A cathode ray tube display device has conductive plates mounted adjacent the four sides of the CRT faceplate. These plates are positioned to sense electromagnetic noise radiation generated by the CRT. The plates are coupled to differential circuits so that normally the noise signals generated in the plates cancel. However when a finger or other object is placed at or near the CRT faceplate, the noise radiation field is disturbed, and the changed signals generated in the plates are sensed by the circuits to provide output signals indicative of the coordinate position of the object at the faceplate. The plates are preferably mounted in the front bezel of the display cabinet.
In an arrangement wherein an inquiry and a choice of respones thereto are displayed on a CRT screen, a selection is made by holding a touch-screen device against the area of the screen corresponding to the desired response. Such a touch-screen device is designed to have an inductive coil in its tip. When an electron beam which scans the CRT screen sweeps across the tip of the touch-screen device, an electrical signal is induced on the coil. The touch-position or the selection is determined based on a knowledge of the position of the electron beam on the screen at the time of the electrical signal induction.
A method of providing for resistance to attack by monitoring of an integrated circuit by means of monitoring I.sub.dd current changes. The method comprises the step of including a spurious noise generation circuit as part of the integrated circuit, to increase the Signal to Noise Ratio in the I.sub.dd signal and obscure meaningful information.
A conductive coating on the front surface of the display screen is used to determine the position of an object, such as a user's finger, touching the screen. Sensors at the edge of the conductive coating detect changes in the level of the ambient field pickup when the user's finger touches the display screen. The conductive coating may optionally be divided into blocks with separate connections to each block, or may have a resistivity profile so as to allow full X and Y co-ordinate determination of the position of the finger. Also, optionally, a stylus generating an electromagnetic field when in contact with the display may be used in place of the finger.
A field emission device pen-based system comprising a pen stylus 20 and a field emission device having a cathode 2 coupled to an anode 1, row and column drivers 68 and 66 coupled to the cathode and to a controller 64, row and column lines 96 and 98 respectively coupled to the row and column drivers 68 and 66, and receive circuitry 81 and 91 coupled to the controller 64 and to the row and column lines 96 and 98; wherein the row and column drivers 68 and 66 send a pulse on the row and column lines 96 and 98 in response to an input signal from the controller 64, and the receive circuitry 81 and 91 receive a pulse from the stylus on the row and column lines 98 and 96. The receive circuitry 81 and 91 send an output signal to the controller 64 responsive to the received pulses and the controller 64 determines the x-y location of the stylus 20 based on that output signal.
An integrated graphic tablet/touchpad can be toggled between an absolute (graphic tablet) input mode and a relative (touchpad) input mode. In the relative mode, a graphics window appears on an associated display only when pressure is exerted on an input surface, and a cursor can be moved by stroking the input surface. In contrast, in the absolute mode the window is always displayed, and the cursor is relocated to a new position in the window each time a stylus or finger is moved onto the input surface. A graphic tablet armrest bridge is also disclosed, as is a one-piece stick-on device that converts a portion of the area of a position sensitive cursor control input device into a cursor control area having cursor control characteristics that are different than those of the remainder of the input device.
