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MY USB footswitch
controller |
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This page shows how to hack a USB keyboard and
turn it into a USB footswitch.
Here's a short movie showing how my switching
experiment works with Mixcraft
This is the first PS2 keyboard experiment
http://www.el34world.com/Misc/Movies/MX5.wmv
I am using this footswitch to send a string of keyboard
commands to my recording software.
The footswitch triggers a keyboard character
and then I have a program that intercepts that
character and then triggers a
macro of many keyboard commands
This lets you set up a very complex sequence
of events with just one keyboard character.
This is not Midi, it is taking advantage of
all the things you can do via keyboard
commands, only you can do them with your feet.
I am using a USB keyboard because I want to be
able to plug it in on the fly, which you can
do with USB devices.
I tested this footswitch idea using a PS2
keyboard, and it worked fine also.
You don't have to make a USB footswitch from
scratch, they actually sell them
Note that in most cases, you would want one
that you can program the keys that are
triggered
You would not want one that is limited to only
certain keys because those keys are used in
normal program typing
Here's a web page that has many different
styles of USB footswitches
http://www.delcomproducts.com/products_usbfsw.asp
They also sell USB controller boards for use
in home made arcade type games
These boards are supposedly way better quality
than a cheapo USB keyboard like I am using.
From what I have read, the arcade type boards
are able to generate many keyboard commands at
one time
Joysticks and arcade games may have many keys
pressed at the same time during game play.
A USB keyboard is only able to do 6 keys at
one time which is way more than I need
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Here's how the basic modern keyboard works.
There are three plastic sheets that are tacked
together with spot welds
The upper and lower sheets have carbon traces
and the middle sheet is just a plain clear
sheet with no carbon traces
The carbon traces conduct electric current.
The middle clear sheet is just an insulator to
keep the two sheets from touching until you
press a key.
When you press down on a key you are pressing
the two sheets that have carbon traces
together to make a switch connection.
The middle sheet has holes everywhere there is
a keyboard switch so it does not get in the
way when you press the upper and lower sheets
together.
Once you press a key, the circuit board
figures out what key was pressed and then
sends that info to the computer.
There is a computer chip on the circuit board
that handles all that complex stuff.
The two sheets that have the carbon traces
have very small traces that lead back to the
circuit board.
So, you can duplicate a key being pressed if
you find the spot on the plastic sheets and
follow the traces back to the circuit board.
Then all you do it solder tiny wires to the
circuit board and use foot switches to
simulate pressing a key down on the keyboard.
It's way easier to understand if you take a
keyboard apart and study it.
Don't take your favorite keyboard apart, you
make never get it back together and working
again.
There's a ton of small parts that can fly out
and be impossible to reconstruct back into a
working keyboard.
This page has some info regarding keyboard
hacks
http://www.instructables.com/id/Hacking-a-USB-Keyboard/
Also, you can do a Google search for keyboard
hacks and find lots of info.
Seems that it is very popular thing to do.
People are using keyboard hacks to make home
made arcade game controllers.
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This is the program that I run in the system
tray that triggers the macro's
http://www.autohotkey.com/
What you do is take the stock config file
called AutoHotkey.ahk
and alter it to suit your needs.
You will have to download it and read the help
file to get a better idea of how the whole
thing works.
It's a great little free program that can do
many things.
The Auto Hot Key code I am using for my
particular footswitch needs is shown below
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The ^ character shown below is a shortcut for
the Control key
So ^r is Control + R
The ; character is a comment line, everything
after the ; is ignored
The code below is simple, it just starts and
stops recording when I press the [ key
; Mixcraft - Start and Stop recording
[::
Send, ^r
return
This bit of code is a bit more complex and
does many things
All of the items in this sequence are keyboard
shortcuts in Mixcraft
When I press the ] character the macro below
will execute and Mixcraft will execute each
keyboard command in the macro
; Mixcraft rewind sequence
]::
Send, ^g ;Add a new audio track
Sleep, 100
Send, {DOWN} ;Move the clip down to the new
track
Sleep, 100
Send, ^u ;move the selected track up one
Sleep, 100
Send, {ESC} ;un-highlight the clip
Sleep, 100
Send, ^m ; mute the track you just recorded
; The sequence below rewinds to the last
marker flag and then stops
Sleep, 100
Send,
{SHIFTDOWN}{CTRLDOWN}{SPACE}{SHIFTUP}{CTRLUP}
Send, {SPACE}
return
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Click on images to see a larger image |
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Here's my victim, a $7.84 USB keyboard from
Wal-Mart.
How can they make and sell something this
complex for that cheap? |
The inside of the keyboard.
The circuit board is on the upper left.
The clear sheets have been pulled forward. |
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Click on images to see a larger image |
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Here's the guts of the whole thing. These are
the only parts we will use.
The circuit board and the USB cable |
Lay the sheets back on the keyboard and map
out the keys with a sharpie
You don't have to do them all, only the keys
you are interested in. |
The electrical connection between the clear
sheets and the circuit board is only a press
fit.
The circuit board has copper traces, but the
traces are coated with some sort of carbon
dust.
When you press the carbon traces on the
circuit board up against the carbon traces on
the sheets, they make the electrical contact.
You have to lightly sand the carbon dust off
the copper traces in order to be able to
solder wires to the copper traces.
I have seen other keyboard hack web sites
where they have just glued wires to the carbon
dust and not removed it.
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Click on images to see a larger image |
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Split the spot welded sheets apart carefully.
Don't rip the plastic sheets apart and break
any of the traces
I have the sheets laid out like an open book
here.
Only one side of each sheet has the carbon
traces.
You can use a multimeter set to
continuity-Beep to trace the round key pads
back to the area that contacts the circuit
board traces.
It's a whole lot easier with a meter that
beeps.
If you don't have a meter that beeps, you will
have to follow the small traces back manually.
When you press a key, the two sheets come
together to make a connection.
For every key pressed, you have to trace two
connections back to the circuit board, one
from each sheet.
The red circled area on the upper left is the
area that contacts the circuit board traces.
Count over from left to right the number of
traces and make note of that for each key you
want to use.
On my project I am only using the [ and ] keys.
The [ key mapped out to #14 and #20 on the
circuit board traces
The ] key mapped out to #7 and #20 on the
circuit board traces
So, if I solder a wire to #14 and #20 and I
touch those wires together, it will trigger
the [ key.
The key mapping is going to be different for
every type of keyboard, so my map above is no
good for other keyboards.
You will have to map out your particular
keyboard.
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Click on images to see a larger image |
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Here's the inside of the foot switch unit I am
going to use. |
Another shot with everything tapped down and
the wire secured |
On the left above you can see that I have
soldered tiny wires to the #7, #14 and #20
copper traces
The lower end of the circuit board is trace #1
and the upper end is trace #26
The blue and orange wires will trigger a [
character when I step on a switch and connect
those two wires
The yellow and orange wires will trigger a ]
character when I step on a switch and connect
those two wires
Both of those characters will set off a macro
consisting of multiple keyboard commands
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Click on images to see a larger image |
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The controller I am using here is the Rig
Kontrol from Guitar Rig #1
It's not usable in later version of Guitar rig
and so it's now my experiment
There's a solid state pre-amp inside that still works
if I ever needed that. |
Here's the controller all assembled with the
two switches I am using
I have two more switches for future use. |
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