Abstract: A keypad arrangement for an electronic device comprises a keypad comprising activatable keys. It comprises also input signal means (801, 802, 901, 1001, 1601) for bringing an electric input signal to the keypad, and signal conversion means (703, 705, 807, 808, 809, 810, 811, 812, 813, 818, 1208, 1206) for responding to a key activation by selectively converting the input signal into an electric output signal the value of which depends on the activated key. Additionally there are output signal detection means (902, 903, 904, 1002, 1602) for detecting the value of the electric output signal. The arrangement comprises a first electromagnetic coupling (706, 708, 709, 710, 803) between the input signal means and the signal conversion means, and a second electromagnetic coupling (707, 711, 804) between the signal conversion means and the output signal detection means.

Abstract: A control member of the capacitive type for controlling at least one functional member in particular of a motor vehicle, the control member including a rigid support structure, at least one capacitive touch-sensitive detection cell located on or close to one of the faces of the support structure, and at least one control operating zone located on or close to the other face of the support structure in registration with the capacitive touch-sensitive detection cell, wherein the control operating zone includes an elastically deformable part.

Abstract: A structure and method is disclosed for dissipating electrostatic charges comprising an underlying dielectric layer disposed over capacitor plates of sensor circuitry, and a conductive layer and passivation layers disposed over the underlying dielectric layer wherein the conductive layer diffuses electrostatic charges at the surface of the integrated circuit.

Abstract: A touch sensor which is able to detect the touch of a finger with reasonable accuracy. In this touch sensor, the oscillator unit supplies a high-frequency signal to the electrode unit. If the item detected is a biological entity of a human body such as a finger, the impedance of the electrode unit will change. The impedance is initially matched to that on the input side of the electrode when the finger is in touch with the electrodes. The reflected wave will be smaller because of the matching of impedance when the finger is in touch with the electrode. By detecting this reflected wave and comparing it with a reference signal in the discriminator unit, it can be determined that the reflection level is lower and so a conclusion can be made that the electrode is touched by a person.

Abstract: A capacitive sensor (30) for use with a automotive vehicle (200) having a power sliding door (202) has a flexible housing (44). The housing (44) has a first set of electrodes (12) and a second set of electrodes (14) interdigitally spaced from each other and a ground electrode (15) made from a flexible metallic braid.

Abstract: Proximity of a body, which may be a user's finger, to an electrode pair is sensed by a charge transfer capacitive measurement approach. The electrode pair thus acts as a key that can be arrayed with other electrode pairs to form a keypad, keyboard, linear slider control, or liquid level sensor. In one embodiment of the invention each key is associated with an alternating voltage source and a pair of electrodes mounted on or within a solid dielectric substrate or panel so as to be separated from each other by a gap. The voltage source is connected to a driven electrode, a sampling charge detector is connected to a second, receiving, electrode, and the output of the charge detector is, in turn, fed into a signal processor. Disturbances in coupling between the two electrodes are detected through the solid substrate or panel material when a substance or object approaches or contacts the panel.

Abstract: A distance sensor has a capacitive element in turn having a first capacitor plate which is positioned facing a second capacitor plate whose distance is to be measured. In the case of fingerprinting, the second capacitor plate is defined directly by the skin surface of the finger being printed. The sensor comprises an inverting amplifier, between the input and output of which the capacitive element is connected to form a negative feedback branch. By supplying an electric charge step to the input of the inverting amplifier, a voltage step directly proportional to the distance being measured is obtained at the output.

Abstract: A compact sensor which maps fingerprints for identification purposes. The sensor consists of an array of pixels with each pixel configured with one or more pickup conductive electrodes surrounded by voltage electrodes of different phases. This configuration performs capacitive differencing to eliminate the large background capacitance without the need for complex sensor circuitry. In addition, the readout lines are electrically shielded from the input voltage lines by an intermediate grounded conductive layer, thereby eliminating the parasitic capacitance and allowing the detection of minute capacitance variation of the finger surface.

Abstract: A process for detecting the point of touching of a tactile surface. A high frequency signal is sequentially supplied to four corners of a plate having a capacitive surface. This is accomplished by supplying one diagonal with the others being idle. The output voltages are measured at the four corners for all the various possible positions of touching. Relations between voltages are established from these measurements obtained for each diagonal. During touching, the relations obtained are compared with those stored in order to locate the point of touching.

