Abstract
The basic elements of the optical computer mouse (OCM) are; a light emitting diode (LED), image
acquisition system (IAS) which acquires images via the lens and a digital signal processor (DSP) to
implement the algorithm to determine direction and distance of motion. Here, we describe the light
speckles produced from different colour LEDs and laser sources to design and implement a new optical
computer mouse. The speckle pattern will be used also to determine the responsivity and velocity of the
device relative to the surface it slides on it. The most important and critical property of speckles is their
average diameter, which is independent of the type of the surface being illuminated by coherent (He-Ne
laser and diode laser) or partially coherent light (LEDs). The average diameter of a speckle pattern is
function of the diameter of the illuminated area of the pad surface, the distance between the pad
surface and the detector, and the wavelength of the used light.
In this work, we replaced the OCM light source by a small powerful coloured LEDs and laser sources
and studying the resulting coloured speckle patterns to investigate the effect of different wavelengths
and the distance between the pad surface and the detector on the speckle diameters which affects the
response of the OCM.