An electronic drum has two or more batons, each baton having a transmitter which transmits a distinct radio frequency signal at a position in space. The electronic drum determines the current X, Y, and Z coordinates of each baton transmitter. To determine the position of each baton transmitter, the drum...http://www.google.com.hk/patents/US4980519?utm_source=gb-gplus-share專利 US4980519 - Three dimensional baton and gesture sensor
