Abstract: A projection apparatus includes a projection component, a camera device, and at least one processor in connection with the camera device and the projection component respectively. The at least one processor is configured to execute instructions to cause the display apparatus to: in response to a projection command input from a user, control the projection component to project a first graphic card onto a screen, and obtain a first image taken by the camera device for the first graphic card; cut the first graphic card in the first image to obtain a first graphic card image; perform binarization processing on the first graphic card image, and obtain a white connected region in the first graphic card image based on a binarization result; position a to-be-projected region based on the white connected region; and control the projection component to project a to-be-projected content to the to-be-projected region.

Abstract: A transmission device for multi-frequency equal-amplitude non-harmonic electrical prospecting signal includes a single-chip microcontroller, a field programmable gate array (FPGA), a digital to analog conversion (DAC) module, an isolation amplifier circuit, a differential amplifier module, a digital power amplifier circuit, and a sensor module connected successively. A plurality of output ends of the digital power amplifier circuit is in cascade connection with a grounding electrode A and a grounding electrode B to form a loop with ground. An input end of the sensor module is connected with the digital power amplifier circuit. An output end of the sensor module is connected with the single-chip microcontroller.