Combination mouse/trackball input device

A combination mouse/trackball input device for an electronic computer functions as either a mouse or a trackball, depending on which of two operating modes the user selects. The user selects the desired mode by moving a selector handle to one of two positions, which causes a tracking ball to be raised to trackball mode or lowered to mouse mode. In mouse mode, the tracking ball makes contact with the mouse pad or other flat surface on which the device rests so that the ball rotates when the device is moved. This mode is suitable for general purpose use. In trackball mode, the tracking ball is elevated so that it does not make contact with the mouse pad, but it projects through an aperture in the top face of the enclosure. In this mode, which is preferred for applications requiring fine control over the cursor position, the user rotates the ball directly with his or her fingers. The device permits easy switching between the two modes with minimal interruption of the user's work. In both modes, rollers sense the rotation of the tracking ball along two axes and a photo detector mechanism converts this rotation into electrical pulses which are sent to the attached computer. The computer uses the pulses to calculate the movement of the tracking ball along two axes and to move an on-screen cursor accordingly.