Abstract: A contact switch having a sensor element with a flat sensor surface, with which is associated an illuminated display in a housing. The sensor surface passes over the housing and has a cutout corresponding to the shape of the lighting means. The sensor surface surrounds the lighting means in a substantially non-overlapping manner and in particular additionally rests on the housing. The sensor surface can also be provided with an elastic, electrically conductive plate for improved adaptation to irregular covers.

Abstract: The distance sensor has a capacitive element (33, 34) in turn having a first plate (23) which is positioned facing a second plate (18) whose distance is to be measured. In the case of fingerprinting, the second plate is defined directly by the skin surface of the finger being printed. The sensor includes an inverting amplifier (13), between the input and output of which the capacitive element (33, 34) is connected to form a negative feedback branch. By supplying an electric charge step to the input of the inverting amplifier, a voltage step directly proportional to the distance being measured is obtained at the output.

Abstract: The sensitive coordinate input device of the present invention adopts a system in which the finger F of the operator is regarded as one electrode, and the electrostatic capacitance is varied depending on the changes in the distances between the finger and another electrode which is separated therefrom via a dielectric. Four electrodes are preferably disposed at regular angular positions. Among the four electrodes, two electrodes, and two electrodes which are located at opposite positions are spaced at intervals, respectively. Across the four electrodes, a sensitive member 15 is laid. The surface of the sensitive member is to be touched with the operator's finger F. The sensitive member is preferably formed by a dielectric having a high dielectric constant, such as a ceramic plate. According to the present invention, the area of sensitive area can easily be increased, and the determination of the cursor position on the screen of the CRT display apparatus can readily be performed.

Abstract: A compact non-contact electrical switch for use in an electrical box mounted on a wall has a capacitance sensor for detecting a presence of a hand placed adjacent to the switch and for generating a first data bit, and a CPU for receiving the data bit and for calculating a power output in response to the first data bit The CPU generates a control signal for controlling a triac or relay and thus the power supplied to an electrical circuit passing through the box, for on/off and optionally dimmer control responsive to the proximity of the hand.

Abstract: A capacitive trackpoint device employs three capacitive sensors rather than four to increase sensitivity while reducing power consumption. Use of capacitive rather than resistive sensors provides a more sensitive and consistent signal with respect to pressure and a greater dynamic range than can be obtained from a resistive or strain gauge sensor, while use of larger area capacitive sensors for a given total area reduces the power requirements for reading the sensors both by having fewer capacitive sensors to read and by reducing the oscillating frequency. Because a more sensitive sensor is utilized, sampling of the signal may be made for a shorter time during periods of inactivity. The overall reduction in power consumption is particularly important for battery operated, hand-held input devices. Use of three sensors rather than four allows sampling of only two in a power-saving mode during periods of inactivity.

Abstract: A fingertip-operated solid state capacitance switch detects a capacity change that is induced by the physical contact of an ungrounded fingertip to an external dielectric surface of the solid state switch. The input and output of a solid state signal-inverting amplifier are respectively connected to two relatively large and ungrounded capacitor plates that are associated with, but electrically isolated from, the switch's external dielectric surface. An ungrounded fingertip forms a third capacitor plate on the switch's external surface. The solid state amplifier detects the presence of a fingertip on the switch's external surface by way of a change in capacitance within a compound, three plate, capacitor that includes the two ungrounded capacitor plates and the ungrounded fingertip that is resident on the switch's external surface.

Abstract: A key structure comprises base plate, elastic member, frame and cap wherein the conductive membrane thereof is single-film structure, the contact of the conductive membrane corresponding to each key is of meshed-hook shape (), a venting aperture is provided at the center of the contact. A transparent and insulating layer is arranged upon the conductive membrane to prevent the short circuit of the circuit in the conductive membrane. An opening is provided at the transparent and insulating layer and corresponding to the conductive membrane. Both ends of the elastic member are attached to the cap and the transparent and insulating layer by adhesive. A conductive bump with a conductive layer is provided on the elastic member such that the conductive bump of the elastic member is connected to the contact of the conductive membrane and a closed loop is formed within the key when the cap is pressed down, whereby the signal generated by key stroking action is transmitted to the computer.

