Introduction: Low Cost Multi-touch Trackpad

As a interaction design researcher interested in interfaces and physical interaction I often find myself in the situation of building new interfaces or testing and improving new ones. Since multitouch trackpads are so expensive and the don´t offer a simple way to interpret the touch input in programming software I build my own low cost multitouch trackpad following this instructable. This is what I found in my build, and once created you can use any programming software to follow, interpret and play around with the touch input.

Sounds great? Then follow this simple instructable and build your own within just a few minutes.

Step 1: Materials

Here´s what you need to build your own low cost multitouch trackpad:

> Cardboard (or box)
> Webcam (any webcam should work. I am using the Playstation Eye Camera due to its high framerate)
> Electrical tape (or ducktape)
> Glass (or transparent acrylic. I am using a picture frame since it already has a glass and makes a nice finishing of the trackpad)
> Plastic cup (or any other cup)
> white sheet of paper (any paper should be fine)
> Hobby knife or scissors to cut things

Step 2: Picture Frame

First of all we´ll build the actual tracking surface out of a picture frame with a glass (or acrylic) and a piece of paper:

1. Take apart the picture frame into its three pieces. The frame, the glass and pedestal.
2. Measure the inlet size of the picture frame and cut out an accordingly big piece of paper.
3. Place the paper into the picture frame and put the glass on top.

After this step you should have a picture frame with a white piece of white paper in it. The picture pedestal is removed and replaced by a piece of glass or acrylic. 

Step 3: Camera Mounting

In this step we´ll build a camera mounting out of a plastic cup.

1. Get your webcam and the plastic cup.
2. Cut the plastic cup into two pieces.
3. Thrust a little hole into the lower part of the plastic cup. The hole should be big enough to put the webcams cable through.
4. Place the camera on top of the plastic cup with the lens facing up.
5. Fix the cameras positions with tape.

After this step you should have a plastic cup with a upwards facing webcam attached to it.

Step 4: Measuring

Next we´ll figure out how tall our trackpad is going to be. Mine is about 25cm heigh but this depends on the webcam you are using as well as on the cameras position on the mounting you build. 

1. Take the camera and place it right next to a vertically erected ruler.
2. Plug the camera in to your laptop / computer and open up a software (e.g. CCV) to see the webcams picture.
3. Take the picture frame and place it within the camera picture.
4. Adjust the height of the picture frame until it almost fills out the camera image.
5. Write down the approximately height.

After this step you should know how tall your cardboard box is going to be.

Step 5: Cutting the Box

Almost done! We now want to cut the pieces for the cardboard box.

1. Take a pencil and draw down the four sides of the cardboard. (The edge lengths of the box are equal to the edge lengths of the paper.)
2. Cut out the four sides with a knife.
3. Take a ruler to measure the material thickness of your cardboard.
4. Cut off two times the material thickness of two opposing cardboard plates.

You should now have 4 pieces of cardboard that fit into your picture frame.

Step 6: Cardboard Box

The final steps...

1. Take the 4 pieces of cardboard and put them together using the electrical tape.
2. Cut in a hole on the lower side of the box for the camera cable to come through.

Now you should have a cardboard box of the size of the picture frame inlet.

Step 7: Setup

Final step: Putting things together.

1. Put the cardboard box into the picture frame inlet.
2. The glass of the picture frame should be inside the box and the piece of paper on top.
3. Plug the camera in to your laptop.
4. Put the cardboard box over your camera.
5. Open a software to see the cameras image (e.g. CCV) to adjust the image selection.

Done :)

Step 8: Result

Congratulations!
You can now use tracking software like CCV or reacTIVision to detect your fingers on your trackpad and have lots and lots of fun :)

Final thoughts and hints:
If you are unfamiliar with multitouch technologies, the terminology or you don´t know how to set up CCV check out the following sites.
http://sethsandler.com/multitouch/
http://sethsandler.com/multitouch/terminology/
http://sethsandler.com/multitouch/community-core-vision-guide/
> http://sethsandler.com/multitouch/community-core-vision-installation-configuration/ 

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Bio: Ix Designer. Sports addict. Music lover. Loves the outdoors. Spends too much time indoors. Reads everything from Douglas Adams. Does understand Schwyzerdütsch.
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