Patent ID: 8562147

Claim:
A projector controlled by a control command of a first infra ray (IR) signal provided by a remote controller, the first IR signal having a frame period length, wherein the projector comprises: a lens; an IR emission circuit for emitting a second IR signal to detect whether an obstacle is positioned on an optical path of the projection light, wherein the IR emission circuit emits the second IR signal during a first period and stops emitting the second IR signal during a second period, the first period and the second period are periodically repeated, the second period is N times of the frame period length, and N is a natural number larger than 1; a first IR reception circuit, comprising: a first output end; and a first IR receiver electrically connected to the first output end, wherein the first IR receiver provides a first output signal in response to the first IR signal via the first output end, and when the obstacle is positioned on the optical path, the second IR signal is reflected to the first IR receiver via the obstacle, and the first IR receiver provides a second output signal in response to the second IR signal via the first output end; and a central processing circuit coupled to the first output end, wherein the central processing circuit alters an operational mode of the projector in response to the second output signal, and controls the projector based on the first output signal.