Patent ID: 7439952

Claim:
An electronic pointing or cursor control device comprising a first chamber and a second chamber, wherein: the first chamber is fluid tight; the two chambers are adjoined and separated by a fluid-tight separating wall; the first chamber contains electronic components; the second chamber comprises an aperture; the second chamber contains a ball, the ball protruding through said aperture; the said separating wall comprises an optically permeable region; and the electronic components include an optical detector directed towards the optically permeable region and the ball, the optical detector being operable in use to detect motion of the ball and to generate electronic signals representative of said motion, wherein the distance in the second chamber between the surface of said optically permeable region and the surface of the ball is sufficiently small such that any liquid between the ball and the optically permeable region of the separating wall is thinly dispersed and does not prevent optical transmission between the ball and the optical detector.