Abstract: Capacitive coupling is used to transmit data and power through a user's body. In one implementation, a transmitter carried by the user transmits power and data to a receiver, which is also carried on the user's body. The signal that the transmitter applies to the user's body not only contains a data component, but also powers the receiver and enables it to detect and decode the data. In other implementations, the transmitter or the receiver is physically displaced from the user's body (although both receiver and transmitter are coupled to environmental ground), and data and power are transmitted when the transmitter and receiver become sufficiently proximate—via the user's body—to permit capacitive coupling. The disclosed approach is amenable to a wide variety of applications, ranging from “interbody” exchange of digital information between individuals through physical contact (e.g., a handshake) to “intrabody” data transfer (e.g.

Abstract: A combination keyboard and pointing device is incorporated in a portable computer and includes a dielectric base member on a top side of which a spaced series of electrically conductive pad member portions of a capacitance-based proximity sensing system are formed. Manually depressible key members are positioned above the pads. With the sensing system switched to a typing mode, the pads capacitively sense the proximity, velocity and acceleration of a user's fingers depressing their associated keys and output signals useable by the computer to display the character associated with the depressed key. A sensed increased stroke velocity of each manually depressed key may be used to alter the key character image displayed on the screen, for example capitalizing, bolding or underlining the character.

Abstract: A touchpad is formed of an electrically insulating membrane (10) with a first series of spaced apart conductors (12) on a first face of membrane (10) and a second series of spaced apart conductors (14) on or proximal thereto, in which there is no electrical contact between the first and second series of conductors (12, 14) Each conductor in the first and second series of conductors is sensitive to the proximity of a finger to modify the capacitance of the proximate conductor to detect the presence of the finger positioned close to that conductor. A scanning system operative to sample one of the conductors in turn from both the first and second series of conductors (12, 14) in order to measure and store a capacitance value associated with that respective conductor. The scanning system is operative to maintain all conductors (12-n, 14-n) at a common potential equal to the potential of the conductor being sampled when the remaining conductors are not actively being sampled by the scanning system.

Abstract: An input detection circuit includes a matrix of keys formed by the intersection of a plurality of columns of keys and a plurality of rows of keys, with a crossover capacitor connected across the intersecting row and column of one of the keys. The input detection circuit further includes circuits for generating a difference in voltage potential across the capacitor, and circuits responsive to the difference in voltage potential across the capacitor for generating a signal representative of the presence of the capacitor. By knowing which keys have been connected with a crossover capacitor, the processor of the telephone will also know what scan options have been programmed.

Abstract: A computer system includes a touchpad with one or more overlays providing the computer system with various input control functions. The overlay preferably includes tactile response elements to provide tactile feedback to the operator as an indication that a portion of the overlay has been pressed. The touchpad includes a capacitive sensor. Electronics coupled to the touchpad determine which portion of the touchpad sensor surface area has been touched or pressed. The amount of tactile feedback to the computer operator can be varied through the design and construction of the overlay and the overlay may be provided with no tactile feedback, if desired. As such, numerous overlays can be placed on the touchpad of the computer system, thereby providing the computer system with multiple different input control functions. The computer operator may manually input the type of overlay being used into the computer.

Abstract: A fingertip-operated solid state capacitance switch detects a capacity change that is induced by the physical contact of an ungrounded fingertip to an external dielectric surface of the solid state switch. The input and output of a solid state signal-inverting amplifier are respectively connected to two relatively large and ungrounded capacitor plates that are associated with, but electrically isolated from, the switch's external dielectric surface. An ungrounded fingertip forms a third capacitor plate on the switch's external surface. The solid state amplifier detects the presence of a fingertip on the switch's external surface by way of a change in capacitance within a compound, three plate, capacitor that includes the two ungrounded capacitor plates and the ungrounded fingertip that is resident on the switch's external surface.

Abstract: The present invention provides a computer pointing device which uses capacitors installed in various directions to generate pointing signals. The pointing device comprises a circuit board, a cap, and a detecting unit. The circuit board comprises a center point, a first conducting plate installed in a first direction and a second conducting plate installed in a second direction. The cap is movably installed above the center point of the circuit board. The bottom side of the cap has a top conducting plate which forms first and second capacitors with the first and second conducting plates separately. The detecting unit is electrically connected to the top, first and second conducting plates to detect the capacitance of the first and second capacitors and generate corresponding pointing signals to reflect the position of the cap in the first and second directions.

Abstract: 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.

