Driving An OLED Screen With A 6502 Single-Board Computer

October 24, 2023 by Lewin Day 12 Comments

Twenty years ago, if you wanted an LCD for a project, you’d probably end up with something salvaged from a mobile phone or an HD44780 character display. These days, little OLEDs can be had for a few bucks and they’ve taken the maker world by storm. [Anders Nielsen] has recently been experimenting with driving these displays from the vintage 6502 CPU, and he’s even got scrolling operation down pat.

The best part is that [Nielsen] is doing all this on a single-board computer running his own assembly code. That’s right – there’s no compilers here. It’s bare metal coding at it’s best. The build uses a 6507 chip running at 1 MHz, paired with a 6532 RIOT and just 128 bytes of RAM—a similar setup to the Atari 2600.

The video explains how the code stacks up and drives the display, achieving the scrolling effect. It makes a huge difference to usability, especially compared to chunking pages at a time to the postage stamp-sized screen. He demonstrates a legitimate usage case too, using the setup as a serial terminal for a Raspberry Pi.

The 6502 architecture still looms large in the collective consciousness; we’ve been talking about programming it in assembly for years. Video after the break.

Continue reading “Driving An OLED Screen With A 6502 Single-Board Computer” →

Bringing An ADM-3A Back To Life

August 16, 2023 by Chris Lott 21 Comments

[David] at Usagi Electric ended up with an old Lear Siegler ADM-3A terminal in a trade a couple of years ago. But the CRT face was plagued with so-called cataracts, and the condition of the insides was unknown. The video ( below the break ) shows the restoration process, which went quite smoothly. [David] was relieved that the CRT repair in particular was easy, a fact he attributes to the Texas weather —

The temperature was 110 F / 43 C when he set the CRT outside to bake in the sun for a few hours. Afterwards, removing the “integral implosion protection” plastic screen went better than expected. Everything cleaned up nicely and the screen reinstalled. Introduced in 1976, the main electronics board is chock full of TTL chips with nary a microprocessor in sight. Fortunately the board was substantially intact, and a single missing chip was found hidden underneath the board. [David] gets the terminal up and running in short order, and is confronted with an annoyance familiar to gray-haired programmers who grew up in this era. Most terminals had different sets of commands to control features such as cursor control and clearing parts or all of the screen. Programs often assumed a certain type of terminal. Some terminals could be configured to behave in different ways, and some programs offered the user a choice of terminals. Today your terminal emulator probably still has a few choices of which kind of terminal to emulate, VT-100 being the most common. And eventually some operating systems provided a terminal abstraction, like Unix’s termcap for example.

If you were around in the era where terminals like the ADM-3A were scattered everywhere, what was your favorite terminal and/or terminal feature? And today, do you have any favorite terminal emulator to recommend? Let us know in the comments below.

Continue reading “Bringing An ADM-3A Back To Life” →

Selectric Typewriter Goes From Trash Can To Linux Terminal

July 25, 2023 by Dan Maloney 19 Comments

If there’s only lesson to be learned from [alnwlsn]’s conversion of an IBM Selectric typewriter into a serial terminal for Linux, it’s that we’ve been hanging around the wrong garbage cans. Because that’s where he found the donor machine for this project, and it wasn’t even the first one he’s come across in the trash. The best we’ve ever done is a nasty old microwave.

For being a dumpster find, the Selectric II was actually in pretty decent shape. The first couple of minutes of the video after the break show not only the minimal repairs needed to get the typewriter back on its feet, but also a whirlwind tour of the remarkably complex mechanisms that turn keypresses into characters on the page. As it turns out, knowing how the mechanical linkages work is the secret behind converting the Selectric into a teletype, entirely within the original enclosure and with as few modifications to the existing mechanism as possible.

Keypresses are mimicked with a mere thirteen solenoids — six for the “latch interposers” that interface with the famous whiffletree mechanism that converts binary input to a specific character on the typeball, and six more that control thinks like the cycle bail and control keys. The thirteenth solenoid controls an added bell, because every good teletype needs a bell. For sensing the keypresses — this is to be a duplex terminal, after all — [alnwlsn] pulled a page from the Soviet Cold War fieldcraft manual and used opto-interrupters to monitor the positions of the latch interposers as keys are pressed, plus more for the control keys.

The electronics are pretty straightforward — a bunch of MOSFETs to drive the solenoids, plus an AVR microcontroller. The terminal speaks RS-232, as one would expect, and within the limitations of keyboard and character set differences over the 50-odd years since the Selectric was introduced, it works fantastic as a Linux terminal. The back half of the video is loaded with demos, some of which aptly demonstrate why a lot of Unix commands look the way they do, but also some neat hybrid stuff, like a ChatGPT client.

