First you need a basic understanding on how a keyboard works and what this project
is about.
About the project: I want to design a control panel, layout the switches where
ever I want them and then rig the switches to the keyboard's circuit. When a button is
pushed on our control panel, this will close a circuit and depending where in the matrix
of the keyboard this circuit was closed a character will be sent to the computer. Simple ;)
Imagine it like extending your keyboard's keys. Or never mind...
Status: Hot Progress!
keyboard 1:
I bought the keyboard for $4.00 + tax at a thrift store in
Athens Ohio. It happened they were having a 1/2 off sale.
I actually ended paying $2.00 + tax.
IBM
Part no. 1391401
S/N No 2051477
Date 12 mar 87
Plt No F2 Model M Matrix: 16x8
Connector: ps2
First thing I did was use a program called keyscan to find out how many
keys I can press at once without ghosting or blocking. My
result was 19 keys. I wrote down the keys on a piece of paper.
I kept this paper safe because I would need it later when I go
to map/find The Matrix.
I opened the keyboard casing keeping everything intact. This keyboard uses maylar
to connect keys to a small printed circuit board (pcb) in a 16x8 matrix.
I disconnected the maylar from the PCB noting its previous position.
I removed the pcb from the keyboard casing and set the casing aside intact.
Since the PCB uses maylar, it had a pinch type terminal which needed to be changed to a pin
strip terminal in order for me to use ribbon/IDE wire.
I changed the original pinch type terminal to a single row pin connector ( pic-1,
pic-2, pic-3)
I could not find any other wire that would fit in the single
row of pins other than IDE. All I had laying around was an ide cable. Because
of the way ide cables are made I had to pick what wires worked
and what wires didn't.
IDE Connector: <-count direction
Top pin holes: 9 7 5 3 1
Bottom pin holes: 10 8 6 4 2
I chose the top row and I needed to discard the wires from the
bottom row. On the flat ribbon IDE it goes like:
1 wire keep, next wire cut.
1 wire keep, next wire cut.
1 wire keep, next wire cut.
<--Look
It would have been easier to buy a single row wire adapter
(which i didn't do) or to solder the wires to the board (which I do not plan to do.)
After striping the other end of the wires I connected
them to the three Dual Terminal Barrier Strips I got from Radio Shack
Cat.#: 910-3197.
I named two bariers 'Alpha' (the barriers that are close together in the picture) and the other one 'Numeric' (the single barrier you see in the picture. The part number varies according to the Radio Shack Web site so
does the price.
Beseech The MatriX
To map the matrix I mean to draw an X/Y table and fill in the blanks according
to what happens when you join X with Y. So in my case, I drew a table with its
columns named A1 through a16 and its rows named b1 through b8 making my a16xb8 matrix.
Example:
a#
0 a1 a2 a3 a4 a5 a6 a7 a8 a9 a10 a11 a12 a13 a14 a15 a16
b1
b2
b3
b4
B# b5
b6
b7
b8
I then took a 9v battery, a test light, and an aligator clip and made a
"poor mans continuity tester to be used on the maylar (not the pcb)
I took the end of the maylar (the part that connects to the PCB) and set
an aligator clip on what would be known now as b1. (see illustration.) Then
I took the continuity testor and poked at a-1. I proceeded to press every key until
I got a light :) then I wrote down that key that generated the light.
If you look at my matrix you will see that by shorting a2+b2="Left control". If none
turned on the light, I move on to a-2 leaving the aligator clip on b-1. While the gator
clip is on b-1 you must test a-1 through a-10. Then you move the
gator clip to b2 and test from a-1 to a-10 again. you do this until you run the gator clip through
all b#'s.
(((1 bag of doritos, 24oz of dr.peper and 2 hours later)))
At last! What I have been looking for! Muhahah! The Matrix in which the Keyboard
operates. Match a# with b# and your result is a character.
For example:
Reverse Engineering a keyboard
