1. Field of the Invention
This invention relates to electrical control circuits and in particular to capacitive touch panel control circuits.
2. Description of the Background Art
In one form of conventional touch control illustrated in U.S. Pat. No. 3,974,472 of Robert R. Gould, Jr. a conductive pad is provided on the user's side of a glass panel. On the rear of the panel, additional conductive pads are associated with the conductive pad on the user's side. An oscillator and a level detector are connected to the conductive pads on the rear of the panel with the circuit arranged so that when the conductive pad on the user's side is untouched, the level detector provides a high or logic one level output. When the conductive pad on the user's side is touched, additional capacitance is introduced into the circuit between ground and the junction between the two capacitors formed by the conductive pads so as to attenuate the input to the level detector to produce a lower logic level zero output from the detector.
Leslie S. Jordan shows, in U.S. Pat. No. 4,056,699, a generally similar touch plate wherein the rear surface of the glass panel is provided with a nonconductive coating.
In U.S. Pat. No. 4,013,835 of Joseph J. Eachus et al, the touch sensitive device includes a printed circuit board arrangement of conductors which define the data input locations that are touch sensitive. A layer of variable resistance material is disposed over the printed circuit board which is highly conductive when subjected to touch pressure.
A somewhat similar structure is illustrated in U.S. Pat. No. 4,055,735 of Joseph J. Eachus et al.
John L. Otterlei, in U.S. Pat. No. 4,145,584, illustrates the use of indicia on a painted layer on the surface of a metal laminae which is spaced from keyboard components by ridges in an insulating layer.
In U.S. Pat. No. 4,161,766, Donald E. Castleberry et al disclose a laminated capacitive touch-pad having a thin film touch-plate electrode deposited upon a first surface of a first relatively thin dielectric layer and having spaced transmitter and receiver electrodes deposited upon a second surface of the first layer within the outline of and opposite to the touch electrode. A relatively thick backing layer of dielectric material is laminated upon the second surface to provide a total thickness as measured between the furthest opposed surfaces of the first and second layers, as required for high voltage insulation purposes. The patentees teach that the touch, transmitter and receiver electrodes may be of thin film construction.
Ferenc Ledniczki et al, in U.S. Pat. No. 4,221,975, show a touch activated controller for generating up and down control signals in response to movement of a person's finger along a control surface thereof.