An auditory playing device has a plurality of circular or polygonal tone plates marked with respective identification codes. Each of the tone plates has concentric dark and bright stripes that are placed, one at a time, in a recess defined in a casing substantially in any direction with respect to the...http://www.google.es/patents/US5451178?utm_source=gb-gplus-sharePatente US5451178 - Auditory playing device
