Mini-Multitouch Interface

Step 2 Prepare the webcam to detect infrared light

This step describes the setup of the webcam used to record the blobs of infrared light emitted when you touch the touch surface.

This mini-multitouch display relies on four LED lights to shine light into a sheet of Lexan, where it will bounce around without escaping, due to the index of refraction. This is called Total Internal Reflection. When pressure (such as that from a finger) is applied to the Lexan, it compresses a little, changing the index of refraction, and allowing the light to escapes. The places where the light escapes will only be where the surface is compressed, making nice glowing blobs where something is pressing on the Lexan.

This is where the webcam comes in! You can watch the blobs with a webcam, and with special software use them as input into your computer, like a mouse or keyboard.

For this project (and most multitouch displays) the light being used for touch detection is in the infrared range and the webcam must be modified to see in the infrared range. This is easily done by exchanging your existing webcam lens for one which can 'see' infrared light..

The LED used by the mini-multitouch interface, at 880 nm frequency, is within the range of 'night vision' surveillance cameras. You can swap your existing webcam lens for a 'night vision' lens, and you'll be ready to go. If you are using the recommended SPC900NC, you can use any 4.3MM x 4.3 MM CCTV Camera IR lens. Try searching e-bay or a local security camera shop.

Before removing the existing lens on your webcam, install the webcam software on your PC and test the webcam, to make sure the camera works. Note: it is critical to do this BEFORE voiding your warranty by opening it up and changing the lens! Once you've successfully taken a few pictures and ensured that the webcam works nicely, you are ready to switch the lens.

To replace the lens on the SPC900 camera (or other comparable cameras), you first need to pry off the ring around the lens using a screwdriver. Once that ring is gone, it is easy to replace the regular lens with a 'surveillance' lens by carefully (but firmly) unscrewing the lens.
The ring is just for looks, so you can put it back on, or leave it off. I

After you've swapped the lens, check the webcam to make sure it still works using the webcam software. You may also need to adjust the focus of the new lens. The images you get back from the webcam won't look like they do with a regular lens, this only means that it is working as expected.

Finally, if the camera has a built-in light to shine on what it's filming, cover the light with some duct tape to block it. If you don't, it will add some light 'noise' and will make your display have 'ghost' touch points.

Comments

[7577122]

Can we use IR camera directly instead of converting webcam into IR camera??? Thanks.

[theXmaker]

yes sure u can

[MK2MR2]

^ I'd like to know that as well