The Web Cam

Allot of people in the multitouch diy community are using the Philips .. web cam for their multitouch builds. Its relatively cheap a (I got a deal at sams club) easy to find and obviously is tried and tested to work with infa-red.
The camera resolution is ...x.. with a maximum of 60 fps.Which should be plenty for tracking moving blobs.

Most digital cameras can see the infra red spectrum "naturally" as the semiconductor sensors they use a greater bandwidth than human eyes. However the camera comes with a lens that has a IR filter. The filter is coated on the surface of the lens and is next to impossible to get off with any ease so the best thing to do is just replace the lens.
I used the .. 35 mm CCTV lens that can be found on ebay [] The seller is reliable and inexpensive.
CCTV lenses don't have the ir filter because they are commonly used in low light environments when invisible ir flash lights are used to illuminate dark areas giving clear night vision.



Once you have got the lens the next thing you have to do is remove the old lens and replace it with the cctv lens. With the Philips .. web cam its simple matter of using a thin knife to lever the rim of the lens off and unscrew the lens from the sensor housing.

Preparing The Acrylic Screen

The Factory Cut Acrylic Sheet
I finally decided on using a 4ft by 3ft acrylic screen. So i had to cut the 6ft by 4ft piece of sheet acrylic I had originally I had purchased. Luckily the place where I bough it (a local plastic fabrication company) very nicely cut it for free. Plus getting the sheet factory cut ensures so the edges are flat and the corners nice and perpendicular.


Sanding The Edges
First of all I sanded the edges of the acrylic with a plane sander. Starting with a 80 grain and building up to a grain of 320. A rigid plane sander is preferable to a sponge sander or just the paper in your hand as the suface must be as flat and perpendicular as possible.


Polishing with A Buffer
After the sanding was complete I busted out the plastic polishing kit I bought. It attaches to my Dewalt drill and rotates to buff out as many of the remaining small scratches with requiring too much elbow work.


Chemically Polishing The Edges
I used Brasso to remove a few layers of the acrylic and really smooth out the edge as much as possible. Just wipe on leave for a few seconds then wipe off with a clean rag. Any more and it can etch off to much of the plastic. Its officially a metal polisher but has the same effect on plastic and it can be bought off the shelf in most supermarkets.
Braso can also be use to remove scratches from ipod screens which is where I got the idea.