Input interface device with semiconductor strain gage

Abstract

The invention provides for an interface device that measures strain on a specific area of the printed circuit board. The measurements are converted into an electrical signal and sent for processing. The processing results in the apparatus performing a desired function. The interface device includes a printed circuit board. The printed circuit board comprises a plurality of layers, including a conductive layer. The interface device further includes a strain sensing device. The strain sensing device is mounted on the printed circuit board and includes a substrate, a strain sensing element, and associated circuitry. In some instances, the strain sensing device includes one strain sensing element and in other instances multiple strain sensing elements can also be used. In one embodiment, the strain sensing device can include a piezoresistive strain gage combined with signal conditioning circuitry such that a single electronic component can be mounted on the printed circuit board for reduced cost and improved signal-to-noise performance. In operation, a user or another device applies force on the printed circuit board in the area of the strain sensing device. The strain sensitive element deforms in response to the applied force or strain on the printed circuit board. The deformation results in the change of resistance or conductivity of the strain sensitive element. The associated circuitry, which can be a signal conditioning circuit, converts the change in resistance or conductivity into a digital signal. Once the conversion occurs, the associated circuitry uses the conductive layer of the printed circuit board to communicate the digital signal to either the processor or the processing circuit of the electronic apparatus. The processor or processing circuit receives the digital signal and responds by performing a desired action. In one instance the interface device may be used to measure the magnitude of the force applied by a finger pressing on the touch screen of an electronic apparatus such as a cell phone. The magnitude of the applied force can then be used to control, the operation of the cell phone. A high magnitude force would result in a higher strain being sensed and can cause the apparatus to operate in one way, whereas a low magnitude force would result in a lower strain being sensed and can cause the apparatus to operate in another way, e.g., in a mobile phone environment where an application is used to draw a picture, a light force applied to the touch screen could be processed to result in a thin line being drawn and a stronger force could be processed to result in a wider line being drawn. In another instance the interface device may be used to measure the magnitude of the force applied to a control toggle on the steering wheel of a car. The toggle may be used to control the intensity of the sound emitted from the audio system in the car. A high magnitude force could be processed to cause the intensity of the sound to change rapidly whereas a low magnitude force could be processed to cause the intensity of the sound to change slowly.