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Picture of GENIAC (Electric Brain) Replica

GENIAC, which stood for "GENIus Almost-automatic Computer", was an educational toy billed as a "computer" sold from 1955 through the sixties for about $20. Designed and marketed by Edmund C. Berkeley, with Oliver Garfield, it was widely advertised in science and electronics magazines. GENIAC provided many youths of the day with their first exposure to computer concepts and Boolean logic.

Sold as a kit, GENIAC consisted of a Masonite back panel with six areas of concentric perforations, six similarly perforated Masonite disks, and some additional hardware listed in the supplies section below.

Slotted brass bolts were positioned on the main back panel in such a way that brass "jumpers" inserted into the underside of the Masonite disks would create electrical connections when the disks were rotated over them. The bolts were wired together along with a battery and some lights to create "programs", basically single purpose "machines".

Technically GENIAC was a collection of configurable N-pole by N-throw rotary switches, which could be set up to cascaded and thus perform logical functions. As a result GENIAC could use combinational logic only, its outputs depending entirely on inputs manually set. However, projects outlined in the manual, which started with basic logic circuits, ultimately progressed to such things as a NIM machine and TIC-TAC-TOE machine.

You can find more information about GENIAC at the following links:

Here is a wonderful video the shows how some of the projects from the GENIAC manual could be interpreted as interactive narratives:

I have included PDFs of all of the original GENIAC manuals. These are a great reference where you will find the plans to build many cool GENIAC "machines".

This Instructable outlines how I made my GENIAC Replica, and includes all the CAD files and instructions necessary so that you can make one too. I did not have an original model to work from as they are quite rare and fairly expensive (if you can even find them on the vintage markets). My replica is based on the GENIAC manuals and photos available online.

There are two models presented here. The "Classic" version as seen above is a pretty close facsimile to the original GENIAC. I've used hardboard instead of Masonite for the base and disks, and the jumpers are not brass plates but are mostly 3D printed. Otherwise I was able to source parts that pretty closely match the pictures online. With the second version presented later in this Instructable, I have taken some liberties to improve on the original, especially with respect to the reliability of the mechanical switches.

Step 1: Create the Main Board and Switch Tops

Picture of Create the Main Board and Switch Tops

Using the attached "cut" files, create one Main Board and six Switch Tops. I used 1/8 inch (3 mm) hardboard which I laser cut at my local maker space (check out the awesome Kwartslab). I haven't tried it, but you should be able to mill these pieces as well. I would not recommend trying to manually produce them as the precision required for the switches to work reliably is quite high.

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temple run
hugheswho22 days ago
DiegoD5723 days ago
It is far beyond excellent! That is exactly the kind of project I like to see on Instructables. Thanks for sharing.
megardi (author)  DiegoD5723 days ago
I make these mostly for myself, but its really great that other people like them too. Thanks.
larry0305223 days ago
If you are interested in Geniacs you must've seen Digi-Comp I. Are you aware of You can buy their re-engineered, modern version of the classic Digi-Comp I for a quite-reasonable price.
megardi (author)  larry0305223 days ago
I had a Digi-Comp I as a kid. A few years back I purchased the Minds-On Toys version. More recently I built this version from Thingiverse:

This is what actually got me interested in making replicas of these great old devices.
rafununu24 days ago
When I was a kid, my parents offered me a construction game by Philips called Mechanical Engineering Kit ME1201. I spent so many hours bulding cranes, 4WD cars and a lot of things, that I recently bought 2 (but not complete) on Ebay. There are wheels with holes to insert pins, springs, axles, all of different sizes, a perfect base to build mechanical protos. I'm going to make your converter and will post a picture. Thanks a lot for this diving in the past.
rock0625 days ago
it looks complecated
megardi (author)  rock0624 days ago
It’s not too bad once you start wiring things together. You just have to follow the plan for each “machine”.
Racer1TN25 days ago
I too had one of these as a kid in the 60's. My grandfather got it for me, what a blast from the past. I remember building things and making the lights change. Too cool to find this! I still have some of the little brass jumpers and the insulators.
megardi (author)  Racer1TN24 days ago
I didn’t ever have one of these growing up but I remember wanting one. Only took me 50+ years to accomplish that goal :-). My 60’s toy was a Digi-Comp I and thanks to this Thing:

I have a new one of those now too. Thanks for sharing.
It composes music, forecasts the weather and demonstrates quantum mechanics? Wow :)
megardi (author)  needfulthing1 month ago
There was a bit of hyperbole in their advertising for sure.
fdavison1 month ago
Man, that brings back memories! I had one of those when I was about ten years old. Thanks for posting this!
megardi (author)  fdavison1 month ago
Thank you for sharing.
billbillt1 month ago
I remember these!.. thanks for sharing..........
mje1 month ago
Fantastic! I had a Geniac when I was a child. I’ve occasionally thought of trying to reproduce it, but as you note, the precision required for the drilling is a bit daunting- and no doubt the reason for the price of the original.
megardi (author)  mje1 month ago
I’ve wondered about the price. $20 in 1955 is about $191 in today’s dollars. My time aside all of the materials and parts came to maybe $30 for the “Classic” version. So maybe the labor of creating the base and disks plus they did a lot of advertising explains the difference. Or maybe they just had a great profit margin :-).

Having access to a laser cutter certainly made the difference for me when I decided to tackle this project.
Alex in NZ1 month ago
Wow! Impressive recreation of an impressive original. Thank you for sharing all you've done to make this available. :-)
megardi (author)  Alex in NZ1 month ago
Thanks Alex!