How to make a computer from a cereal box

One of the things I’ve returned from sabbatical determined to do, is learn to code. I’ve always been interested in computers, but I’ve never been a coder. I’ve decided it’s high time I started, as I want to be able to create stuff, data-mine and sharpen my research skills. In planning to put this right, I started thinking about my earliest experience with computing. It came in the shape of a cornflakes box.

When I was a kid, I learned how to make a programmable computer using nothing more than an old cereal packet and some handmade punch cards. It’s a really great project for a kid aged anywhere between 6 and 10 (in my experience it’s maybe even more fun for the adult making the computer and helping the kid out!). As well as it being a fun craft project, it teaches the relationship between inputs and outputs, and teaches the basis of logic gates in a really tangible way.

Here’s how to make one.

You’ll need a cereal box, some thickish card (like the back of a sketchpad), around 10 pencils or skewers, sticky tape, masking tape and a supply of thinish card (say around 10 old Christmas or birthday cards). The tools you’ll need will be scissors and a hole punch.

1. Take a large cereal box and cut off the flaps, so it’s open at the top.

2. Cut a flap out of the front of the box, to around half way up.

3. Push this flap to the back of the computer and stick the top of it to the inside of the back of the packet.

4. Cut a slit along the front of the hole left by the flap on the front of the box. Do the same along the back of the box at the same height.

5. Through the slits fit a piece of stiffish card about as wide as the cereal box. This is the “enter” bar.

6. Along the top edge of the box and hole-punch around 8 to 10 holes on the front and back. Make sure that these holes line up with one another. You’ll see why in step 7.

7. Push a pencil or skewer through each of the holes.

8. Below the holes, put a piece of masking tape, or something that can be written on (and replaced).

9. Measuring from the “Enter” bar, to just above the holes at the top of the computer, cut around 10 punch cards from card that’s around as thick as the cereal box.

10. Using the pencils or skewers to mark the cards, make holes in all of the cards so the skewers can pass from the holes in the box and through them all.

You should now be ready to start programming!

The holes at the top of the punch cards are “zeros”. They denote negative answers. Cutting into the hole, so it becomes a U-shaped slot (so the skewer no longer holds the card if the enter bar is removed) denotes positive answers (i.e. a “one”).

Let’s think of some questions.   How about “things that fly”

Dragonfly
Jumbo Jet
Butterfly
Arrow
Hot air balloon
Helicopter
Space Shuttle
Fairy
Frisbee

Each answer get written on a separate card, and put into the top of the computer. These form the computer’s data set.

Now we need questions that will reveal different answers (These get written on the front of the box on the masking tape, one question per hole).

Is it an insect?
Dragonfly
Butterfly

Can it kill you?
Jumbo Jet
Arrow
Hot air balloon
Helicopter
Space Shuttle
Frisbee

Can it hover?
Dragonfly
Helicopter
Fairy
Hot air balloon

Is it made of metal?
Jumbo Jet
Helicopter
Space Shuttle

Anyway, you get the idea…

The holes at the top of each card are opened into slots to where ever the respective answer is positive, and left closed as zeroes where the answer is negative.

Keep the first hole on the front of the box without a question. Removing this will be like a mouse click that will execute the programme, so the corresponding punchcard holes for should always be a zero.

To run the programme, take the enter bar out of the computer. The cards are now being held only by the skewers which denote negative answers. between the holes and slots.   All skewers are removed except for the “click” skewer.   To input a question, push a skewer into the hole corresponding to the question you want to ask. When the “click” skewer is removed, the cards which answer this question will be outputted through the chute. Of course, you can input combinations of questions.

Input: Is it made of metal? (and) Can it hover?   Output: Helicopter

So that’s how I got started. I’ll try to build a virtual cereal box computer as one of my first coding projects, and I’ll put it up here. In the meantime, have fun, and stay away from computers that are sugar frosted and dipped in chocolate.