Viewing distance control device

The viewing distance of human body is measured and controlled based on combination of ultrasonic ranging and human body infrared detection; on one hand, the distance, more than 6cm, of an object in a limited range is accurately measured by the mature ultrasonic ranging technology, an ultrasonic generator and a receiver calculate the distance of a barrier according to the ultrasonic delay reflected back through a singlechip technology, and simultaneously, output a control signal according to the preset warning distance; on the other hand, whether the barrier is the human body is detected and judged by a human body infrared pyroelectric sensor, and the output of ultrasonic detection is controlled according to the output of the distance judgment, so as to distinguish false triggering caused by non-human sheltering; an output end is controlled by combination of the two judging modes, so that a screen power supply or the screen brightness of a viewed video device can be controlled, and the viewed video is lowered or closed when a predetermined video warning range is reached.