Force invariant touch sensitive actuator

A user interface for a lighting control, the user interface comprising:

• a touch sensitive front surface having a longitudinal axis and a lateral axis;
• a three-wire resistive touch pad responsive to a point actuation on the touch sensitive front surface, the resistive touch pad having a longitudinal resistive element and an output with a DC supply voltage coupled across the longitudinal resistive element, such that the output is operable to provide an output voltage representative of the position of the point actuation along the longitudinal axis;
• a controller having first and second inputs;
• a first capacitor coupled between the first input of the controller and a circuit common, the first capacitor operable to charge and discharge through the longitudinal resistive element of the resistive touch pad to stabilize the first control signal;
• and
• a first switch responsive to the controller and coupled between the output of the resistive touch pad and the first input of the controller;
• a second switch responsive to the controller and coupled between the output of the resistive touch pad and the second input of the controller;
• wherein the controller is operable to render the second switch conductive, such that the voltage at the second input is representative of whether the touch sensitive front surface is presently being actuated, and to render the first switch conductive such that the first capacitor is operable to stabilize the output voltage of the resistive touch pad and the voltage at the first input is representative of the position of the point actuation along the longitudinal axis.

A method of reading outputs of a four-wire resistive touch pad having a longitudinal resistive element and a lateral resistive element for a load control device for controlling the amount of power delivered to an electrical load from an AC power source, the method comprising the steps of:

• coupling a DC supply voltage across the lateral resistive element;
• generating a first output voltage at the longitudinal resistive element in response to an actuation of the touch pad;
• determining that the actuation of the touch pad is presently occurring in response to the first output voltage;
• coupling the DC supply voltage across the longitudinal resistive element;
• generating a second output voltage at the lateral resistive element in response to the actuation of the touch pad;
• stabilizing the second output voltage;
• and
• controlling the amount of power provided to the electrical load in response to the second output voltage only when the first output voltage indicates that the touch pad is presently being actuated.

A load control device for controlling an amount of power delivered to an electrical load from an AC power source, the load control device comprising:

• a semiconductor switch operable to be coupled in series electrical connection between the source and the load, the semiconductor switch having a control input for controlling the semiconductor switch between a non-conductive state and a conductive state;
• a controller operatively coupled to the control input of the semiconductor switch for controlling the semiconductor switch between the non-conductive state and the conductive state;
• a touch sensitive front surface having a longitudinal axis and a lateral axis;
• a four-wire resistive touch pad responsive to a point actuation on the touch sensitive front surface, the resistive touch pad having a longitudinal resistive element for providing a first control signal representative of the position of the point actuation along the longitudinal axis to the controller, and a lateral resistive element for providing a second control signal representative of the position of the point actuation along the lateral axis to the controller;
• a first capacitor adapted to be coupled between the lateral resistive element and a circuit common, the first capacitor operable to charge and discharge through the longitudinal resistive element of the resistive touch pad to stabilize the first control signal;
• and
• first, second, and third switches responsive to the controller, each of the switches comprising first, second, and third terminals, and operable to be controlled between a first position in which the first terminal is electrically connected to the second terminal, and a second position in which the first terminal is electrically connected to the third terminal, the switches coupled to the four-wire resistive touch pad, such that when the controller controls all of the switches to the first position, a DC supply voltage is coupled across the longitudinal resistive element, the controller is coupled to the lateral resistive element, and the first capacitor is coupled between the lateral resistive element and the circuit common, and when the controller controls all of the switches to the second position, the DC supply voltage is coupled across the lateral resistive element and the controller is coupled to the longitudinal resistive element;
• wherein the controller is operable to determine if the touch sensitive front surface is presently being actuated in response to the second control signal, and to determine the position of the point actuation along the longitudinal axis in response to the first control signal.