Paper Title
Perpendicular Detection Level for Land Surveying

Abstract
The objective of this research is to develop a device to detect perpendicular. This device is applicable to land surveying operations. In the land survey, theodolites or poles are set to be perpendicular. Usually people check the perpendicular visually. We are developing a digital level which is simple but have enough accuracy. The digital level measures the variation of the angle as the change of voltage. It uses a cheap and relatively simple circuit composed of LED and photo transistor. An LED is set just above the circular level. The LED sends an infrared right to a circular level to detect perpendicular. The bubble in the center of the circular level works as a concave lens. A photo detector is set directly below of the circular level. The appearance of the bubble is an indication that the piece is level. There is a shadow under the bubble. The quantity of light is measured by the phototransistor Keywords- three-dimensional survey, digital level, phototransistor, AD conversion