Abstract:
A tactile matrix switch has a planar electrically conductive layer dielectrically spaced between contacts of individual switch elements and an actuating mechanism such as a finger on the body of a human being who may carry an electrostatic charge. Some switch contacts are electrically connected through external circuitry to ground. The conductive layer is also electrically connected to ground. When a human operator carrying an electrostatic charge brings his finger near the face of the matrix switch for applying a tactile force to actuate an individual switch element, the conductive layer electrically conducts the electrostatic charge to ground and away from the switch contacts for protecting the electrical circuitry connected to the latter. In one embodiment, the conductive layer is electrically conductive printer's ink, having a resistivity of less than 50 k ohms per square, that is silk screened onto the back of a face plate of the matrix switch. In an alternate embodiment, the conductive layer is printed onto the same broad side of a flexible dielectric plate to which the tactile force is applied, switch contacts being formed on the opposite broad side thereof.