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I started by taking apart an old
keyboard. This is hard to understand by the pictures so I will try to
explain more as I go along. Once most modern day keyboards are torn apart
and the tops, with keys and little rubber plungers, are thrown away, you get
down to three layers of plastic laminates. It looks like one piece of
plastic with lines on it here----but is really three layers.
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These plastic laminates are really like a
printed circuit board in that the lines that you see conduct electricity.
There is a top layer of lines, then a sheet in between, and a bottom layer of
lines. This is the top.Here is the middle sheet of plastic.
There are holes under every dot that leads to a key on the board. I've
held some white paper under them to make them a bit more visible
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Here is the bottom layer with yet another
array of contacts. So what is happening is that the top contacts are
insulated from the bottom contacts with the thin center layer of plastic with no
contacts on it. But remember the holes. Those holes allow the key to
press the top contact--through the hole---to touch the bottom contact.
Hence each spot like that becomes a switch.
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It took awhile to trace the plastic to see
where the Ctrl and C and V contacts were and what they shorted out. I'll
explain it more at the end in greater detail as I need to make up some more
pictures to better show it. For now let me say that I first tried to
short the correct combinations of Ctrl/C and Ctrl/V with a regular DPDT
switch. But there was a problem. You don't normally hit Ctrl and C
at the same time. If you accidently get C first---you simple print a
C. So sometimes the switch would contact what made a C before the Ctrl
part. This is why I moved on to the next idea..
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I decided I was going to use to micro lever
switches, bolted together, with some sort of plunger that would hit them at
different times. I would do this for each copy/paste function. There
are dozens of inventive ways to do this. What I did probably took more
effort than it was worth....but here it is anyway. I started with the
thread part of a 1/4 bolt and drilled an 1/8 inch hole down the middle. I
wanted a threaded outside so I could adjust the thing up or down later---if
needed
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Here you see the completed hole and the
treaded outer part of the sawed off bolt.
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I then took a short section of what was
handy for 1/8 inch rod. In this case I took an 1/8 inch welding rod and
removed the flux coating. I chopped off a section and finished cleaning it
by putting it in a drill press and spinning it while holding sandpaper against
it.
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Here is my home made push button. The
bolt with the hole becomes the shell and the rod becomes the inner button
part. What came together next was not in any real way planned. I
just sort of winged it as I went along. I wasn't sure how everything would
mount and work...but this is what i finally came up with.....
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Here are the micro lever switches bolted
together. There is a bolted pair to the left and a single one to the
right. Note they have two holes. I used one set to bolt them tightly
together while the other hole will become a pivot point for them. You'll
see what I mean as I go along.
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Here is the project box with a small stud
bolted in place. I won't bore you with the complications of doing
this---as it was a pain in you know what. But I wanted it to come out so
that the lever parts of the switches hit the raised groves in the box.
Hence the one wrong hole showing. Oops! But you'll see why I wanted
these in a certain position...as you go on.
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This shows one of the button plungers ready
to hit the lever switches. I didn't use any return springs on the push rod
as I found the natural return of the lever switches, by their own internal
spring, worked just fine.
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I did want to stop the plunger from falling out if the
box though, if it was ever turned upside down. So I place the plunger into
the drill press again and held a hacksaw blade against it until I had a small
grove. I later placed a hairpin clip (or at least that's what I call them)
around the grove, once the plunger was in place.
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This concept may be confusing. What I did was
grind down the part of this raised slot so that ONE lever, on each of the
two levers, would hit it. Am I making that clear enough? I wanted
each SET of levers to have one lever hit a HIGH spot (the part not ground down)
and the other lever a LOW spot (the part that is ground down) Remember
that spacing I needed for Ctrl to make contact before C or V?
This does that. The lever on the higher part closes before the lever
on the lower part.
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Again, this is not easy to see. But here both
plungers are raised up (no hairpin clips yet) to show the lever switches in
place and ready to do their thing.
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This may be a bit better to see what is
happening.
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OK---we are jumping around here. Now we are back
to the keyboard chip. As you will see further down. the chip is used to
convey the correct commands through the USB cable to the computer. We are
using it to convey the Ctrl and C and V commands that we will switch on and off
by the lever switches. Again---I don't want to bore you with too much
detail. But I wanted to contact only 5 spots on the chip. There is
no real easy way to solder to them so I have a way that I make a plastic plate
to press against them. In the chip's original use the contacts from the
plastic sheets were pressed against it. But I do it with a small home made
contact plate. The plate is drilled with a hair-fine drill for wires to
pass through that will contact the chip and yet allow their other ends to have
wires soldered to them. For a really full description of this. please go
to my Proximity sensor page and scroll about half way down... http://www.grubbypawsproductions.com/electronics/proximity/proximity.html
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Here are the chip board and my home made contact board
bolted together. I now have 5 wires I can solder to.
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Finally I was ready to solder things together.
These parts were waaaay too small to deal with. I would use bigger lever
switches next time. Someone with better electronics knowledge could
probably use switching transistors or something electronic instead, to get the
spaced pulses needed for the commands.
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Here is the unit going together. It's hard to trace
what I did with the wires as I used some old black cable I had and there are
multiple sections of it showing----along with the cable that was originally
attached to the chip and that plugs into the USB on the computer. But I'll
do a schematic further down to explain.
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Here is the unit going together. It's hard to trace
what I did with the wires as I used some old black cable I had and there are
multiple sections of it showing----along with the cable that was originally
attached to the chip and that plugs into the USB on the computer. But I'll
do a schematic further down to explain.
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The little chip board was secured to a small post on
the left with a screw. It just sort of dangles in the middle of the
box---but that is fine. It doesn't show here, but I made a small grove
where the face plate bolts so as to allow the USB cable to come through
that. Now I'll try to explain more about the circuit design. It may
be different for a board you use, but this is what happened for me.
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Finally we have the completed unit. the cable coming out is the original USB cable attached to the chip inside. Just plug it in and Windows should recognize it. I should note here that some keyboards do seem to not be recognized by Windows at first. So to save any problems, test the keyboard, before you tear it apart, with the computer it's going to first be used on.
Now for more details about the wiring.....
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Click the picture to the left for a much more detailed description of the schematic. You won't get just a pop-up....but rather a whole new page that opens on top of this one. When you are done with the new page, simply close it to find this page still underneath.
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