(This instructable only documents the construction of the mat, and not the computer programming aspects, which were done in Max/MSP and Adobe Flash. If you would like info on those, feel free to contact me through my Instrucables account.)
Step 1: Materials
1 Twister game ($12 dollars at Target)
200 feet of thin, flexible wire (solid or stranded core will work)
1 I-Pac controller with USB cable (available here: http://www.ultimarc.com/ipac1.html) or a microcontroller with at least 24 inputs
2 sheets of headliner foam, 54 x 72 inches each (available at any fabric store)
1 sheet of painting plastic, 54 x 72 inches
1 roll of aluminum foil
1 roll of duct tape
Small flathead screwdriver
Step 2: The Bottom Layer
The bottom layer is simply a layer of foam with 4 strips of aluminum foil taped to it. There is one strip for every row of circles on the Twister mat. These strips will be connected to the ground terminal on the I-Pac board later on.
Lay out 4 strips of aluminum foil so they span the long way across the headliner sheet. Make sure that every they line up with the rows of circles on the Twister mat. Then tape the edges of the aluminum foil to the headliner with duct tape.
That's it! You're already done with the first step!
Step 3: The Middle Layer
You will need to make holes in one of the sheets of headliner fabric. These holes will need to coincide with the colored circles on the Twister mat, so you will need to make a template using the painters plastic.
Place the plastic over the Twister mat and trace over the circles. Then cut out the circles you've drawn on the painters plastic. Then you can place the sheet of plastic on top of the fresh sheet of headliner fabric and trace the circles onto it. Now you have a piece of headliner with the same circle pattern as the Twister mat.
You can cut these circles out completely, or cut smaller holes at the centers of these circles. It's best to start small with one hole and then continue on with the next steps. Then you can test the switches (to be made next) and increase the size of the hole as needed.
Place this headliner layer on top of the bottom layer from the previous step so that the strips of aluminum foil can be seen through the hole(s).
Step 4: Aluminum Foil Switches!
The ground is now at the bottom of the hole, and now you must construct the other half of the switch on top of the hole. Place a 6 x 6 inch square of aluminum foil over the hole. Tape all four sides down, keeping the foil taught.
This must eventually do be done for all the holes.
Step 5: The Wire
The wire must be cut to 6 different lengths:
You will need 4 of each of these lengths:
8 feet, 7 feet, 6 feet, 5 feet, 4 feet, 3 feet
and 8 at 2 feet each. You will also need one six inch length of wire.
Strip a half inch off of each end.
Step 6: Attaching the Wire to the Switches
The electronics will be located at the end of the Twister mat, so pick which end you would like them at. The longest wires will be attached to the aluminum foil switches which are furthest from the electronics. The wires will then get shorter as you get closer to the electronics.
After some trial and error I found it is best to simply bend the stripped portion of the wire in half and then duct tape it to the corner of the aluminum foil switch (the top layer).
The four extra 2-foot-long wires are for the grounds (the four strips of aluminum foil on the bottom layer). These should be attached to the strips near the end with the electronics.
You should end up with a mess of wires, as shown.
Step 7: Connecting to the I-Pac Controller
HELPFUL HINT: When you plug the I-Pac controller into your USB port, the computer will register it as a keyboard. (It is essentially the electronics from inside of an old keyboard) When the top layer of the aluminum foil is stepped on, it will contact the bottom layer of foil, completing the circuit. The I-Pac controller will then send a the corresponding message for that port to the computer, like pressing a key on the keyboard. There are therefore a handful of inputs on the I-Pac which I would recommend avoiding (e.g. ports which will send messages such as ENTER or ESC or SHIFT to the computer, confusing whatever program you might be using). It is best to use ports which correspond to letter and number messages. The list of ports and corresponding messages can be viewed here: http://www.ultimarc.com/ipac2.html
(Connecting the 4 ground wires is in the next step)
There is nothing else to worry about when making connections. Simply loosen the small screws on the I-Pac ports, put the wires in, and tighten the screws. Aside from avoiding the previously mentioned ports, it does not matter what goes where, as you can adjust accordingly in your programming on the computer.
Step 8: Connecting the Ground
As you may have noticed, there are 4 ground wires and only two ground ports. There are two simple ways around this. One requires soldering equipment, the other requires a small prototyping board. You could get by using duct tape instead of solder, but I would not recommend it.
To avoid soldering: Attach one end of the short wire to the ground port on the I-Pac, and insert the other end into the prototyping board (anywhere). Then insert the four loose ends from the ground cables into the the same row on the prototyping board, as shown. This essentially connects all the wires, so they act as if they are all plugged into the ground port on the I-Pac.
If you'd rather solder, take the five wires which would be inserted into prototyping board and twist their ends together. Then coat the connection with a little bit of solder so that they won't come loose.
Or wrap the connection with a bit of duct tape to keep it from coming apart. (not nearly as stable or interesting)
Step 9: Organize the Wires
Gather the wires by row (bundles of six) and tape them down in the unused space so they won't shift during use and interfere with the switches. Leave the center space open so the mat can be folded in half for easier transport.
SIDE NOTE: The little yellow box is something I found at a surplus store and I used it to house my electronics.
Step 10: Top Layer
Place the Twister mat on top of everything and test all the switches by stepping in the middle of all the circles. You can make sure they're working by opening a text editor on your computer and make sure messages are being sent. This is a good time to determine which keyboard messages will be sent from each circle on the Twister mat.
Once your satisfied that all the switches are working correctly, tape the three layers together around the edges with duct tape. This will allow for easy access later should something stop working or become disconnected.
Step 11: Last Step - Play Twister!!
Now you can use Twister to control another program on your computer as if it were the keyboard.
Have fun, and feel free to contact me with questions.