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:

• Wikipedia
• Old Computer Museum
• The Computer Museum

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.

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

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.

Print Resolution: .3 mm

Infill: 20%

Perimeters: 2

Filament: AMZ3D PLA

Notes: All parts were printed in PLA. For best results you should print the parts in the default orientation. The Wire Jumpers and Stand pieces will need supports.

To build a Classic GENIAC machine you will need to print the following:

• 20+ Wire Jumper - You may need more for some "machines".
• 6 Disk Spacer
• 12 Washer
• 20+ Locking Tab
• 6 Locking Tab With Pointer
• 2 Stand

Despite looking at many online images, and scouring the GENIAC manual I was never able to find a picture of what the brass jumpers looked like. The manual describes pushing the jumper "arms" through adjacent holes along a spoke on the disks and bending them over to hold the jumper in place (see the excerpt from the manual above). Also I believe that various versions of GENIAC used slightly different types of jumpers. So in the end, after some trial and error, I designed and 3D printed my own. They seem to work reasonably well.

Update August 10, 2019 Al Williams from Hackaday was kind enough to send me a photo (seen above) of a brass jumper from his GENIAC. I'm going to try to make a few and will update this Instructable with my results.

Update August 12, 2019 Again thanks to Al Williams a possible source for the jumpers:

Weaver Leather Supply - Loop Staples

I've ordered some and will try these before attempting to make my own.

After you have carefully removed the supports from the 3D printed Wire Jumper parts, you need to attach a short length of copper wire to the underside. This is what will complete the circuit between pairs of brass bolt heads mounted on the main board.

I used the 12 AWG bare ground wire from a short length (about 3 feet) of house wiring. Cut from this pieces about 16 mm long, making sure that they are as straight as possible.

Attach the wire to the shallow groove in the bottom of the printed Wire Jumper pieces as in the photo above. I used a liquid gel super glue for this and it worked well. Note: Be careful not to get glue on the exposed part of the wire. I spent some time "debugging" my first GENIAC "machine" only to finally realize that one of the copper wires was coated with a thin layer of invisible insulation since the glue I used dries clear!

If you have completed the previous steps, and acquired the other parts, you should be ready to create a GENIAC machine. I built "THE TRANSLATOR FROM BINARY TO DECIMAL" project found on page 40 of the "Manual for Geniac Electric Brain Construction Kit", with the wiring diagram on the last page of the "Supplementary Wiring Diagrams" booklet. The completed machine can be seen below.

Start by inserting the brass bolts into the base board from the top in the positions indicated by the black dots on the diagram. Hold them in place with a single nut from below tightened enough so that the bolt will no longer turn in place. Be sure that the slots on the heads of the bolts are precisely aligned with the center point of the cluster. The second picture above is for the 1's switch area of the base. Place a second nut loosely on the bolt. This will be used to hold the wires in place.

Install the battery holder, light socket, and blade switch onto the main board. I used some M3 x 8 mm bolts and nuts for the battery holder, and 1/8 inch x 1 inch bolts and nuts for the other two. See the main photo at the top of the Instructable for a suggested placement.

Use the diagram above to wire the machine. The wires should be firmly held in place between the two nuts on the back of each bolt. With few exceptions there will only be one wire attached to each bolt. The third picture above is the back of the Binary to Decimal Translator fully wired.

Once the wiring was done I attached the two Stand pieces to either side of the main board with M3 x 8 mm bolts.

Attach the Wire Jumpers to the undersides of the Switch Top disks. On the diagram the appropriate spots are indicated with small rectangles. Push the legs of the jumpers through the holes of the disk from the bottom and secure them in place with the Locking Tabs on the tops (one of which should be a Locking Tab With a Pointer). The last two pictures above show the underside and the top of the 1's switch.

Mount the switch tops to the main board with the 3/16 inch x 1 1/4 inch bolts. Slide one of the washers onto the bolt followed by the switch top and a Disk Spacer. Push this assembly through the appropriate hole in the base and hold it in place with a second washer then two nuts (the second acting as a lock washer). The switch top should rotate freely and you should feel and hear a "click" when the Wire Jumpers snap into the slots on the bolt heads.

