Patent ID: 8730167

Claim:
A computer input device comprising: a light source assembly forming an incident light beam that strikes an area on a top surface of a piece of glass beneath the input device at an angle between 75 and 85 degrees from a normal to the top surface, wherein a portion of the incident light beam is scattered by the top surface to form scattered light, a portion of the incident light beam is reflected by the top surface of the piece of glass to form a first specular reflection and a portion of the incident light is reflected by a bottom surface of the piece of glass to form a second specular reflection, wherein the light source further comprises a lens that focuses the incident light beam so that the first specular reflection from the top surface of the piece of glass converges on a first focal point and the second specular reflection from the bottom surface of the piece of glass converges on a second focal point; a light sensing assembly that is positioned to receive light from the piece of glass, wherein the light sensing assembly is spaced from the specular reflections and is positioned between the specular reflections and a space directly above the area of the top surface where the incident light beam strikes the top surface, such that a majority of the received light comprises the scattered light from the top surface; a light barrier in a space located directly above the area on the top surface where the incident light beam strikes the top surface, wherein at least a portion of the light barrier is located along a line extending directly between the light source assembly and the light sensing assembly so as to block light from traveling along the line from the light source assembly to the light sensing assembly; and a printed circuit board to which the light source assembly, the light sensing assembly and the light barrier are mounted.