Episode: 3775
Title: HPR3775: Emergency Show posted in 2014. How to make a punch-card computer
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr3775/hpr3775.mp3
Transcribed: 2025-10-25 05:14:16

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This is Hacker Public Radio Episode 3,775 for Friday the 20th of January 2023.
Today's show is entitled, Emergency Show Posted in 2014.
How to Make a Punch Card Computer.
It is hosted by Mike Reg and is about 14 minutes long.
It carries a clean flag.
The summary is, how to make a punch card computer from stuff from the kitchen.
Hi everybody, we're really short of shows at the moment, so I've had to take this one
out of the reserve queue.
If you have shows, can you please send them in?
Because HPR as a project will cease to exist if we don't continue to get shows from listeners
like you.
This is something I've had in my head for decades.
I can vaguely remember when I was very small, making one of these punch card computers.
It may have been me or me, it may have been my older brother, more likely to have been
my older brother.
I think we probably made it in response to seeing it on the TV or reading it in a book
or something.
I have this vague recollection of a serial box with some of my mum's knitting needles sticking
through the box and putting out the needles and cards dropping out at the bottom.
Now we're not going to use knitting needles, but we're going to update it a bit.
I've not done it since I was probably over 40 years ago, but it's just something I've
remembered for years.
So what you will need, the main body of the computer, it consists of an empty breakfast
serial box.
Have any sort of average size or just a normal breakfast serial size box.
The first thing to do is to cut off the flaps at the top of the box where the box has been
opened and the serial has been removed.
Through the flaps away, except for one of the long flaps from the long side of the box,
we're going to use that on a made-coming handy as a template when we get a little bit
further on down what we're going to do.
The other thing we're going to need is some cards about the same width as the box and
these can be made from another serial box sliced up.
An empty box of the same sort of size will yield about four cards, possibly six if you
make them not very deep from top to bottom.
Another thing you need is some bamboo skewers.
These are the things that are going to take the place of the knitting needles.
When the example I was talking about from when I was very young, Richard Stallman was
still in short trousers.
You're going to need some scissors and or a sharp craft knife, possibly some glue, preferably
or something washable and optionally some sticky tape.
So what you do, the first thing we're going to do is to make a shoot, a sort of shoot
at the bottom of the box.
Now the box, when it's used as a computer, it's going to stand on the table, on the way
it would stand normally.
We're going to cut a flap out of the bottom and stick it back as a shoot and we'll
do this by making a horizontal cut across the box, about four inches or so, ten centimeters
or so above the bottom.
So it's a horizontal cut all the way across and then we're going to cut down the front
edges of the box.
From that horizontal cut down to the bottom of the box, this will form a flap that you
can fold out by sticking your hand in the top of the box and pushing it out.
When you're done that, you need to make a fold in that flap about a centimeter or half
an inch from the front edge of the flap, the bit which came away from the horizontal
slot that you cut across the box.
Then you coat the inside of that flap between the fold and the edge with glue and then you
push it back into the box until the glued part of that flap is against the back wall of
the box and then use some sticky tape to stick it down while the glue dries.
If you can imagine what that forms is a kind of shoot at the bottom.
If you drop something into the top of the box now, it will hit the shoot and slide out
the hole in the front where the shoot was cut away from.
Now take the long flap that you cut from the top of the box and draw a horizontal line across
it, across the wide length of it, about half way down so that you're effectively dividing
the flap into two halves along its length.
Here's where we need to do some rest of the technique.
You're going to mark out eight or perhaps even sixteen points along the line, equally
distant so if you've got eight, if it's an eight bit computer you've got eight points
so there are nine gaps between the points, measure the width of the flap, mark off the
points with a ruler and then stick that to one side.
Now we're going to punch some holes in the box at near the top, near the opening and
we're going to do this by holding the template flap that we've just made at the top against
the box and punching through with a bamboo barbeque skewer or something sharper, perhaps
a knitting needle if such things still exist to make the holes in the box to take the bamboo
skewers and we're going to do the same on the other side because the bamboo skewers are
going to pass all the way through the box from front to back and they need to be quite
accurately inserted so that each skewer is the same distance from the top of the box, the
same distance between it and its neighbours and so that the skewers are nice and parallel.