Abstract: A keyboard according to the present invention, which includes one or more keys and corresponding electromechanical converting elements, is characterized in that it includes a film construction (42) which includes an electret film with a bubble construction known as EMF by which said electromechanical converting elements corresponding to the keys are formed, and a solid, stiff cover plate (43) which covers the EMF construction (42) and in which an area (A-D) in the vicinity of each electromechanical converting element forms a key. In one embodiment of the present invention, a frame of the keyboard forms the cover plate and the EMF construction affixed behind the cover plate is covered with a sufficiently thick and stiff layer of plastic. The cover plate may be steel or aluminum, for example, and other materials such as plastic, glass or ceramic materials can be used. The thickness of the cover plate may be approximately 2 mm, for example.

Abstract: A proximity sensor system includes a sensor matrix array having a characteristic capacitance on horizontal and vertical conductors connected to sensor pads. The capacitance changes as a function of the proximity of an object or objects to the sensor matrix. The change in capacitance of each node in both the X and Y directions of the matrix due to the approach of an object is converted to a set of voltages in the X and Y directions. These voltages are processed by digital circuitry to develop electrical signals representative of the centroid of the profile of the object, i.e, its position in the X and Y dimensions. Noise reduction and background level setting techniques inherently available in the architecture are employed.

Abstract: A computer system includes a touchpad with one or more overlays providing the computer system with various input control functions. The overlay preferably includes tactile response elements to provide tactile feedback to the operator as an indication that a portion of the overlay has been pressed. The touchpad includes a capacitive sensor. Electronics coupled to the touchpad determine which portion of the touchpad sensor surface area has been touched or pressed. The amount of tactile feedback to the computer operator can be varied through the design and construction of the overlay and the overlay may be provided with no tactile feedback, if desired. As such, numerous overlays can be placed on the touchpad of the computer system, thereby providing the computer system with multiple different input control functions. The computer operator may manually input the type of overlay being used into the computer.

Abstract: A capacitive touch detection system, which can be used to inhibit motorized faders in an audio mixing system, includes touch detection circuits each having a respective conductive area for touch determination by detection of increased capacitance at the conductive area. The touch detection circuits are operable during predetermined active periods initiated by a clock generator which activates a pulse generator to produce an enable pulse EP1 for one detection circuit. The trailing edge of that enable pulse EP1 generates a non-overlapping enable pulse EP2 for the next detection circuit, and the process continues so that no more than one detection circuit is active at any time. This minimizes interaction between detection circuits if more than one conductive area is touched simultaneously.

Abstract: The multichannel coder embodying the invention comprises a knob coupled with a code wheel associated with a means for detecting the angular position and, possibly, the direction of rotation of the wheel. It comprises, on the one hand, a channel selection means incorporated into the knob, and, on the other hand, a means enabling the association, with the information provided by the detection means, of information relating to the channel that has been selected on the aforesaid selection means. The invention can be used to modify parameters.

Abstract: A touch control system that is responsive to a user input selection includes an electrically non-conducting substrate, such as glass ceramic, and at least one capacitive-responsive touch pad on the substrate. A source signal having a primary frequency that is greater than 150 kHz, and preferably in the range of between 150 kHz and 500 kHz, is applied to one portion of the touch pad. The touch pad couples the electrical signal to another portion of the touch pad in order to develop a detection signal, which is decoded in order to determine the presence of the capacitance of a user. The decoder preferably includes a peak detector composed of a low gain circuit in order to avoid distortion of the detection signal. Greatly improved performance in the presence of liquids, such as water, on the touch pad is provided. This is especially useful when the touch pad is applied to a horizontal surface, such as a cook top, upon which liquid spills may occur.

Abstract: A remote control assembly for operating an audio component in a motor vehicle includes a steering wheel having a front side and a back side, and a control for operating a function of the audio component located on the back side of the steering wheel such that a driver's finger can operate the control.

Abstract: A touchpad, which may include a keypad array, digitizing tablet, touch screen or an electronic mouse, is operable through a suitable dielectric medium, operating by capacitive effect and suitable for use as a computer interface in conjunction with a monitor screen, or as a computer input device in a number of applications, for example, as a cash till keypad.

