Retro Computer Trainer Gets A Raspberry Pi Refit

We know what you’re thinking: this is yet another one of those “Gut the retro gear for its cool old case and then fill it up with IoT junk” projects. Well, rest assured that extending and enhancing this 1970s computer trainer is very much an exercise in respecting the original design, and while there’s a Pi inside,  it doesn’t come close to spoiling the retro goodness.

Like many of a similar vintage as [Scott M. Baker], the Heathkit catalog was perhaps only leafed through marginally less than the annual Radio Shack catalog. One particularly desirable Heathkit item was the ET-3400 microcomputer learning system, which was basically a 6800-based computer surrounded by a breadboarding area for experimentation. [Scott] got a hold of one of these, but without the optional expansion accessory that would allow it to do interesting things such as running BASIC or even supporting a serial port. So [Scott] decided to roll his own expansion board.

The expansion card that [Scott] designed is not strictly a faithful reproduction, at least in terms of the original BOM. He turned to more modern — and more readily available — components, but still managed to provide the serial port, cassette interface, and RAM/ROM expansion of the original unit. The Raspberry Pi is an optional add-on, which just allows him to connect wirelessly if he wants. The card fits into a 3D-printed case that sits below the ET-3400 and maintains the original trainer’s look and feel. The longish video below shows the build and gives a tour of the ET-3400, both before and after the mods.

It looks as though trainers like these and other artifacts from the early days of the PC revolution are getting quite collectible. Makes us wish we hadn’t thrown some things out.





11 thoughts on “Retro Computer Trainer Gets A Raspberry Pi Refit

  1. I’m tired of hearing about all these projects where somebody guts a retro case and crams a RasPi inside!

    It is like a Hollywood movie, where each movie is the same as the last, just rearranged some.

    1. He does a lot more than that: ” The Raspberry Pi is an *optional* add-on, which just allows him to connect wirelessly if he wants.”

      I found the build and schematics etc. quite interesting. Watching projects like these helps revise and refine your knowledge,

    2. Funny, that the first sentence in the article adresses exactly this, by explaining the this isn’t whats happening here. And the Link provides a profound insight, that the original kit isn’t touched whatsoever. Talk about kneejerk comment…

    3. Yeah, well RTFA. The ET-3400 has an expansion header but the expansion unit is rare. [Scott] designed a more modern version of the expansion unit with an optional RasPi for wireless connectivity and the ET-3400 itself is unmodified. I’m going to be thinking hard about building one of these for my ET-3400.

  2. I have a couple of the old IC trainers – I think the one I put together combines digital & analog but might be mistaken – then I have another model that is still in the original shipping box – guess someone will get a couple of collector items sometime –

    Never got very far with the texts – but did use the trainer for several other projects when I needed a test bed – nice trainer

    1. I have about 6 of these old Lab-Volt 6502 trainers.
      (the local Vo-Tech was clearing out their Electronics Lab a decade ago).
      They came with LOTS of peripheral boards (i.e. serial, parallel, disk controller, IEEE 488?), that daisy chain together, as well as the “racks” and power supplies.
      One of the peripheral boards has a breadboard for additional experiments.
      TBH, the hardest thing to obtain (for me) was the classroom and instructor texts.
      I don’t see them listed on the WorldWideGarageSale anymore.

  3. Must be love to go through all that work only to run Tiny BASIC. -12V is for Op amps too. Snicker. Some folks bitched there wasnt a -5V and insufficient current on all rails. Could have gone old school 1488/9 for the bit bang 232. White cer-dip sure is purty. Discolorations probably part tobacco smoke, sweat, tears, and blood. Blood may have been sacrificial offerings to the digital gods. Didnt see any pentagrams, seals, or angelic script so possibly safe.

    1. But at the time, adding the extras and TinyBasic gave you a reasonable computers.

      The problem was that they weren’t intended for expansion, so it was messy. I remember articles about expanding the KIM-1 that were so extensive that one might as well build a cpu board.

      I used a breadboard with my KIM-1, but never built a formal box. I suppose I’m now obligated to add a Raspberry Pi to it, or to my 8085 board from Intel.

      1. Its silly unless theres some specific reason for expanding mostly extinct dinosaurs. Historical, Nostalgia ,mountain climbing , and love likely the only excuses to invest resources. Raspberry PI
        Zero has seemingly boundless capability compared to venerable mc6800.
        KIMs were Revolutionary CPU boards. Wonderfully cheap so had some cash left over to expand and play on private/hobbiest level. Hassle free compared to quite a few ‘eval’ boards of the time. Boxes? Dont need no stinking boxes. Thats for suits, investors and other that couldnt differentiate cow and silicon chips.

  4. Neat project. But as above “must be love to go through all that work …” . We all have different hobbies that turn our cranks. Go for it!

    Personally I have no problem gutting an old obsolete computer and ’emulating’ the functionality of the old or just using the case for something ‘new’. I don’t see the big deal. If I run into a C64 or some such … and I felt up to it…. that is what would happen here — go retro-fit :) .

  5. I have an ET-3400 and the ETA-3400 expansion unit is basically unobtanium, with rare eBay appearances going for $300-$400. I’ve pondered what it would take to roll my own. Gotta love Hackaday for serving up that one other guy out there that needs this more than I do. 😁 I’ll definitely take a look at this. Why? Because retro!

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