Abstract: A display device includes a processor, a memory, an interface and a keypad. The keypad, separably connected to the interface, includes a signal generator. When the display device is connected to a power source, the processor sends a first signal to the interface. The signal generator generates a second signal in response to the first signal. The processor determines whether the second signal is correct based on data stored in the memory. If yes, the display device may be activated. A method for activating the display device via the separable keypad comprises the steps of: connecting the display device to the power source; the display device sending the first signal to the interface; determining whether the second signal is correct; and if yes, activating the display device.

Abstract: A light source device for a projection system is provided. The light source device includes a base, a frame, a light-emitting element and an eccentric element, wherein the frame has a pivot connected to the base; the light-emitting element is contained in the frame and provides a light source for the projection system; the eccentric element is mounted on the frame and props the frame, wherein when the eccentric element has a specific movement, the frame will be swung with the pivot and the light-emitting element will be moved accordingly so as to adjust a focal position of the light source device.