Abstract: An improved capacitive sensor for detecting the presence of objects in a sensing region. The sensor is a multilayer structure with alternating layer of condutive and insulating materials. The sensor structure has three electrodes: a touch plate, a guard layer, a ground plane, each of which are separated from each other by insulating layers. The sensor is operated by detection electronic circuitry which function in a either a self excited mode or an externally excited mode. This sensor is capable of detecting objects in a sensing region several feet away from the sensing surface and is particularly suitable for automobile applications, such as detecting potentially jamming objects in power (auto-closing) windows, doors, and the like.

Abstract: A communication interface between a computer and a vehicle device employs at least one large-area function element of the vehicle device which is developed as counter-electrode for an electrode of a capacitive coupling adapter. The adapter is connected to a computer, and can be applied from the outside to the vehicle device.

Abstract: The padless touch sensor is used for detecting a touch at a sensing location onto a dielectric element by a user coupled to earth. The sensor comprises a conductive plate attached under the dielectric element and in registry with the sensing location. A predetermined potential is applied on the conductive plate. Simultaneously, test pulses are produced into earth. When the user touches the dielectric element at the sensing location, a potential variation in the conductive plate is produced during a test pulse due to a capacitive circuit formed between earth, the user and the sensor. No deposition of conductive pads on the dielectric element or other special processes are required. Foreign matter or objects placed directly on top of the dielectric element will not erroneously produce a touch condition.

Abstract: An electronic control arrangement for an electrical heating appliance with several separately heatable electrical loads, particularly cooking points or hotplates, contains an electronic master switch, which has its own power supply. The master switch is followed by a control unit having for each electrical load in each case one control subunit. For each hotplate the control unit has a temperature sensor, which responds if the control unit becomes too hot at this point.

Abstract: A finger operable control device that includes a sensor having five conductive plates. The conductive plates are coupled to a detector circuit arranged to sense capacity imbalance due to the presence of a finger or an earthed object on or by one or more of the conductive plates. The device is utilized as a mouse or joystick.

Abstract: The present invention relates to a capacitive touch sensor including a plurality of horizontal sensor bars arranged in a single direction. The touch sensor preferably receives differential sensor signals from the sensor array to reduce proximity effects and noise associated with conventional capacitive touch sensors. The touch sensor also utilizes an isolation circuit or floating interface to reduce the effects of external interference and increase the accuracy of touch sensing and localization. The bars are preferably comprised of indium tin oxide oriented in the machine direction of roll for superior linearity. The touch sensor may be utilized with display screens having thick dielectrics and also eliminates the need for a rear guard layer.

Abstract: A proximity sensor system includes a sensor matrix array having a characteristic capacitance between horizontal and vertical conductors connected to sensor pads. The capacitance changes as a function of the proximity of an object or objects to the sensor matrix. The change in capacitance of each node in both the X and Y directions of the matrix due to the approach of an object is converted to a set of voltages in the X and Y directions. These voltages are processed by analog circuitry to develop electrical signals representative of the centroid of the profile of the object, i.e, its position in the X and Y dimensions. The profile of position may also be integrated to provide Z-axis (pressure) information.

Abstract: A circuit for encoding and decoding key input data from a matrix of switches with a single transmission wire. The circuit for encoding and decoding key input data with a single transmission wire includes a control circuit, a charge storage circuit and a keyboard matrix circuit. The keyboard matrix circuit is composed of a group of resistors connected in series. Each resistor is coupled to ground via a manually actuated switch. When one of the switches is actuated or closed the switch provides an electrical path to ground through the resistors that precede the switch and shorts the resistors that follow the switch. When one of the switches is closed the charge stored on the charge storage circuit dissipates through the electrical path to ground provided by the actuated switch, at a rate related to the sum of the resistance preceding the switch.

Abstract: A touch sensitive control panel in accordance with the invention includes a plate having a front side and a back side. The front side has at least one marking identifying at least one corresponding touch sensitive area of the plate. Each touch sensitive area when touched by a user completes an operative coupling with one of a plurality of electrodes of at least one electronic circuit disposed on the back side to cause the production of a selected control signal by the at least one electronic circuit to which the operative coupling is completed by touching one touch sensitive area of the front side. The at least one electronic circuit and the plurality of electrodes are held in surface contact with the back side without the use of an intermediate plate.

Abstract: A low impedance touch sensor detects manual contact of a dielectric substrate by a human user. The touch sensor includes a first conductive electrode pad having a closed, continuous geometric form and a second conductive electrode which substantially co-planarly surrounds the first electrode and is spaced from the first electrode by a channel. The first and second electrodes are disposed on the same surface of the substrate. An active electrical component, such as a transistor is located on the substrate proximate the first and second electrodes, and is electrically coupled to the first and second electrodes.

