hooking a power pad to my computer

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i a graphic design student working on a project in which i would like
to hook up a nintendo power pad or a similar device (or even building
something simple on my own) to my computer in such a way that each
button would registter on the computer as a keypress.  this way i can
make an interactive presentation in flash with simple key commands and
have the user control it by walking on the pad.  is this doable?  what
do i need to hook up the pad to the computer (mac)?  what do i need to
do to register the button presses as specific keystrokes?
i don't have any electronics background but i am willing to learn.
any help would really be appreciated!

Re: hooking a power pad to my computer

rastomel@gmail.com wrote:
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For an over the top retrofit, check out this article.
Lots of mechanical engineering and butchering of an
existing device. Good fun, if you have nothing but
time on your hands. Too much sawing and drilling
for me...


It looks like there are plenty of different commercial
implementations, the only difficulty being the
controller interface (and the uber pricing). The
Inventgeek article mentions that the Xbox version
can be plugged into a USB port on a computer. While
that doesn't guarantee an easy integration project,
at least then it is "just software" :-)

If you want to do a device from the ground up, FTDI makes
a few USB devices with convenient interfaces (it saves you
on developing a whole USB logic block). Using a driver
they provide, you get a data stream from the device. And then
it is a relatively easy matter to convert switch closures from
your mat invention, into bytes you feed to the USB chip. The
FTDI USB chip and driver, then presumably gives you a virtual
serial port. Open the serial port in your software, write
some code to convert the received stream into events, and
feed that somewhere else. This would be pretty geeky...


You know, now that I think about it, hacking up a USB keyboard
comes pretty close to doing what you want. All you have to
remember, is that the typical keyboard is a scanned matrix
(row and column wires, and a keyswitch closes a certain row
to a certain column - the controller in the keyboard scans
the array at high speed, to detect key-down and key-up events).
The only thing wrong with this concept, is if you attached long
wires to the thing, it would probably stop working. (The keyboard
controller cannot be expected to drive a high capacitance load.)
I cannot guarantee this approach would be anything but frustrating,
but at least with a USB keyboard, you know the computer is going to get
instant input. So at least the computer end of things is simplified
to some extent. Maybe if the keyboard was hacked and fastened
to the bottom of your home made mat (to keep the wires a bit
shorter), who knows, it might work. Note that all your mat
wires have to be connected, to prove the concept. Only connecting
enough wires for a single switch closure test would not be enough
(to prove or disprove the capacitive loading issue).

By fitting some buffer devices between the mat, and the keyboard,
you can solve the capacitive loading problem. But that is
more electronics.

In terms of professional data acquisition devices. a device like
this can monitor a logic level on up to 24 things. It has a USB
interface, which means it could be connected to a Mac or a PC.
The only question here, is whether the software they provide,
could be integrated with what you're trying to do. Stuff like
this can be pricy, but is used in big companies for automating
test setups in factories or laboratories.

NI.com USB 6501 (USB, 24-ch, 8.5 mA) Low Cost USB Digital I/O Device

To some extent, this is a time versus money trade off. I didn't spend
a lot of time searching, and maybe if you have $1000 to blow,
someone makes a stainless steel version of exactly what you want.


Re: hooking a power pad to my computer

On Sun, 16 Dec 2007 05:38:16 -0800 (PST), rastomel@gmail.com

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Get a USB numberpad, then if you can't just use that as-is,
crack it open and trace back the # of keys you need to
control the presentation and wire your separate enclosure
with switches installed to correspond to the controller
board contacts the numberpad uses per the respective

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