Device for forming signals which are characteristic of the position of a point determined on a surface

Claim 1

Device for forming signals which are characteristic of the position of a point determined on a surface, especially by pressure exerted at right angles to this point, comprising a first insulating substrate (1) covering the surface, a first grid of conductive tracks (2) placed on one face of this first substrate and spaced apart from each other, a second substrate (5) of flexible insulating material, covering the face of the first substrate carrying the said conductive tracks (2), a second grid of conductive tracks (6) placed on the face of the second substrate located opposite to the first grid of tracks (2), the tracks of this second grid being spaced apart from each other and extending transversely with respect to the tracks of the first grid, elements (4) maintaining the second substrate in a firm position so that each track of its grid remains distant from any of the tracks of the first grid as long as no pressure is exerted on at least one zone of the said second substrate, means for locating the tracks of the said grids brought into mutual contact when the said second substrate is subjected to the said pressure, wherein these means comprise: two resistive voltage dividers (R AX , R AY ), one of which (R AX ) is associated with the first of the two grids of tracks and the other (R AY ) is associated with the second of these grids, each track of one grid being attached at one end to one point of the respective divider in such a manner that the ohmic resistance between this point and one of the ends of this divider is characteristic of the position occupied by this track in its grid, first and a second switching elements (P a , P c ) respectively associated with the first and second voltage dividers and permitting one of the ends of the corresponding divider to be connected either to a reference voltage (V m ) in a first active switching state of each element, or to a voltage signal collection means (L 2 , M e ), in a second active state of each element, a third switching element (P b ) permitting the other end of one or the other divider to be connected to ground (T) or to be disconnected from it, elements (CDE) for periodically controlling the said switching elements (P a , P b , P c ), arranged in such a manner that each of the said first (P a ) and second (P c ) switching elements is set to the first of these two active states when the other of these elements is in the second of these states, and conversely, and in such a manner that said third element (P b ) connects the second end of each divider to ground (T) when the first end of the divider is connected to the said reference voltage sources (V m ), this ground connection being interrupted by this third element (P b ) when the first end of the divider is connected to said voltage signal collection means (L 2 , M e ), the whole being arranged in such a manner that, following a pressure exerted on any point of the said surface corresponding to a zone of electric contact between at least two tracks of which each belongs to a separate grid, the said collection means (L 2 , M e ) receives, alternately and in synchronism with the arrival of the said switching elements (P a , P b , P c ) in one or the other active states, voltage signals the amplitudes of which are successively characteristic of the abscissa and ordinate of the position of the said tracks and consequently of the said point of the surface.