An Open-source Scientific RPN Calculator

June 5, 2021 by Jenny List 69 Comments

Why reach for a bland, commercially available calculator when you be using a model that employs RPN (Reverse Polish Notation) in its calculations and be a custom build all at the same time? The kids may have colour TFTs and graphing functions, but your keyboard has no equals sign, and that means something.

Unfortunately for RPN enthusiasts, the RPN calculator is a little on the rare side. Since classic models from the 1970s and ’80s are rather pricey, [Anton Poluektov]’s just build his own called the OpenCalc. This glorious specimen is an open hardware RPN calculator with more than a nod to the venerable Hewlett Packard HP42 in its design.

At its heart is an STM32L476 low-power ARM processor and a Sharp Memory LCD, all on a PCB clad in a 3D-printed case you’d have been proud to own in the 1980s. It runs from a CR2032 which is more than can be said for some modern styles of calculator, and it gives the user everything you could wish for in a scientific calculator. The key legends are a set of printable stickers, which when printed on self-adhesive laser film prove durable enough to last. All the resources can be found in a GitHub repository, so if RPN is your thing there’s nothing to stop you building one for yourself.

If RPN interests you, it’s a subject we’ve looked at in greater detail in the past.

Vintage Calculator Design Shows Just How Much We Take For Granted Today

February 20, 2021 by Donald Papp 14 Comments

[Amen]’s Rockwell 920 calculator from the 70s was a very impressive piece of hardware for its time. It sported a 16-digit display, a printer, and it could run programs. It even had a magnetic card reader/writer that could be used to store programs and data externally. Seen through today’s eyes, it was less like a calculator and more like what we would call a single-board computer. They are also a window into another era, a time when many of the electrical design assumptions we take for granted hadn’t happened yet. When the time came to dig into what made the calculator tick, [Amen] had a lot of work to do just to get basic tools running.

For example, [amen]’s Blue Pill (an open-source, multipurpose test and measurement tool) is, on one hand, the perfect tool to snoop on the inner workings. However, those inner workings happen to use negative logic at -17 Volts, which means a logical zero is -17 V and a one is 0 V. Oh, and it uses an oddball clock rate, to boot. Since the Blue Pill doesn’t support -17 V negative logic (does anything?) a bit of custom work was needed to craft an interface. Once that was working, the Blue Pill was off to the races.

The unfamiliar elements didn’t end there. The pins on each IC, for example, are in a staggered layout quite unlike the DIP pattern most of us (and our tools, breadboards, and IC clips) are familiar with. As for the processor itself, [amen] has access to low-level documentation on Rockwell processors and instruction sets, but the timing diagrams are puzzling until one realizes the processor has two clock inputs at two different frequencies, resulting in what [amen] describes as four separate “clock phases”.

These design decisions were certainly made for good reasons at the time, and they even have a certain internal harmony to them, but it’s still a window into an era when the elements underpinning much of what we now have and work with had not yet happened.

Check out the video embedded below to see [amen] explain what it took to hook the Blue Pill up to a Rockwell 920. Also, if you’d like to see one of these vintage machines demonstrated in all its functioning glory, here’s a video of one being put through its paces.

Continue reading “Vintage Calculator Design Shows Just How Much We Take For Granted Today” →

Reverse Engineering Silicon From The First Pocket Calculator

December 29, 2020 by Jenny List 4 Comments

We’ve seen so many explorations of older semiconductors at the hands of [Ken Shirriff], that we know enough to expect a good read when he releases a new one. His latest doesn’t disappoint, as he delves into the workings of one of the first hand-held electronic calculators. The Sharp EL-8 from 1969 had five MOS ICs at its heart, and among them the NRD2256 keyboard/display chip is getting the [Shirriff] treatment with a decapping and thorough reverse engineering.

The basic functions of the chip are explained more easily than might be expected since this is a relatively simple device by later standards. The fascinating part of the dissection comes in the explanation of the technology, first in introducing the reader to PMOS FETs which required a relatively high negative voltage to operate, and then in explaining its use of four-phase logic. We’re used to static logic that holds a state depending upon its inputs, but the technologies of the day all called for an output transistor that would pull unacceptable current for a calculator. Four phase logic solved this by creating dynamic gates using a four-phase clock signal, relying on the an output capacitor in the gate to hold the value. It’s a technology that lose out in the 1970s as later TTL and CMOS variants arrived that did not have the output current drain. Fascinating stuff!

[Ken] gave a talk at the Hackaday Superconference a couple of years ago, if you’ve not seen it then it’s worth a watch.

Another Kind Of “Bare Metal”: 6502 Computer Powers RPN Calculator

November 17, 2020 by Dan Maloney 11 Comments

[Mitsuru Yamada] states that one of the goals for this 6502 computer build was to make it strong enough to survive real-world usage. In that regard alone we’d call this a success; the die-cast aluminum enclosures used are a little blast from the past and lend a nice retro industrial look to the project. The main chassis of the computer fairly bristles with LEDs and chunky toggle switches for setting the data and address busses. The interior is no less tidy, with the 6502 microprocessor — date code from 1995 — and associated support chips neatly arranged on perf board. The construction method is wire wrapping, in keeping with the old-school look and feel. Even the hand-drawn schematic is a work of art — shades of [Forrest Mims].

