Wire Wrap Odyssey: A 7400-series Homebrew 8-bit Computer

February 27, 2024 by Maya Posch 15 Comments

The Wire Wrap Odyssey's first Hello World from the CPU module, here hooked up to a logic analyzer in July of 2020. (Credit: Paul Krizak) — The Wire Wrap Odyssey’s first Hello World from the CPU module, here hooked up to a logic analyzer in July of 2020. (Credit: Paul Krizak)

As part of his computer science curriculum at Texas A&M University in the early 2000s, [Paul Krizak] took a computer architecture course on the basics of their functioning. This and being exposed to dozens of homebuilt computer projects inspired him to begin building his own 8-bit computer in 2010, which eventually grew into the Wire Wrap Odyssey. This name covers both the primary construction method chosen around 2019 in the form of wire-wrapped connections, as well the harrowing journey to reach this point with a functioning computer system despite many choices and setbacks.

The Odyssey CPU is an 8-bit microcoded design with 16-bit address bus, using mostly 74HC-series logic. A VGA graphics card is also part of the design, which can output a 640×480 text display, with character glyphs read from the system ROM (32 kB AT28C256). As for the RAM, this is an extravagant 32 kB dual-port SRAM (Renesas 7007), which also allows both the CPU and video card to use the same SRAM. Currently the system has four peripherals: a PS/2 keyboard controller, an RTC and timer (DS1511Y+), 82C52 UART and 1 MB of extended RAM, but an ATA port and parallel port are in development.

Perhaps the most impressive part about this product is the level of documentation, from the early stages including paper doodles to the current state of the system, including the GitHub repository for the software. [Paul] was also an exhibitor at the Vintage Computing Festival (VCF) SoCal recently with his Wire Wrap Odyssey, where he was able to show off the progress so far. Next year he hopes to visit VCF SoCal again, with the remaining planned peripherals implemented.

Op-Amp Drag Race Turns Out Poorly For 741

February 23, 2024 by Dan Maloney 32 Comments

When it was first introduced in 1968, Fairchild’s 741 op-amp made quite a splash. And with good reason; it packed a bunch of components into a compact package, and the applications for it were nearly limitless. The chip became hugely popular, to the point where “741” is almost synonymous with “op-amp” in the minds of many.

But should it be? Perhaps not, as [More Than Electronics] reveals with this head-to-head speed test that compares the 741 with its FET-input cousin, the TL081. The test setup is pretty simple, just a quick breadboard oscillator with component values selected to create a square wave at approximately 1-kHz, with oscilloscope probes on the output and across the 47-nF timing capacitor. The 741 was first up, and it was quickly apparent that the op-amp’s slew rate, or the rate of change of the output, wasn’t too great. Additionally, the peaks on the trace across the capacitor were noticeably blunted, indicating slow switching on the 741’s output stage. The TL081 fared quite a bit better in the same circuit, with slew rates of about 13 V/μS, or about 17 times better than the 741, and nice sharp transitions on the discharge trace.

As [How To Electronics] points out, comparing the 741 to the TL081 is almost apples to oranges. The 741 is a bipolar device, and comparing it to a device with JFET inputs is a little unfair. Still, it’s a good reminder that not all op-amps are created equal, and that just becuase two jelly bean parts are pin compatible doesn’t make them interchangeable. And extra caution is in order in a world where fake op-amps are thing, too.

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FLOSS Weekly Episode 771: Kalpa — Because Nobody Knows What Hysteresis Is

February 21, 2024 by Jonathan Bennett 6 Comments

This week, Jonathan Bennett and Dan Lynch talk with Shawn W Dunn about openSUSE Kalpa, the atomic version of openSUSE Tumbleweed, with a KDE twist. What exactly do we mean by an Atomic desktop? Is ALP going to replace openSUSE Tumbleweed? Are snaps coming to Kalpa?

Shawn gives us the rundown of all the above, and what’s holding back a stable release of Kalpa, what’s up with Project Greybeard, and why Kalpa really doesn’t need a firewall.

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Rebuilding A $700k Refrigerator

February 21, 2024 by Bryan Cockfield 20 Comments

When cleaning out basements, garages, or storage units we often come across things long forgotten. Old clothes, toys, maybe a piece of exercise equipment, or even an old piece of furniture. [Ben] and [Hugh] were in a similar situation cleaning out an unused lab at the University of California Santa Barbara and happened upon an old refrigerator. This wasn’t just a mini fridge left over from a college dorm, though. This is a dilution refrigerator which is capable of cooling things down to near absolute zero, and these scientists are trying to get it to its former working state.

The pair are hoping to restore the equipment to perform dark matter experiments, but the refrigerator hasn’t been in use since about 2016 (and doesn’t have an instruction manual), which is a long time for a piece of specialty scientific equipment to be collecting dust. The first step is to remove wiring and clean it of all the grime it’s accumulated in the last decade. After that, the pair work to reassemble the layers of insulation around the main cooling plate and then hook up a vacuum pump to the device which also needed some repair work.

The critical step at this point is to evacuate the refrigerant lines so they can be filled with expensive Helium-3 and Helium-4. The problem is that there’s still some of this valuable gas in the lines that needs to be recovered, but the risk is that if any air gets into the cold section of the refrigerator it will freeze and clog the whole system. After chasing some other electrical and vacuum gremlins and discovering a manual from a similar refrigerator, they eventually get it up and running and ready for new scientific experiments. While most of us won’t discover a fridge like this cleaning out our attics, this refrigerator powered by rubber bands is a little more accessible to the rest of us.

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FLOSS Weekly Episode 770: 10% More Internet

February 14, 2024 by Jonathan Bennett 7 Comments

This week, Jonathan Bennett and Doc Searls talk with David Taht about the state of the Internet and, specifically, IPv4 exhaustion. We’re running out of IPv4 addresses! But we’ve been running out for something like ten years now. What gives? And why are nearly 20% of the world’s IPv4 addresses sitting unused? David has a hack that would give the world 10% more Internet, but Amazon might have something to say about it.

There’s even more, like Kessler Syndrome, some musing on what the Interplanetary Internet will look like, the worth of real paper books, and a long-term bet for some IPv4 addresses to come to fruition in 2038.

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EasyThreed K9: The Value In A €72 AliExpress FDM 3D Printer

February 12, 2024 by Maya Posch 27 Comments

The hot end of the EasyThreed K9 is actually pretty nifty. (Credit: [Thomas Sanladerer])

Recently, [Thomas Sanladerer] bought an EasyThreed K9 off AliExpress for a mere €72, netting him an FDM printer with a 10 x 10 x 10 cm build volume. The build plate is unheated, with optional upgrade, and there is no display to interact with the device: just a big multi-function ‘play’ button and five smaller buttons that direct the print head to preset locations above the build plate to allow for build plate leveling using the knobs on each corner. There’s also a ‘home’ button on the back for homing the print head, which pretty much completes the user interface. As the printer comes in a rather small box, the first step is to assemble the parts into something resembling a 3D printer.

What follows is both a mixture of wonder and horror, as the plastic build quality is everything but convincing, while at the same time, the self-contained nature of each of the three axes of the cantilevered design makes for very easy assembly. The print head has a nifty flip-up cover for easy access to the hot end, which makes the best of the anemic 24-watt power supply for the entire printer. A cooling fan with an air duct even provides part cooling, making this print head a contender for the ‘cheap but not terrible’ category. You can check out his full video review below.

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