Screw a light into the socket and insert a battery into the holder. I printed labels onto some removable label stock, cut them out, and attached them to the main board as appropriate.

Turn on the machine. If you have built the Binary to Decimal Translator as I did, you can test it by setting the four binary switches to either one or zero (say to 1100 for example) then turning the decimal switch slowly until the light turns on. The number pointed to when the light goes on is the decimal equivalent (12 in this case).,

You should hear an audible click and feel the switch lock in place when you have correctly lined up the jumpers and the bolt slots. If your machine does not work as expected start by checking the wiring. Use a multi-meter to verify each of the connections. Make sure that when the switch is locked in place the expected bolt pairs conduct a current. As already mentioned make sure the jumpers do not have excess glue insulating the copper wire.

Despite the fact that my 3D printed jumpers worked way better than expected, they are not 100% reliable. Anecdotally I understand that the original GENIAC was not any better. I wanted to apply some lessons that I learned from building my Mostly 3D Printed Rotary Switch.

So GENIAC Redux was born. The brass bolts have been replaced by magnetic reed switches and the jumpers with magnets. Additional magnets are employed to create the "detents" or "stops" to make sure that the reed switches and magnets align at the proper positions. I used "markerboard", hardboard with a dry erase surface on one side, for the base and switch disks. Finally just for fun I designed my own battery and switch holders.

So in addition to the parts required for a "Classic" GENIAC you will need the following:

• 100 M3 x 8 mm brass bolts
• 200 M3 nuts
• 20+ Reed Switches - Digi-Key part number 2010-1087-ND
• 40+ Disk Magnets - 6 mm (diameter) x 3 mm (height)
• 3 feet of 22 AWG copper wire
• 1 DPDT Panel Mount Slider Switch - (optional) Found at a surplus store cheap. The mounting holes should be 28 mm apart center to center.
• 1 2 x 2 foot sheet of 3 mm markerboard (optional) You could use any 3 mm board.

Note: If you are only building a Redux you don't need the #6 - 32, 1/2 inch bolts or nuts or the 12 AWG wire from the "Classic".

Print the following:

• 1 Battery Holder - (optional) You could use the one from the "Classic" or any other one available
• 1 Switch Holder - (optional) You could use the switch from the "Classic"
• 1 Switch Label - (optional) Pause the print at the 1.1 mm mark to change filament for the text
• 40+ Magnetic Jumper - I strongly suggest printing half in one color and the rest in a different color
• 20 Pole Bottom
• 20 Pole Top
• 40+ Locking Tab (from the Classic version)
• 2 Stand (from the Classic version)

When the Magnetic Jumpers have been printed, populate them with the disk magnets. The reason that I suggest using two colors for these is so that you can insert all the magnets into one color of the Magnetic Jumpers with one polarity, and the use the opposite polarity for all the others. This way the different color Magnetic Jumpers will always attract making it easier when you are setting up the switches later. My magnets friction fit pretty well. Use a bit of glue as necessary.

Insert the magnetic reed switches into the Pole Top printed pieces. Start by cutting short lengths (about 1 inch) of 22 AWG solid wire. Slide two pieces of wire into the shaft holes of the Pole Top. Bend the leads from the reed switches in towards the center until they are at about a 30 degree angle to the bottom. Line the wires from the Pole Top up with the bent leads and solder them together. Try not to leave too much excess solder. The second photo above shows the setup just prior to soldering. Gently press the reed switch down towards the Pole Top until it rests part of the way into the slot. Image three show what this should look like when done. At this point its a good idea to test the reed switch with a multi-meter and magnet to make sure it's working as expected.

Attach the two Battery Holder pieces together. I used small eyelets but you could just as easily glue them.

Assemble the Switch Holder. The Slider Switch is mounted from beneath held in place along with the Switch Label on top by two M3 x 8 mm bolts and nuts.

For this example I chose the "THE FOX, HEN, CORN, AND THE HIRED HAND - THE FARMER'S MACHINE" project found on page 14 of the "Manual for Geniac Electric Brain Construction Kit", with the wiring diagram in the "Supplementary Wiring Diagrams" booklet. The completed machine can be seen below.

