OT: Cat and Mouse

For those of you looking for IIS information, this blog post is not for you. For those of you that just like general computer information, read on and enjoy.

The computer mouse has come a long way over the years.  When Doug Engelbart invented the computer mouse, it was rather crude looking but was none-the-less very revolutionary.  Engelbart showed his invention to the world in 1968 during a presentation now know as “The Mother of All Demos.”  The mouse that Engelbart demoed was an electromechanical device that leveraged a large sphere to turn x and y coordinate counters as the device was rolled across a surface. Each click of the counter would tell the computer how far the mouse had “traveled”.  For several years the mouse kept the same basic principal. We improved on the original idea and replaced a large sphere with small rubbery balls with x,  i and often an additional diagonal gear wheel. The diagonal indicator was used to help correct the cursor movement if the mouse was rotated or tilted. The rubber helped the ball move across slick surfaces when a mouse pad just wasn’t cutting it. The downside to this rubbery surface was that pet owners ended up with a lot of cat (or dog) fur rolling into the mouse.  You would often have to open the bottom portion of the mouse and clean the hair and other debris out to make your pointing device work efficiently again.  Playing Doom or Quake with a junked-up mouse was an instant indication of a n00b that needed serious pwning.

Roll forward to the present day and we find optical mice taking the electromechanical device’s place. The optical approach solves a lot of the problems associated with older mice. For one, the new mice don’t have the rolling dowel-like rollers (counters) that can get gunked up anymore.  A rubbery ball is not picking up every piece of debris and yanking it into the mouse cavity as though it were a time-capsule for desktop debris.  So, why does your mouse still freak out when a piece of fur gets trapped under your optical mouse? 

The answer is pretty interesting and I’m sure will be solved with the next iteration of mouse invention. Many optical mice are created using a camera or an optoelectric sensor, an optical processor to compare images taken by the camera/sensor, and an LED  that illuminates the surface under your mouse.  The camera/sensor takes ~1500 picture samples a second!  The pictures are small (usually 10-20 square pixels) and gray-scale (usually registering fewer than 100 shades).  The optical processor examines and compares the picture samples to determine the relative position of the mouse to its previous position.

Now introduce your cat’s hair to the equation.  The cat hair gets entangled in the small cavity of the mouse where the optical sensor lives. As the mouse rolls across the desk, static builds up and flips the hair around wildly. As your mouse snaps those thousands of pictures, the hair position is captured and the optical processor gets confused by the sudden movement of the cat hair in the picture comparisons.  You can move your mouse slowly to the right, but if the hair is flipped around within the mouse cavity, the processor will think that you have jerked the mouse to the left or sharply downward.  If your cat is watching the computer screen as mine often does, these sharp movements may cause the cat to attack your monitor — truly creating an interesting game of cat and mouse.

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