So once you've done that, if you imagine you've done eight holes and you've inserted
eight skewers, you've got eight parallel skewers passing all the way through the box, a
bit like a magic trick where a man sticks a sword through a wardrobe with a beautiful
blonde inside it. So now we've made the body of the computer with the eight or sixteen
or nine or ten, we can make a nine bit computer skewers through the box, we're going to make
the cards. Now we need to make, if we've got an eight bit computer that's got eight skewers
through it, we're going to need to make eight cards. These cards need to be almost as wide
as the box but not quite so that they fit nice and snug but with no friction in the top
of the box and the depths of them, it's perhaps about four or five inches, ten or twelve
centimetres from top to bottom, big enough to write some stuff on but not deep enough
to be visible through the hole at the bottom where you cut the flap for the shoot. Now
along the long edge of each card you're going to measure and make some holes, we need
our template again for this, to template that you used to make the holes for the skewers.
We're going to hold against each card and punch some holes, again probably starting
with by using a bamboo skewer but the holes need to be bigger than the diameter of the
skewer, perhaps about five millimeters or a quarter of an inch or so in diameter. Nice
and wide so that the skewer passes easily through the holes. A single hole handheld, a hole
punch is good for this but it's not absolutely necessary. It doesn't matter if the holes
are square, as long as the hole is bigger than the actual skewer and that the holes line
up with where the skewers are. Now once you've made eight of those cards take each card
in turn and convert seven out of the eight holes into slots by slicing from the side of
the hole to the top of the card so you actually remove a little piece of card between the hole
and the top edge so you've now got, with each card you've now got one hole in seven slots
and for card zero the left hand hole if it's a little Indian is still a hole and the rest
of them are slots and then for the next card the first one will be a slot, the next one
will be a hole and the remaining six are slots. So you can probably see where I'm going
with this you do it with each card and in each in turn holes zero to seven become, remain
as holes and the rest become slots. Okay so now we've made our cards. We need some
data to put on the cards. Now it would help if you've got eight children at this point
because if you've got eight children you need never forget their birthdays ever again.
The right piece of data on each card and write something on the box next to the hole
which corresponds to the intact hole on the card. Now once you've written all the data
then put the cards together in a stack and put them into the top of the box hold them
with one hand and then insert the skewers through the holes and slots through the front
of the computer and out the back. So when you stand it up on its bottom end what you've
got is a serial box with a nice slippery shoe to the bottom where something can come
out. Eight skewers through the top of the box in a line and eight punched cards suspended
in the top of the box but of course each card has got seven slots and one hole each in a
different position. So each card is only held in position and prevented from falling by one skewer.
So if you now pull out one of the skewers the card which corresponds to that skewer should
drop out the bottom. So if you have eight children and a third one was called Bobby pull out
Bobby's skewer and Bobby's card will drop out the bottom with his birthday on it and that is a
punched card computer. Now I know that some people will be saying well that's not a computer and
it's not and it's eight bits and it's only got eight bits of random access memory and the main
problem with it is that each time you remove a piece of data by putting out the skewer that data
is not copied it's you know you've not got the data out but it's still in the computer it's
the computer now only contains seven bits of data so it's not it's not really a computer but
it's fun and like I say it's one of those things I have way back in a dim and distant past my brain
one of these days I'm going to get around to making another one. Oh I should do a little bit of
trouble shooting information here if for some reason when you pull out a skewer nothing drops
through this could be because of a number of reasons there's too much friction between the cards
now when you load the cards into the top of the computer try and sort of spread them out a little
bit so they're not all packed closely in together it could be that the cards are too wide and
that they have left some friction between the left and right edges of the cards and the side of
the box or it could be because the slots are not wide enough and are actually producing some
friction between the remaining skewers and the side of the slot so that the card is unable to drop
down when you pull out its skewer those are the only things that we can go wrong it's as simple as
that if you make this then you really need to get out more and stop wasting your time and
everybody else's. You have been listening to Hacker Public Radio at Hacker Public Radio does
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