what is whiteboard coding., No special pen, finger, etc. Writing pointer or touch 3 , long service life , the reaction faster , lower cost disadvantages: 1 , no sense of pressure reactor 2 , may be affected by the infrared light intensity using this Major manufacturers of technology: USA: 3M UK: Sahara and Luidia Japan: HITACHI China: IQBoard IV: The principle of ultrasonic ultrasonic technology is: using the characteristics of slower transmission speed of ultrasonic waves, calculating the transmission point to receiving according to the ultrasonic transmission to the receiving time The distance of the point. The principle of using the planar positioning is to place two ultrasonic receiving devices distributed at a fixed distance on one side of the screen, and the pen for positioning is an ultrasonic transmitter, and the ultrasonic wave emitted when the pen moves on the surface of the screen It is detected by the receiver along the surface of the screen, and the distance between the pen and the two receivers can be converted by the time of receiving the ultrasonic waves. The principle of three-point positioning is adopted, that is, according to the three side lengths of the triangle, the apex principle of the pen can be determined, and the position coordinates of the pen are calculated. It is a ranging positioning mode. Advantages and disadvantages of technology analysis advantages: 1 , relatively accurate positioning 2 , adaptability, can be used in different areas of equipment disadvantages: 1 , positioning accuracy is uneven 2