Abstract: In one aspect of the present invention, a joystick is disclosed. The joystick includes a control shaft having an operator handle and a base. A cardan joint is provided to pivotally mount the control shaft to the base. An actuating body is rigidly attached to the control shaft. Advantageously, a plurality of electrically non-contacting sensors is provided to sense the relative position of the shaft relative to the base. The sensors include a pair of spaced apart electrodes establishing an electrostatic capacity with each other, and a dielectric body being disposed between the electrode pair. Accordingly, as the control shaft pivots, the actuating body engages the dielectric body which moves the dielectric body relative to the electrode pair thereby modifying the capacitance of the sensor.

Abstract: A touch control system that is responsive to a user input selection includes an electrically non-conducting substrate, such as glass ceramic, and at least one capacitive-responsive touch pad on the substrate. A source signal having a primary frequency that is greater than 150 kHz, and preferably in the range of between 150 kHz and 500 kHz, is applied to one portion of the touch pad. The touch pad couples the electrical signal to another portion of the touch pad in order to develop a detection signal, which is decoded in order to determine the presence of the capacitance of a user. The decoder preferably includes a peak detector composed of a low gain circuit in order to avoid distortion of the detection signal. Greatly improved performance in the presence of liquids, such as water, on the touch pad is provided. This is especially useful when the touch pad is applied to a horizontal surface, such as a cook top, upon which liquid spills may occur.

Abstract: A proximity sensor system includes a sensor matrix array having a characteristic capacitance on horizontal and vertical conductors connected to sensor pads. The capacitance changes as a function of the proximity of an object or objects to the sensor matrix. The change in capacitance of each node in both the X and Y directions of the matrix due to the approach of an object is converted to a set of voltages in the X and Y directions. These voltages are processed by circuitry to develop electrical signals representative of the centroid of the profile of the object, i.e, its position in the X and Y dimensions. Noise reduction and background level setting techniques inherently available in the architecture are employed.

Abstract: Methods for recognizing gestures made by a conductive object on a touch-sensor pad are disclosed. Tapping, pushing, hopping, and zigzag gestures are recognized by analyzing the position, pressure, and movement of the conductive object on the sensor pad during the time of a suspected gesture, and signals are sent to a host indicating the occurrence of these gestures. Signals for compensating for unintended motion of the conductive object on the touch-sensor pad during the gestures are also sent to the host.

Abstract: A method and apparatus for determining a valid selection of a capacitance tactile keyboard as a function of a selection state and validation state of the keyboard. The selection state is determined from measured capacitive values of each key by during a first phase of a cycle. The validation state is determined from measured pressure on the keyboard, for certain key selection states only, during a second phase of the cycle.

Abstract: A data processing device comprises a touch screen with a touch position sensor. The position sensor is suitable to detect a touch position on the screen from a change in a current pattern in a conductive panel. The device also comprises a touch force sensor provided with a second conductive panel which extends substantially parallel to the touch screen. The screen is at least partly movable relative to the second panel in a direction transversely of the second panel. The force sensor is suitable to determine a force from a capacitance value between the touch screen and the second panel. The device is suitable for the combined processing of the position and force detected in response to touching.

Abstract: A capacitance-sensitive switch unit including a capacitive element operable to produce an effective capacitance dependent upon the physical proximity of objects relative thereto, a first selector signal input connected to the capacitive element to enable a first input signal to charge the effective capacitance, a threshold signal producing circuit connected to the capacitive element, for producing a threshold signal which is rendered active when the effective capacitance charges to a pre-defined potential, a switching circuit for selectively connecting the capacitive element to the threshold signal producing circuit in response to a switching signal and a discharge control circuit connected to the capacitive element, for selectively discharging the effective capacitance independently of the input signal, in response to a discharge signal. Also disclosed is a switch array employing structure similar to the above.

Abstract: A touch sensitive pad consists of a number of electrical conductive pads (10) surrounded by a conductive pad (11). Each pad (10) is connected via a respective capacitive blocking filter to a multiplexer (13) and an oscillator (14). When the touch pad is touched directly to effectively bridge between one of the pads (10) and the surrounding pad (11), a change in effective impedance is detected by a resultant variation in the frequency of the oscillator (14).