An exemplary controller includes a transparent chamber, an opaque liquid, and four photoelectric sensors. The transparent chamber includes four pipe-shaped arms. The four pipe-shaped arms are in a common plane parallel to the vertical direction and extend away from a common end towards vertical up, horizontal left, vertical down, and horizontal right directions to form four closed distal ends when the controller is in a normal orientation. The opaque liquid is sealed within the transparent chamber so that an air bubble is formed within the transparent chamber. The four photoelectric sensors are U-shaped and cap the four closed distal ends respectively and are configured for detecting which closed distal end the air bubble is located, thereby outputting electrical signals to be coded as control signals.