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 capacitive touch panel system (10) having a faceplate (14) with an electrically conductive layer (20) of a consistent resistivity employs a position measurement apparatus (12) to generate an address signal indicative of a position (46) on the faceplate in contact with a stylus (48). The position measurement apparatus includes a position measurement signal source (56) that generates a square-wave measurement signal of a frequency that varies in a substantially random manner. The position measurement signal is applied to a first pair of opposed electrodes (36) and (40) and a second pair of opposed electrodes (38) and (42) positioned along respective side margins (26, 30, 28, and 32) of the faceplate. The resistivity of the conductive layer establishes effective resistances of R.sub.x and R.sub.y between the respective first and second pairs of electrodes. Position measurement subcircuits (54a-54d) are locked-in with the random measurement signal frequencies to measure currents drawn through the electrodes whenever the stylus contacts the conductive layer, thereby to form an address signal indicative of the location at which the stylus contacts the faceplate. The random measurement signal frequencies reduce the susceptibility of the position measurement apparatus to electromagnetic noise and distributes over a relatively broad bandwidth the electromagnetic noise generated by the position measurement apparatus.

There are provided an apparatus for detecting an approaching conductor and an approach point or position of a conductor, in which a signal processing is simply performed and an improvement in the noise resistance is performed without the influence of a floating capacity. The apparatus has a voltage-oscillating system for equivalently receiving electric oscillation (AC signal) from a detected conductor so that the received electric oscillation is processed as a signal to ground and the processed signal is send to a non-oscillating system through an isolator, the system including a sensor panel or a sensor conductive array, a shield plate, a signal processing circuit, a ground, and power source. In addition, in order to clearly and securably identify a cause of the false earth effect of a detected conductor such as a human body, over 200 kHz oscillation frequency is provided. There is also provided an electrostatic capacity coupling type touch panel apparatus, in which an AC signal is applied into a finger, AC signal being 200 or more kHz frequency.

A touch sensor switch that responds to touching, or even to the proximity of an object, is disclosed. The switch includes a number of capacitance elements, or touch pads, that produce an effective capacitance dependent upon the physical proximity of the object. A microcontroller under control of a program stored in a read-only memory causes its I/O port to set a transient voltage on each capacitance element as a logic level. Each transient voltage is at variance with the capacitive element's preferred voltage level. The program then reads the I/O port, and hence the logic levels of the capacitance elements, as the capacitive elements revert to their preferred voltage levels, and calculates the proximity of the object, or touching, from relationships among recorded signals. The circuit may also be embodied in an application specific integrated circuit.

In a panel member of a coordinates input device, a first input unit and a second input unit are set on a pair of transparent electrodes and the first input unit only allows input by a member of a relatively large pressing pressure such as by using a pen. The second input unit also allows input by pressing with a member of a relatively small pressing pressure, such as a finger, and thus is not limited to a pen. In order to achieve a coordinates input device of enhanced accuracy in the reading of pressing position by accurately measuring the pressing level at the pressing position, the device possesses a structure in which an X-direction resistive film and a Y-direction resistive film are separated by a tiny clearance and, when the pressing position is pressed, various switches are controlled by a specified procedure such that the X-direction and Y-direction levels of the contact resistance due to the pressing of the position are detected and, only when the pressing levels are sufficient, are coordinates of the pressing position measured.