retrocomputing

322 Articles

Building A MiniPET Is Better With Friends

July 17, 2023 by 4 Comments

[Taylor and Amy] love taking on retro computer projects. This week they’re building a MiniPET from Tynemouth and The Future is 8 Bit.  It’s a pretty awesome kit which sadly isn’t available anymore. Taylor bought one of the last ones as part of a charity sale at the 2023 Vintage Computer Festival Southwest.

If you haven’t seen their YouTube channel yet, check it out! The two have been best friends since 1984. Their channel has just the right mix of education and comedy, with pacing fast enough to keep things interesting. It’s really refreshing to see two people enjoying a project together.

The MiniPET is of course a reproduction of the hardware in the Commodore PET, the machine which predated the VIC-20 and of course the Commodore 64. The kit starts with installing a few discrete parts — resistors,  capacitors, and diodes.  Then come the IC sockets. [Taylor and Amy] ran into a bit of trouble when it came time to install the chips. While installing the 40-pin 65C21 Peripheral Interface Adapter (PIA), one pin bent under the socket. [Taylor] popped the chip back out, and replaced it — which resulted in 3 bent pins!

Anyone who’s installed new DIP parts has been through this. The pins are always bent out a bit from the factory. The old “Bend it in using a table” method usually works — but if you want perfect pins, try a pin straightener. These versatile tools can even be 3D printed.

Once the pin problems are solved, it’s time to power up the kit and see if it will work.  That’s when we get to see that magic moment when a project first comes to life. Check out the video – you’ll see what we mean.

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Reverse-Engineering Helps Typesetting Machine Punch Paper Tape Again

July 11, 2023 by 14 Comments

[Scott M. Baker] wants a paper tape punch for his retrocomputer collection. That’s fine with us, we don’t judge. In fact,  these electromechanical peripherals from the past have a lot going for them, especially the noise. But alas, such things are a little hard to come by these days, and rolling one from scratch would be a difficult proposition indeed. What to do?

Luckily, we live in the future, and eBay holds all sorts of wonders, including these typesetter keyboards from the 1970s, which [Scott] promptly reverse-engineered. We’ll get to the details in a minute, but first, can we just take a moment to think about the workflow these things were part of? These aren’t terminals — they lack any kind of IO apart from the punched paper tape they spewed out. The operator’s job was to punch in copy without any kind of feedback that they were hitting the right keys, and just sent the paper tap record of the session off to the typesetting machines. And you think your job sucks.

To give this thing an interface, [Scott] first had to revive the power supply, whose capacitors had seen sunnier days. With that out of the way, he set about understanding the CPU-less machine by analyzing its 7400-series logic, as well as planning how to make the native 6-bit output into a more manageable 8-bit. Thankfully, the tape punch already had solenoids for the top two bits, but finding a way to drive them wasn’t trivial.

The solution was to bypass a buffer so that the bits for the desired character can be set with a Raspberry Pi and an ATF22V10 programmable logic device. That’s enough to force the punch to do its thing; actually getting it to talk to something else, perhaps even [Scott]’s Heathkit H-8 computer.

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Bringing Back The Minitel

June 19, 2023 by 16 Comments

If you didn’t live in France in the 80s or 90s, it’s likely you missed out on one of the most successful computer networks in existence prior to the modern Internet. Known as Minitel, it was an online service available over existing phone lines that offered a connected computer terminal for users to do most things we associate with the modern world, such as booking travel, viewing news, looking up phone numbers, and plenty of other useful activities. While a lot of the original system was never archived, there are still some efforts to restore some of its original functionality like this MiniMit.

The build requires either an original or a recreation of a Minitel terminal in all its 80s glory, but pairs an ESP32 to support modern network connectivity. The ESP32 interfaces with the Minitel’s DIN socket and provides it with a translation layer between WiFi and the networking type that it would have originally expected to see from the telephone lines. Two of the original developers of Minitel are working on restoring some of the services that would have been available originally as well, which means that the entire system is being redeveloped and not just the original hardware.

We’ve mentioned that this system was first implemented in the 80s, but the surprising thing is that even well after broadband Internet would have been available to most people in France, the Minitel system still had widespread use, not being fully deactivated until 2012. They remain popular as inspiration for other projects as well, like this one which was brought a little more up-to-date with the help of a modern display and Raspberry Pi.

If Not Ethernet…

June 17, 2023 by 64 Comments

It is hard to imagine today, but there was a time when there were several competing network technologies. There was Ethernet, of course. But you could also find token ring, DEC Net, EcoNet, and ARCNet. If you’ve never dug into ARCNet, [Retrobytes] has a comprehensive history you can watch that will explain it all.

Like token ring, ARCNet used a token-passing scheme to allow each station on the network to take turns sending data. Unlike token ring and Ethernet, the hardware setup was much less expensive. Along the way, you get a brief history of the Intel 8008 CPU, which, arguably, started the personal computer revolution.

Like most networking products of the day, ARCNet was proprietary. However, by the late 1980s, open standards were the rage, and Ethernet took advantage. Up until Ethernet was able to ride on twisted pairs, however, it was more expensive and less flexible than ARCNet.

