A includes a shaft having a length, a first end, and a second end; the second end has an oblique reflective surface defined thereon; the first end fixedly attached to the knob. Containing the shaft is a rotation body, having a receptacle to accommodate the second end of the shaft with the oblique reflective surface exposed. An integrated circuit optical module is optically coupled to the rotation body. The optical module detects a light irradiance profile from the oblique reflective surface and includes a solid state light source and a plurality of photo detectors which generate an electrical signal upon exposure to light. As the knob is rotated, the oblique reflective surface generates a changing asymmetric irradiance profile, the change being translated into an electrical signal via the photo detectors, which signal corresponds to the degree of rotation of the knob.