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Kenbak-1 Replica

Functional replica of the world’s first personal computer.

Details

The Kenbak-1 is the world’s first personal computer in the world, born 4 years before the Altair 8800, and that you probably never heard of. I ran across it randomly while searching for a simple vintage computer with LED and switches that I could easily write an Arduino emulator for, since this is the first emulator I wrote.
I discovered the Kenbak-1 just before my high school ending exams (which impacted my revisions quite a bit) and I fell in love with it! ❤️ Its design, its simplicity, its clear instruction set well separated by octal digits are many reasons that make me like this computer.

An original Kenbak-1

The Kenbak-1 was designed and marketed by John Blankenbaker in 1971. The first microprocessor, the Intel 4004, was also marketed in 1971. Thus, the Kenbak-1 doesn’t have a microprocessor and all the logic was implemented with TTL logic integrated circuits. In fact, you can find all the logic schemas in the book “Theory of Operation”.

John Blankenbaker and its Kenbak-1
Part of the Kenbak-1’s publications: schemas, flowcharts…

With a device as attractive as the Kenbak-1, I needed one! Sadly, a bit less than 50 devices were made in total, before Kenbak Corporation ended. In 2015, a Kenbak-1 was sold at an auction for more than $40,000! I must tell you I’d prefer to buy a MX-5 RF at that price! 😃
Now I just have to make a replica. Grant Stockly made real replicas at some point, but he’s not giving any sign of life and his replicas cost several hundred dollars because they were identical to the original Kenbak-1.

Beautiful replica by Grant Stockly

So I wanted to make a low-cost replica, with modern components, which allows, beside reducing the cost and the size of the replica, to appreciate the technological evolution of the last 50 years or so.
My second semester project’s of my DUT coming, I proposed the idea to my friends to make this replica, which allowed me to work on the replica on my project hours and to have access to my school’s equipment to make the PCB.

The electronic circuit made at the IUT and the case

A first prototype was made entirely on breadboards, the electronic circuit being really simple thanks to today’s technology.

Prototype on breadboards with its multiple overlay iterations
PCB tested with the prototype

The case is made with high-impact polystyrene, which got thermally folded, with its two aluminum handles milled.
The front plate is in plastic and was also cut with a numerically controlled milling machine. An A3 paper printed, cut, laminated and glued onto the plate serves as an overlay trying to mimic the original metallic front plate of the Kenbak-1.
The keys are mechanical Gateron blue keys that make a lot of noise (vintage!). Keycaps are translucid ones painted from the inside in black or white with acrylic paint.
The mini halogen bulbs were replaced by LEDs with small plastic supports for a great finish.

Only the keycaps are missing!

The back plate is transparent and gives access to the micro-USB charging port because yes, that Kenbak-1 is a laptop! You can see through that plate the PCB on which the I/O extender (MCP23017), LED controller (TLC5940), buttons, switches and LEDs are placed. We can also see the Arduino, shamefully mounted on a breadboard (I really must spend some time making a proper motherboard).

The emulator is entirely handmade and its code is available on the GitHub repo.

Replica finished!

It’s not as cool as the original (plastic) but it works the same, has the same front dimensions and only costs about $30. At least now, I have a Kenbak-1 on my shelf that I can program games on when I get bored (okay I rarely get bored…)!