Computer input device using orientation sensor

A hand-held device for controlling cursor movement on a data terminal having a display. An internal orientation sensor provides an electrical signal that is related to the orientation of the device without it being adjacent to any fixed surface. The orientation sensor includes a hollow spherical housing having at least one LED and one phototransistor mounted opposingly in the inner wall, along an axis extending through the center point of the housing. The housing is half-filled with a transparent liquid having a specified viscosity and index of refraction and half-filled with air. A light beam emitted from the LED is refracted upon passing through the boundary between the air and the liquid. As the orientation sensor rotates with respect to the vertical axis, the changing refraction angle of the light beam causes the phototransistor to detect changing intensities of light, which are representative of the angle of rotation.