In this case, for each pair of adjacent black dots on the diagram, we will be inserting a Pole Top piece assembled in the previous step from the top of the main board. From the underside of the board slide a Pole Bottom over the shafts protruding through the holes. Screw two of the M3 x 8 mm bolts part way into the Pole Bottom holes. Wrap the wires from the magnetic reed switch around the bolt between the Pole Bottom and the head, then secure the bolt in place with an M3 nut. Loosely screw a second nut onto the bolts to be used when attaching wires. See the second photo above for details. It's a good idea at this point to double check that the reed switch is working properly using a multi-meter.

Install the battery holder, two light sockets, and the switch onto the main board. I used some M3 x 8 mm bolts and nuts for the battery holder and switch, and 1/8 inch x 1 inch bolts and nuts for the two light sockets. Use photo three as a guide to placement.

Use the diagram above to wire the machine. The wires should be firmly held in place between the two nuts on the back of each bolt attached to the Pole Bottoms. With few exceptions there will only be one wire attached to each bolt. The fourth picture above is the back of the Farmer's Machine fully wired. Once the wiring was done I attached the two Stand pieces to either side of the main board with M3 x 8 mm bolts.

Attach the Magnetic Jumpers to the undersides of the Switch Top disks. On the diagram the appropriate spots are indicated with small rectangles. Push the legs of the jumpers through the holes of the disk from the bottom and secure them in place with the Locking Tabs on the tops (one of which should be a Locking Tab With a Pointer).

Additional magnets are attached to the main board and to the underside of the switch tops to act as "detents" or "stops" so that the reed switches and magnets line up properly when the switch is rotated. These detent magnets are installed in pairs so that the pull on the switch is balanced. The fifth picture above shows the main board top for the corn area with the reed switches and detent magnets attached. The corresponding corn switch can be seen from the bottom in the last photo with the grouped pair of magnets acting as jumpers and the two additional magnets for the detents. Notice that I am using different colored Magnetic Jumpers for the base and switch to ensure that the polarity for each will be different an thus will attract when aligned.

As with the Classic GENIAC mount the switch tops to the main board with the 3/16 inch x 1 1/4 inch bolts. Slide one of the washers onto the bolt followed by the switch top and a Disk Spacer. Push this assembly through the appropriate hole in the base and hold it in place with a second washer then two nuts (the second nut acting as a lock washer). The switch top should rotate freely. In this case you will not hear a click but will definitely feel when the magnets align with their corresponding opposites.

Screw lights into the sockets and insert a battery into the holder. I used markerboard for this project so that the labels could be written directly onto the surface with dry erase markers.

Turn on the machine. Try rotating the various switches between Barn 1 and Barn 2. You should feel the switches snap into place when they are aligned properly. If the Fox and Hen or the Hen and the Corn are ever in a barn without the Man the Danger light should turn on. Otherwise the Safety light will be on. Unlike the Classic machine, you should never have an issue with the reed switch not making proper contact. If there are problems check the wiring.

There was a lot of hyperbole in the marketing literature for GENIAC:

The devices you can build test intelligence, code and decode, count, play Tic-Tac-Toe, solve problems, and now compose music!

I mean they called it an Electric Brain. That sets a pretty high bar. I'm sure that there were many eager recipients that were disappointed with the reality of GENIAC. However, the kit as sold was not without its merits. Since it did not require soldering and was battery powered it was accessible to a large audience, especially children say 12 and older. GENIAC was certainly a reasonable tool for teaching electric circuits, Boolean logic, as well as binary and decimal arithmetic. Plus as postulated in his lecture "I sing the story Electric" (linked above) Brian Moriarty points to GENIAC as an early example of interactive narrative. Without a doubt GENIAC was an important early (1955) step on the road to general computer literacy.

As with my other replica projects my goal here is to shed some new light on an important part of our non-digital computer related past. Kudos to Edmund C. Berkeley and Oliver Garfield for their work. I'm sure that GENIAC helped to set a significant number of young people on the road to computer related careers.