A touch panel input device includes a sensor for detecting that an operator's finger has approached toward a touch input key, to prevent the operator from performing an erroneous key input operation. The sensor includes a multiplicity of optical element pairs each made up of a light emitting diode for emitting a light beam and a photodetector receiving the light beam from the light emitting element. Light beams generated by the optical element pairs are arranged in the form of a matrix to form a detection plane. When the operator's finger traverses the detection plane, a cursor is displayed on the display screen at a position corresponding to the position of the finger on the detection plane. Accordingly, the operator can correct the movement of the finger toward a desired key position by observing the cursor.

An improved touch overlay for the viewing surface of a display for detecting both finger touch and stylus location is disclosed. An upper and a lower set of transparent conductors are disposed on at least one transparent flexible insulating substrate and are oriented orthogonally with respect to each other. Depending on the orientation of the transparent conductors, top and bottom cover layers may be added to the overlay. The separation between the upper and lower conductors and a separation from the user's finger on the top surface of the overlay from the upper conductors is optimized. To speed finger touch sensing, the ambient capacitance of the overlay is reduced by increasing the separation between the upper and lower conductors layers. For improved operation, the present invention features a separation of at least 3 mils between upper and lower conductors. The separation between the top surface and the upper conductors is held to a minimum consistent with the preservation of integrity of the upper conductors when stylus pressure is applied. Means are also included in the overlay to improve the durability of the overlay with respect to repeated stylus pressure on top surface.

A capacitive switch is formed of a dielectric layer having a first electrode disposed on or adjacent one surface and a second electrode and a conductive pad, such as a touch pad, disposed on the opposite side of the dielectric layer. The conductive pad and the second electrode are in superimposed relationship to the first electrode. The conductive pad and second electrode may be side by side, with a small gap between or they may be superimposed on one another with a further dielectric layer between. Such switches may be formed into an array and may be combined with a display by being superimposed over a display medium, such as an electroluminescent layer, having a display electrode on one side and the first electrode on the other side. In this arrangement all the components, except the display medium and the display electrode, are of transparent material.

A touch pad machine control system uses a touch pad having an overlay to define control strip surface areas which perform different functions. The contact of an operator's finger along one of the defined control strips selects a desired function and produces the desired machine motion from the rate, distance or duration of finger contact according to the desired function. The result is equivalent control motion without the need for moving parts.

A touch panel has panel scanning signals selectively applied to the four sides of a touch sensing surface of the panel so as to establish alternating current voltage gradients in desired directions across the touch sensing surface. When the panel is touched, touch signals result and are utilized by a touch location circuit in determining the location of touch. The impedence touch current resulting from a user's touch may also be determined and used. The touch panel circuit automatically compensates for any variations in touch signals which occur when the touch panel is untouched and automatically nulls the touch signals under such circumstances to enhance the accuracy of touch location determination.