The standard used RG-62/U coax and either passive or active hubs in a star configuration. The coax could be up to 2,000 feet away, so very large networks were feasible. It was also possible to share the coax with analog videoconferencing.

Looking back, ARCNet had a lot to recommend it, but we know that Ethernet would win the day. But [Retrobytes] explains what happened and why.

If you missed “old-style Ethernet,” we can show you how it worked. Or, check out EcoNet, which was popular in British schools.

Persistence Pays In TI-99/4A Cassette Tape Data Recovery

June 16, 2023 by 11 Comments

In the three or four decades since storing programs on audio cassettes has been relevant, a lot of irreplaceable personal computing history has been lost to the ravages of time and the sub-optimal conditions in the attics and basements where tapes have been stored. Luckily, over that time we’ve developed a lot of tools and techniques that might make it possible to recover some of these ancient treasures. But as [Noel] shows us, recovering data from cassette tapes is a tricky business.

His case study for the video below is a tape from a TI-99/4A that won’t load. A quick look in Audacity at the audio waveform seems to show the problem — an area of severely attenuated signal. Unfortunately, no amount of boosting and filtering did the trick, so [Noel] had to dig a bit deeper. It turns out that the TI tape interface standard, with its redundant data structure, was somewhat to blame for the inability to read this particular tape. As [Noel] explains, each 64-bit data record is recorded to tape twice, along with a header and a checksum. If neither record decodes correctly, then tape playback just stops.

Luckily, someone who had already run into this problem spun up a Windows program to help. CS1er — our guess would be “Ceaser” — takes WAV file input and loads each record, simply flagging the bad ones instead of just bailing out. [Noel] used the program to analyze multiple recordings of the same data and eventually got enough good records to reassemble the original program, a game called Dogfight — or was it Gogfight? Either way, he managed to get most of the data off the tape, and since it was a BASIC program, it was pretty easy to figure out the missing bytes by inspection.

[Noel]’s experience will no doubt be music to the ears of the TI aficionados out there. Of which we’ve seen plenty, from the TI-99 demoscene to running Java on one, and whatever this magnificent thing is.

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Crafting Ribbon Cables For Retro Hardware

June 10, 2023 by 23 Comments

Building a modern computer is something plenty of us have done, and with various tools available to ensure that essentially the only thing required of the end user is to select parts and have them delivered via one’s favorite (or least expensive) online retailer. Not so with retro hardware, though. While some parts can be found used on reselling sites like eBay, often the only other option is to rebuild parts from scratch. This is sometimes the best option too, as things like ribbon cables age poorly and invisible problems with them can cause knock-on effects that feel like wild goose chases when troubleshooting. Here’s how to build your own ribbon cables for your retro machines.

[Mike] is leading us on this build because he’s been working on an old tower desktop he’s calling Rosetta which he wants to be able to use to host five different floppy disk types and convert files from one type to another. Of course the old hardware and software being used won’t support five floppy disk drives at the same time so he has a few switches involved as well. To get everything buttoned up neatly in the case he’s building his own ribbon cables to save space, especially since with his custom cables he won’t have the extraneous extra connectors that these cables are famous for.

Even though, as [Mike] notes, you can’t really buy these cables directly anymore thanks to the technology’s obsolescence, you can still find the tools and parts you’d need to create them from scratch including the ribbon, connectors, and crimping tools. Even the strain relief for these wide, fragile connectors is available and possible to build into these projects. It ends up cleaning up the build quite nicely, and he won’t be chasing down any gremlins caused by decades-old degraded multi-conductor cables. And, even though [Mike] demonstrated the floppy disk drive cables in this build, ribbon cable can be used for all kinds of things including IDE drive connectors and even GPIO cables for modern electronics projects.

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Magnetic Bubble Memory Brought To Life On Heathkit

June 9, 2023 by 11 Comments

There are all kinds of technology that appear through the ages that find immediate success, promise to revolutionize the world, but fade to obscurity almost as quickly. Things like the ZIP disk, RDRAM, the digital compact cassette, or even Nintendo’s VirtualBoy. Going even further back in time [smbaker] is taking a look a bubble memory, a technology that was so fast and cost-effective for its time that it could have been used as “universal” memory, combining storage and random-access memory into a single unit, but eventually other technological developments overshadowed its quirks.

[smbaker] is placing his magnetic bubble memory module to work in a Heathkit H8, an Intel 8080-based microcomputer from the the late 70s. The video goes into great detail on the theory of how these devices used moving “bubbles” of magnetism to store information and how these specific devices work before demonstrating the design and construction of a dedicated support card which hosts the module itself along with all of the necessary circuitry to allow it to communicate with the computer. From there he demonstrates booting the device using the bubble memory and performs several write and read actions using the module as a demonstration.

Eventually other technologies such as solid-state RAM and various hard disk drives caused the obsolescence of this technology, but it did hang on for a bit longer in industrial settings due to its ability to handle high vibrations and mechanical shocks, mostly thanks to the fact that they had no moving parts. Eventually things like Flash memory came around to put the final nail in the coffin for these types of memory modules, though. The Heathkit H8 is still a popular computer for retrocomputing enthusiasts nonetheless, and we’ve seen all kinds of different memory modules put to work in computers like these.

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