A crt optical filter device includes a transparent plastic sheet and a transparent glass panel, each of which is provided with a transparent conductive circuit layer and a pair of conductors. The outer surface of the glass panel is disposed adjacent to the inner surface of the transparent plastic sheet, while the inner surface thereof is to be disposed adjacent to a screen of a computer monitor. A plurality of spacers, which are made of an insulative material, normally space apart the conductive circuit layers of the transparent plastic sheet and the glass panel. An interface card is connected electrically to the conductors and is to be connected electrically to a computer. The interface card receives analog X and Y signals that correspond to a selected part of the transparent plastic sheet from the conductors when the conductive circuit layers are brought into electrical contact due to application of pressure on the selected part of the transparent plastic sheet. The interface card processes the analog X and Y signals into corresponding digital signals for controlling the computer to move a cursor on the screen of the computer monitor so as to coincide with the selected part of the transparent plastic sheet and for controlling the computer to accomplish predetermined functions.

An M-sequence signal is generated in an M-sequence generation circuit, and the M-sequence signal, which is successively delayed by a column-electrode driving circuit or a row-electrode driving circuit, is applied to a column-electrode group or a row-electrode group. A correlator finds a correlation between the M-sequence signal and a detection signal that has been detected by amplifying electrostatically induced voltage that appeared in the detection electrode of an electronic pen so that a position specified by the electronic pen is detected by a detection circuit as a coordinate signal. Thus, it is possible to obtain a coordinate detection signal having a superior S/N ratio without reducing the coordinate detection speed, and consequently to carry out a coordinate detecting operation with high precision.

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.

Methods, systems and devices are described for detecting noise in a touchpad or other sensor that produces an output in response to a stimulus that is applied at or near a sensing region. According to various embodiments, a carrier signal is applied to the sensing region at two or more frequencies to thereby produce an output from the sensing region at each frequency. Each of the outputs is demodulated and filtered by a demodulation filter having a demodulation filter bandwidth. The various frequencies applied to the carrier signal are selected such that a difference between the frequencies is less than the demodulation filter bandwidth. At least some of the effects of the stimulus are removed from the outputs produced by the various carrier frequencies to produce two or more filtered outputs. The filtered outputs are then added, combined or otherwise processed to detect noise contained therein. If noise contained in one or more of the filtered outputs reaches an unacceptable level, the carrier signal may be shifted to a new sensing frequency for subsequent operation of the sensor.

A signal control apparatus includes an electrically resistive strip (4) allowing close proximity of a finger. A signal can be coupled into the strip, and a signal output (V1) can be detected at one end of the strip. The structure (1, 3) for coupling a signal into the strip (4) produces a high frequency signal in the strip and a signal output (V2) can be detected at the other end of the strip. These outputs (V1, V2) are dependent, in use, on the position along the strip of a finger in close proximity thereto and provide, by capacitive coupling to the strip (4), a leakage path for some of the signal. The last position of a finger along the strip (4) can be visually indicated when that finger has been removed. The strip (4) is on the underside of an insulating plate (10), the upper side of which has a path (11) for a finger to follow.