Hats off to [alnwlsn] for tackling a difficult project while maintaining the integrity of the original hardware.

Continue reading “Selectric Typewriter Goes From Trash Can To Linux Terminal” →

Mythic I: An Exploration Of Artisanal Computing

May 17, 2023 by Tom Nardi 14 Comments

While computers have become ever faster and more capable over the years, it’s hard to say they’ve become any more exciting. In fact, they’ve become downright boring. Desktop, laptop, or mobile, they’re all more or less featureless slabs of various dimensions. There’s not even much in the way of color variation — the classic beige box is now available with white, black, or metallic finishes.

Believing that such a pedestrian appearance isn’t befitting a device that puts the world’s collected knowledge at our fingertips, [Keegan McNamara] started exploring a more luxurious approach to computing. Gone is the mass produced injection molded plastic, in its place is hand-carved maple and Tuscan leather. Common computing form factors are eschewed entirely for a swooping console inspired by fine furniture and classic sports cars. The final result, called the Mythic I, is equal parts art and science. Not just a bold reimaging of what a computer can be, but an object to be displayed and discussed. Continue reading “Mythic I: An Exploration Of Artisanal Computing” →

Before You Sudo Rm -rf /, Take Some Precautions

April 21, 2023 by Bryan Cockfield 40 Comments

Maintaining or administering a computer system remotely is a common enough task these days, but it’s also something that can go sideways on you quickly if you aren’t careful. How many of us are guilty of executing a command, having it fail, and only then realizing that we weren’t connected to the correct computer at all? [Callan] occasionally has this issue as well, but in at least one instance, he deleted all of the contents of the wrong server by mistake. To avoid that mistake again, he uses color codes in the command line in a fairly unique way.

The solution at first seems straightforward enough. Since the terminal he’s using allows for different colors to be displayed for the user and hostname on the bash prompt, different text and background colors are used for each server. The only problem with this is that his friends also have access to these servers, and one of them is red/green colorblind, which led to another near-catastrophic mix-up. To ensure no edge cases are missed, [Callan] built a script which runs on every new server he spins up which selects two random colors, checks that they contrast well with each other, don’t create problems for the colorblind, and then applies them to the bash prompt.

For a problem most of us have had at some point or another, it’s a fairly elegant solution that helps ensure we’re sending the right commands to the right computer. This adds a layer of automation to the process and, while some color combinations do look similar, there are enough to help out most of us in some way, especially since he has released the source code on his GitHub page. For other helpful server administration tips, we’d recommend the Linux-Fu article about deploying your own dynamic DNS.

A Thoroughly Modern Serial Terminal

March 1, 2023 by Jenny List 16 Comments

The humble desktop serial terminal may have long disappeared from the world of corporate IT, but there are still plenty of moments when professionals and enthusiasts alike need to hook up to a serial port. Many of us use a serial port on our laptops or other mobile devices, but [Neil Crawforth] has gone one better than that with the VT2040. It’s an old-style serial terminal in a super-handy portable format, and as one might guess from the name, it has an RP2040 microcontroller at its heart.

Attached to the chip is a rather nice keyboard, and an ILI9488 480×320 LCD display. The software is modular, providing a handy set of re-usable libraries for the different functions including a PIO-based serial port. His main application seems to be talking to an ESP8266, but we’re guessing with a MAX232 or other level shifter chip it could drive a more traditional port. Everything can be found in the project’s GitHub repository, allowing anyone to join the fun.

As long-time readers will know, we’ve been partial to a few serial terminals in the past. Particularly beloved is this extremely retro model with vintage dot matrix LEDs.

CoreFreq Gives Peek At CPU Performance Info On Linux

December 24, 2022 by Lewin Day 9 Comments

The CPU is the part of the computer that makes everything else tick. While GPUs have increasingly become a key part of overall system performance, we still find ourselves wanting to know how our CPU is doing. CoreFreq is a Linux tool that aims to tell you everything you want to know about your modern 64-bit CPU.

The tool relies on a kernel module, and is coded primarily in C, with some assembly code used to measure performance as accurately as possible. It’s capable of reporting everything from core frequencies to details on hyper-threading and turbo boost operation. Other performance reports include information on instructions per cycle or instructions per second, and of course, all the thermal monitoring data you could ask for. It all runs in the terminal, which helps keep overheads low.

The hardcore among us can build it from source, available on GitHub, though it’s reportedly available in package form, and as a live CD, too. We could imagine data captured from CoreFreq could be used for some fun performance visualizations, too. If you’ve been whipping up your own nifty command-line tools, be sure to drop us a line!