The present invention relates to a planar product in which a plurality of fibrous plies are bonded to each other with the aid of an adhesive containing a polymer with units derived from a vinylamine. The microspheres may be glass-coated microspheres, which are bound together by sintering the outer layers of glass together. The apparatus includes a digital engine and a digital-to-analog converter. A comparator circuit is coupled to each of the plurality of decision circuits, and is operative to provide an event occurrence signal in response to the bit decision output signals from each of the plurality of decision circuits.