based DIY calculators, they decided to use a WCH RISC-V processor this time around. The calculator’s architecture is intentionally modular, with the display and keyboard housed in completely separate enclosures communicating by a serial interface. If the bulkiness alone doesn’t exclude it from being pocket-sized, the 170 VDC power supply and 1/2 W per digit power consumption certainly does. This modularity does lend itself to DIYers replacing the display, or the keyboard, with something different. [Eric] wants to build a mechanical flip-digit display for his unit. As for the software, [Eric] reviews the firmware approach and some future upgrades, such as making it programmable and emulating other flavors of HP calculators.

If you’re embarking on a similar project yourself, check out this talk and take notes — there are a lot of interesting tidbits on using Nixie tubes in the 21st century. If [Eric]’s name sounds familiar, you may know him from the Nonpareil calculator software used on many emulators and DIY calculator projects, one of which we covered some years ago. [John] is also a long-time tinkerer, and we wrote about his gorgeous D16/M HCMOS computer system back in 2012. Thanks to [Stephen Walters] for sending in the tip.

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Partial Relay-Based Calculator Puts The Click Where It Counts

November 3, 2023 by 15 Comments

It looks like [Michal Zalewski] is raising the next generation the right way. First, his eldest son asks for help building a one-bit computer from discrete transistors. Not to be left behind, his little brother then asked for help with an even more retro project, which resulted in this partially relay-based calculator. Maybe there is some hope for the future.

Now, purists will no doubt notice the ATmega64 microcontroller sitting in the middle of the main PCB on this project and cry “Foul!” But perfect is the enemy of done, and as [Michal] explains, at $6 a pop for the Omron relays he and his son chose, there’s only so far you can go with relay logic before you’re taking out a second mortgage. So the relays are limited to the ALU of the calculator, along with the drivers for the six seven-segment LED displays. The microcontroller is just there for housekeeping functions like scanning the keyboard and decoding digits. All the actual calculations are in the relay logic, not silicon. And we’d be remiss not to praise his son’s stylistic choices for this design — that it uses relays with clear covers, and that it has single-sided PCBs with curvy, hand-drawn traces traces that look hand-drawn on old-school yellow substrate. [Michal]’s heart must swell with pride to have fathered someone with such exquisite taste.

For his part, [Mikal] did some really good documentation for this build, including excellent descriptions of Boolean math with half- and full-adders and how relays are used to create the basic logic gates that comprise them. The calculator itself is still a work in progress, with microcontroller code still in development, but it’s working enough that you can enjoy the display driver’s clickiness in the video below. If that doesn’t do it for you, we’ve got other relay calculators to scratch that click itch. Continue reading “Partial Relay-Based Calculator Puts The Click Where It Counts” →

Pocket Calculator Isn’t A Brain Or Magic

October 20, 2023 by 18 Comments

If you predate the pocket calculator, you may remember slide rules. But slide rules take a a little skill to use. There was a market for other devices that were simpler or, in some cases, cheaper. One common one was the “magic brain” or Addiator which was a little metal box with some slots that could add numbers. However, using clever tricks it could also subtract and — in a fashion — multiply. [Our Own Devices] has a teardown of the device you can see in the video below. It is deceptively simple, and the description of how it works is at least as interesting as the peek inside.

We remember these on the market and, honestly, always thought they were simple tally mechanisms. It turns out they are both less and more than that. Internally, the device is a few serrated sheet metal strips in a plastic channel. The subtraction uses a complement addition similar to how you do binary subtraction using 2’s complement math. Multiplication is just repetitive addition, which is fine for simple problems.

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HP1973 Project Highlights Workings Of HP-45 Calculator

July 24, 2023 by 3 Comments

[Sarah K Marr] dabbles in retrocomputing and has a fascination with the Hewlett Packard HP-45 calculator, the second calculator in HP’s series introduced in 1973. Over a year ago, she wrote an HP-45 emulator for use on a terminal, dubbed HP45TERM. Not content with success, she upped the challenge and decided to build an even better emulator with a full-featured GUI written in Python. Oh, and she made it multi-platform as well. The result is the HP1973 project.

[Sarah] thought it would take just a few days, but it grew into a much bigger project, as often happens. We’re glad it did because the results are fantastic. The emulator gives you access not only to the calculator itself but can see everything under the hood. The emulator provides full ROM visibility, hardware registers, and standard debugging operations like single stepping. ROM images are available for the HP-45, the HP-35, and the HP-80. The GUI display is configurable, and there’s a plethora of help and information explaining the calculator’s internals. Pre-built binaries are available for MacOS, Windows, and Python source code (3.10.10+) for all operating systems (you’ll need to `pip install numpy` first). The emulation is faithful to the original calculator, and even the hidden timer function can be accessed.

Check this out if you’re into retro calculators. Our own Al Williams wrote about the history of the HP-35 back in 2018 if you want to learn more. Thanks to [J Peterson] for sending in the tip.

A Pi Calculating Pi For Pi Day

March 14, 2023 by 12 Comments

What is it about pi that we humans — at least some of us — find so endlessly fascinating? Maybe that’s just it — it’s endless, an eternal march of digits that tempts us with the thought that if we just calculate one more digit, something interesting will happen. Spoiler alert: it never does.

That doesn’t stop people from trying, of course, especially when “Pi Day” rolls around on March 14 every day  — with apologies to the DD/MM set, of course. This year, [Cristiano Monteiro] commemorated the day with this Pi-based eternal pi calculator. The heart of the build is a Raspberry Pi Pico board, which does double duty thanks to its two cores. One core is devoted to running the pi calculation routine, while the other takes care of updating the seven-segment LED display with the last eight calculated digits. Since the calculation takes increasingly more time the farther into pi it gets, [Cristiano] thoughtfully included a 1-Hz heartbeat indicator, to assure users that the display isn’t frozen; the video below shows how slow the display gets even just a few seconds after starting up, so it’s a welcome addition.

This is actually [Cristiano]’s second go at a Pi Day pi calculator; last year’s effort was a decidedly tactical breadboard build, and only supported a four-digit display. We applaud the upgrades, and if anyone wants to replicate the build, [Cristiano] has posted his code.

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Probably The Most Over-Specified Calculator To Ever Be Manufactured

March 7, 2023 by 38 Comments

It’s possible quite a few of our older readers will remember the period from the 1960s into the ’70s when an electronic calculator was the cutting edge of consumer-grade digital technology. By the 1980s though, they were old hat and could be bought for only a few dollars, a situation that remains to this day. But does that mean calculator development dead?

Perhaps not, as [Li Zexi] writes for CNX Software, when he reviews a simple non-scientific calculator that packs an Alwinner A50 tablet SoC and the Android operating system. As shipped they lack the Android launcher, so they aren’t designed to run much more than the calculator app. Of course that won’t stop somebody who knows their way around Google’s mobile operating system for very long — at the end of the review, there’s some shots of the gadget running Minecraft and playing streaming video.

These devices can be had for not a lot on the Chinese second-hand electronics market, and after an extensive teardown he comes to the conclusion that besides their novelty they’re an older specification so not really worth buying.

But it does beg the question as to why such a product was put into production when the same task could have been performed using very cheap microcontroller. Further, having done so they make it a non-scientific machine, not even bestowing it with anything that could possibly justify the hardware. Is there a use case he, and us, have missed? We’d love to know.

We cover a lot of calculator stories here at Hackaday. Sometimes they’re classic machines, but more often they’re modern takes on an old idea.