Computable Minds -

How works an optical mouse

Posted on: Dec, 7th 2010
camera of an optical mouse
On 1980, Steve Kirsh and Richard F. Lyon developed independently the first prototypes of optical mouse, technology that will began to replace the old ball mechanical mice in the 2001. Opposite to the mechanicals, the optical mice can't stuck by the dirt and are lot of more precise. Here you will discover how works exactly.

If we look below of our mouse we can see a little camera that have a resolution about 18x18 in black and white, and pointing directly downward. This camera, get images of the surface where rests the mouse, approximately at 1.500 times by second. This speed so high of getting images, is needed to that the mouse can be sensible to the movements more fast of the hand.

In order to that the images have the necessary illumination and appear shadows that can be detected, the mouse have a small led diode that usually are red (more cheaper than other colors), that isn't put on one side of the camera, but pointing to it and a prism deviate the light to direct it down.

Following, the obtained images are sent to a DSP (Digital Signal Processor), that is a chip that there are in circuitry of the mouse, and is the responsible of calculate the displacement produced between the actual image and the prior one from its differences, that is called in artificial intelligence the calculus of optical flow. With the firsts personal computers we had not DSP's at a size and reduced cost, for that the invention of the optical mice also have been possible thanks to that continuously emerge more powerful and cheaper processors.

At last, and in the same way as any other mouse, through the USB cable, send a message to the computer with the position that must move, this message travel in the motherboard by a line called interruption line, because it interrupts temporally anything that was doing the processor in that moment and force it to execute the program of the driver of the mouse, that put the pointer in its corresponding place. When the execution of the driver ends, the processor continues with that was doing, and as all this occurs in nanoseconds, never we could arrive to realize that a program it's delaying due to the movements of the mouse.

However, the optical mice can't do something that the old ball mechanical mice yes it can, I'm referring to work over polished surfaces, transparent or reflecting, where the camera or it can't get variations between the successive images or get too many light. Another disadvantage that has the optical mice is that needs more energy, overall due to the consumption of the DSP.

There are to mention also a important advance of this technology: the laser mice. These use a laser instead a led diode and a camera with more resolution, making it a lot of more precise, arriving as maximum to the 3.600 dpi (dots per inch), is that to say that recognize 3.600 points inside 2'54 cm, instead of the 800 dpi that can achieve an optical mouse. This increase of precision is due to that the laser light have more quality, because is the only kind of light source that is coherent, is that to say that all the electromagnetic waves of the light that emits have the same phase (we could say, that all the waves go out at the same time), that allows get images of more resolution and quality. This kind of mice is thought for graphic designers and for players of videogames that require a lot of precision.

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