Multitouch Zero Force Setup Based on IR Laser Light
Here is the setup that I’ve been working on for a while now. It is based on front IR illumination by IR laser.
For this project I’ve been using my old Orange Micro iBot firewire camera with great success. This low-cost camera generates 640x480 at 30fps uncompressed images in Y800 format. I found that because of all of this and the IR sensitivity this camera is very suitable for IR multitouch application:
After removing the original lens and mounting the new lens without IR blocking filter, I placed the double-sided tape on top of the lens and cut the opening in it:
IR Bandpass Filter
In the past I used photo negative with some success, but found that using narrow bandpass filter is by far the best in removing any unwanted IR noise and visible light:
Here is the filter mounted on the camera:
Currently I’m in the process of redesigning the table. Right now it is an open-frame setup:
And now the most important part. I use the 850nm IR Laser light to illuminate the front of the surface. When finger or any object interfere with the laser light, the camera below picks up the bright spot and runs it through the image processing algo to generate detected blob information.
Here is the view from the surface:
The laser is mounted on a tripod on a tri-point adjustable platform so that it can be positioned is a way that it generates a light beam that is parallel to the glass surface:
The IR laser is positioned just above the glass surface:
Even though I could use touchlib for blob processing/tracking, having a lot of experience in image processing, I found that it was easier for me to write a highly optimized version blob tracking software. Because of this, I achieve very low latency and low CPU usage running my blob tracking software (around 3-4% on my E6600 2.4GHz system).
Here are some screenshots of my blob tracking app:
As you can see blobs are very bright and clean:
Here is my iPhone placed on the surface:
Here you can see the system in action. While using FTIR the blobs become dimer during the fast movement, using the laser method the blobs are always bright
Short video of the system: