Touch control arrangement for graphics display apparatus having saw

Abstract

A system for recognizing touch positions along a predetermined coordinate axis on a surface of a touch panel display apparatus comprises a substrate having a surface capable of propagating surface acoustic waves and is so characterized that a touch on that surface causes amplitude damping of a surface wave passing through the region of touch. An input surface wave transducer, coupled to the substrate surface launches a burst of surface waves on the surface in a first direction parallel to the aforesaid axis. An output surface wave transducer is also coupled to the substrate. A first surface wave reflecting means derives wave components from the launched wave and reflects them across the display surface to a second wave reflecting means that redirects the reflected components in a second direction opposite to the aforesaid first direction. The first and second reflecting means causes wave components to traverse the display surface orthogonally to the coordinate axis along a progression of paths associated with different positions along the coordinate axis. Circuit means coupled to the input and output transducers initiate surface wave bursts across the surface as well as detect touch-induced damping of the received waves. The circuit means further includes means for developing an electrical signal representative of the time occurrence of the damping and thus an indication of which of the plurality of paths was traversed by the touch-damped wave and thereby the location of the touch on the display surface. The first and second wave reflecting means are silk-screened onto the surface, and comprise a baked frit material containing a refractory nucleation-accelerating agent.