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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.

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.

Here is a list of the additional parts that you will require to build GENIAC machines:

50 feet Wire - I used solid 22 AWG hookup wire
1 1.5V D Cell Battery
1 Battery Holder - Digi-Key part number 36-175-ND
10 Bulbs - Amazon - Pack of 10 E10 Miniature Screw Base Light Bulb
10 Sockets for Bulbs - Amazon - E10 Mini Bulb Holder
100 Slotted Brass Bolts, #6 - 32, 1/2 inch
200 Nuts, #6 - 32, 1/4 x 3/32 inch
1 On-Off Switch - Amazon - SEOH Knife Switch Single Pole Single Throw
6 Bolts, 3/16 inch, 1 1/4 inch - To mount the Switch Tops
12 Nuts, 3/16 inch - To mount the Switch Tops
3 feet 12 AWG bare copper wire
1 2 x 2 foot sheet of 3 mm hardboard
A few miscellaneous nuts and bolts”

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