DIY MT-50 Multitouch Table


Step 11: Installing the Cameras

Picture of Installing the Cameras
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Three PT Grey Firefly MV (Firewire version) cameras are used in the MT-50 to track the finger movements on the table surface. The cameras come in a small plastic case with a mount assembly. Before mounting the cameras, they need to be taken apart to install the band pass filter.

Remove the case of the cameras to reveal a small circuit board.

There will be a lens mount attached to the board by two screws. Remove the lens mount to reveal a rubber grommet and a small clear lens. You will also see the small CMOS sensor in the middle of the board. This is essentially the ‘lens’ of the camera, so be sure not to allow anything to come into contact with it.

Remove the rubber grommet, and take out the clear lens. Replace the clear lens with the band pass filter. Reassemble the camera.

Once the plastic case is back together, you can then put on the camera lens, and attach the mounting hardware.

Use a 20 x 20 gusset to attach each camera to the camera rig. You will need to drill out one side of the gusset with a ¼” drill bit to enable it to fit the camera screw hole. Using a rubber washer to prevent the gusset from damaging the side of the camera, screw the gusset onto the camera with an M6 screw. Put a screw with 20 mm T-nut into the other side of the gusset and screw the camera to the rig.

Camera spacing is very important to ensure stitching and may need to be adjusted once the tracking software is installed. See the attached diagram to get an idea of the rough spacing that should be used if using a 3-camera system. 

The cameras are powered and controlled via FireWire. When the camera feed is cropped within the tracking software, it actually communicates with the camera's BIOS and tells it to ignore those extraneous pixels, making the processing very stable and lowering the amount of bandwidth needed to run the cameras. The middle camera runs on its own Firewire card, since it has a larger area to monitor, and the outer two share one, ensuring that the camera feed won't exceed the available bandwidth, which can cause the OS to throw a stop code (Blue screen of death) and force the computer to be restarted.
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