A battery-powered magnetic pen has an oscillator for generating a magnetic field at a contact frequency and a proximity frequency. The oscillator is connected to a resettable timer. The pen also includes a tip switch that is actuated in response to the pen being brought into engagement with an object and disengaged from the object. The tip switch is connected to a pulse generator and to the oscillator. Each time the pen is brought into engagement with an object, the pulse generator resets the timer to initiate the timing of a time out period. Assuming the oscillator is off, the first time the pen contacts an object, the resetting causes the oscillator to be turned on. So long as the oscillator is on, the opening and closing of the tip switch causes the oscillator to switch between the contact frequency and the proximity frequency. Should the timer reach the end of a predetermined time out period, the oscillator is shut off. Thus, if the tip switch is continuously actuated for the time out period, such as might occur due to improper storage of the pen, the oscillator is shut off to prevent the battery from becoming discharged.

An electromagnetic pen digitizer is integrated into a flat panel display assembly using "bent TAB" active electronics. Integration is performed by placing a discrete electromagnetic pen digitizer further inside the flat panel display assembly itself behind the diffuser backlight component, but in front of the "bent TAB" active electronics. Interference from the active electronics is avoided because they are not in between the digitizer and the pen operating upon the flat panel display. The electromagnetic pen digitizer is integrated into the flat panel display assembly by inserting the digitizer into the flat panel display assembly behind the diffuser backlight during the routine manufacture of the flat panel display assembly. Alternatively, the discrete electromagnetic pen digitizer is bonded to the diffuser backlight earlier in the manufacturing process; the combined diffuser backlight/digitizer component is placed into the flat panel display assembly during the routine manufacture of the complete flat panel display assembly. By integrating such a digitizer into the routine manufacturing process of a flat panel display, a standard "off-the-shelf" flat panel display may be used. The digitizer may be directly coated onto the diffuser backlight through an indium tin oxide (ITO) coating on the backlight itself. Also, an electromagnetic digitizer may be fabricated onto the front of the diffuser backlight by using a thin-film etched flexible circuit technique or a silk screen printed thin-film technique. Integrating an electromagnetic pen digitizer in this fashion allows for greater use of "off-the-shelf" display panels with only slight modifications.

A computer input device for use as a computer mouse or keyboard comprises a thin, insulating surface covering an array of electrodes. Such electrodes are arranged in a grid pattern and can be connected in columns and rows. Each column and row is connected to circuitry for measuring the capacitance seen by each column and row. The position of an object, such as a finger or handheld stylus, with respect to the array is determined from the centroid of such capacitance values, which is calculated in a microcontroller. For applications in which the input device is used as a mouse, the microcontroller forwards position change information to the computer. For applications in which the input device is used as a keyboard, the microcomputer identifies a key from the position of the touching object and forwards such key identity to the computer.

In a method and apparatus for detecting the position of a coordinate probe relative to a digitizing tablet, a sensing coil grid provided on a working region of the tablet includes a plurality of sensing coils, each of which is U-shaped and has a front section and a grounded rear section. The coils are arranged in parallel along an axis of the working region in an overlapping manner with the front sections of consecutive ones of the coils being arranged in succession, and with the rear sections of the coils also being arranged in succession. During the sequential scanning of the coils in order to detect the electric currents induced therein and to generate a grid signal when the coordinate probe is disposed on the working region, a phase selection circuit inverts one of front and rear half-cycles of the grid signal, depending on whether a front scanning or rear scanning operation is being performed, and a signal processing circuit detects the presence of a predetermined transition of the inverted signal from the phase selection circuit. The signal processing circuit generates a count output corresponding to time elapsed before the predetermined transition is detected, and the count output is converted by a processor into a coordinate of the coordinate probe along the axis of the working region of the tablet.

A pressure sensitive pointing device or pen is described for use with an electronic tablet that determines the position of the pointing device on the surface of the tablet. The pointing device incorporates a variable reluctance circuit responsive to the force exerted on the pen point for modulating a radiating frequency, emanating from the pen, in proportion to the force.