As for programming, this machine is as low-level as it gets. Nothing but 6502 machine language here, entered manually with the toggle switches, or via an externally programmed ROM. The machine can only address 1k of memory, a limit which the code to support the RPN calculator add-on [Yamada] also built brushes up against, at 992 bytes. The calculator keypad has a 20-key matrix pad and an eight-digit dot-matrix LED display, and can do the four basic operations on fixed-point binary-coded decimal inputs. The brief video below shows the calculator in action.

We love the look of this build and we’re eager to see more like it. We’ve seen a ton of 6502 builds from discrete chips lately, and while we love those too, it’s nice to see one of the big old DIPs put back in action for a change.

Continue reading “Another Kind Of “Bare Metal”: 6502 Computer Powers RPN Calculator” →

Binary Calculator For All 0b10 Types

November 10, 2020 by Dan Maloney 15 Comments

You know the old joke: There are 10 types of people in the world — those who understand binary, and those who don’t. Most of us on Hackaday are firmly in the former camp, which is why projects like this circuit sculpture binary calculator really tickle our fancies.

Inspired by the brass framework and floating component builds of [Mohit Bhoite], [dennis1a4] decided to take the plunge into circuit sculpture in an appropriately nerdy way. He wisely decided on a starter build, which was a simple 555 timer circuit, before diving into the calculator. Based on an ATMega328P in a 28-pin DIP, the calculator is built on an interesting hybrid platform of brass wire and CNC-routed wood. The combination of materials looks great, and we especially love the wooden keycaps on the six switches that make up the keyboard. There’s also some nice work involved in adapting the TLC5928 driver to the display of 16 discrete LEDs; suspended as it is by fine magnet wires, the SSOP chip looks a bit like a bug trapped in a spider web.

Hats off to [dennis1a4] for a great entry into our soon-to-conclude Circuit Sculpture Contest. The entry deadline is (today!) November 10, so it might be a bit too late for this year. But rest assured we’ll be doing this again, so take a look at all this year’s entries and start thinking about your next circuit sculpture build.

Continue reading “Binary Calculator For All 0b10 Types” →

Retro Calculator Design Has Creative Tactile Touchscreen

October 18, 2020 by Lewin Day 25 Comments

We’ve all heard it a thousand times – they don’t make ’em like they used to. Sometimes, that’s for good reason, but there is a certain build quality to electronics of the mid-20th century that is hard to find in hardware today. This inspires great nostalgia and dedication in some, like [Michael Park], who set out to build a calculator reminiscent of the best HP designs from yesteryear.

The scissor mechanism allows the touch screen to move linearly and activate the tactile switch without twisting, no matter where along its surface it is pressed.

One of the major factors for [Michael] was the great feel of the keys on these classic units. Wanting to experiment with different layouts without a lot of rewiring, the idea of keys with individual displays became attractive. Existing parts on the market were prohibitively expensive, however. Instead, [Michael] used a single touchscreen with a switch mounted underneath to provide tactile feedback with a nifty scissor-arm guide mechanism. Combined with individual see-through plastic overlays, the MP-29 has a fully reconfigurable pad of 30 keys with dynamically updatable labels.

It’s a creative choice, and one that looks highly satisfying to use. It has all the tactile benefits of individual keys, both in the keypresses and being able to navigate the keypad without looking. Combined with the benefit of reconfigurable keys thanks to the touch screen underneath, it’s a great way to build a user-interface.

The rest of the calculator design closely mimics the HP-29, though [Michael] is also experimenting with alternative layouts too. There are plenty of religious wars in the calculator community over usability, after all – mostly over which side of the pad has the arithmetic functions.

We’ve lamented the demise of the standalone calculator recently; with so many smart devices around, it’s hard to see it making a major comeback anytime soon. Of course, if you’re opinionated on the topic, sound off in the comments below. Video after the break.

Continue reading “Retro Calculator Design Has Creative Tactile Touchscreen” →

Retrotechtacular: The $5,000 40 Pound HP Classroom Computer

October 2, 2020 by Al Williams 21 Comments

See if you can talk your local school district into buying a computer that costs about $5,000 and weighs 40 pounds. That was HP’s proposition to schools back in 1968 so really it is more like $35,000 today. The calculator had a CRT display for the RPN stack that you could mirror on a big screen. You could also get a printer or plotter add-on. Pretty hot stuff for the ’60s.

The 1970 videos promoting the HP 9100, posted by the [Computer History Archive Project], shows something we’d think of as a clunky calculator, although by the standards of the day it was a pretty good one with trig functions and a crude programming capability.

Continue reading “Retrotechtacular: The $5,000 40 Pound HP Classroom Computer” →